Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget

Accepted Manuscript Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget

Shaily Rahman, Joseph J. Tamborski, Matthew A. Charette, J. Kirk Cochran PII: DOI: Reference:

S0304-4203(18)30223-8 https://doi.org/10.1016/j.marchem.2018.11.006 MARCHE 3614

To appear in:

Marine Chemistry

Received date: Revised date: Accepted date:

31 August 2018 10 November 2018 12 November 2018

Please cite this article as: Shaily Rahman, Joseph J. Tamborski, Matthew A. Charette, J. Kirk Cochran , Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget. Marche (2018), https://doi.org/ 10.1016/j.marchem.2018.11.006

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget

T

Shaily Rahmana,b , Joseph J. Tamborskic* , Matthew A. Charetted , J. Kirk Cochrana

a

IP

School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, 11794 USA

CR

b

Present Address: Department of Geological Sciences, University of Florida, Gainesville, Florida 32611 USA Department of Geosciences, Stony Brook University, Stony Brook, New York, 11794 USA

US

c

*Present Address : Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, 02543 USA d

M

AN

Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, 02543 USA

ED

Corresponding Authors: Shaily Rahman ([email protected]), Joseph Tamborski ([email protected])

PT

Keywords:

AC

CE

Dissolved silica, marine groundwater, lithogenic dissolution

Abstract Groundwater’s role in the global marine budget of dissolved silica (DSi), an essential nutrient, is constrained using DSi groundwater concentrations from multiple endmember lithologies and a global terrestrial submarine groundwater discharge (SGD) model. We report new DSi concentrations in nine subterranean estuaries throughout the world, including Panama, Mauritius, 1

ACCEPTED MANUSCRIPT Guam, Yucatan (Mexico), Chile, Argentina, Southwest Florida (USA), Long Island Sound (USA) and Waquoit Bay (USA). These new data are augmented with a literature survey of DSi endmember concentrations in the subterranean estuary to determine the global DSi endmember in SGD, classified by the regional lithology (carbonate, shale, sandstone, extrusive igneous,

T

shield and “complex”). DSi fluxes to the ocean from terrestrial (fresh) SGD equal 0.7 ± 0.1 Tmol

IP

y-1 , more than half of which enters the Pacific Ocean. Non-conservative DSi enrichment was

CR

observed in marine groundwaters circulated through extrusive igneous and complex lithology sediments for twenty different study sites. Dissolution rate calculations indicate that non-

US

conservative DSi enrichments in marine groundwaters can be supported, in part, by lithogenic

AN

dissolution of the coastal sediment, rather than biogenic silica dissolution. We make preliminary estimates of DSi inputs via marine SGD in shallow coastal aquifers of ~3 Tmol y-1 . Considering

M

recent revisions to the marine silica budget (e.g., increased estimates of biogenic silica storage

ED

via reverse weathering reactions, increased estimates of standing stocks of biogenic silica, and changing estimates of silica burial efficiency), sources and sinks in the marine Si budget can be

PT

balanced when taking into account estimates of new DSi inputs from total SGD (terrestrial and

CE

marine flow paths). These findings impact the residence time of oceanic Si and mass balances of

AC

the stable Si isotopes, as well as associated silicate weathering products, including Li and Ge.

1 Introduction In past derivations of the marine silica budget, dissolved silica (DSi) inputs via submarine groundwater discharge (SGD) were generally given a cursory treatment based on limited, mostly inland aquifer data (e.g., (Laruelle et al., 2009; Tréguer and De La Rocha, 2013; Frings et al., 2016), despite the fact that several local and regional-scale studies have identified significant inputs of DSi from both terrestrial and marine SGD (e.g., Burnett et al., 2009; Georg et al., 2009; 2

ACCEPTED MANUSCRIPT Schopka and Derry, 2012; Wang et al., 2015 Anschutz et al., 2016). Of the known inputs of dissolved silica to the global ocean, riverine sources remain the most constrained and best documented, whereas the magnitudes and uncertainties of other input fluxes are highly variable (Tréguer and De La Rocha, 2013; Frings et al., 2016). At present, documented inputs of DSi in

T

marine budgets to the ocean, which has a total DSi inventory of 97,000 Tmol (Tréguer and De

IP

La Rocha, 2013), are via riverine supply (7.3 – 8.1 Tmol y-1 ), terrestrial (fresh) SGD (0.7 ± 0.5

CR

Tmol Si y-1 ), eolian deposition (0.5 Tmol y-1 ), marine basalt weathering of the seafloor (1.9 Tmol y-1 ) and hydrothermal circulation (0.6 Tmol y-1 ) (e.g., Tréguer and De La Rocha, 2013; Figure

US

1). These various Si sources can drive up to 75% of primary productivity in coastal systems, as

AN

silica is an essential nutrient in the ocean for diatoms (Conley, 1997; Tréguer et al., 2018). Recently, total SGD (terrestrial + marine) inputs of DSi have been estimated to contribute 3.8 ±

M

1.0 Tmol Si y-1 to the global ocean; however, it remains to be seen how much of this DSi is from

ED

net new (e.g., lithogenic dissolution) versus recycled sources (e.g., biogenic silica dissolution) (Cho et al., 2018). To date, global oceanic DSi budgets have only considered fresh, terrestrial

PT

flow paths, neglecting marine groundwater (Tréguer and De La Rocha, 2013; Frings et al.,

CE

2016). In this study, we discuss the biogeochemical behavior of DSi in subterranean estuaries

AC

and how total SGD broadly impacts the global oceanic silica budget. Submarine groundwater discharge is a mixture between terrestrial (i.e., fresh) meteoric groundwater and marine (i.e. saline) groundwater that discharges over spatial scales from meters to kilometers (Burnett et al., 2003; Moore, 2010; Figure 1). The term “marine groundwater” refers to water that may have originated as seawater but has since obtained a unique geochemical signature from biogeochemical reactions and water-rock interactions beneath the subsurface, making marine groundwater fundamentally different from seawater. The mixing zone between

3

ACCEPTED MANUSCRIPT groundwater and seawater in the coastal aquifer is termed the subterranean estuary (STE) (Moore, 1999), where many chemical species behave non-conservatively due to sharp gradients in salinity, redox and pH (Beck et al., 2007; O'Connor et al., 2017). The terrestrial and marine flow paths are geochemically distinct, and often disparate in volumetric proportions (Taniguchi

IP

T

et al., 2002; Moore et al., 2008; Kwon et al., 2014). Terrestrial SGD is driven through permeable sediments by a positive inland hydraulic

CR

gradient between the coastal aquifer and the sea and may occur in the form of submarine springs

US

or diffuse, non-point source seepage (Santos et al., 2012). Fresh, terrestrial SGD may be found several kilometers offshore with increased continuity between geologic units (Guo & Li, 2015;

AN

Michael et al., 2016), while there is significant evidence for offshore reservoirs of freshwater

M

beneath the continental shelf (Post et al., 2013). Terrestrial SGD is a source of new DSi to the coastal ocean via weathering of the aquifer sediment (Davis, 1964). Marine SGD is a potential

ED

source of both recycled and new DSi to the coastal ocean. New DSi sources in marine SGD

PT

results from weathering in the STE and permeable coastal sediments in the presence of high salinity (Anschutz et al., 2009; Anschutz et al., 2016; Ehlert et al., 2016b). Recycled DSi fluxes

CE

can be driven by the regeneration of biogenic Si (Anschutz et al., 2009). Marine SGD is driven

AC

by a variety of physical forcing mechanisms (Santos et al. 2012); thus, the net DSi flux from marine SGD is dependent upon the magnitude of these various marine SGD flow paths (Figure 1). Close to the shoreline, these physical processes include wave-setup (Li et al., 1999) and tidal pumping, of which the latter may extend along the continental shelf (Li et al., 1999; Moore et al., 2002; Moore & Wilson, 2005). Farther offshore, marine groundwater flow can be driven by density gradients imposed by heterogeneous aquifer structures (Michael et al., 2016) and geothermal convection (Kohout, 1967; Wilson et al., 2001).

4

ACCEPTED MANUSCRIPT Groundwater within the STE may be impacted by biogeochemical transformations during mixing between dissimilar water masses (Beck et al., 2007; Burnett et al., 2003; Moore, 1999; Robinson et al., 2018). For Si, this can include removal via biological consumption and neoformation of aluminosilicate phases (e.g., Ehlert et al., 2016; Daux et al., 1997; Oelkers and

T

Gislason, 2001; Staudigel et al., 1998; Techer et al., 2001); addition can occur via lithogenic

IP

particle (sediment) dissolution (e.g., Anschutz et al., 2009; Brehm et al., 2005; Ehlert et al.,

CR

2016; Georg et al., 2009; Morin et al., 2015; Tamborski et al., 2018) and biogenic silica dissolution (e.g., Frings, 2017; Tréguer and De La Rocha, 2013). Therefore, coastal groundwater

US

samples are more likely to represent the SGD endmember, rather than groundwater sampled

AN

from inland wells. In this study, coastal groundwater samples from over 50 different study locations worldwide were used to help determine the behavior of DSi in the STE, constrain the

M

global SGD-driven DSi flux, and determine its relative importance in the marine silica budget.

ED

Though we focus on the modern marine silica budget, it is important to note that fluxes from these sources likely varied over geologic time in response to glacial/interglacial transitions and

CE

(Froelich et al., 1992).

PT

sea-level variations, with evidence for greater riverine DSi fluxes during glacial periods

AC

2 Materials and Methods 2.1 SGD studies Surface water and groundwater samples were collected from a wide variety of study sites, some over multiple seasons, representing different types of coastal aquifers, including carbonate, extrusive igneous and complex lithologies (Figure 2). A detailed description of each study site and design can be found with the location’s associated reference; previously unpublished data are described in the Supplemental Information (Text S1). Groundwater from the coastal aquifer and STE was sampled either from preexisting wells, push-point piezometers, shallow beach pits 5

ACCEPTED MANUSCRIPT or manual seepage meters, whereas cenotes (groundwater filled sinkholes) and springs from karstic study sites were sampled by direct pumping. In general, groundwater sampling proceeded after purging ≥ 3 volumes, and collected after ancillary water quality parameters (temperature, salinity, DO, ORP) had stabilized in a multi-probe. Samples for nutrient analyses were syringe-

T

filtered with 0.45 µm filters and stored frozen at -20°C until analysis. DSi was analyzed

IP

colorimetrically using a molybdate blue method (Strickland and Parsons, 1972). DSi endmember

CR

concentrations in groundwater were categorized by lithology (Table S2). Conservative and nonconservative DSi behavior was determined for each environment, relative to simple two-

US

endmember mixing between terrestrial groundwater (salinity <1) and surface marine waters.

AN

2.2 Literature survey of SGD studies The new data presented here were supplemented by a literature survey of DSi in

M

terrestrial and marine groundwaters (Figure 2). Whereas previous studies relied on samples

ED

exclusively from inland monitoring wells (Frings et al., 2016), we only consider SGD-related studies to represent the DSi concentration at the point of discharge. The studies used to

PT

determine the terrestrial SGD DSi endmember have been grouped by major lithology and are

CE

summarized in Table S2; studies were classified according to their site descriptions and, when little information was available, from a coarse-resolution global lithology classification map

AC

(Gibbs and Kump, 1994). Study sites were categorized as a “complex” lithology if the regional geology encompassed more than one type of major lithology and includes unconsolidated glacial sediments. Data from multiple studies of the same geographic region were averaged together to avoid any geographical bias in determining the mean DSi endmember concentration. The lithological endmembers for which we summarized studies were: “extrusive igneous” (Burnett et al., 2006; Dollar and Atkinson, 1992; Georg et al., 2009; Holleman, 2011; Hwang et al., 2005a; Johnson et al., 2008.; Knee et al., 2010, 2016; Mandal et al., 2011; Schopka and Derry, 6

ACCEPTED MANUSCRIPT 2012; Street et al., 2008; Zavialov et al., 2012); “carbonate” (El-Gamal et al., 2012; GarciaSolsona et al., 2010a, 2010b; Gonneea et al., 2014; Hernández-Terrones et al., 2011; HerreraSilveira, 1994; Null et al., 2014; Rocha et al., 2015; Tamborski et al., 2018; Tovar-Sánchez et al., 2014; Young et al., 2008); “sandstone” (Sugimoto et al., 2017; Weinstein et al., 2011);

T

“shield/granite ” (Lecher et al., 2016; Onodera and Saito, 2007; Rengarajan and Sarma, 2015;

IP

Wang et al., 2015); “shale” (Kim et al., 2005; Lee et al., 2012; Luo et al., 2014; Ye et al., 2016);

CR

and “complex” (Anschutz et al., 2016; Boehm et al., 2004; Burnett et al., 2007; Charette et al., 2013; Charette and Sholkovitz, 2006; Ehlert et al., 2016; Godoy et al., 2013; Hwang et al., 2005;

US

Johannes and Hearn, 1985; Kim et al., 2008; Lecher et al., 2015; Lee et al., 2010, 2009; Li et al.,

AN

2014; Liu et al., 2011; Niencheski et al., 2007; Null et al., 2012; Su et al., 2011; Swarzenski et al., 2007b, 2007a; Tamborski et al., 2017; Ullman et al., 2003; Urquidi-Gaume et al., 2016;

M

Waska and Kim, 2011). Only samples with a salinity ≤6 were considered for the terrestrial

ED

endmember to reduce the influence of mixing between dissimilar water masses. Data for DSi in marine SGD for different lithologies were compiled whenever available, taken as the mean

PT

difference between marine groundwater and seawater DSi concentrations (Table S3). Only

CE

marine groundwater samples with salinities approximately greater than or equal to site-specific marine surface waters were considered for each region. DSi values in brackish waters showing

AC

signs of conservative, linear mixing between terrestrial groundwaters and surface waters were disregarded. Marine groundwater endmembers were categorized as the same lithology as the terrestrial groundwater endmember. 2.3 Global terrestrial SGD model and DSi fluxes Zektser et al. (2006) used an integrated hydrologic-hydrogeological model framework to quantify terrestrial SGD to the global ocean from the world-wide hydrogeological mapping and assessment program (WHYMAP, UNESCO, 2000). The world-wide hydrogeology dataset 7

ACCEPTED MANUSCRIPT includes, but is not limited to, structural hydrogeological units, coastal aquifers, transboundary aquifer systems, groundwater runoff, hydrodynamic conditions, aquifer thickness and storage volume. In this model, only groundwater discharge from the upper zone of active flow under modern conditions within the coastal aquifer was considered, neglecting any deep, “paleo” SGD

T

and deep SGD from confined aquifers (Post et al., 2013). Coastal areas were divided into

IP

different drainage basins based on a World Hypsometric Map (1:2,500,000); groundwater

CR

discharge was only considered in coastal areas that were not directly drained by rivers, resulting in 122 total catchment areas. The world shoreline length, excluding Antarctica and other high-

US

latitude regions, was taken to equal 600,000 km in the model calculations.

AN

This terrestrial SGD model has been previously applied to estimate the global terrestrial

M

SGD-driven strontium (Sr) flux (Beck et al., 2013), with major lithological categories (2̊ by 2̊ spatial resolution) (Gibbs and Kump, 1994) applied to each coastal region from the terrestrial

ED

SGD model. The model has also been used to determine carbon, nitrogen, phosphorus, and

PT

radiocesium inputs to the ocean via SGD (Szymczycha et al., 2014; Powley et al., 2017; Rodellas et al., 2015; Sanial et al., 2017). Here, we employ a similar approach to Beck et al. (2013) by

CE

using average DSi endmember concentrations for carbonate, shale, sandstone, extrusive igneous,

AC

shield (granite) and complex lithologies (Figure 2) and applying these average concentrations (Table S2) to the coastal zones encompassed in the terrestrial SGD model (Table S4). The lithological classification scheme represents the regional surface geology and includes both fractured bedrock aquifers and coastal unconsolidated sediment derived from the regional parent rock material. It is important to note that there are no reported uncertainties in this global terrestrial SGD model. Kwon et al. (2014) estimated a relative uncertainty of 25% in their global total SGD volume flux, whereas between two recent separate studies (Befus et al., 2017; Sawyer

8

ACCEPTED MANUSCRIPT et al., 2016) there is a 2 – fold difference in SGD volumetric flux estimates along the east coast of the United States. Here, we cautiously adopt a 100% relative uncertainty in the terrestrial SGD volume fluxes in the Zektser et al. (2006) model. The relative uncertainty in the terrestrial SGD DSi endmember concentration is taken as the standard deviation of the average DSi

T

concentration from each study within a lithological category (Table S2). Uncertainty in the DSi

IP

flux from terrestrial SGD was estimated by standard rules of error propagation for uncorrelated

CR

variables, where we assume a normal Gaussian distribution around the mean (Supplemental Information). Terrestrial SGD DSi flux calculations, with error propagation calculations as

US

suggested by the IPCC and other organizations (IPCC, 2006), are presented in full in Table S4.

AN

If seawater is the original source of marine groundwater, then it is important to

M

understand if DSi can be added to marine groundwater as it resides beneath the subsurface over time. The rates of this process have rarely been quantified in situ, however, a number of studies

ED

have theoretically and experimentally determined initial dissolution rates of borosilicate glass,

PT

synthetic basalts under varying conditions (i.e. pH, temperature, surface area to volume ratios, flow rate) (Daux et al., 1997; Advocat et al., 1998; Oelkers and Gislason, 2001; Techer et al.,

CE

2001; Gislason and Oelkers, 2003; Oelkers et al., 2011; Morin et al., 2015; and references

AC

therein) as well as dissolution rates of natural volcanic, basaltic, and terrigenous riverine particulate material (Loucaides et al., 2008; Jones et al., 2012; Oelkers et al., 2012; Jones et al., 2014). Using experimentally derived dissolution rates (Anschutz et al., 2009; Ehlert et al., 2016b; Morin et al., 2015; Techer et al., 2001), reasonable ranges of marine SGD volume flowing through each endmember, and reasonable estimates of marine groundwater residence time (Anschutz et al., 2009; Goodridge and Melack, 2014; Oh and Kim, 2016; Tamborski et al., 2017), simple quantitative calculations of theoretical DSi concentrations in the STE were made

9

ACCEPTED MANUSCRIPT to determine the potential for non-conservative DSi enrichment in marine groundwaters from extrusive igneous and complex lithology endmembers (Supplemental Information). We used laboratory-derived dissolution rates of natural silica substrates, synthetic basalt glass, and natural sediments to calculate the potential DSi enrichment in the STE and permeable marine sediments

T

(Supplemental Information). Potential marine SGD DSi concentrations and annual fluxes

CR

IP

derived from dissolution rate parameters for the global STE are summarized in Table 2.

US

3 Results and Discussion 3.1 Global terrestrial SGD DSi flux The mean terrestrial SGD endmembers, arranged by major lithology, represent a combination of data from the literature and from this study (Figure 2; Figure 3). It is important

AN

to note that the number of samples used to compute the DSi endmember average reflects an

M

average of multiple geographical regions; uncertainties are equal to ± 1 SD. Carbonate aquifers

ED

have, on average, the lowest DSi endmember in terrestrial SGD (80 ± 63 µM; n=9), whereas extrusive igneous aquifers have the highest (604 ± 192 µM; n=11). The complex lithology

PT

endmember (288 ± 245 µM; n=22) here is lower than a previous groundwater endmember average, estimated from inland wells (380 ± 250 µM) (Frings et al., 2016). Mean (±SD) DSi

CE

endmember concentrations for each lithology are summarized in Table 1; the distribution of DSi

AC

concentrations in each endmember is depicted in Figure 4. The global terrestrial SGD-driven DSi flux is equal to (0.7 ± 0.1) Tmol y-1 (Figure 5), which is approximately 10% of the global riverine DSi flux, and similar to previous estimates (0.7 ± 0.5 Tmol y-1 ) (Tréguer and De La Rocha, 2013; Frings et al., 2016). Results from the global terrestrial SGD model, along with propagated uncertainties, are summarized in Table S4. The majority of the global terrestrial SGD-driven DSi flux is derived from extrusive igneous (37%) and complex lithologies (31%), followed by shield (13%), shale (9%), sandstone (6%) and 10

ACCEPTED MANUSCRIPT carbonate lithologies (3%). In terms of ocean basins, terrestrial SGD-driven DSi inputs are greatest to the Pacific Ocean (58%), followed by the Atlantic Ocean (27%), Indian Ocean (9%), Arctic Ocean (3%) and Mediterranean Sea (3%; Figure 5). For comparison, riverine DSi fluxes into the Pacific Ocean, Atlantic Ocean, Indian Ocean, Arctic Ocean and Mediterranean Sea are

T

32%, 45%, 17%, 5% and 1% of total gross riverine DSi fluxes (6.24 Tmol DSi y-1 ), respectively

IP

(Dürr et al., 2011; Figure 5). For each coastal region in the terrestrial SGD model, because we

CR

assumed a 100% uncertainty in the SGD volumetric flux, the regional DSi flux uncertainty is ≥100%; however, when considering the global terrestrial SGD-driven DSi flux, this additive

US

propagated uncertainty, for each of the 122 coastal catchment areas, is reduced to ~20% (Table

AN

S4).

M

3.2 Marine SGD Marine groundwater that circulates through a permeable beach face or nearshore

ED

permeable sediment from physical exchange processes (i.e. tides, waves, flow driven by density gradients), may become enriched in DSi from the dissolution of quartz, basalt, and

PT

aluminosilicates in the presence of seawater, with DSi concentrations increasing with increasing

CE

subsurface residence time (Techer et al., 2001; Anschutz et al., 2009; Morin et al., 2015; Ehlert et al., 2016b). Marine groundwater residence times can vary on short time-scales (hours to

AC

weeks) due to the complex interaction between sediment characteristics, wind speed and direction, tidal range, terrestrial hydraulic gradient and beach slope (Tamborski et al., 2017; Zhang et al., 2017). Longer marine groundwater residence times (months to years) can result from flow driven by density gradients, geothermal convection and seasonal oscillations of the water table (Abarca et al., 2013; Michael et al., 2005; Michael et al., 2011; Michael et al., 2016; Wilson, 2005). Marine groundwater residence times are significantly greater farther offshore along the continental shelf, with low flow rates (Michael et al., 2016; Wilson, 2005; Moore, 11

ACCEPTED MANUSCRIPT 2010). Considering the large volumetric flux of marine SGD (Kwon et al., 2014), this mechanism represents a potentially significant, yet poorly constrained, source of net new DSi to the global ocean. Samples from this study showed non-conservative enrichment of DSi in SGD from

IP

T

extrusive igneous (Mauritius) and complex lithologies (Argentina, Southwest Florida, Long Island Sound, Waquoit Bay; Figure 3). In Waquoit Bay (MA, USA), marine groundwater

CR

samples (mean DSi = 131 µM; mean salinity = 27.0 ± 0.6; n = 30) are significantly enriched over

US

surface waters (mean DSi = 13 µM; mean salinity = 28.0 ± 2.3; n = 28), for an average nonconservative enrichment of 118 µM for this complex glacial environment (Table S3). Marine

AN

groundwater from a barrier beach along Long Island Sound (NY, USA) suggest a similar

M

relationship to Waquoit Bay, where intertidal pore waters are enriched in DSi (mean DSi = 44

ED

µM; mean salinity = 28.0 ± 1.4; n = 86) with respect to seawater (DSi = 6 µM; salinity = 26.5) for a non-conservative enrichment of 39 µM (Table S3). Seepage meters sampled adjacent to the

PT

barrier beach, where there are no terrestrial SGD inputs, indicate that marine SGD is enriched in

CE

DSi over surface waters, with a mean non-conservative DSi enrichment equal to 35 ± 17 µM over a tidal cycle (Table S1; n=19; Tamborski et al., 2015). Non-conservative DSi enrichments

AC

were observed in marine groundwaters for other complex lithology environments from the literature review, including the French Aquitanian coast (Anschutz et al., 2016), Monterey Bay, California (Lecher et al., 2015) and Yeoja Bay, Korea (Hwang et al., 2005b; Lee et al., 2010). In Mauritius (this study), an extrusive igneous lithology, linear regression of brackish pore water samples (salinity 7 – 23) to a salinity of zero suggests a DSi SGD endmember equal to 677 µM, which is enriched by ~20% over mean terrestrial groundwater (564 µM; Figure 3; Table S3). Literature data from Hawai’i and Jeju Island (Korea), both categorized as extrusive igneous 12

ACCEPTED MANUSCRIPT endmembers, exhibit similar (10 – 20%) enrichments of DSi in marine groundwaters over terrestrial groundwater concentrations (Hwang et al., 2005a; Street et al., 2008). Average marine groundwater DSi endmember concentrations equal (59 ± 43) µM for extrusive igneous (n=4) and (50 ± 41) µM for complex (n=14) lithologies, after correcting for surface water DSi

T

concentrations (Table 1). It is again important to note that the number of samples used to

IP

compute the endmember average reflects an average of multiple samples from a single study.

CR

Calculations using laboratory-derived mineral dissolution rates were made to determine

US

whether our estimated DSi enrichment in marine groundwater could be supported by weathering processes in the STE and permeable marine sediment (Table 2, Supplemental Information). In

AN

the following calculations, we assumed residence times ranging from 1 and 28 days, somewhere

M

between the ~0.5 – 40 days range observed for seawater circulation through the STE in these endmembers (Anschutz et al., 2009; Goodridge and Melack, 2014; Oh and Kim, 2016;

ED

Tamborski et al., 2017b). An exposure or subsurface residence time of 1 – 7 days leads to a

PT

global marine SGD-driven DSi flux of 0.1 – 1.2 Tmol y-1 from lithogenic dissolution of extrusive igneous sediment, or marine groundwater DSi concentrations of ~7 – 102 µM. For complex

CE

lithology sediments, a marine SGD-driven DSi flux of ~0.04 – 1.4 Tmol y-1 , or marine DSi

AC

concentrations of ~1.6 – 40 µM, will be released from lithogenic dissolution after ~7 and 28 days residence time, respectively, using dissolution rates observed in incubations under flow-through conditions (Anschutz et al., 2009; Ehlert et al., 2016; Supplemental Information). If we assume higher surface area values, such as those observed in marine basalts, these estimates would be even higher (Nielsen and Fisk, 2010). Further, surface area and porosity increase by a factor of six from un-weathered to weathered igneous rocks (Navarre-Sitchler et al., 2013). Several studies have found orders of magnitude lower dissolution rates for above ground terrestrial

13

ACCEPTED MANUSCRIPT weathering processes via carbonic acid (Dessert et al., 2003; Navarre-Sitchler and Brantley, 2007), however, these studies do not fit the criteria needed to represent the STE. It should be noted that the residence times taken here are primarily reflective of nearshore circulation processes, whereas deeper marine groundwater flow paths, including those flow paths farther

T

offshore, may have substantially longer subsurface residence times (Michael et al., 2011; Wilson

IP

2005), which may approach a saturated equilibrium-state with silicate minerals. Other factors

CR

such as the formation of protective gel-like layers on mineral surfaces (e.g., Daux et al., 1997; Oelkers and Gislason, 2001; Techer et al., 2001; Gislason and Oelkers, 2003), reprecipitation of

US

secondary mineral phases (Daux et al., 1997; Staudigel et al., 1998), and the presence of

AN

microbes or organic ligands will enhance or inhibit Si release rates into solution (Ahmed and Holmström, 2015; Brehm et al., 2005; Staudigel et al., 1998, 1995; Ullman et al., 1996,

M

Supplemental Information).

ED

Extrapolation of the range of DSi concentrations (i.e., 7 – 102 µM for igneous extrusive,

PT

and 1.6 – 40 µM for complex endmember) derived from dissolution rate experiments (Supplemental Information) to the global STE suggests that lithogenic dissolution, rather than

CE

dissolution of biogenic Si alone, can drive the observed non-conservative DSi enrichments in

AC

marine SGD (Table 1, Table 2, Figure 4). It is critical to distinguish between dissolution of sediments and biogenic silica when considering the impacts of marine DSi fluxes on other elemental budgets (e.g., Li and Ge) and isotope ratios of elements associated with silicate mineral weathering. For example, the Ge/Si ratio from biogenic silica is much lower than Ge/Si ratio from mineral dissolution (Mortlock and Froelich,1987; Kurtz et al., 2002). Silicon isotope ratios should also be different in DSi sourced from minerals (i.e., δ 30 Si ~0‰) versus biogenic

14

ACCEPTED MANUSCRIPT opal dissolution (i.e., δ 30 Si ~ -2‰), whereas secondary mineral formation will preferentially incorporate the light isotope (e.g., Ehlert et al., 2016a, Frings et al., 2016). The global DSi flux from total SGD was recently estimated to equal 3.8 ± 1.0 Tmol y-1 (Cho et al., 2018) from a global total SGD volume of 1.2 ± 0.3 *1014 m3 y-1 (Kwon et al., 2014).

T

Subtracting the terrestrial SGD DSi flux calculated here, 0.7 ± 0.1 Tmol y-1 , suggests that the

IP

marine component of SGD is responsible for an input of 3.1 ± 1.0 Tmol y-1 of net new dissolved

CR

silica to the ocean. This value implies that global marine groundwater has an average DSi

US

concentration of ~26 µM, which is within a factor of ~2 of the extrapolated DSi enrichment factors in extrusive igneous and complex endmember lithologies (Table 1, Figure 4). It is not

AN

surprising that this derived value of 26 µM DSi is approximately two times lower than our

M

reported marine enrichment values of 50 µM (complex) and 59 µM (extrusive igneous) as we assume, based on the behavior of DSi which we observe in these compiled studies, that the other

ED

four lithologies do not contribute significant net new DSi from marine groundwaters (Table 1;

PT

Figures 3 and 4). Our DSi enrichment factors underestimate the global non-conservative DSi enrichment in brackish SGD, which is captured in the analysis of Cho et al. (2018). However,

CE

Cho et al. (2018) fail to capture the true terrestrial SGD DSi endmember, as they exclude coastal

AC

groundwater samples with a salinity <10. 3.3 Uncertainties From the current analysis, the SGD-driven net new DSi fluxes from terrestrial and marine groundwater to the global ocean are 0.7 ± 0.1 Tmol y-1 and 3.1 ± 1.0 Tmol y-1 , respectively. These DSi fluxes will vary depending on factors such as the volume of terrestrial SGD, volume of marine SGD and DSi enrichment factors in the STE. Observed non-conservative DSi enrichments in marine SGD (Table 1, Figures 3 and 4), which is supported by DSi dissolution

15

ACCEPTED MANUSCRIPT experiments (Section 3.2; Table 2, Supplemental Information), clearly point toward a substantial marine SGD-driven DSi flux to the global ocean. Here there are two primary sources of uncertainty: (1) the volume of terrestrial SGD to the global ocean and (2) the global lithology dataset. These points are discussed in detail below.

IP

T

(1): We use the volume of terrestrial SGD (2.4 *1012 m3 y-1 ) estimated by Zektser et al. (2006) to estimate the terrestrial SGD-driven DSi flux to the global ocean. The global river

CR

discharge to the ocean is between (30 – 35) *1012 m3 y-1 (Milliman and Farnsworth, 2013), such

US

that terrestrial SGD from the model used here is between 6 – 8% of global runoff. One recent modeling estimate suggests that terrestrial SGD for the contiguous United States is between 1 – 2

AN

% of surface runoff (Sawyer et al., 2016), while another estimate suggests this value could be as high as 13% (Befus et al., 2017). A previous study suggested that global terrestrial SGD varies

M

between 0.01 – 10% of the global riverine discharge (Taniguchi et al., 2002). Uncertainty in the

ED

terrestrial SGD flux will inherently lead to uncertainty in the terrestrial SGD-driven DSi flux to

PT

the ocean. The uncertainty in observed terrestrial SGD DSi concentrations (Table 1; Figure 4, Table S2) reflects natural variability in the global DSi endmember. We note that there are no

CE

reported uncertainties for the terrestrial SGD volume (Zektser et al., 2006). Here, we assume a

AC

100% uncertainty based on the observed 2 – fold difference in the terrestrial SGD volume flux estimate along the east coast of the United States (Befus et al., 2017; Sawyer et al., 2016). For the purposes of this study, we are only concerned with the ocean basin-scale and global-scale SGD estimates for our terrestrial SGD DSi flux calculations. The terrestrial SGD model of Zekster et al. (2006) represents an average annual terrestrial SGD volume. Terrestrial SGD is known to vary seasonally in response to variations in aquifer recharge (via precipitation) and specific storage. The migration of the freshwater-saltwater16

ACCEPTED MANUSCRIPT interface in the coastal aquifer can displace large volumes of marine groundwater (Michael et al., 2005), controlled by both the elevation of the groundwater head and variations in sea level (Gonneea et al., 2013). For example, terrestrial SGD-driven DSi fluxes lagged seasonal rainfall by approximately three months along a karstic Mediterranean shoreline (Garcia-Orellana et al.,

T

2010a). However, total SGD may be in steady-state on decadal time-scales, as suggested for the

IP

North Atlantic Ocean (Charette et al., 2015).

CR

(2): In this analysis, we have utilized a global lithology classification with a 2̊ by 2̊ raster

US

spatial resolution (Gibbs and Kump, 1994) to estimate a DSi endmember for each of the coastal catchment areas in the global hydrologic-hydrogeological model (Zektser et al., 2006). At

AN

present there are higher resolution global lithological maps available (Dürr et al., 2005;

M

Hartmann and Moosdorf, 2012). However, it is not suitable to use these higher resolution models with the current hydrologic-hydrogeological model, as the distribution of coastal catchment areas

ED

in the present model (122 in total) is too coarse to accurately reflect overlying spatial

PT

heterogeneity in surface lithology at such a fine-scale (Zektser et al., 2006). The future development of high-resolution global SGD models will allow for the proper implementation of

CE

these higher-resolution global lithology datasets; indeed, such an analysis may reveal spatial

AC

variability in SGD-driven DSi fluxes (and other solutes) that are not apparent in the present analysis. As can be seen in Figure 2, the lack of data from the African continent and Southern/Eastern coasts of Asia adds another layer of uncertainty. These regions require further study. 3.4 Implications for the global DSi mass balance The total SGD-driven DSi flux to the global ocean is estimated as (3.8 ± 1.0) Tmol y-1 from

228

Ra/Si ratios and a global

228

Ra inverse model (Cho et al., 2018). This flux is up to ~50%

17

ACCEPTED MANUSCRIPT of the global maximum riverine DSi flux and is up to 1.4 Tmol greater than annual DSi inputs from hydrothermal vents and seafloor weathering (Figure 6). SGD is the second largest ocean DSi input source, after rivers; hence, SGD is an important vector in transporting DSi to the global ocean. Depending on local conditions and diagenetic regime, the SGD DSi flux from

T

shallow aquifers will likely be processed through some form of a coastal or estuarine filter before

IP

reaching the open ocean.

CR

The largest estimated source of silica to the ocean is via rivers: ~6.2 ± 1.8 Tmol y-1 as

US

dissolved silica (DSi) and an additional 1.1 – 1.9 Tmol y-1 as amorphous Si (ASi), or noncrystalline siliceous particulates such as riverine biogenic silica (Conley, 1997; Laruelle et al.,

AN

2009; Tréguer and De La Rocha, 2013; Frings et al., 2016), which dissolve upon contact with brackish and saline water, for a total dissolved riverine DSi flux of 7.3 – 8.1 Tmol y-1 . Addition

M

of the various flux terms brings the total DSi flux to the global ocean to 14.1 – 14.9 Tmol y-1 ,

ED

considering the range of SGD inputs and the range of riverine DSi inputs (Figure 6). The

PT

additional, previously undocumented source of DSi via marine SGD (3.1 ± 1.0 Tmol y-1 ) will play an important role in coastal primary production. As the coastal ocean becomes more

CE

enriched in anthropogenic-derived nutrients, there may be a fundamental shift in ecosystem

AC

functioning, for example, a shift in tropical ecosystems from coral-dominated to macroalgaedominated. Relatively high DSi fluxes from SGD were suggested to help maintain mixed algal populations in a heavily industrialized bay (Lee et al., 2009). SGD-driven nutrient fluxes, including DSi, were associated with coastal primary production in diffuse- flow environments along permeable coastlines in Japan, but not from volcanic freshwater spring environments (Sugimoto et al., 2017). Marine SGD may be a critical and overlooked source of this nutrient in coastal areas draining extrusive igneous and complex lithologies. Comparison between the

18

ACCEPTED MANUSCRIPT terrestrial SGD-driven DSi flux (0.7 Tmol y-1 ) to that of the global terrestrial SGD-driven NO3 -N flux of 0.1 Tmol y-1 (Beusen et al., 2013) suggests that the global input of terrestrial groundwater has a N:Si ratio of ~0.14, approximately 14 times lower than Redfield ratio. Terrestrial SGDdriven N loads will continue to increase in the near future (decadal time scales) due to

T

anthropogenic activities, while terrestrial SGD-driven DSi (and DIP) fluxes are expected to

IP

remain relatively constant, aside from any seasonal variation in outflow or reductions due to

CR

damming and groundwater withdrawal (Tréguer and De La Rocha, 2013).

US

At present, more data are needed to explicitly distinguish between relative contributions of biogenic Si dissolution and lithogenic Si dissolution via marine SGD to the total benthic Si

AN

flux to the water column. Such data may include proxies which can trace biological versus

M

lithological sources, such as stable Si isotopes (e.g., Ehlert et al., 2016; Frings et al., 2016) or Ge/Si ratios (e.g., Baronas et al., 2017; Kurtz et al., 2002, 2011) of water overlying the sediment

ED

water interface, and accurate estimates of sedimentary biogenic silica storage in the distal coastal

PT

zone. This is an important distinction because biogenic silica dissolution would not constitute a new source of DSi to the ocean. Previous conceptual models of the marine silica cycle did not

CE

consider DSi input fluxes from marine SGD (Laruelle et al., 2009; Tréguer and De La Rocha,

AC

2013; Frings et al., 2016). Several large-scale global studies on the marine silica cycle may lend support to the magnitude of this marine SGD DSi flux pathway. Consider that total sedimentary silica storage estimates and burial fluxes in the proximal coastal zone are approximately four – five times higher than in previous budgets (i.e., 2 Tmol y-1 versus 7.8 – 8.6 Tmol y-1 burial) once biogenic silica sequestration via reverse weathering reactions is taken into account (Figure 6; Laruelle et al., 2009; Rahman et al., 2017). In order to reconcile this observation with dissolved and biogenic silica fluxes in detailed box models such as the one constructed by Laruelle et al.

19

ACCEPTED MANUSCRIPT (2009), either the standing stock of biogenic silica in the proximal coastal zone must be higher than 4.5 Tmol Si y-1 , or the average Si/C ratio of the biogenic silica burial flux must be higher than 0.15 in this region. Another explanation is that the biogenic silica export flux from the proximal coastal zone to the open ocean must be higher than 1.1 Tmol y-1 , or total continental

T

weathering fluxes (which includes SGD) must be greater than 14.6 Tmol y-1 . These changes can

IP

be supported in the conceptual model of the marine silica cycle when reverse weathering

CR

reactions, increased DSi inputs from SGD (both terrestrial and marine) and standing stocks of silicifiers other than pelagic diatoms (Baines et al., 2012; Krause et al., 2017) are considered.

US

Estimates of biogenic silica arriving to the sea floor in the open ocean are ~40% lower than

AN

sedimentary DSi fluxes to the water column (Honjo et al., 2008). This led Frings et al. (2017) to propose that there must be additional sources of DSi from the benthos to the water column,

32

Si-based estimates of sedimentary biogenic silica storage fluxes (Rahman et al., 2017)

ED

addition,

M

beyond biogenic silica dissolution, to reconcile sediment trap data with benthic fluxes. In

may exceed regional riverine DSi input fluxes. For example, biogenic silica storage estimates in

PT

Long Island Sound are ~0.003 – 0.0035 Tmol y-1 whereas riverine DSi inputs are ~0.0018 Tmol

CE

y-1 , evidence which supports an additional pathway for net DSi inputs via marine SGD (Garcia-

AC

Orellana et al., 2014; Tamborski et al., 2017). This additional DSi efflux to the ocean will impact current conceptual marine models of other elements (and their respective isotopic compositions) closely associated with silicate minerals and silicate weathering, such as Li (Misra and Froelich, 2012) and Ge (Baronas et al., 2017), as well as the stable isotopes of Si. Marine records of Ge and the isotopes of Li have been proposed as past continental weathering proxies, whereas δ 30 Si of biogenic silica is being investigated as a paleo-nutrient utilization proxy (De La Rocha et al., 1998). The DSi flux from

20

ACCEPTED MANUSCRIPT marine SGD may carry a unique δ 30 Si signature (Ehlert et al., 2016b) from that of terrestrial groundwater inputs, which has important implications in the global δ 30 Si budget (Frings et al., 2016). If marine SGD is also important in the marine Ge and Li budgets, then the missing marine sinks of Ge and Li are greater than previously thought (King et al., 2000; Misra and Froelich,

IP

T

2012; Baronas et al., 2017). Inclusion of total SGD in the global marine silica budget will lower the estimate of the

CR

average oceanic residence time of Si by 25%, from ~10,000 y to ~7,500 y. If more observational

US

evidence supporting the estimate of dissolution of riverine quartz is found (~2 – 8 Tmol y-1 ) (Morin et al., 2015), then including this additional input flux will further reduce the estimated

AN

residence time of Si by at least 2,000 – 2,500 y. This calls into question whether the marine silica cycle is in steady-state and further complicates interpretations of several paleo-proxies. Oceanic

M

silica sinks include biogenic opal burial in deep ocean sediments, ~2 Tmol y-1 in the Southern

ED

Ocean and ~1 Tmol y-1 in the open ocean (Tréguer and De La Rocha, 2013). Based on C:Si

PT

ratios, approximately 3.3 Tmol y-1 of Si burial has been proposed for continental margins and coastal zones (DeMaster, 2002; Tréguer and De La Rocha, 2013), which has left ~4 – 5 Tmol y-1

CE

of silica unaccounted for in the global marine budget, i.e. the “missing silica sink” (DeMaster,

AC

2002). Recently, two overlooked sinks of biogenic silica, which may constitute the bulk of this missing marine sink, have been reported via burial of sublittoral sponges (~3.6 Tmol y-1 ) (Maldonado et al., 2011; Tréguer and De La Rocha, 2013) and reverse weathering reactions in the proximal coastal zone (4.5 – 4.9 Tmol y-1 ; Rahman et al., 2017). At present, there is greater evidence of sedimentary silica sequestration via rapid authigenic clay formation (see Michalopoulos and Aller 2004 and Rahman et al. 2017 and references therein for further review) than for biogenic silica burial via sponges (Maldonado et al., 2011; Bertolino et al., 2017).

21

ACCEPTED MANUSCRIPT Considering the addition of DSi via marine SGD and only removal via rapid authigenic clay formation in the marine budget (Figure 6), then the total global ocean silica sink is ~10.8 – 11.6 Tmol y-1 . If steady-state is assumed, this suggests that there is between ~1 – 3 Tmol y-1 of biogenic silica (more if one considers Morin et al., 2015) remaining unaccounted for in the

T

marine silica cycle. Burial by sponge spicules in colder high- latitude waters may account for this

IP

sink, or authigenic clay formation in distal coastal zone regions (Odin, 1990; Rao et al., 1995;

CR

Ehlert et al., 2016a; Presti et al., 2016) or other shelf, slope and open ocean regions (Rickert et al., 2002; Ku and Walter, 2003; Baldermann et al., 2015; Tatzel et al., 2015) where there is

US

evidence of reverse weathering. In addition, the biogenic silica burial flux in continental margins

AN

as unaltered biogenic opal, currently estimated at 3.3 – 3.7 Tmol Si y-1 (Tréguer and De La Rocha, 2013; Rahman et al., 2017), may be revised as we begin to explicitly constrain this sink

M

with more coupled Si and C burial studies (DeMaster, 2002; Tréguer and De La Rocha, 2013).

ED

SGD-driven DSi fluxes may vary over geologic time, particularly during

PT

glacial/interglacial transition periods. Riverine DSi fluxes are approximately two-fold greater during glacial periods despite reduced surface runoff, compared to non-glacial periods (Froelich

CE

et al., 1992); as such, terrestrial SGD-driven DSi fluxes may vary proportionally in magnitude, in

AC

part due to greater groundwater recharge from subglacial meltwater (Boulton et al., 1996). It remains to be seen how marine SGD may vary over glacial/interglacial periods, due to the complex interplay between exposed permeable shorelines, sea-level height and tidal variations, which, taken together, determine the spatial extent of marine SGD and its overall magnitude. Georg et al. (2009) used a 2-box model, adapted from De La Rocha and Bickle (2005), to assess the relative importance of variable groundwater discharge fluxes over the last 32,000 years. Their results suggest that changes in river and groundwater DSi fluxes were too small to

22

ACCEPTED MANUSCRIPT significantly alter the global ocean DSi inventory, while only slightly lowering the global ocean δ30 Si during glacial periods. An inherent assumption in the original model (De La Rocha and Bickle, 2005) is that the stable Si isotope composition of inputs did not vary over time, however, this idea requires further verification (Opfergelt et al., 2013; Frings et al., 2016) since δ30 Si

T

groundwater signatures appear to vary with depth and source (terrestrial vs. marine) in a sandy

IP

beach STE (Ehlert et al., 2016b). Further, these modeling efforts assumed a residence time of Si

CR

in the ocean of ~10,000 y. Regardless, these variable inputs and their associated δ 30 Si signatures may impact interpretations of δ 30 Si in the marine record when reconstructing past nutrient

US

utilization over glacial/interglacial cycles (Frings et al., 2016).

AN

4 Conclusions In this study, we present new data on dissolved silica (DSi) in nine subterranean

M

estuaries, representing different endmember lithologies. These data, combined with literature-

ED

derived DSi endmembers in terrestrial and marine submarine groundwater discharge (SGD), were compiled with strict salinity ranges to calculate terrestrial endmember DSi concentrations

PT

(salinity ≤ 6) and marine SGD DSi enrichment factors (salinity ≥ surface seawaters). These

CE

endmember values were used, in turn, in a global terrestrial SGD model to reevaluate the DSi flux from SGD to the global ocean. Results suggest that the terrestrial (fresh) SGD input of DSi

AC

is ~10% of the global river flux, or 0.7 ± 0.1 Tmol y-1 , 58% of which enters the Pacific Ocean. A recent estimate of the total (terrestrial + marine) SGD DSi flux to the global ocean (3.8 ± 1.0 Tmol y-1 ; Cho et al., 2018) suggests that marine SGD is accountable for supplying over 3 Tmol Si y-1 . Revision of SGD-driven net new DSi inputs, supported by lithogenic dissolution rate calculations, increases the total DSi input (riverine, SGD, eolian, hydrothermal and seafloor weathering) to the global ocean by ~25 – 30%, for a total of ~14.1 – 14.9 Tmol y-1 , depending upon the volumetric flux of marine groundwater. These results indicate that SGD is, at present, 23

ACCEPTED MANUSCRIPT the second largest source of DSi to the global ocean; this process must play a major role in regulating fluxes of this nutrient to the global coastal ocean and likely impacts coastal zone primary production. Sea-level rise will further inundate coastal aquifers with seawater, which may further enhance the dissolution of quartz, basalt and aluminosilicates, leading to potentially

T

greater DSi fluxes from SGD to the global ocean. The SGD-driven DSi flux may alter the δ30 Si

IP

signatures in the ocean and impact its use as a nutrient utilization and water-mass mixing proxy.

CR

Finally, our results indicate that the residence time of Si in the ocean may be significantly shorter

US

than the ~10,000 y estimate in the current global marine Si budgets.

AN

Acknowledgments, Samples, and Data The authors thank Christina Heilbrun, Bob Aller and Henry Bokuniewicz for discussions and logistical support. We thank Paul Henderson and the WHOI Nutrient Analytical Facility for

M

dissolved Si analyses, and Meagan Gonneea, Alexandra Rao and Henrieta Dulai for help with

ED

sample collection. We thank Sambuddha Misra and an anonymous reviewer for their insight and helpful comments when revising this manuscript. M. Charette acknowledges funding from NSF

PT

OCE-0751525 and OCE-1458305. J. Tamborski and J.K. Cochran acknowledge funding from

CE

New York Sea Grant R/CMC-12. The authors declare no competing financial interests. Corresponding authors are S. Rahman ([email protected]) and J. Tamborski

AC

([email protected] mip.fr). Material requests may be submitted to J.K. Cochran (Long Island Sound samples) and M. Charette (all other samples). Tables S1, S2, S3 and S4 are presented in a separate Microsoft Excel document. References Abarca, E., Karam, H., Hemond, H., Harvey, C.F., 2013. Transient groundwater dynamics in a coastal aquifer: The effects of tides, the lunar cycle and the beach profile, Water Resour. Res. 49, 2473-2488. doi:10.1022/wrcr.20075. 24

ACCEPTED MANUSCRIPT Advocat, T., Chouchan, J. L., Crovisier, J. L., Guy, C., Daux, V., Jegou, C., Gin, S., Vernaz, E., 1998. Borosilicate Nuclear Waste Glass Alteration Kinetics: Chemical Inhibition and Affinity Control, MRS Proc. 506, 63–70. doi:10.1557/PROC-506-63. Ahmed, E., Holmström, S. J. M., 2015. Microbe – mineral interactions : The impact of surface attachment on mineral weathering and element selectivity by microorganisms, Chem. Geol. 403, 13–23. doi:10.1016/j.chemgeo.2015.03.009.

IP

T

Anschutz, P., Smith, T., Mouret, A., Deborde, J., Bujan, S., Poirier, D., Lecroart, P., 2009. Tidal sands as biogeochemical reactors. Estuar. Coast. Shelf Sci. 84(1), 84–90. doi:10.1016/j.ecss.2009.06.015.

CR

Anschutz, P., Charbonnier, C., Deborde, J., Deirmendjian, L., Poirier, D., Mouret, A., Buquet, D., Lecroart, P., 2016. Terrestrial groundwater and nutrient discharge along the 240-kmlong Aquitanian coast. Mar. Chem. 185, 38–47. doi:10.1016/j.marchem.2016.04.002.

US

Baines, S. B., Twining, B. S., Brzezinski, M. A., Krause, J. W., Vogt, S., Assael, D., McDaniel, H., 2012. Significant silicon accumulation by marine picocyanobacteria. Nature Geoscience. 5(12), 886. doi: 10.1038/ngeo1641.

AN

Baldermann, A., Warr, L. N., Letofsky-Papst, I., Mavromatis, V., 2015. Substantial iron sequestration during green-clay authigenesis in modern deep-sea sediments. Nat. Geosci. 8(11), 885–889. doi:10.1038/ngeo2542.

M

Baronas, J. J., Hammond, D. E., McManus, J., Wheat, C. G., Siebert, C., 2017. A Global Ge isotope budget. Geochim. Cosmochim. Acta. 203, 265–283 . doi:10.1016/j.gca.2017.01.008.

PT

ED

Beck, A. J., Tsukamoto, Y., Tovar-Sanchez, A., Huerta-Diaz, M., Bokuniewicz, H. J., SañudoWilhelmy, S. A., 2007. Importance of geochemical transformations in determining submarine groundwater discharge-derived trace metal and nutrient fluxes. Appl. Geochemistry. 22(2), 477–490. doi:10.1016/j.apgeochem.2006.10.005.

CE

Beck, A. J., Charette, M. A., Cochran, J. K., Gonneea, M. E., Peucker-Ehrenbrink, B., 2013. Dissolved strontium in the subterranean estuary - Implications for the marine strontium isotope budget. Geochim. Cosmochim. Acta. 117, 33–52. doi:10.1016/j.gca.2013.03.021.

AC

Befus, K.M., Kroeger, K.D., Smith, C.G., Swarzenski, P.W., 2017. The magnitude and origin of groundwater discharge to Eastern U.S. and Gulf of Mexico coastal waters. Geophysical Research Letters. 44, 10,396-10,406. doi:10.1002/2017GL075238 Bertolino, M., Cattaneo-vietti, R., Pansini, M., Santini, C., Bavestrello, G., 2017. Siliceous sponge spicule dissolution : In field experimental evidences from temperate and tropical waters. Estuar. Coast. Shelf Sci. 184, 46–53. doi:10.1016/j.ecss.2016.10.044. Beusen, A.H.W., Slomp, C.P., Bouwman, A.F., 2013. Global land-ocean linkage: direct inputs of nitrogen to coastal waters via submarine groundwater discharge. Environ. Res. Lett. 8, 034035. doi: 10.1088/1748-9326/8/3/034035. Boehm, A. B., Shellenbarger, G. G., Paytan, A., 2004. Groundwater discharge: Potential association with fecal indicator bacteria in the surf zone. Environ. Sci. Technol. 38(13), 3558–3566. doi:10.1021/es035385a. 25

ACCEPTED MANUSCRIPT Boulton, G. S., Caban, P. E., van Gijssel, K., Leijnse, A., Punkari, M., a. van Weert, F. H., 1996. The impact of glaciation on the groundwater regime of Northwest Europe. Glob. Planet. Change. 12(1–4), 397–413. doi:10.1016/0921-8181(95)00030-5. Brehm, U., Gorbushina, A., Mottershead, D., 2005. The role of microorganisms and biofilms in the breakdown and dissolution of quartz and glass. Geobiology: Objectives Concepts, Perspectives. 219, 117–129. doi: 10.1016/B978-0-444-52019-7.50011-5

IP

T

Burnett, W. C., Bokuniewicz, H., Huettel, M., Moore, W., Taniguchi, M., 2003. Groundwater and pore water inpunts to the coastal zone. Biogeochemistry. 66, 3–33. doi:10.1023/B:BIOG.0000006066.21240.53.

CR

Burnett, W. C. et al., 2006. Quantifying submarine groundwater discharge in the coastal zone via multiple methods. Sci. Total Environ. 367(2–3), 498–543. doi:10.1016/j.scitotenv.2006.05.009.

US

Burnett, W. C., Wattayakorn, G., Taniguchi, M., Dulaiova, H., Sojisuporn, P., Rungsupa, S., Ishitobi, T., 2007. Groundwater-derived nutrient inputs to the Upper Gulf of Thailand. Cont. Shelf Res. 27(2), 176–190. doi:10.1016/j.csr.2006.09.006.

AN

Charette, M. A., Sholkovitz, E. R., 2006. Trace element cycling in a subterranean estuary: Part 2. Geochemistry of the pore water. Geochim. Cosmochim. Acta. 70(4), 811–826. doi:10.1016/j.gca.2005.10.019.

ED

M

Charette, M. A., Henderson, P. B., Breier, C. F., Liu, Q., 2013. Submarine groundwater discharge in a river-dominated Florida estuary. Mar. Chem. 156, 3–17. doi:10.1016/j.marchem.2013.04.001.

PT

Charette, M.A., Morris, P.J., Henderson, P.B., Moore, W.S., 2015. Radium isotope distributions during the US GEOTRACES North Atlantic cruises. Mar. Chem. 177, 184-195. doi:10.1016/j.marchem.2015.01.001.

CE

Cho, H.M., Kim, G., 2016. Determining groundwater Ra end-member values for the estimation of the magnitude of submarine groundwater discharge using Ra isotope tracers. Geophys. Res. Lett. 43(8), 3865-3871. doi: 10.1002/2016GL068805.

AC

Cho, H.M., Kim, G., Kwon, E.Y., Moosdorf, N., Garcia-Orellana, J., Santos, I.R., 2018. Radium tracing nutrient inputs through submarine groundwater discharge in the global ocean. Nature Scientific Reports. 8:2439. doi: 10.1038/s41598-018-20806-2 Conley, D. J., 1997. Riverine contribution of biogenic silica to the oceanic silica budget. Limnol. Oceanogr. 42(4), 774–777. doi:10.4319/lo.1997.42.4.0774. Daux, V., Guy, C., Advocat, T., Crovisier, J.-L., Stille, P., 1997. Kinetic aspects of basaltic glass dissolution at 90°C: role of aqueous silicon and aluminium. Chem. Geol. 142, 109–126. doi:10.1016/S0009-2541(97)00079-X. Davis, S.N., 1964. Silica in streams and ground water. American Journal of Science. 262(7), 870–891. doi:10.2475/ajs.262.7.870. De La Rocha, C. L., Bickle, M. J., 2005. Sensitivity of silicon isotopes to whole-ocean changes in the silica cycle. Mar. Geol. 217(3–4), 267–282. doi:10.1016/j.margeo.2004.11.016. 26

ACCEPTED MANUSCRIPT De La Rocha, C. L., Brzezinski, M. A., DeNiro, M. J., Shemesh, A., 1998. Silicon- isotope composition of diatoms as an indicator of past oceanic change. Nature. 395, 680–683. DeMaster, D. J., 2002. The accumulation and cycling of biogenic silica in the Southern Ocean: Revisiting the marine silica budget. Deep. Res. Part II Top. Stud. Oceanogr. 49(16), 3155– 3167. doi:10.1016/S0967-0645(02)00076-0.

T

Dessert, C., Dupré, B., Gaillardet, J., Franois, L.M., Allégre, C.J., 2003. Basalt weathering laws and the impact of basalt weathering on the global carbon cycle. Chem Geol. 202(3-4), 257273. doi: 10.1016/j.chemgeo.2002.10.001.

CR

IP

Dollar, S. J., Atkinson, M. J., 1992. Effects of nutrient subsidies from groundwater to nearshore marine ecosystems off the island of Hawaii. Estuar. Coast. Shelf Sci. 35(4), 409–424. doi:10.1016/S0272-7714(05)80036-8.

US

Dürr, H.H., Meybeck, M., Dürr, S.H., 2005. Lithologic composition of the Earth's continental surfaces derived from a new digital map emphasizing riverine material transfer. Global Biogeochem. Cycles. 19(4), GB4S10. doi: 10.1029/2005GB002515.

AN

Dürr, H. H., Meybeck, M., Hartmann, J., Laruelle, G. G., Roubeix, V., 2011. Global spatial distribution of natural riverine silica inputs to the coastal zone. Biogeosciences. 8(3), 597– 620. doi:10.5194/bg-8-597-2011.

ED

M

Ehlert, C., Doering, K., Wallmann, K., Scholz, F., Sommer, S., Grasse, P., Geilert, S., Frank, M., 2016a. Stable silicon isotope signatures of marine pore waters - Biogenic opal dissolution versus authigenic clay mineral formation. Geochim. Cosmochim. Acta. 191, 102–117. doi:10.1016/j.gca.2016.07.022.

PT

Ehlert, C., Reckhardt, A., Greskowiak, J., Liguori, B. T. P., Boning, P., Paffrath, R., Brumsack, H.-J., Pahnke, K., 2016b. Transformation of silicon in a sandy beach ecosystem: Insights from stable silicon isotopes from fresh and saline groundwaters. Chem. Geol. 440, 207–218. doi:10.1016/j.chemgeo.2016.07.015.

CE

Frings, P.J., 2017. Revisiting the dissolution of biogenic Si in marine sediments: a key term in the ocean Si budget. Acta Geochimica. 36(3), 429-43. doi: 10.1007/s11631-017-0183-1.

AC

Frings, P. J., Clymans, W., Fontorbe, G., De La Rocha, C. L., Conley, D. J., 2016. The continental Si cycle and its impact on the ocean Si isotope budget. Chem. Geol. 425, 12–36. doi:10.1016/j.chemgeo.2016.01.020. El-Gamal, A. A., Peterson, R. N., Burnett, W. C., 2012. Detecting Freshwater Inputs via Groundwater Discharge to Marina Lagoon, Mediterranean Coast, Egypt. Estuaries and Coasts. 1–14. doi:10.1007/s12237-012-9539-2. Froelich, P. N., Blanc, V., Mortlock, R. A., Chillrud, S. N., Dunstan, W., Udomkit, A., Peng, T. H., 1992. River Fluxes of Dissolved Silica to the Ocean Were Higher during Glacials: Ge/Si In Diatoms, Rivers, and Oceans. Paleoceanography. 7(6), 739–767. doi: 10.1029/92PA02090 Garcia-Orellana, J., Cochran, J. K., Bokuniewicz, H., Daniel, J. W. R., Rodellas, V., Heilbrun, C., 2014. Evaluation of 224 Ra as a tracer for submarine groundwater discharge in Long Island Sound (NY). Geochim. Cosmochim. Acta. 141, 314–330, 27

ACCEPTED MANUSCRIPT doi:10.1016/j.gca.2014.05.009. Garcia-Solsona, E., Garcia-Orellana, J., Masqué, P., Rodellas, V., Mejías, M., Ballesteros, B., Domínguez, J. A., 2010a. Groundwater and nutrient discharge through karstic coastal springs (Castelló, Spain). Biogeosciences. 7(9), 2625–2638. doi:10.5194/bg-7-2625-2010.

T

Garcia-Solsona, E., Garcia-Orellana, J., Masqué, P., Garcés, E., Radakovitch, O., Mayer, A., Estradé, S., Basterretxea, G., 2010b. An assessment of karstic submarine groundwater and associated nutrient discharge to a Mediterranean coastal area (Balearic Islands, Spain) using radium isotopes. Biogeochemistry. 97, 211-229. doi: 10.1007/s10533-009-9368-y.

CR

IP

Georg, R. B., West, A. J., Basu, A. R., Halliday, A. N., 2009. Silicon fluxes and isotope composition of direct groundwater discharge into the Bay of Bengal and the effect on the global ocean silicon isotope budget. Earth Planet. Sci. Lett. 283(1–4), 67–74. doi:10.1016/j.epsl.2009.03.041.

US

Gibbs, M. T., Kump, L. R., 1994. Global chemical erosion during the Last Glacial Maximum and the present: Sensitivity to changes in lithology and hydrology. Paleoceanography. 9(4), 529543. doi:10.1029/94PA01009.

M

AN

Gislason, S. R., Oelkers, E. H., 2003. Mechanism, rates, and consequences of basaltic glass dissolution: II. An experimental study of the dissolution rates of basaltic glass as a function of pH and temperature. Geochim. Cosmochim. Acta. 67(20), 3817–3832. doi:10.1016/S0016-7037(00)00176-5.

ED

Godoy, J. M., Souza, T. A., Godoy, M. L. D. P., Moreira, I., Carvalho, Z. L., Lacerda, L. D., Fernandes, F. C., 2013. Groundwater and surface water quality in a coastal bay with negligible fresh groundwater discharge: Arraial do Cabo, Brazil. Mar. Chem. 156, 85–97. doi:10.1016/j.marchem.2013.05.004.

CE

PT

Gonneea, M. E., Charette, M. A., Liu, Q., Herrera-Silveira, J. A., Morales-Ojeda, S. M., 2014. Trace element geochemistry of groundwater in a karst subterranean estuary (Yucatan Peninsula, Mexico). Geochim. Cosmochim. Acta. 132, 31–49. doi:10.1016/j.gca.2014.01.037.

AC

Gonneea, M.E., Mulligan, A.E., Charette, M.A., 2013. Climate-driven sea level anomalies modulate coastal groundwater dynamics and discharge. Geophys. Res. Lett. 40, 2701-2706. doi:10.1002/grl.50192. Goodridge, B.M., Melack, J.M., 2014. Temporal evolution and variability of dissolved inorganic nitrogen in beach pore water revealed using radon residence times. Environ. Sci. Technol. 48, 14211-14218. doi: 10.1021/es504017j. Guo, Q., Li, H., 2015. Terrestrial-originated submarine groundwater discharge through deep multilayered aquifer systems beneath the seafloor. Hydrol. Process. 29, 295-309. doi:10.1002/hyp.10163. Hartmann, J., Moosdorf, N., 2012. The new global lithological map database GLiM: A represntation of rock properties at the Earth surface. Geochem. Geophys. Geosyst. 13, Q12004. doi: 10.1029/2012GC004370. Hernández-Terrones, L., Rebolledo-Vieyra, M., Merino-Ibarra, M., Soto, M., Le-Cossec, A., 28

ACCEPTED MANUSCRIPT Monroy-Ríos, E., 2011. Groundwater pollution in a karstic region (NE Yucatan): Baseline nutrient content and flux to coastal ecosystems. Water. Air. Soil Pollut. 218(1–4), 517–528. doi:10.1007/s11270-010-0664-x. Herrera-Silveira, J. A., 1994. Spatial heterogeneity and seasonal patterns in a tropical coastal lagoon, J. Coast. Res., 10(3), 738–746.

T

Holleman, K., 2011. Impact of flux, residence time and nutrient load of submarine groundwater discharge on coastal phytoplankton growth in coastal waters of Hawai’i, University of Hawaii.

CR

IP

Honjo, S., Manganini, S. J., Krishfield, R. A., Francois, R., 2008. Particulate organic carbon fluxes to the ocean interior and factors controlling the biological pump: A synthesis of global sediment trap programs since 1983. Progress in Oceanography. 76(3), 217-285. doi: 10.1016/j.pocean.2007.11.003.

US

Hwang, D.-W., Lee, Y.-W., Kim, G., 2005a. Large submarine groundwater discharge and benthic eutrophication in Bangdu Bay on volcanic Jeju Island, Korea. Limnol. Oceanogr. 50(5), 2005, 1393–1403.

AN

Hwang, D. W., Kim, G., Lee, Y. W., Yang, H. S., 2005b. Estimating submarine inputs of groundwater and nutrients to a coastal bay using radium isotopes. Mar. Chem. 96(1–2. 61– 71. doi:10.1016/j.marchem.2004.11.002.

M

Hydrogeoscience Press 1999. World map of hydrogeological conditions and groundwater flow Water Problem Institute of the Russian Academy of Sciences, UNESCO.

ED

IPCC 2006, 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan.

PT

Johannes, R. E., Hearn, C. J., 1985. The effect of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off Perth, Western Australia. Estuar. Coast. Shelf Sci. 21(6), 789–800. doi:10.1016/0272-7714(85)90073-3.

CE

Johnson, A.G., 2008. Groundwater discharge from the leeward half of the Big Island, Hawai’i, Masters in Science thesis, University of Hawai’i.

AC

Jones, M. T., Pearce, C. R., Oelkers, E. A., 2012. An experimental study of the interaction of basaltic riverine particulate material and seawater. Geochim. Cosmochim. Acta. 77, 108 – 120. doi: 10.1016/j.gca.2011.10.044. Jones, M. T. Gislason, S. R., Burton, K. W., Pearce, C. R., Mavromatis, V., Pogge von Strandmann, P. A. E., Oelkers, E. H., 2014. Quantifying the impact of riverine particulate dissolution in seawater on ocean chemistry. Earth Planet. Sci. Lett. 395, 91 – 100. doi:10.1016/j.epsl.2014.03.039. Kim, G., Ryu, J. W., Yang, H. S., Yun, S. T., 2005. Submarine groundwater discharge (SGD) into the Yellow Sea revealed by 228 Ra and 226 Ra isotopes: Implications for global silicate fluxes. Earth Planet. Sci. Lett. 237(1–2), 156–166. doi:10.1016/j.epsl.2005.06.011. Kim, G., Ryu, J. W., Hwang, D. W., 2008. Radium tracing of submarine groundwater discharge 29

ACCEPTED MANUSCRIPT (SGD) and associated nutrient fluxes in a highly-permeable bed coastal zone, Korea. Mar. Chem. 109(3–4), 307–317. doi:10.1016/j.marchem.2007.07.002. King, S. L., Froelich, P. N., Jahnke, R. A., 2000. Early diagenesis of germanium in sediments of the Antarctic South Atlantic: In search of the missing Ge sink. Geochim. Cosmochim. Acta. 64(8), 1375–1390. doi:10.1016/S0016-7037(99)00406-8.

IP

T

Knee, K., Street, J. H., Grossman, E. G., Paytan A., 2010. Nutrient inputs to the coastal ocean from submarine groundwater discharge in a groundwater-dominated system: Relation to land use (Kona coast, Hawaii, U.S.A.). Limnol. Oceanogr. 55(3), 1105–1122. doi:10.4319/lo.2010.55.3.1105.

CR

Knee, K. L., Crook, E. D., Hench, J. L., Leichter, J. J., Paytan, A., 2016. Assessment of submarine groundwater discharge (SGD) as a source of dissolved radium and nutrients to Moorea (French Polynesia) coastal waters. Estuaries and Coasts, 39(6), 1651–1668. doi:10.1007/s12237-016-0108-y.

US

Kohout, F.A., 1967. Ground-water flow and the geothermal regime of the Floridian Plateau. Trans. Gulf Coast Assoc. Geol. Soc. 17, 339-354.

M

AN

Krause, J. W., Brzezinski, M. A., Baines, S. B., Collier, J. L., Twining, B. S., Ohnemus, D. C., 2017. Picoplankton contribution to biogenic silica stocks and production rates in the Sargasso Sea. Global Biogeochemical Cycles. 31(5), 762-774. doi: 10.1002/2017GB005619.

ED

Ku, T. C. W., Walter, L. M., 2003. Syndepositional formation of Fe-rich clays in tropical shelf sediments, San Blas Archipelago, Panama. Chem. Geol. 197(1–4), 197–213. doi:10.1016/S0009-2541(02)00363-7.

PT

Kurtz, A. C., Derry, L. A., Chadwick, O. A., 2002. Germanium-silicon fractionation in the weathering environment. Geochim. Cosmochim. Acta. 66(9), 1525-1537. doi: 10.1016/S0016-7037(01)00869-9.

CE

Kurtz, A.C., Lugolobi, F. and Salvucci, G., 2011. Germanium‐silicon as a flow path tracer: Application to the Rio Icacos watershed. Water Resources Research 47(6), W016516. doi:10.1029/2010WR009853.

AC

Kwon, E. Y., Kim, G., Primeau, F., Moore, W. S., Cho, H.-M., DeVries, T., Sarmiento, J. L., Charette, M. A., Cho, Y.-K., 2014. Global estimate of submarine groundwater discharge based on an observationally constrained radium isotope model. Geophys. Res. Lett. 41, 8438–8444. doi:10.1002/ 2014GL061574. Lander, M.A., Jenson, J., Beausoliel, C., 2001. Responses of well water levels on northern Guam to variations of rainfall and sea level, Technical Report No. 94: Water and Environmental Research Institute of the Western Pacific University of Guam. 1-36. www.weriguam.org/docs/reports/94.pdf. Laruelle, G. G. et al., 2009. Anthropogenic perturbations of the silicon cycle at the global scale: Key role of the land-ocean transition. Global Biogeochem. Cycles. 23(4), 1–17. doi:10.1029/2008GB003267. 30

ACCEPTED MANUSCRIPT Lecher, A. L., Mackey, K., Kudela, R., Ryan, J., Fisher, A., Murray, J., Paytan, A., 2015. Nutrient loading through submarine groundwater discharge and phytoplankton growth in Monterey bay, CA. Environ. Sci. Technol. 49(11), 6665–6673. doi:10.1021/acs.est.5b00909. Lecher, A. L., Chien, C.-T., Paytan A., 2016. Submarine groundwater discharge as a source of nutrients to the North Pacific and Arctic coastal ocean. Mar. Chem. 186, 167–177. doi:10.1016/j.marchem.2016.09.008.

IP

T

Lee, C. M., Jiao, J. J., Luo, X., Moore W. S., 2012. Estimation of submarine groundwater discharge and associated nutrient fluxes in Tolo Harbour, Hong Kong. Sci. Total Environ. 433, 427–433. doi:10.1016/j.scitotenv.2012.06.073.

US

CR

Lee, Y.W., Kim, G., Lim, W.A., Hwang, D.W., 2010. A relationship between submarine groundwater borne nutrients traced by Ra isotopes and the intensity of dinoflagellate redtides occurring in the southern sea of Korea. Limnol. Oceanogr. 55(1), 1–10. doi:10.4319/lo.2010.55.1.0001.

AN

Lee, Y. W., Hwang, D. W., Kim, G., Lee, W. C., Oh, H. T., 2009. Nutrient inputs from submarine groundwater discharge (SGD) in Masan Bay, an embayment surrounded by heavily industrialized cities. Korea, Sci. Total Environ. 407(9), 3181–3188. doi:10.1016/j.scitotenv.2008.04.013.

M

Li, L., Barry, D. A., Stagnitti, F., Parlange, J.-Y., 1999. Submarine groundwater discharge and associated chemical input to a coastal sea. Water Resour. Res. 35(11), 3253–3259. doi:doi:10.1029/1999WR900189.

ED

Li, R. H., Liu, S. M., Li, Y. W., Zhang, G. L., Ren, J. L., Zhang, J., 2014. Nutrient dynamics in tropical rivers, lagoons, and coastal ecosystems of eastern Hainan Island, South China Sea. Biogeosciences. 11(2), 481–506. doi:10.5194/bg-11-481-2014.

CE

PT

Liu, S. M., Li, R. H., Zhang, G. L., Wang, D. R., Du, J. Z., Herbeck, L. S., Zhang, J., Ren, J. L., 2011. The impact of anthropogenic activities on nutrient dynamics in the tropical Wenchanghe and Wenjiaohe Estuary and Lagoon system in East Hainan, China. Mar. Chem. 125(1–4), 49–68. doi:10.1016/j.marchem.2011.02.003.

AC

Loucaides, S., 2009. Dissolution of biogenic silica: Roles of pH, salinity, pressure, electrical charging and reverse weathering, Utretch University. Loucaides, S., Van Cappellen, P., Behrends, T., 2008. Dissolution of biogenic silica from land to ocean: Role of salinity and pH. Limnol. Oceanogr. 53(4), 1614–1621. doi:10.4319/lo.2008.53.4.1614. Luo, X., Jiao, J. J., Moore, W. S., Lee, C. M., 2014. Submarine groundwater discharge estimation in an urbanized embayment in Hong Kong via short-lived radium isotopes and its implication of nutrient loadings and primary production. Mar. Pollut. Bull. 82(1–2), 144– 154. doi:10.1016/j.marpolbul.2014.03.005. Maldonado, M., Navarro, L., Grasa, A., Gonzalez, A., Vaquerizo, I., 2011. Silicon uptake by sponges: a twist to understanding nutrient cycling on continental margins. Sci. Rep., 1. 2011. doi:10.1038/srep00030. 31

ACCEPTED MANUSCRIPT Mandal, A. K., Zhang, J., Asai, K., 2011. Stable isotopic and geochemical data for inferring sources of recharge and groundwater flow on the volcanic island of Rishiri, Japan. Appl. Geochemistry, 26(9–10), 1741–1751. doi:10.1016/j.apgeochem.2011.05.001. Michael, H.A., Charette, M.A., Harvey, C.F., 2011. Patterns and variability of groundwater flow and radium activity at the coast: A case study from Waquoit Bay, Massachusetts. Mar. Chem. 127, 100-114. doi: 10.1016/j.marchem.2011.08.001.

IP

T

Michael., H.A., Mulligan, A.E., Harvey, C.F., 2005. Seasonal oscillations in water exchange between aquifers and the coastal ocean. Nature. 436(7054), 1145-1148. doi: 10.1038/nature03935.

CR

Michael, H.A., Scott, K.C., Koneshloo, M., Yu, X., Khan, M.R., Li, K., 2016. Geologic influence on groundwater salinity drives large seawater circulatio n through the continental shelf. Geophysical Research Letters. 43, 10,782-10,791. doi:10.1002/2016GL070863.

US

Michalopoulos, P., Aller, R. C., 2004. Early diagenesis of biogenic silica in the Amazon delta: Alteration, authigenic clay formation, and storage. Geochim. Cosmochim. Acta. 68(5), 1061–1085. doi:10.1016/j.gca.2003.07.018.

AN

Milliman, J. D., Farnsworth, K.L., 2013. River Discharge to the Coastal Ocean: A Global Synthesis, Cambridge Univ. Press, 24(4), 143–160. doi:10.5670/oceanog.2011.108.

M

Misra, S., Froelich, P. N., 2012. Lithium isotope history of Cenozoic seawater: changes in silicate weathering and reverse weathering. Science (80). 335(6070), 818–823. doi:10.1126/science.1214697.

ED

Moore, W. S., 1999. The subterranean estuary: A reaction zone of ground water and sea water. Mar. Chem. 65(1–2), 111–125. doi:10.1016/S0304-4203(99)00014-6.

PT

Moore, W.S., 2010. The effect of submarine groundwater discharge on the ocean. Annu. Rev. Marine Sci. 2, 59-88. doi:10.1146/annurev- marine-120308-081019.

CE

Moore, W.S., Krest, J., Taylor, G., Roggenstein, E., Joye, S., Lee, R., 2002. Thermal evidence of water exchange through a coastal aquifer: Implications for nutrient fluxes. Geophys. Res. Lett. 29(14), 1704. doi:10.1029/2002GL014923.

AC

Moore, W. S., Sarmiento, J. L., Key, R. M., 2008. Submarine groundwater discharge revealed by 228 Ra distribution in the upper Atlantic Ocean. Nat. Geosci. 1(5), 309–311. doi:10.1038/ngeo183. Moore, W.S. Wilson, A.M., 2005. Advective flow through the upper continental shelf driven by storms, buoyancy, and submarine groundwater discharge. Earth Planet. Sci. Lett. 235, 564576. doi:10.1016/j.epsl.2005.04.043. Morin, G. P., Vigier, N., Verney-Carron, A., 2015. Enhanced dissolution of basaltic glass in brackish waters: Impact on biogeochemical cycles. Earth Planet. Sci. Lett. 417, 1–8. doi:10.1016/j.epsl.2015.02.005. Mortlock, R. A., Freohlich, P. N., 1987. Continental weathering of germanium: GeSi in the global river discharge. Geochimica et Cosmochimica Acta. 51(8), 2075-2082. doi: 10.1016/0016-7037(87)90257-2. 32

ACCEPTED MANUSCRIPT Navarre-Sitchler, A., Brantley, S., 2007. Basalt weathering across scales. Earth Planet. Sci. Lett. 261(1-2), 321-334. doi: 10.1016/j.epsl.2007.07.010. Navarre-Sitchler, Cole, A. K., D. R., Rother, G., Jin, L., Buss, H. L., Brantley, S. L., 2013. Porosity and surface area evolution during weathering of two igneous rocks. Geochim. Cosmochim. Acta. 109, 400–413. doi:10.1016/j.gca.2013.02.012.

T

Nielsen, M. E., Fisk, M. R., 2010. Surface area measurements of marine basalts: Implications for the subseafloor microbial biomass. Geophys. Res. Lett. 37(15), 1–5. doi:10.1029/2010GL044074.

CR

IP

Niencheski, L. F. H., Windom, H. L., Moore, W. S., Jahnke, R. A., 2007. Submarine groundwater discharge of nutrients to the ocean along a coastal lagoon barrier, Southern Brazil. Mar. Chem. 106(3–4), 546–561. doi:10.1016/j.marchem.2007.06.004.

US

Null, K. A., Dimova, N. T., Knee, K. L., Esser, B. K., Swarzenski, P. W., Singleton, M. J., Stacey, M., Paytan, A., 2012. Submarine groundwater discharge-derived nutrient loads to San Francisco Bay: Implications to future ecosystem changes. Estuaries and Coasts. 35(5), 1299–1315. doi:10.1007/s12237-012-9526-7.

M

AN

Null, K. A., Knee, K. L., Crook, E. D., de Sieyes, N. R., Rebolledo-Vieyra, M., HernándezTerrones, L., Paytan, A., 2014. Composition and fluxes of submarine groundwater along the Caribbean coast of the Yucatan Peninsula. Cont. Shelf Res. 77, 38–50. doi:10.1016/j.csr.2014.01.011.

ED

O'Connor, A.E., Krask, J.L., Canuel, E.A., Beck, A.J., 2017. Seasonality of major redox constituents in a shallow subterranean estuary. Geochim. Cosmochim. Acta. 224, 344-361. doi:10.1016/j.gca.2017.10.013.

PT

Odin, G. S., 1990. Clay mineral formation at the continent-ocean boundary: the verdine facies. Clay Miner. 25, 477–483. doi:10.1180/claymin.1990.025.4.06.

CE

Oelkers, E. H., Gislason, S. R., 2001. The mechanism, rates and consequences of basaltic glass dissolution: I. An experimental study of the dissolution rates of basaltic glass as a function of aqueous Al, Si and oxalic acid concentration at 25°C and pH = 3 and 11. Geochim. Cosmochim. Acta. 65(21), 3671–3681. doi:10.1016/S0016-7037(01)00664-0.

AC

Oelkers, E. H., Gislason, S. R., Eiriksdottir, E. S., Jones, M., Pearce, C. R., Jeandel, C., 2011. The role of riverine particulate material on the global cycles of the elements. Appl. Geochemistry. 26, S365–S369. doi:10.1016/j.apgeochem.2011.03.062. Oelkers, E. H., Jones, M. T., Pearce, C. R., Jeandel, C., Eiriksdottir, E. S., Gislason, S. R., 2012. Riverine particulate material dissolution in seawater and its implications for the global cycles of the elements, G. R. Geosci., 344, 646 – 651. Oh, Y.H., Kim, G., 2016. Large seasonal changes in the recharge of seawater in a subterranean estuary revealed by a radon tracer. Hydrol. Process. 30, 2525-2532. doi: 10.1002/hyp.10807. Onodera, S., Saito, M., 2007. Nutrient dynamics with groundwater – seawater interactions in a beach slope of a steep island , western Japan., A New Focus on Groundwater-Seawater Interactions. IAHS Publ. 312, 150–158. 33

ACCEPTED MANUSCRIPT Opfergelt, S., Burton, K. W., Pogge von Strandmann, P. A. E., Gislason, S. R., Halliday, A. N., 2013. Riverine silicon isotope variations in glaciated basaltic terrains: Implications for the Si delivery to the ocean over glacial- interglacial intervals. Earth Planet. Sci. Lett. 369–370, 211–219. doi:10.1016/j.epsl.2013.03.025. Post, V.E.A., Groen, J., Kooi, H., Person, M., Ge, S., Edmunds, W.M., 2013. Offshore fresh groundwater reserves as a global phenomenon, Nature., 504, 71-78. doi:10.1038/nature12858.

IP

T

Powley, H. R., Krom, M. D., Van Cappellen, P., 2017. Understanding the unique biogeochemistry of the Mediterranean Sea: Insights from a coupled phosphorus and nitrogen model. Global Biogeochem. Cycles. 31, 1010–1031. doi:10.1002/ 2017GB005648.

CR

Presti, M., Michalopoulos, P., Kamperi, E., Anagnostou, C., 2016. Biogenic silica storage in the Danube Delta.

US

Rahman, S., Aller R. C., Cochran, J. K., 2017. The missing silica sink: revisiting the marine sedimentary Si cycle. Global Biogeochem. Cycles. 31, 1559-1578. doi:10.1002/2017GB005746.

AN

Rao, V. P., Thamban, M., Lamboy, M., 1995. Verdine and glaucony facies from surficial sediments of the eastern continental margin of India. Mar. Geol. 127(1–4), 105–113. doi:10.1016/0025-3227(95)00056-5.

ED

M

Rengarajan, R., Sarma, V. V. S. S., 2015. Submarine groundwater discharge and nutrient addition to the coastal zone of the Godavari estuary. Mar. Chem. 172, 57–69. doi:10.1016/j.marchem.2015.03.008.

PT

Rickert, D., Schlüter, M., Wallmann, K., 2002. Dissolution kinetics of biogenic silica from the water column to the sediments. Geochim. Cosmochim. Acta. 66(3), 439–455. doi:10.1016/S0016-7037(01)00757-8.

CE

Rocha, C., Wilson, J., Scholten, J., Schubert, M., 2015. Retention and fate of groundwater-borne nitrogen in a coastal bay (Kinvara Bay, Western Ireland) during summer. Biogeochemistry. 125(2), 275–299. doi:10.1007/s10533-015-0116-1.

AC

Rodellas, V., Garcia-Orellana, J., Masqué, P., Feldman, M., Weinstein, Y., 2015. Submarine groundwater discharge as a major source of nutrients to the Mediterranean Sea. Proc. Natl. Acad. Sci. U. S. A. 112(13), 3926–30. doi:10.1073/pnas.1419049112. Sanial, V., Buesseler, K. O., Charette, M. A., Nagao, S., 2017. Unexpected source of Fukushimaderived radiocesium to the coastal ocean of Japan. Proc. Natl. Acad. Sci. U. S. A. 114(42), 11092 – 11096. doi:10.1073/pnas.1708659114. Santos, I. R., Eyre, B. D., Huettel, M., 2012. The driving forces of porewater and groundwater flow in permeable coastal sediments: A review. Estuar. Coast. Shelf Sci. 98, 1–15. doi:10.1016/j.ecss.2011.10.024. Sawyer, A. H., David, C. H., Famiglietti, J. S., 2016. Continental patterns of submarine groundwater discharge reveal coastal vulnerabilities. Science. 353(6300), 705–707.. doi: 10.1126/science.aag1058. 34

ACCEPTED MANUSCRIPT Schopka, H. H., Derry, L. A., 2012. Chemical weathering fluxes from volcanic islands and the importance of groundwater: The Hawaiian example. Earth Planet. Sci. Lett. 339–340, 67– 78. doi:10.1016/j.epsl.2012.05.028. Staudigel, H., Chastain, R. A., Yayanos, A., Bourcier, W., Livermore, L., 1995. Biologically mediated dissolution of glass. Chemical Geology. 126, 147–154. doi: 10.1016/00092541(95)00115-X.

IP

T

Staudigel, H., Yayanos, A., Chastain, R., Davies, G., Verdurmen, E. A. T., Schiffman, P., Bourcier, R., De Baar, H., 1998. Biologically mediated dissolution of volcanic glass in seawater. Earth Planet. Sci. Lett. 164, 233–244. doi:10.1016/S0012-821X(98)00207-6.

CR

Street, J. H., Knee, K. L., Grossman, E. E., Paytan, A., 2008. Submarine groundwater discharge and nutrient addition to the coastal zone and coral reefs of leeward Hawai’i. Mar. Chem. 109(3–4), 355–376. doi:10.1016/j.marchem.2007.08.009.

US

Strickland, J. D. H., Parsons, T. R., 1972. A practical handbook of seawater analysis, 2nd ed., Fishery Research Board of Canada, Ottawa.

AN

Su, N., Du, J., Moore, W. S., Liu, S., Zhang, J., 2011. An examination of groundwater discharge and the associated nutrient fluxes into the estuaries of eastern Hainan Island, China using 226 Ra. Sci. Total Environ. 409(19), 3909–3918. doi:10.1016/j.scitotenv.2011.06.017.

ED

M

Sugimoto, R., Kitagawa, K., Nishi, S., Honda, H., Yamada, M., Kobayashi, S., Shoji, J., Ohsawa, S., Taniguchi, M., Tominaga, O., 2017. Phytoplankton primary productivity around submarine groundwater discharge in nearshore coasts. Estuaries and Coasts. 563, 25–33. doi:10.3354/meps11980.

PT

Swarzenski, P. W., Simonds, F. W., Paulson, A. J., Kruse, S., Reich, C., 2007a. Geochemical and geophysical examination of submarine groundwater discharge and associated nutrient loading estimates into lynch cove, Hood Canal, WA. Environ. Sci. Technol. 41(20), 7022– 7029. doi:10.1021/es070881a.

CE

Swarzenski, P. W., Reich, C., Kroeger, K. D., Baskaran, M., 2007b. Ra and Rn isotopes as natural tracers of submarine groundwater discharge in Tampa Bay, Florida. Mar. Chem. 104(1–2), 69–84. doi:10.1016/j.marchem.2006.08.001.

AC

Szymczycha, B., Maciejewska, A., Winogradow, A., Pempkowiak, J., 2014. Could submarine groundwater discharge be a significant carbon source to the southern Baltic Sea? Oceanologia. 56(2), 327 – 347. doi:10.5697/oc.56-2.327. Tamborski, J., Bejannin, S., Garcia-Orellana, J., Souhaut, M., Charbonnier, C., Anschutz, P., Pujo-Pay, M., Conan, P., Crispi, O., Monnin, C., Stieglitz, T., Rodellas, V., Andrisoa, A., Claude, C., van Beek, P., 2018. A comparison between water circulation and terrestriallydriven dissolved silica fluxes to the Mediterranean Sea traced using radium isotopes. Geochim. Cosmochim. Acta. 238, 496–515. doi:10.1016/j.gca.2018.07.022. Tamborski, J. J., Cochran, J. K., Bokuniewicz, H. J., 2017. Application of 224 Ra and 222 Rn for evaluating seawater residence times in a tidal subterranean estuary. Mar. Chem. 189, 32–45. doi:10.1016/j.marchem.2016.12.006. Tamborski, J.J., Rogers, A.D., Bokuniewicz, H.J., Cochran, J.K., Young, C.R., 2015. 35

ACCEPTED MANUSCRIPT Identification and quantification of diffuse fresh submarine groundwater discharge via airborne thermal infrared remote sensing. Remote Sens. Environ. 171, 202-217. doi: 10.1016/j.rse.2015.10.010 Taniguchi, M., Burnett, W. C., Cable, J. E., Turner, J. V., 2002. Investigation of submarine groundwater discharge. Hydrol. Process. 16(11), 2115–2129. doi:10.1002/hyp.1145.

T

Tatzel, M., von Blanckenburg, F., Oelze, M., Schuessler, J. A., Bohrmann, G., 2015. The silicon isotope record of early silica diagenesis. Earth Planet. Sci. Lett. 428, 293–303. doi:10.1016/j.epsl.2015.07.018.

CR

IP

Techer, I., Advocat, T., Lancelot, J., Liotard, J. M., 2001. Dissolution kinetics of basaltic glasses: Control by solution chemistry and protective effect of the alteration film. Chem. Geol. 176(1–4), 235–263. doi:10.1016/S0009-2541(00)00400-9.

US

Tovar-Sánchez, A., Basterretxea, G., Rodellas, V., Sánchez-Quiles, D., García-Orellana, J., Masqué, P., Jordi, A., López, J. M., Garcia-Solsona, E., 2014. Contribution of groundwater discharge to the coastal dissolved nutrients and trace metal concentrations in Majorca Island: Karstic vs detrital systems. Environ. Sci. Technol. 48, 11819-11827. doi:10.1021/es502958t.

AN

Tréguer, P. J., De La Rocha, C. L., 2013. The world ocean silica cycle. Ann. Rev. Mar. Sci. 5(1), 477–501. doi:10.1146/annurev- marine-121211-172346.

ED

M

Tréguer, P., Bowler, C., Moriceau, B., Dutkiewicz, S., Gehlen, M., Aumont, O., Bittner, L., Dugdale, R., Finkel, Z., Iudicone, D., Jahn, O., Guidi, L., Lasbleiz, M., Leblanc, K., Levy, M., Pondaven, P., 2018. Influence of diatom diversity on the ocean biological carbon pump. Nature Geoscience. 11, 27-37. doi:10.1038/s41561-017-0028-x.

PT

Ullman, W. J., Chang, B., Miller, D. C., Madsen, J. A., 2003. Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA). Estuar. Coast. Shelf Sci. 57(3), 539–552. doi:10.1016/S0272-7714(02)00398-0.

CE

Ullman, W. J., Kirchman, D. L., Welch, S. A., Vandevivere, P., 1996. Laboratory evidence for microbially mediated silicate mineral dissolution in nature. Chem. Geol. 132, 11–17. doi:10.1016/S0009-2541(96)00036-8.

AC

Urquidi-Gaume, M., Santos, I. R., Lechuga-Deveze, C., 2016. Submarine groundwater discharge as a source of dissolved nutrients to an arid coastal embayment (La Paz, Mexico). Environ. Earth Sci. 75(2), 1–13. doi:10.1007/s12665-015-4891-8. Valiela, I., Camilli, L., Stone, T., Giblin, A., Crusius, J., Fox, S., Barth-Jensen, C., Monteiro, R. O., Tucker, J., Martinetto, P., Harris, C., 2012. Increased rainfall remarkably freshens estuarine and coastal waters on the Pacific coas of Panama: Magnitude and likely effects on upwelling and nutrient supply. Global and Planetary Change. 92-93, 130-137. doi: 10.1016/j.gloplacha.2012.05.006. Wang, G., Wang, Z., Zhai, W., Moore, W. S., Li, Q., Yan, X., Qi, D., Jiang, Y., 2015. Net subterranean estuarine export fluxes of dissolved inorganic C, N, P, Si, and total alkalinity into the Jiulong River estuary, China. Geochim. Cosmochim. Acta. 149, 103–114. doi:10.1016/j.gca.2014.11.001. 36

ACCEPTED MANUSCRIPT Waska, H., Kim, G., 2011. Submarine groundwater discharge (SGD) as a main nutrient source for benthic and water-column primary production in a large intertidal environment of the Yellow Sea. J. Sea Res. 65(1), 103–113. doi:10.1016/j.seares.2010.08.001. Weinstein, Y., Yechieli, Y., Shalem, Y., Burnett, W. C., Swarzenski, P. W., Herut, B., 2011. What is the role of fresh groundwater and recirculated seawater in conveying nutrients to the coastal ocean? Environ. Sci. Technol. 45(12), 5195–5200. doi:10.1021/es104394r.

T

WHYMAP, UNESCO 2000. World-wide Hydrogeological Mapping and Assessment Programme.

CR

IP

Wilson, A.M., 2003. The occurrence and chemical implications of geothermal convection of seawater in continental shelves. Geophys. Res. Lett. 30(21), 2127. doi:10.1029/2003GL018499. Wilson, A.M., 2005. Fresh and saline groundwater discharge to the ocean: A regional perspective Water Resour. Res. 41, W02016. doi:10.1029/2004WR003399.

AN

US

Wilson, A.M., Sanford, W., Whitaker, F., Smart, P., 2001. Spatial patterns of diagenesis during geothermal circulation in carbonate platforms. Am. J. Sci. 301, 727-752. doi:10.2475/ajs.301.8.727. Ye, Q., Liu, J., Du, J., Zhang, J., 2016. Bacterial diversity in submarine groundwater along the coasts of the yellow sea. Front. Microbiol. 6, 1–14. doi:10.3389/fmicb.2015.01519.

ED

M

Young, M. B., Gonneea, M. E., Fong, D. A., Moore, W. S., Herrera-Silveira, J., Paytan, A., 2008. Characterizing sources of groundwater to a tropical coastal lagoon in a karstic area using radium isotopes and water chemistry. Mar. Chem. 109(3–4), 377–394. doi:10.1016/j.marchem.2007.07.010.

CE

PT

Zavialov, P. O., Kao, R. C., Kremenetskiy, V. V., Peresypkin, V. I., Ding, C. F., Hsu, J. T., Kopelevich, O. V., Korotenko, K. A., Wu, Y. S., Chen, P., 2012. Evidence for submarine groundwater discharge on the Southwestern shelf of Taiwan. Cont. Shelf Res. 34, 18–25. doi:10.1016/j.csr.2011.11.010. Zektser, I. S., Dzhamalov, R. G., 2006. Submarine Groundwater, edited by L. G. Everett, CRC Press.

AC

Zhang, Y., Li, L., Erler, D.V., Santos, I., Lockington, D., 2017. Effects of beach slope breaks on nearshore groundwater dynamics. Hydrol. Process. 31(14), 2530-2540. doi: 10.1002/hyp.11196.

37

ACCEPTED MANUSCRIPT Table 1. Summary of average DSi endmember concentrations in terrestrial groundwater, and marine groundwater DSi enrichments, with respect to surface waters. Marine DSi enrichments are not reported for sandstone, shield and shale lithologies due to a limited number of field observations, but a summary of available studies for these endmembers is in Table S4.

Shield (granite)

Maui and Kuai Moorea, French Polynesia Panama (Pacific Coast)

768 467 296

8 n/a n/a

Mauritius Island (Flic en Flac Beach) Jeju Island, Korea

515 749 593

Rishiri Island, Japan AVG ± STD

330 604 ± 192

Castello, Spain Minorca, Spain Majorca, Spain

M

Holleman [2011]; Schopka and Derry [2012] Street et al., [2008] Schopka and Derry, [2012] Knee et al., [2016] This study

113 65

Burnett et al., [2006]; Si data this study Hwang et al., [2005a]

n/a

Georg et al., [2009]

AN

Ganges-Brahmaputra Southwestern Shelf, Taiwan

523

IP

n/a n/a

CR

827 747

US

Oahu Molokai

T

Dollar and Atkinson [1992]; Johnson et al., [2008]; Street et al., [2008]; Knee et al., [2010]; Holleman, [2011]; Schopka and Derry, [2012]

50

Zaviolov et al., [2012] Mandal et al., [2011]

56 ± 43

60 66 42

0 0 0

Garcia-Solsona et al., [2010a] Garcia-Solsona et al., [2010b] Tovar-Sanchez et al., [2014]

La Palme Lagoon, France

114

0

Yucatan Peninsula

95

0

Celestun Lagoon, Yucatan

228

n/a

Stieglitz et al., [2013] Null et al., [2014], HernandezTerrones et al., [2011], Gonneea et al., [2014] Young et al., [2008]; HerreraSilveira, [1994]

Guam Kinvara Bay, Ireland Marina Lagoon, Egypt AVG ± STD

18 76 27 80 ± 63

0 n/a n/a

This study Rocha et al., [2015] El-Gamal et al., [2012]

Dor Bay, Israel

228

Evidence of nonconservative DSi

Weinstein et al., [2011]

Obama Bay, Japan AVG ± STD

90 159 ± 80*

n/a

Sugimoto et al., [2016]

Western Japan

467

Evidence of nonconservative DSi

Onodera and Saito, [2007]

AC Sandstone

Associated Reference

826

PT

Carbonate

Marine DSi Enrichment (µM)

Big Island, Hawai'i

ED

Extrusive Igneous

Terrestrial DSi (µM)

Locations

CE

Aquifer Type

38

ACCEPTED MANUSCRIPT Godavari Estuary, India Jiulong River, China

77 687

n/a ---

Rengarajan and Sarma, [2015] Wang et al., [2015]

Alaska, US AVG ± STD

107 334 ± 255

8

Lecher et al., [2016]

17 - no surface water data reported

Kim et al., [2005]; Ye et al., [2016] Lee et al., [2012]; Luo et al., [2014]

Yellow Sea 214 151 182 ± 91*

117

Patos-Mirim Lagoon, Brazil Arraial do Cabo, Brazil

747 294

18 n/a

La Paz, Mexico Aquitanian Coast, France Waquoit Bay, Massachusetts

998 245

25 12

Smithtown Bay, New York

59

Lych Cove, Washington

170

Tampa Bay, Florida

731

Southwest Florida

130

93

T

Tolo Harbor, Hong Kong AVG ± STD

AN

Shale

US

CR

IP

Complex

40

118

M

39

n/a Evidence of nonconservative DSi

Niencheski et al., [2007] Godoy et al., [2013] Urquidi-Gaume et al., [2016] Anschutz et al., [2016] Charette and Sholkovitz [2006]; Si data this study Tamborski et al., [2015, 2017]; Si data this study Swarzenski et al., [2007a] Swarzenski et al., [2007b]

n/a

Monterey Bay, CA Huntington Beach, CA

390 55

32 7

Lecher et al., [2015] Boehm et al., [2004]

Perth, Australia

225

Johannes and Hearn, [1985]

PT

Hainan Island, China

ED 356

Charette et al., [2013]; Si data this study Su et al., [2011], Liu et al., [2011]; Li et al., [2014]

221

Glacial Fjord, Chile Rio Susana, Argentina San Fransisco Bay, California

56 259

0 61

This study This study

189

n/a

Yeoja Bay, Korea

180

145

Null et al., [2012] Hwang et al., [2005b]; Lee et al., [2010]

Yeongil Bay, Korea Masan Bay, Korea Hampyeong Bay, Korea

86 276 n/a

n/a 23 29

Kim et al., [2008] Lee et al., [2009] Waska and Kim, [2011]

Chao Phraya, Thailand Spiekeroog, Germany AVG ± STD

279 355 288 ± 245

55 44 50 ± 41

Burnett et al., [2007] Ehlert et al., [2016]

AC

CE

Cape Henlopen, Delaware

0 Evidence of nonconservative DSi

*50% uncertainty assumed for Sandstone and Shale endmember

39

Ullman et al., [2003]

ACCEPTED MANUSCRIPT

Table 2: Summary of parameters used in the dissolution rate calculations to estimate marine SGD DSi concentrations and fluxes to the global ocean. Details can be found in Supporting Information. Marine SGD volume Scenario

(m3 y-1 )

Dissolution Rate (mol Si m-2 s-1 )

Surface area of sediment encountering marine SGD (m2 )

Surface Area (m2 g-1 )

2.35–3.52*1013

3.39–7.41*10-13 (a)

0.00566

1.85–2.77 *1017

b

2.35–3.52*1013

5.62–7.41*10-13 (b)

0.0056

1.85–2.77 *1017

c

2.35–3.52*1013

0.55–1.0*10-12 (c)

0.0134

5.83–8.74 *1017

U N

A

M

Marine SGD DSi concentrations (µM)

Marine SGD DSi Flux (Tmol y-1 )

7 – 28

1.6–6.4

0.04–0.23

7 – 28

7.4–39

0.17–1.4

7 – 28

8 – 15

0.19 – 0.53

1–7

7 – 102

0.16 – 1.2

T P

I R

C S

Complex a

Residence Time (days)

Extrusive Igneous

d

1.17–2.35*1013

4.9 *10-12 (d)

D E

0.084a

1.97 – 3.95 *1017

T P

a

Anschutz et al. (2009), dissolution rate in static incubations Anschutz et al. (2009), dissolution rate in flow-through incubations c Ehlert et al. (2016b), dissolution rate in incubations with higher solid:volume ratios d Dissolution from Techer et al. (2001), modified for temperature and salinity commonly observed in the subterranean estuary b

E C

C A

40

US

CR

IP

T

ACCEPTED MANUSCRIPT

Figure 1. Major silica sources (dashed boxes) and sinks (solid boxes) to the ocean in the global

AN

marine budget as summarized from Tréguer and De La Rocha (2013) and Frings et al. (2016).

M

Updated sinks of biogenic silica burial via rapid reverse weathering (Rahman et al., 2017) in the proximal coastal zone and as unaltered biogenic opal in continental margin sediments are

ED

included. An unknown sink of ~1–4 Tmol y-1 of silica may be via burial of sponge spicules or

PT

authigenic clay formation in other shelf, slope or open ocean regions. Idealized SGD flow paths are depicted by letters (not to scale), including terrestrial SGD driven by a positive hydraulic

CE

gradient (A), density-driven flow and flow induced by seasonal oscillations of the water table

AC

(B), wave-setup and tidal-pumping (C). Tidal-pumping and density-driven flow can extend farther offshore along the continental-shelf (D). Terrestrial and marine SGD flow paths can extend offshore from deep confined aquifers (E). Blue arrows indicate terrestrial DSi sources. Refer to Santos et al. (2012) for a complete review of SGD driving forces and mechanisms.

41

US

CR

IP

T

ACCEPTED MANUSCRIPT

AN

Figure 2. Global distribution of compiled study sites by lithology classification. Open symbols

AC

CE

PT

ED

M

are new data from this study (see Figure 3); closed symbols denote previously published studies.

42

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

CE

Figure 3. Dissolved Si versus salinity for surface water, groundwater (pore waters),

sites.

AC

springs/seeps and cenotes for the sampled study sites. Note the different y-axis scales between

43

ACCEPTED MANUSCRIPT Figure 4: Box and whisker plots of groundwater DSi distributions from major lithologies, as classified by Gibbs and Kump (1994) and Beck et al. (2013) for (A) terrestrial SGD and (B) marine SGD. Terrestrial DSi concentrations are taken from studies summarized in Table S2, whereas marine SGD DSi concentrations are taken from studies summarized in Table S3. Note

T

that the box and whisker plots include all data points summarized in this study; mean

CR

IP

endmember values reported in Table 1 reflects an average of individual study averages.

1800

1400

AN

1200 1000

M

800 600

ED

400 200

PT

0

CE

Igneous Carbonate Sandstone Shield Extrusive (granite)

AC

Terrestrial DSi (µM)

(A)

US

1600

44

Shale

Complex

ACCEPTED MANUSCRIPT 300 (B)

200

T

150

50 0

Shale

CE

PT

ED

M

AN

US

Igneous Carbonate Sandstone Shield Extrusive (granite)

CR

IP

100

AC

Marine SGD DSi (µM)

250

45

Complex

ACCEPTED MANUSCRIPT Figure 5: Summary of riverine and terrestrial SGD-driven DSi fluxes, arranged by ocean basin. Percentages denote the relative contribution of the riverine and terrestrial SGD-driven DSi flux to that basin. River DSi fluxes are summarized from Dürr et al. (2011), and do not include inputs

AC

CE

PT

ED

M

AN

US

CR

IP

T

from amorphous Si.

46

ACCEPTED MANUSCRIPT Figure 6. Revised global marine silica budget with updated terrestrial and marine SGD DSi inputs to the proximal coastal zone from this study. Marine SGD DSi inputs calculated as the difference between total SGD DSi estimates from Cho et al. (2018) and terrestrial SGD DSi inputs from this study (i.e., 0.7 ± 0.1 Tmol y-1 ). Major silica sources (dashed boxes) and sinks

T

(solid boxes) to the ocean in the global marine silica budget as summarized from Tréguer and De

IP

La Rocha (2013), Frings et al. (2016) and Rahman et al., (2017). Idealized SGD flow paths as

CR

summarized in Figure 1. Blue arrows indicate terrestrial DSi sources, red arrows indicate marine

AC

CE

PT

ED

M

AN

US

DSi sources, and grey arrows depict mixed sources.

47

AC

CE

PT

ED

M

AN

US

CR

IP

T

ACCEPTED MANUSCRIPT

48

ACCEPTED MANUSCRIPT Dissolved silica in the subterranean estuary and the impact of submarine groundwater discharge on the global marine silica budget

T

Shaily Rahmana,b , Joseph J. Tamborskic* , Matthew A. Charetted , J. Kirk Cochrana

a

IP

School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York, 11794 USA

CR

b

Present Address: Department of Geological Sciences, University of Florida, Gainesville, Florida 32611 USA Department of Geosciences, Stony Brook University, Stony Brook, New York, 11794 USA

US

c

*Present Address : Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, 02543 USA d

M

AN

Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, 02543 USA

ED

Corresponding Authors: Shaily Rahman ([email protected]), Joseph Tamborski ([email protected])

PT

Keywords:

CE

Dissolved silica, marine groundwater, lithogenic dissolution

AC

Highlights:  DSi from terrestrial (fresh) SGD is 0.7 Tmol y-1  Fluxes of DSi from SGD increase total ocean inputs by 25 – 30% over previous estimates, to ~14.1 – 14.9 Tmol y-1  Taking into account DSi inputs from SGD implies the residence time of Si is ~25% less than 10ka

49

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6