Biogeochemistry and dynamics of particulate organic matter in a shallow-water hydrothermal field (Kueishantao Islet, NE Taiwan)

Journal Pre-proof Biogeochemistry and dynamics of particulate organic matter in a shallow-water hydrothermal field (Kueishantao Islet, NE Taiwan)

Yu-Shih Lin, Jay Lee, Li-Hung Lin, Ke-Hsien Fu, Chen-Tung Arthur Chen, Yu-Huai Wang, I-Huan Lee PII:

S0025-3227(20)30009-8

DOI:

https://doi.org/10.1016/j.margeo.2020.106121

Reference:

MARGO 106121

To appear in:

Marine Geology

Received date:

3 October 2019

Revised date:

13 December 2019

Accepted date:

16 December 2019

Please cite this article as: Y.-S. Lin, J. Lee, L.-H. Lin, et al., Biogeochemistry and dynamics of particulate organic matter in a shallow-water hydrothermal field (Kueishantao Islet, NE Taiwan), Marine Geology (2020), https://doi.org/10.1016/j.margeo.2020.106121

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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.

© 2020 Published by Elsevier.

Journal Pre-proof

Biogeochemistry and dynamics of particulate organic matter in a shallow-water hydrothermal field (Kueishantao Islet, NE Taiwan)

Yu-Shih Lin1, Jay Lee1,2, Li-Hung Lin3, Ke-Hsien Fu1,4,

Department of Oceanography, National Sun Yat-Sen University, 80424 Kaohsiung,

-p

1

ro

of

Chen-Tung Arthur Chen1, Yu-Huai Wang1, I-Huan Lee1,*

Taiwan Ocean Research Institute, National Applied Research Laboratories, 80143

lP

2

re

Taiwan

na

Kaohsiung, Taiwan

Department of Geoscience, National Taiwan University, 10617 Taipei, Taiwan

4

National Academy of Marine Research, 80661 Kaohsiung, Taiwan

Jo

ur

3

*Corresponding author. E-mail: [email protected].

Page 1 of 42

Journal Pre-proof Abstract The particulate organic matter (POM) of shallow-water hydrothermal fields has been studied in the context of food web reconstruction, but the processes governing its biogeochemistry and dynamics are poorly explored. Here, we investigate the POM in the Kueishantao hydrothermal field using chemical and hydrodynamic approaches. The depletion of total suspended matter, lower C/N ratios, and higher carbon isotopic values

of

of particulate organic carbon (δ13CPOC) in the vertical plumes relative to values derived

13

C in the fine fraction. The particulate organic carbon

-p

which tend to have more N and

ro

from Si-based models were attributed to the hydraulic sorting of the vented particles,

re

(POC), unlike the total suspended matter, was enriched in the vertical plumes and

lP

explained by physicochemical processes rather than biological addition. The POCenriched plume-top water was found to be a better endmember than the vent fluids to

na

explain particle mixing in the lateral plume. Physical mixing played a steering role in

ur

shaping the particle chemistry of the lateral plumes, but markedly 13C-enriched POC was still observable in several near-vent, low-to-intermediate-Si plume waters, implying

Jo

locally enhanced primary production of at least 0.1–0.4 mg C/m3/h. The presence of eddies, confirmed by flow field measurements, should have contributed to the detection of biogeochemical anomalies via extending the retention time of plume water to 1–2 h. The dominating mixing process resulted in decoupling between the δ13CPOC signatures and carbonate chemistry in this shallow-water hydrothermal plume. Keywords

Page 2 of 42

Journal Pre-proof Shallow-water hydrothermal field; particulate organic carbon; stable carbon isotope; eddy;

Jo

ur

na

lP

re

-p

ro

of

hydraulic sorting; primary production

Page 3 of 42

Journal Pre-proof 1. Introduction Initially as a part of global manifestations of hydrothermalism (Tarasov et al., 2005) and more recently as natural CO2 perturbation laboratories (Hall-Spencer et al., 2008), shallow-water hydrothermal systems have been intensively studied from various aspects, such as gas and fluid chemistry (e.g., Pichler et al., 1999), biota (e.g., Tarasov, 2006),

of

biogeochemistry (e.g., Burrell et al., 2015), and microbiology (e.g., Gomez-Saez et al., 2017). Among these research endeavors, little attention has been given to suspended

ro

particles in the water column. Suspended particles undergo hydraulic sorting, which

-p

governs the distribution of solid matter in the water and on the seafloor. These particles

re

include microplankton, the key participants of element cycles. The particles are also an

lP

integral part of the food web, imparting chemical imprints on the biomass of their feeders (e.g., Chang et al., 2018). Knowledge of suspended particles will advance our

ur

hydrothermal ecosystems.

na

understanding of sedimentology, biogeochemistry, and ecology of shallow-water

Jo

The existing literature on suspended particles in shallow-water hydrothermal fields focuses on inorganic substances and microplankton. It is known that many shallow hydrothermal plumes have particles rich in sulfur, iron, and arsenic at various sizes (Acosta Pomar and Giuffré, 1996; Tarasov et al., 1999; Durán-Toro et al., 2019). The plumes also host abundant populations of phytoplankton and prokaryotes with photosynthetic, chemoautotrophic, and heterotrophic activities (Sorokin et al., 1998, 2003; Robinson, 2000; Burrell et al., 2015). However, few studies address the distribution and dynamics of particulate organic matter in shallow-water hydrothermal fields. In deep-sea hydrothermal studies, particulate organic matter has been a topic of interest since the

Page 4 of 42

Journal Pre-proof 1980s (Comita et al., 1984). Results from several studies show that deep-sea hydrothermal plumes have elevated particulate organic carbon (POC) contents (Comita et al., 1984; Maruyama et al., 1993; Bennett et al., 2011). The low atomic C/N ratio and high prokaryotic biomass (Winn and Karl, 1986; Juniper et al., 1998) suggest microbial addition of organic carbon in the plume water. Recent studies further distinguished between the buoyant vertical plumes, where the microbes mostly originate from entrained

of

background deep seawater and have insufficient response time to grow, and the neutrally-

ro

buoyant plumes, where the majority of microbial growth takes place (Reed et al., 2015;

-p

Sheik et al., 2015). The enrichment of fresh biomass in the otherwise barren deep ocean

re

attracts the surrounding zooplankton (Burd et al., 1992), which possibly contributed to the attenuated POC fluxes in the lateral plume (Roth and Dymond, 1989). The elevated

lP

carbon production and consumption together indicate intensified carbon cycling in the

na

plume water.

ur

To understand the dynamics of constituents carried in a fluid medium, it is essential to consider the water transport processes and retention time (Monsen et al., 2002). For deep-

Jo

sea hydrothermal systems at ocean ridges, plume water movement is mainly driven by buoyancy, geostrophic currents, topography-induced currents (Lupton and Craig, 1981), and boundary currents for plumes at continental margins (Speer and Thurnherr, 2012). The water residence times range from a few minutes in the buoyant vertical plumes (Mottl and McConachy, 1990; Reed et al., 2015) to months in the rotational event plumes (Lupton et al., 1998). Plume water of shallow-water systems is additionally affected by tides, waves, and wind. Because of the shallow water depths and vigorous hydrodynamic conditions typically found in the surface ocean, water residence times are presumably

Page 5 of 42

Journal Pre-proof much shorter than those of deep-sea plumes. For example, based on the modeled current speed at the edge of a vertical plume (Tudino et al., 2014), it took only 20‒30 s for a parcel of water to ascend from the seafloor at 10 m to the sea surface. Some studies already have acknowledged the effect of short water residence times on the experimental design (e.g., Burrell et al., 2015) and data interpretation (e.g., Lin et al., 2019), but few studies on shallow-water hydrothermal research carry out hydrodynamics measurements

of

relevant to the assessment of resident times.

ro

The Kueishantao Islet (121°57’ E, 24°50’ N; Fig. 1a), located in the Ilan Bight offshore

-p

northeast Taiwan, is a volcanic islet that has been active for at least 7 kyrs (Chen et al.,

re

2001). Submarine hydrothermal activities have been reported at various locations off the

lP

southeast coast of the islet (Chen et al., 2005). The region has undergone extensive geochemical investigations that characterize the composition and distribution of gases

na

(Yang et al., 2005; Chen et al., 2016), dissolved species (Yang et al., 2012; Chen et al.,

ur

2018), and sediment (Hung et al., 2018; Yu et al., 2019). The suspended particles have also been examined, but mainly from the perspective of microbial community

Jo

composition and functionality (Zhang et al., 2012; Tang et al., 2013, 2018; Li et al., 2018) and partly for food web reconstruction (Chang et al., 2018). The current field is affected by tides (Han et al., 2014), and the water residence time has been inferred by modeling work (tens of minutes; Lin et al., 2019). Similar to most shallow-water hydrothermal fields, there is a lack of knowledge regarding the particulate organic matter and hydrodynamics for this intensively studied site. Here, we present a study that combines biogeochemical and hydrodynamic approaches to investigate the dynamics of particulate organic matter in the Kueishantao hydrothermal

Page 6 of 42

Journal Pre-proof field. We characterized the bulk biogeochemical properties of suspended particles, including the contents of total suspended matter (TSM) and POC, the atomic C/N ratio of particulate organic matter, and the stable carbon isotopic values of POC (δ13CPOC), in the vent fluids and plume waters. We also collected hydrodynamic data from the hydrothermal field using both acoustic instruments and drifters to provide observational constraints on water motion and residence time. Lastly, we used conservative mixing

of

models, a common practice in estuarine (e.g., Ogawa et al., 1997; Bouillon et al., 2011;

ro

Guo et al., 2015) and deep-sea hydrothermal studies (e.g., Mottl and McConachy, 1990;

-p

Fitzsimmons et al., 2017), to explore the underlying mechanisms controlling the observed

re

biogeochemical pattern, including mixing, hydraulic sorting, and biological alteration. Combining the biogeochemical and hydrodynamic data, we provide estimates on how

na

lP

primary production (PP) was intensified in the near-vent water.

ur

2. Material and Methods

Jo

2.1 Sample collection

Unless otherwise noted, samples for biogeochemical characterization were collected in May 2015 (Table S1). Details of the cruises and sampling have been described in Lin et al. (2019). In short, we took samples from two transects: Transect M is affected by the hydrothermal discharge at the nearshore end, and Transect B serves as a baseline to constrain the nearshore-offshore chemical gradient with minimal hydrothermal impacts (Fig. 1b). In Transect M, there are two series of near-vent stations, Series My in the plume of the Yellow Vent (YV; 7 m water depth), and Series Mw in the plume of the

Page 7 of 42

Journal Pre-proof White Vent (WV; 10 m water depth). The term near-vent refers to the region within 20 m of the vents. The number after the alphabetical site code gives the horizontal distance in meter from the nearshore end. Vent fluid, vertical plume, and near-vent water samples were retrieved by scuba divers with the use of pre-evacuated glass bottles or Niskin bottles. The vertical plumes had dense gas bubbles and/or turbid fluid color and could be visibly distinguished from the near-vent waters. To avoid confusion, the terms ―YV‖ and

of

―WV‖ represent samples taken within the vents, whereas ―My0‖ and ―Mw0‖ refer to

ro

samples of the vertical plumes.

-p

Fluid samples were split into aliquots onboard. Samples for stable carbon isotopic

re

analysis of dissolved inorganic carbon (δ13CDIC) were transferred to glass containers, and

lP

nutrient samples were transferred to plastic containers. Both types of samples were immediately poisoned with a saturated mercury chloride (HgCl2) solution at a volume

na

ratio of 1000:1. For total cell counting, 5 mL of fluid samples were fixed with

ur

paraformaldehyde at a final concentration of 1.45%. All fluid samples were stored at 4 °C in the dark. For particle analysis, 2 L of fluid was filtered using precombusted and

Jo

preweighed Whatman GF/F glass fiber filters (diameter = 25 mm; pore size = 0.7 μm). The filter samples were stored at –20 °C. In August 2017, additional fluid samples were taken from the vents, near-vent region and Site M1230 for chlorophyll a (Chl a) analysis. The samples (0.5–0.8 L) were filtered using glass fiber filters (diameter = 47 mm; pore size = 0.7 μm), which were stored at –20 °C and analyzed in one month. 2.2 Hydrodynamic measurements

Page 8 of 42

Journal Pre-proof To understand the motion of water and the encompassed suspended particles in the hydrothermal field, both observation methods for flow field—Eulerian (moored instruments)

and

Lagrangian

(drifters)—were

applied

in

our

hydrodynamic

measurements during 8–9 August 2017. The mooring instrument set included a bottommounted acoustic Doppler current profiler (ADCP; 1200 kHz; Teledyne RD Instruments) and a taut-line T-string with four temperature-pressure loggers (Star-Oddi DST Centi-

of

TD) and eight temperature loggers (Vemco Minilog 8-bit). The mooring set was

ro

deployed in the vicinity of WV (Fig. 1b). The cell number of ADCP was 30 with 0.5 m

-p

bin size. The T-string with loggers mounted at a depth interval of 1 m was tethered to the bottom-mounted frame (Fig. 1c). All instruments on the mooring set were synchronized

re

with a 1-min sampling rate and averaged into 10-min ensembles to reduce measurement

lP

noise. During the observation, the readings of the topmost pressure sensor varied between

na

3 and 7 m, suggesting the T-string was pulled down by tidal current during stronger flow.

ur

The amplitude of sea-level variation along the east coast of Taiwan is small and in phase, with almost no tidal phase differences between Kueishantao and the nearby tidal station

Jo

Wushi (Hu et al., 2010). Hence, the hourly water elevation measurements at Wushi were used to describe the sea-level variation at Kueishantao. The major tidal components of sea-level variation were lunar semi-diurnal (M2), solar semi-diurnal (S2), luni-solar diurnal (K1), and lunar diurnal (O1), in decreasing order of dominance. The sum of the amplitudes of the four components is ~1 m, with M2 alone contributing ~50 cm. The form ratio (defined as (O1+K1)/(M2+S2)) of <0.25 suggests semi-diurnal tide dominance in our study area (calculated from the data of Hu et al., 2010). The hourly wind speed and

Page 9 of 42

Journal Pre-proof direction were recorded by the Central Weather Bureau wind buoy station off the west coast of the islet. A few wind data were missing during our mooring period. During the daytime, four drifters with a global positioning system (GPS) were released to measure the surface current around the ADCP mooring site in flood (8 Aug) and ebb (9 Aug). Two drifters were equipped with dual GPS systems as duplicate measurements.

of

The drifters were deployed in the vicinity of the mooring site and allowed to record for approximately 1–3 h and then redeployed to avoid stranding or losing track. The received

-p

ro

GPS data was smoothed by a 2-min low-pass filter to eliminate high-frequency noise.

re

2.3 Analytical procedures

Solute measurements. For δ13CDIC analysis, dissolved inorganic carbon (DIC) in fluid

lP

samples was extracted and purified with a glass vacuum system following the procedure

na

described previously (Chou et al., 2007) and measured by a Delta V Plus isotope ratio mass spectrometer (IRMS; Thermo Fisher Scientific) equipped with a dual inlet system.

ur

The reference CO2 gas (Air Liquide USA, LLC) was calibrated with international

Jo

certified standards (NIST 8562, 8563, and 8564). Values of δ13C relative to that of the standard Vienna-PeeDee Belemnite are defined by the equation δ13C (‰) = (Rsample/Rstandard‒1)×1000, with R =

C/12C and Rstandard = 0.0112372×10‒6. Repeated

13

extraction and analysis of laboratory seawater standards show that the precision was ±0.06‰. The sulfur-rich fluid samples (YV, WV, My0 and Mw0) were further purified with a mixture of 1–3 g CuSO4 powder and 1 mL of 85% H3PO4, placed in the cryotrap during vacuum extraction. The uncertainty for these sulfur-rich samples was ±0.5‰,

Page 10 of 42

Journal Pre-proof according to replicates of vent fluids. Si(OH)4 was measured by the silicomolybdenum blue method (Fanning and Pilson, 1973) with a precision of ±2% at 5 μmol/L. Cell enumeration. The fixed cells were subsequently washed with phosphate buffer saline (PBS) three times and dispensed into a 1:1 PBS:ethanol solution for long-term storage at –20 °C. Depending on the cell density, cells concentrated from different volumes of solutions were mixed with 1% low-melting agarose, and spotted on the well of the glass

of

slide. The fixed cells were dried at 60oC, and stained with SYTO-13 and 4',6-diamidino-

ro

2-phenylindole (DAPI) dyes (both from Thermo Fisher Scientific) for 30 minutes.

-p

Excessive dye was washed off using sterilized 18-m water. Cell counting was

re

performed on a microscope (BH-60, Olympus) equipped with a mercury lamp and filter

lP

set at a magnification of 1000X. To ensure the correct identification of cells, fluorescence signals generated from SYTO-13 and DAPI staining were compared. The obtained cell

na

number was converted into the cell density based on the view number and area.

ur

Particle measurements. Filters were first examined microscopically, and identifiable

Jo

zooplankton were removed using forceps. TSM was determined by weighing the dried particles collected on the filters. For the determination of POC, particulate nitrogen (PN) and δ13CPOC, the filters were acidified with 6 N of HCl, rinsed with 18-m water, freeze dried, and analyzed on the IRMS coupled to an elemental analyzer (Flash 2000; Thermo Fisher Scientific). Repeated analyses of a certified soil standard (certificate number 133317; Thermo Fisher Scientific) yielded a precision of ±3% for both POC and PN. The δ13CPOC data were calibrated with international certified standards (USGS40, USGS43, USGS64, USGS73, and NIST8542); the precision was ±0.4‰. Chl a was extracted from the filters with 10 mL of acetone:water = 9:1 (v/v) for 24 h in the dark at 4 °C and

Page 11 of 42

Journal Pre-proof measured with a fluorometer following the procedure summarized in Aminot and Rey (2001). 2.4 Calculation Statistics. The biogeochemical data were statistically analyzed using the software package SPSS Statistics® (version 24.0). The two-tailed t-tests were run assuming

of

unequal variances between the data sets.

ro

Mixing model. The conservative mixing model was adopted to calculate the theoretical

-p

chemical composition of fluid samples after mixing two aqueous endmembers. Following

re

Lin et al. (2019), we used Si(OH)4 as the conservative tracer of hydrothermal input. The mixing model was binary, with the first endmember having a higher hydrothermal

lP

component and the second being the background signal. The fraction contributed by the

na

first endmember (f1) can be derived from Eqn. (1):

ur

(1)

Jo

Si is the Si(OH)4 concentration, and the subscripts 1, 2, and m represent the first endmember, second endmember, and the mixing product, respectively. The theoretical concentration of a chemical species after mixing (Cm) can be computed by Eqn. (2): (

)

(2)

The theoretical isotopic value of a species after aqueous mixing (δm) can be derived from Eqn. (3): (

)

Page 12 of 42

(3)

Journal Pre-proof Eqn. (2) was used to calculate the theoretical TSM, POC, and PN concentrations, and the POC and PN concentrations were further used to calculate the atomic C/N ratio. Eqn. (3) was used to calculate the theoretical δ13CDIC and δ13CPOC values during conservative mixing. The standard deviations (SD) were estimated using the Monte Carlo approach. We assumed normal distribution for all independent variables, and computed the standard errors based on 100,000 permutations for each data point. The computation was

of

performed using the software package MATLAB® (version R2014a). The term

ro

―envelope‖ is used to refer to the upper (mean + SD) and lower (mean – SD) boundaries

-p

of the calculated data.

re

The extent to which a measured value deviates from prediction by the mixing model is

)

(4)

na

(

lP

quantified by Eqn. (4):

ur

Δ is the extent of deviation, xmeas the measured data, xenv the calculated value of the neighboring envelope at the same Si(OH)4 content as xmeas, and Gx the range of the

Jo

measured data set.

Settling velocity of particles. The settling velocity (Ws) of particles with a diameter D is calculated using Eqn. (5) (Soulsby, 1997): (√

)

(5)

ν is the kinematic viscosity of seawater and is calculated following El-Dessouky and Ettouney (2002), and D* is the dimensionless grain size computed as:

Page 13 of 42

Journal Pre-proof

√

(

⁄

)

(6)

g is the acceleration due to gravity, ρs the particle density, and ρ the seawater density. Two density values were used in the calculation: 2650 kg/m3 for silicates, and 2070 kg/m3 for elemental sulfur. A water temperature of 25 °C and salinity of 34 were used to

ro

of

calculate ν and ρ.

-p

3. Results

re

3.1 Chemistry of the vent fluids, vertical plumes, and near-vent waters

lP

All chemical data are listed in Table S2. Figures 2 and 3 summarize the solute and particle chemistry of the vent fluids, vertical plumes, and near-vent waters. The data of

na

the background water (all sites in Transect B) are also plotted for comparison. Table 1

ur

lists the p values of the t tests used to check if there is a significant difference (i) between the vertical plume and near-vent water, and (ii) between the near-vent water and

Jo

background water. The results suggest that the vertical plumes were indistinguishable from the near-vent waters, but the near-vent waters were statistically different from the background seawater in various aspects. The former could be coincidental, because the t tests did not distinguish differences in vertical distribution. In the following paragraphs, we highlight the depth profiles of near-vent waters when they visibly differed from those of vertical plumes. The distribution of Si(OH)4 has been detailed in our earlier work (Lin et al., 2019). In short, Si(OH)4 had the highest concentrations in the vent fluids (YV, 115 μmol/L; WV,

Page 14 of 42

Journal Pre-proof 501 μmol/L), and dropped immediately in the vertical plumes (Fig. 2). The plume and near-vent waters were significantly more enriched in Si(OH)4 (8.7±3.7 μmol/L) compared with the background water (3.0±0.7 μmol/L). The δ13CDIC values, correlating negatively with the logarithm of Si(OH)4 (r2 = 0.85; all sites included), were most negative in the vent fluids (YV, –6.7‰; WV, –6.0‰) and became more positive in the vertical plumes. DIC in the plume and near-vent waters was significantly depleted in 13C

of

(δ13CDIC = –0.75±0.88‰) relative to that of the background water (0.63±0.01‰). Though

13

C-DIC-depleted (p = 0.08) relative to the corresponding near-

-p

enriched (p = 0.13) and

ro

statistically insignificant, the vertical plume waters of YV appeared to be more Si-

re

vent waters. A downward decreasing trend in Si(OH)4 (and an increasing trend in δ13CDIC)

lP

was found in the near-vent waters of WV, but not in those of YV. The fluids of both vents were rich in particles and POC (Fig. 3): the YV had 623±140 mg

na

TSM/L and 0.5±0.1 mg POC/L, whereas the WV had 312±276 mg TSM/L and 1.0±0.5

ur

mg POC/L. The TSM contents dropped rapidly in the vertical plumes and near-vent waters. The distribution of POC contents in Series Mw followed the same distribution

Jo

pattern as TSM. However, in Series My, POC became enriched in the vertical plume relative to the vent fluid, and the near-vent waters of YV were more enriched in particulate matter (TSM = 25±8 mg/L; POC = 0.4±0.2 mg/L) than those near the WV (TSM = 14±3 mg/L; POC = 0.2±0.1 mg/L) and the background waters (TSM = 16±7 mg/L; POC = 0.2±0.1 mg/L). The C/N ratios correlated negatively with the δ13CPOC values (r2 = 0.74; all sites included). The YV fluid (C/N = 23.2; δ13CPOC = –24.6±1.1‰) had particles more depleted in N and

13

C than the WV fluid (C/N = 9.2; δ13CPOC = –

20.8±1.7‰). Particles in the vertical plumes and near-vent waters (C/N = 7.2±1.3;

Page 15 of 42

Journal Pre-proof δ13CPOC = –20.9±1.1‰) showed a trend of N and

13

C enrichment with shoaling depth,

and were significantly different from those of the background waters (C/N = 13.1±2.8; δ13CPOC = –23.3±0.7‰). Cell counts were 10 times higher in the WV (12.6×108 cells/L) than the YV (0.9×108 cells/L). The plume and near-vent waters of WV had significantly higher cell counts than the background seawater (p = 0.02; Table 1). Nevertheless, the highest cell counts (17.9±5.8×108 cells/L) were found at 5 m depth of the near-YV waters.

of

The plume and near-vent waters of both vents had reduced Chl a contents (0.14±0.08

ro

μg/L) relative to the background surface seawater (0.31 μg/L). In the near-vent waters of

-p

both vents, the bottom waters had higher Chl a concentrations than the upper waters.

re

Using Eqn. (1) and measured Si(OH)4 data of the vent fluids and background seawater as

lP

the endmembers, we calculated the hydrothermal component (fHT) of the vertical plume waters, which was then used to calculate the theoretical TSM, POC, C/N ratios, and

na

δ13CPOC following the conservative mixing model (Eqns. (2) and (3)). Figure 4 shows the

ur

results of model-data comparison. The measured data deviate from the model results in different ways: the measured TSM contents and C/N ratios were generally lower than the

Jo

modeled values, but the opposite was found for the POC and δ13CPOC data. 3.2 Chemistry of the lateral plumes The δ13CDIC and three solid-phase parameters of the surface waters (0 and 5 m) were plotted against Si(OH)4 concentration in Figure 5. The results of the mixing model, including the mixing of background waters to plume-top waters and to vent fluids, are also plotted for comparison. Most data deviate from the mixing trajectories to vent fluids,

Page 16 of 42

Journal Pre-proof but conform to the trend defined by background-plume-top mixing. Hence, the latter was adopted in the following model-data comparison. Even with the uncertainties (±1 SD) of modeled values included, some of the measured data were still outside the region bracketed by the envelopes. The δ13CDIC values of the lateral plumes (–1.6 to 0.7‰) decreased almost linearly with increasing Si(OH)4 concentration, and generally fell in the range defined by mixing (–5% < Δ < 5%). In the

of

following text, we focused on ―marked outliers‖, defined as deviating data points with a

ro

Δ value greater than 5% or lower than –5%. TSM (9–32 mg/L) and POC (0.17–0.57

-p

mg/L) contents increased with elevated Si(OH)4 concentration, but they both showed

re

substantial scatter. For TSM, Series My had two marked outliers with positive deviation

lP

(Δ = 13%), whereas Series Mw and Transect M together had six negative marked outliers with negative deviation (Δ = –6 to –15%). While the POC data were mostly in the range

na

defined by mixing, they had two marked outliers: one was in Series My (Δ = 20%), and

ur

the other in Transect M (Δ = –7%). The C/N ratios (6.1–13.0) varied nonlinearly with Si(OH)4, showing lower ratios at higher Si(OH)4 contents. The number of marked outliers

Jo

rose to four in the data set of C/N ratio data set: two negative outliers (Δ = –8%) in Series My, and two positive outliers (Δ = 13–15%) in Transect M. The δ13CPOC values (–23.2 to –19.6‰) exhibited a nonlinear increasing trend with Si(OH)4, and the data set had the highest number of marked outliers: six positive outliers with Δ values ranging from 8 to 26%, and one negative outlier with a Δ value of –14%. 3.3 Hydrodynamics

Page 17 of 42

Journal Pre-proof The moored instruments recorded data for 26 h. Figure 6 shows the sea-level variation at Wushi, the wind at Kueishantao, the horizontal velocity vectors (U, V) and temperature variation, and the vertical speed (W) variation at the mooring site. The winds were relatively weak during our observation period with velocities below 5 m/s. They varied from easterly to northerly winds on 8 Aug, and turned counterclockwise to southerly winds on 9 Aug. The U and V varied from ‒0.75 to 0.72 m/s and from ‒0.68 to 0.60 m/s,

of

respectively. According to Hu et al. (2010), the variations of tidal current and sea level in

ro

the Ilan Bight are almost in phase—the maximum westward flood (maximum eastward

-p

ebb) current occurs near the high (low) tide, and the phase of current leads the phase of

re

sea level for ~40 mins in the M2 frequency and for ~80 mins in the K1 frequency. In Figure 6, the flooding current occurred during 15:00‒22:00 of 8 Aug and 01:00‒09:00 of

lP

9 Aug, and the ebbing current occurred from 23:00 of 8 Aug to 1:00 of 9 Aug and during

na

09:00‒12:00 of 9 Aug. The asymmetric flooding and ebbing currents imply the existence of a westward mean flow. The water temperature at the mooring site rose by 1‒2 °C

ur

during the flood tides and dropped by 1‒2 °C during the ebb tides.

Jo

The variation in tidal flow was not regular, i.e., the current did not flow consistently westward (eastward) as the sea level rose (dropped). The east-west oscillation in tidal currents was frequently interrupted by short-term variations, giving rise to a complicated horizontal flow pattern. These variations were observed at six time slots: (i) 12:00‒15:00, (ii) 16:00‒17:00, (iii) 22:00‒23:30 of 8 Aug, and (iv) 00:00‒01:00, (v) 04:00‒05:00, (vi) 09:00‒10:00 of 9 Aug. During these time slots, the horizontal velocity markedly decreased, and the current changed the east-west direction.

Page 18 of 42

Journal Pre-proof A total of four drifter deployments were performed: F1-1, F1-2, E2-1, and E2-2. According to the sea-level variation, F1-1 and F1-2 were during flooding on 8 Aug, and E2-1 and E2-2 during ebbing on 9 Aug. Among these deployments, F1-1, F1-2, and E2-1 overlapped totally or partially with the first, second, and sixth time slots, respectively, of the aforementioned short-term variations in tidal flow. Figure 7 presents the tracks of the drifters, and all tracks of the four deployments were plotted on Figure 7d for comparison.

of

The tracks exhibited significant spatial differences when the drifters were deployed in

ro

different tidal phases. In the deployment F1-1 (Fig. 7a), all drifters were deployed at the

-p

mooring site (trk1, 2, 4 and 6), and three of them were later retrieved and redeployed at

re

the same start location (trk3, 5 and 7). A small eddy (diameter ca. 200 m) formed and trapped the drifters for almost two hours (13:00‒15:00). The drifters first made one

lP

counterclockwise circle (trk1, 2, 4 and 6), and then moved northwestward with increasing

na

speed (trk1, 3, 5 and 7). Generally, all drifters moved together with slight spatial differences. In the second deployment (Fig. 7b), drifters were deployed at the south of the

ur

mooring. They first moved westward for half an hour, and then made one clockwise

Jo

circular excursion (diameter ca. 100 m) in separate paths for about one hour (16:30‒ 17:30). After the excursion, they gradually accelerated to the southwest and became increasingly distant from each other. In the deployment E2-1 (Fig. 7c), all drifters started from the mooring site and moved together all the way westward with increasing speed. In the last deployment (Fig. 7d), only three drifters were deployed at the mooring site. One drifter (trk1) started at 10:15 and the two others (trk2 and trk3) at about 11:10. With such a small time difference (~1 h) in deployments, the drifters presented different tracks. Trk1 presented simply eastward flow, but trk2 and trk3 presented northward and northeastward

Page 19 of 42

Journal Pre-proof flow after partial eddy-like counterclockwise motion. The drifters deployed during both E2-1 and E2-2 were on the windward side of the islet, but only those of E2-2 moved toward the open ocean. This result suggests that eastward ebbing current in combination with the southerly wind might drive the drifters away from the east side of Kueishantao, probably in the direction toward the Kuroshio (Fig. 1a). Overall, our combined approach of ADCP and drifters surveys suggests that tidal flow induces temporary eddies

of

frequently in the vicinity of WV with lifetimes of 1‒2 h and low current speeds (< 15

ro

cm/s).

-p

Figure 6c shows that W presents strong upward flow (10‒30 cm/s) during our

re

observation, irrespective of flood or ebb tides. Only during the two high tides (18:00‒

lP

22:00 of 8 Aug and 06:00‒9:00 of 9 Aug) and one low tide (01:00‒03:00 of 9 Aug), W decreased markedly and even switched to mild downward flow (ca. ‒10 cm/s), while the

Jo

4. Discussion

ur

na

horizontal current speeds were relatively strong.

4.1 Transport, sorting, and enrichment of particulate organic matter in the vertical plumes Si(OH)4 behaves conservatively in deep-sea hydrothermal plumes (e.g., Campbell and Gieskes, 1984; Mottl and McConachy, 1990) and has been used in previous studies of shallow-water hydrothermal fields as a tracer of hydrothermal inputs (Pichler et al., 1999; Lin et al., 2019). Its behavior in the vertical plumes reflects the dilution of vent fluids via the entrainment of ambient water (Lin et al., 2019). While not exempt from the process of

Page 20 of 42

Journal Pre-proof aqueous dilution, hydrothermal particles are susceptible to the added process of hydraulic sorting. The vent-fluid particles contain a substantial fraction of coarse-grained material: grain-size analysis of vent-fluid samples taken in 2019 shows that particles with diameters larger than 63 μm constituted ~88% of the solid-phase volume (Y. S. Lin, unpublished data). The settling tendency of the coarse-grained particles was counteracted by the turbulent vent discharge that has velocities up to 1.77 m/s at the orifice (Lin et al.,

of

2019). The net result of the interplay between vent-fluid propulsion, aqueous dilution,

ro

and particle deposition is a mild negative deviation of the measured TSM contents from

-p

those predicted by conservative aqueous mixing (Fig. 4a), indicating that particle

re

deposition outweighs suspension in some of the waters.

lP

The negative deviation is in contrast to the observation by Mottl and McConachy (1990), who showed that the deep-sea vertical plume in a spreading center had more particles

na

than mixing models suggest. However, these authors attributed all plume TSM to

ur

precipitates that readily formed when the high-temperature fluids exited the vent opening; TSM was almost absent in the vent fluids they studied (cf. Von Damm et al., 1985). In

Jo

contrast, our vent fluids were already particle-rich when they were freshly collected. When examined microscopically, the vent-fluid particles contained a substantial fraction of clastic debris, which probably came from weathered volcanic rock. Such distinction in TSM content is compatible with the fact that hydrothermal vents in mid-ocean ridges are hosted by bare rock, whereas the Kueishantao hydrothermal field, like many other shallow-water systems, develops on top of a sedimented shelf. The deviation of δ13CPOC and C/N ratios (Figs. 4c and 4d) from the modeled values can also be explained by the process of hydraulic sorting should there be size-specific

Page 21 of 42

Journal Pre-proof chemical signatures for the vent-fluid particles. Such a possibility is supported by the heavier δ13CPOC values of WV particles reported by Chang et al. (2018; –18.2±1.1‰) than by the present work (–20.8±1.7‰). This difference is attributed to the fact that the former was determined using particles with a diameter <63 μm (N. N. Chang, personal communication), whereas the present work used bulk POC. Although Chang et al. (2018) did not report the corresponding C/N ratios, it is reasonable to presume a higher N

of

content in the fine fraction than the coarse fraction based on the detection of cells in the

ro

vent fluids (Fig. 3). Therefore, hydraulic sorting also imparts chemical gradients in the

-p

vertical plumes, resulting in the accumulation of 13C- and N-enriched fine particles in the

re

upper water column.

lP

The aqueous dilution caused by fluid entrainment and the removal of particles by hydraulic sorting should theoretically decrease the POC concentration in the vertical

na

plumes. However, the reverse was found for the POC data, many of which showed

ur

positive deviations from the modeled values (Fig. 4b). POC enrichment has also been observed in deep-sea plumes (Comita et al., 1984; Maruyama et al., 1993; Bennett et al.,

Jo

2011). Four possible mechanisms exist to selectively enrich POC,

13

C, and N in the

particles without significant enhancement of TSM. (i) Biological production adds organic carbon to the POC pool (Comita et al., 1984; Maruyama et al., 1993). (ii) Dissolved organic carbon is adsorbed on the plume particles, thereby enriching POC (Bennett et al., 2011). (iii) Similar to bubble and fluid fluxes (Lin et al., 2019), the fluxes of vent particles are also temporally variable. Intermittent eruptive events might yield fluids with higher TSM:Si(OH)4 ratios than regular emission, because the high venting speeds promote mobilization of particles from fissures or chimney walls. The subsequent

Page 22 of 42

Journal Pre-proof hydraulic sorting removes coarse-grained particles from the water, thus enriching POC in the vertical plumes. (iv) Carbon-rich fine particles are attached to bubbles and shuttled to the upper water column via a process called flotation (Gaudin, 1957). Flotation is well known in the fields of mineral (e.g., Yoon, 2000; Pyke et al., 2003) and pulp (e.g., Emerson et al., 2006) processing, but is rarely discussed in the literature of marine sciences. The bubble- and particle-rich condition of many shallow-water hydrothermal

of

vents would make it possible for flotation to occur naturally.

ro

Plume velocity was simulated as a standard output parameter in our earlier modeling

-p

work (Lin et al., 2019). Based on the simulations, the plume velocity reached its

re

maximum at or right above the orifice, and decreased nonlinearly with shoaling water

lP

depth (Fig. S1). The transit time for a water parcel to ascend from the orifice to the sea surface was as short as 10‒30 s. These results, together with the recent work on deep-sea

na

vertical plumes (Reed et al., 2015), point to a feature possibly shared by hydrothermal

ur

systems of all water depths: the time frame of plume rise is shorter than that needed for microbial biosynthesis. Because of such a physical limitation, we consider the effect of

Jo

PP on the POC contents to be marginal. With this option eliminated, we were left with the conclusion that POC enrichment in the vertical plumes is most likely caused by physicochemical processes. Further field observations will be needed to assess if and the extent to which they contribute to the POC enrichment. 4.2 Eddies in the hydrothermal field The ADCP measurements (Fig. 6) depict the following pattern at the vent site: during flood tides, the currents flowed westwards with a rise in water temperature, whereas the

Page 23 of 42

Journal Pre-proof ebb currents flowed eastwards with a drop in water temperature. The flow direction and thermal property of the water masses suggest that the warm and cool waters originate from the Kuroshio and shelf water, respectively (Lee and Hu, 1998). Both flood and ebb tides were accompanied with strong upwelling (up to 30 cm/s), which was temporarily muted around slack tides. Based on the low wind speed and the lack of a relationship between W and the wind direction, the observed process is unlikely to be wind-driven

of

upwelling. Instead, the obvious connection of W to the tidal phase (Fig. 6c) and the

ro

submarine topography of our study site (Fig. 1b) allude to tide-topography interactions as

-p

the upwelling mechanism. This mechanism has been used to explain local upwelling

re

associated with submarine topographic highs, such as capes (Vargas-Yáñez et al., 2002),

lP

banks (Pereira et al., 2005), and ridges (Jing et al., 2012). Within 26 h of ADCP measurements, short-term variations with reduced horizontal

na

current speeds and a change in flow direction were frequently observed (Fig. 6b),

ur

amounting to a total of six time slots. These variations as manifestations of eddies was inferred from drifter deployments F1-1 and F1-2 (Figs. 7a and 7b). The eddies exhibited

Jo

the following features. (i) Having a diameter of ca. 100‒200 m, the eddies were much smaller relative to the mesoscale eddies frequently occurring in the western North Pacific (300‒500 km in diameter; Lee et al., 2013) or the ―submesoscale coherent vortices‖ associated with event plumes (~20 km in diameter; Lupton et al., 1998), but sizable compared with our target, i.e. the hydrothermal vents and plume water. (ii) The eddies were highly localized, occurring mainly around the area where the vents were located. Such site specificity of eddy formation is illustrated by the drifter tracks of E2-1 (Fig. 7c): by the time the ADCP data suggest eddy formation at the mooring station (9:00‒10:00),

Page 24 of 42

Journal Pre-proof the drifters were already ~1 km west of the vent sites, with no eddies tracked. Furthermore, the locations of occurrence and rotating directions of the eddies were different between deployments F1-1 and F1-2, implying a multi-eddies flow pattern in the vicinity of WV. (iii) The eddies had a lifetime of 1‒2 h. This was in line with the modeling results of Lin et al. (2019), who obtained a residence time of tens of minutes for water in the near-vent region. Such a lifetime, considered along with the frequent

of

occurrence of the eddies (six events per day), argues for a high probability (around 25‒

ro

50%; i.e., 1 or 2 h/event × 6 events/24 h) for the near-vent waters to get involved in the

-p

rotational motion. The eddies extended the retention time of plume water in the

re

hydrothermal field to 1‒2 h, thereby allowing us to detect some biogeochemical signatures that deviated from the mixing trend (see Section 4.4). (iv) The eddies occurred

lP

only when there was measurable upward current, and were absent during the high tides

na

with high horizontal velocities and diminished upwelling. It is unclear whether this apparent connection between the eddies and upwelling reflects a causal link between

ur

these two phenomena. Based on the existing data, we suggest that the eddies were caused

Jo

by the interaction between tidal flow and topography, and are likely to be present in other shallow-water hydrothermal fields with similar topographic settings. More investigation is needed to clarify these issues. 4.3 Mixing and removal of particulate organic matter in the lateral plume Our previous work showed that because of gas transfer in the vertical plumes, the plumetop water is selectively enriched in DIC compared with the vent fluids and is hence construed as the proper hydrothermal endmember for mixing processes in the lateral plume (Lin et al., 2019). In the present study, we show that the plume-top water is also

Page 25 of 42

Journal Pre-proof selectively enriched in POC relative to model predictions (Fig. 4b). This feature is tentatively attributed to physicochemical processes including dissolved organic carbon adsorption, eruptive particle emission, and/or flotation. Moreover, the lateral plume data mostly dot the region defined by binary mixing between the plume-top waters and background seawater (Fig. 5). We conclude that like the case of DIC, the plume-top

of

waters are the pertinent hydrothermal endmembers for POC mixing in the lateral plume. The scattering of TSM and POC data is noteworthy (Fig. 5). Positive outliers of TSM and

ro

POC were mainly associated with Series My, whereas the opposite was found in Series

-p

Mw and/or Transect M. A tenable explanation for the anomalies in Series My is the

re

highly eruptive nature of YV (cf. video footage by Lin et al., 2019), which might have

lP

yielded variable vent-fluid TSM:Si(OH)4 and POC:Si(OH)4 ratios that would then propagate to the lateral plume. The dearth of TSM and POC in the plume waters further

na

offshore in Series Mw and Transect M can be explained by particle settling during plume

ur

spreading and zooplankton feeding. By using Eqns. (5) and (6), the measured mean upward currents of 0.13±0.07 m/s in the near-vent water of WV (Fig. 6c) can only

Jo

suspend silicate and sulfur particles with a diameter smaller than 39±11 and 49±14 μm, respectively, in the upper 5-m water column. Therefore, deposition of coarse silt in the lateral plume was plausible, particularly around the slack tides when the upward velocity was low or absent. The abundance of mesozooplankton was indeed elevated in the hydrothermal field compared with the background seawater (Ka et al., 2011; Mantha et al., 2013), despite the toxicity of the plume water to some of these animals (Mantha et al., 2013). The eat-and-run scenario, previously proposed to explain the reduced POC fluxes

Page 26 of 42

Journal Pre-proof (Roth and Dymond, 1989) and enhanced zooplankton abundance (Burd et al., 1992) in waters around deep-sea vent sites, might also be applicable to our study site. The marked POC outlier in Series My, with a Δ value of 20% (Fig. 5c), is unlikely to be the consequence of high PP. To enhance the POC content from the modeled value at the upper envelope (0.42 mg/L) to the measured value (0.52 mg/L), PP of 50 mg C/m3/h

of

would be needed assuming a water residence time of 2 h. This value greatly exceeds the maximum PP determined for the nearby surface waters in the Southern Okinawa Trough

ro

(7 mg C/m3/d, equivalent to a mean hourly PP of 0.6 mg C/m3/h; Gong et al., 2000). Even

-p

if the lateral plume water is as productive as the inner shelf water of East China Sea

re

(maximum mean hourly PP = 11.8 mg C/m3/h; calculated from Gong et al., 2000), the

lP

resulting increment in POC is only 0.02 mg/L, a value easily obscured by sample variability. Overall, PP is unlikely to leave any measurable imprint in the POC content

na

because of the short time frames of plume rise (tens of seconds) and dispersal (1‒2 h).

ur

4.4 Locally intensified PP in the buoyant plume

Jo

PP left signatures not in the POC contents, but in the δ13CPOC data. While mostly falling in the region defined by aqueous mixing, the δ13CPOC data has up to six marked positive outliers (Fig. 5e). These outliers had low-to-moderate Si(OH)4 concentrations (5.4–9.5 μmol/L), and the samples were distributed mostly in the near-vent region. The Si(OH)4 contents indicate that these waters have undergone a certain level of mixing with background seawater. In a linear scheme for plume dispersal and dilution, waters with such Si(OH)4 concentrations should be found at intermediate to distal sites of the plume.

Page 27 of 42

Journal Pre-proof The fact that these outliers are in the near-vent region suggests the involvement of eddies in creating the heterogeneous Si(OH)4 concentrations with distance from the vents. A straightforward explanation for the isotopic excursion is the incorporation of

13

C-

enriched C from the DIC pool (Fig. 5a). Because of the short water residence time near the vents (Lin et al., 2019; Sect. 4.2) and the negligible effect of PP on the POC pool size (cf. Sect. 4.3),

13

C enrichment caused by PP can be viewed as a form of natural isotope

of

labeling experiments. In this regard, the equation typically used in 14C tracer experiments

-p

ro

can be adopted to calculate PP (cf. Wegener et al., 2012):

(7)

re

⁄

the fraction of 13C in the DIC,

the difference in the

lP

[POC] is the POC content,

fraction of 13C between the outlier and modeled value at the same Si(OH)4 content, t the

na

water residence time, and αDIC/POC the isotopic fractionation factor for PP. αDIC/POC can be

ur

derived from the isotope separation factor (εDIC/POC) using Eqns. (8) and (9): ⁄

Jo

⁄

(8)

(9)

⁄

The mean εDIC/POC value of marine photosynthesis, determined based on a δ13CDIC value of 0‰ and mix layer δ13CPOC values between 40°S and 40°N in the world ocean (Georicke and Fry, 1994), is 20‰. However, genomic and transcriptomic studies revealed molecular signatures of the reductive tricarboxylic acid cycle pathway (Tang et al., 2013; Li et al., 2018), a carbon fixation process with less carbon isotopic fractionation (εDIC/cell as low as 3‰; House et al., 2003). Using both ε values, a residence time of 1–2 h, Page 28 of 42

Journal Pre-proof and the modeled δ13CPOC values at the upper envelope, we obtained PP of 0.1–0.4 mg C/m3/h for the six outliers. These PP values should be interpreted with caution: PP should also be present in other fluid samples plotted in Figure 5e, but the intensity was not strong enough to drive the δ13CPOC values away from the mixing trajectories. Our current data enable us to conclude that (i) the near-vent, low-to-moderate Si plume waters have intensified PP, and (ii) the magnitude of PP enhancement was at least 0.1–0.4 mg C/m3/h.

of

The actual PP of the plume waters awaits future studies using tracer-based techniques.

ro

The preliminary biological data (cell counts and Chl a) indicate distinct microplankton

-p

composition between the plume and background waters (Fig. 3), with the plume water

re

significantly depleted in Chl a compared with the background seawater. However, the

lP

cell counts were elevated in certain plume waters, most likely reflecting increased prokaryotic biomass (Tang et al., 2018). When considered along with the existing

na

microbial and molecular evidence that demonstrated the prevalence of sulfur-

ur

metabolizing prokaryotes and pathways (Zhang et al., 2012; Tang et al., 2013; Li et al., 2018), our results of low Chl a contents but high cell counts in the waters with intensified

Jo

PP accord with the earlier proposition that chemoautotrophy plays a significant role in the primary biomass synthesis (Zhang et al., 2012). Tracer experiments that distinguish light and dark carbon fixation will help clarify this issue from a quantitative perspective. 4.5 δ13CPOC and carbonate chemistry The relationship between δ13CPOC and carbonate chemistry has been intensively investigated in previous decades, partly for the reconstruction of CO2 levels in the geological history (e.g., Freeman and Hayes, 1992). Based on culture experiments,

Page 29 of 42

Journal Pre-proof external dissolved CO2 concentrations were found to exhibit the strongest effect on isotope fractionation, with stronger discrimination found under high CO2 conditions (e.g., Hinga et al., 1994; Fry et al., 1996). Varying δ13CDIC values also affect δ13CPOC, and this result is frequently shown by the positive correlation between δ13CDIC and δ13CPOC in estuarine studies (e.g., Ogawa et al., 1997; Guo et al., 2015). With the high CO2 concentrations in most shallow-water hydrothermal fields, one might envision that these

of

environments provide insights into the response of δ13CPOC to high CO2 under natural

ro

conditions. Such information is useful for both environmental and paleo-environmental

-p

research.

re

Figure 8a displays the εPOC/DIC (see Eqn. (9) for definition) data versus partial pressure of

lP

dissolved CO2 in the plume waters. The results show that the trend of decreasing εPOC/DIC with elevated CO2 partial pressure is in contrast to that of Hinga et al. (1994). This trend

na

cannot be attributed to δ13CDIC, which correlated negatively with the δ13CPOC data (Fig.

ur

8b). The most reasonable explanation for the data set, based on the argument in earlier sections, is the overriding control of physical mixing on the plume waters with short

Jo

residence times. Except for few marked outliers with isotopic imprints from DIC to POC (cf. Section 4.4), most lateral plume samples in this shallow-water hydrothermal field had δ13CPOC signatures decoupled from the carbonate chemistry in terms of biological carbon cycling.

5. Conclusions

Page 30 of 42

Journal Pre-proof We combined biogeochemical and hydrodynamic approaches to investigate the dynamics of particulate organic matter in the Kueishantao shallow-water hydrothermal field. By comparing the biogeochemical data to values calculated from Si-based mixing models, processes other than aqueous mixing were inferred. The depleted TSM, lowered C/N ratios, and increased δ13CPOC values in the vertical plumes were attributed to hydraulic sorting of the vented particles, which tend to have more N and 13C in the fine fraction. A

of

biological explanation for the POC enrichment in the vertical plumes was negated

ro

because of the short time frame (tens of seconds) of plume rise. Instead, this feature was

-p

tentatively explained by physicochemical processes including dissolved organic carbon

re

adsorption, eruptive particle emission, and/or flotation. The POC-enriched plume-top water was found to be a better endmember than the vent fluids, to explain particle mixing

lP

in the lateral plume. Physical mixing played a steering role in shaping the particle 13

C-enriched POC was still observable in

na

chemistry of the lateral plumes, but markedly

several near-vent, low-to-intermediate-Si plume waters, implying locally enhanced PP of

ur

at least 0.1–0.4 mg C/m3/h. The presence of eddies, confirmed using ADCP and drifter

Jo

experiments, should have contributed to the detection of biogeochemical anomalies via extending the retention time of plume water to 1–2 h. Because of the dominating mixing process, the δ13CPOC signatures decoupled from the carbonate chemistry in terms of biological carbon cycling.

6. Data availability Data for the present work are available in Mendeley Data.

Page 31 of 42

Journal Pre-proof

Competing interests The authors declare that they have no conflict of interest.

of

Acknowledgements

ro

We thank the expert support of Seawatch Co. during the cruises to the Kueishantao Islet.

-p

We also thank the captains and crews of the FV Jin-Ling-Da-Fa, FV Sheng-Yu-Man, FV Hong-Yi-Fu, and RV Ocean Researcher II for their competent work. We thank the

re

Marine Research Station, Institute of Cellular and Organismic Biology, Academia Sinica

lP

for providing lab space for sample processing. We thank Ai-Lin Lyu for logistic support,

na

Jung-Tai Lu, Ruei-Long Guo, Ya-Ling Guo, Kuang-Ting Hsiao, Ya-Fang Cheng, and Jin-Jia Liang for their hard work in the field, Huang-Ci Chang and Yi-An Chen for

ur

helping the drifter deployments, and Yu-Min Liao, Shu-Han Chang, Lu-Yu Wang, and

Jo

Bing-Rong Jiang for assistance of the lab work. We thank the two anonymous reviewers for their constructive comments. This work was financed by the Ministry of Science and Technology to YSL [Grant # 104-2611-M-110-013, 104-2911-1-110-507-MY2 and 1052611-M-110-015], the Ministry of Education to LHL [Grant # 108L901002], and the ―Aim for the Top‖ University Program of Taiwan. Experimental data are available in the Supporting Information.

Page 32 of 42

Journal Pre-proof References

Jo

ur

na

lP

re

-p

ro

of

Acosta Pomar, M.L.C., Giuffré, 1996. Pico-, nano- and microplankton communities in hydrothermal marine coastal environments of the Eolian Islands (Panarea and Vulcano) in the Mediterranean Sea. Journal of Plankton Research, 18, 715.730. Aminot, A., Rey, F., 2001. Chlorophyll a: Determination by Spectroscopic Methods. ICES Techniques in Marine Environmental Sciences, No. 30, 17 pp. doi:10.25607/OBP-278. Bennett, S.A., Statham, P.J., Green, D.R.H., Le Bris, N, McDermott, J.M., Prado, F., Rouxel, O.J., von Damm, K., German, C.R., 2011. Dissolved and particulate organic carbon in hydrothermal plumes from the East Pacific Rise, 9°50’N. Deep-Sea Research I, 58, 922-931. Bouillon, S., Connolly, R.M., Gillikin, D.P., 2011. Use of stable isotopes to understand food webs and ecosystem functioning in estuaries. Treatise on Estuaries and Coastal Science, 7, 143-173. Burd, B.J., Thomson, R.E., Jamieson, G.S., 1992. Composition of a deep scattering layer overlying a mid-ocean ridge hydrothermal plume. Marine Biology, 113, 517-526. Burrell, T.J., Maas, E.W., Hulston, D.A., Law, C.S., 2015. Bacterial abundance, process and diversity responses to acidification at a coastal CO2 vent. FEMS Microbiology Letters, 362, 1-8. Campbell, A.C., Gieskes, J.M., 1984. Water column anomalies associated with hydrothermal activity in the Guaymas Basin, Gulf of California. Earth and Planetary Science Letters, 68, 57-72. Chang, N.N., Lin, L.H., Tu, T.H., Jeng, M.S., Chikaraishi, Y., Wang, P.L., 2018. Trophic structure and energy flow in a shallow-water hydrothermal vent: Insights from a stable isotope approach. PLoS ONE, 13, e0204753. doi:10.1371/journal.pone.0204753. Chen, Y.G., Wu, W.S., Chen, C.H., Liu, T.K., 2001. A date for volcanic eruption inferred from a siltstone xenolith. Quaternary Science Reviews, 20, 869-973. Chen C.T.A., Zeng, Z., Kuo, F. W., Yang, T. F., Wang, B. J., Tu, Y. Y., 2005. Tideinfluenced acidic hydrothermal system offshore NE Taiwan. Chemical Geology, 224, 69-81. Chen, X.G., Lyu, S.S., Garbe-Schönberg, D., Lebrato, M., Li, X., Zhang, H.Y., Zhang, P.P., Chen, C.T.A., Ye, Y., 2018. Heavy metals from Kueishantao shallow-sea hydrothermal vents, offshore northeast Taiwan. Journal of Marine Systems, 180, 211-219. Chen, X.G., Zhang, H.Y., Li, X., Chen, C.T.A., Yang, T.F., Ye, Y., 2016. The chemical and isotopic compositions of gas discharge from shallow-water hydrothermal vents at Kueishantao, offshore northeast Taiwan. Geochemical Journal, 50, 341-355.

Page 33 of 42

Journal Pre-proof

Jo

ur

na

lP

re

-p

ro

of

Chou, W.C., Sheu, D.D., Lee, B.S., Tseng, C.M., Chen, C.T.A., Wang, S.L., Wong, G.T.F., 2007. Depth distributions of alkalinity, TCO2 and δ13CTCO2 at SEATS timeseries site in the northern South China Sea. Deep-Sea Research II, 54, 1469-1485. Comita, P.B., Gagosian, R.B., Williams, P.M., 1984. Suspended particulate organic material from hydrothermal vent waters at 21° N. Nature, 307, 450-453. Durán-Toro, V.M., Price, R.E., Maas, M., Brombach, C.C., Rezwan, K., Bühring, S.I., 2019. Amorphous arsenic sulfide nanoparticles in a shallow water hydrothermal system. Marine Chemistry, 211, 25-36. El-Dessouky, H.T., Ettouney, H.M., 2002. Fundamentals of Salt Water Desalination. Elsevier Science, 690 pp. Emerson, Z., Bonometti, T., Krishnagopalan, G., Duke, S., 2006. Visualization of toner ink adsorption at bubble surfaces. TAPPI Journal, 5, 10-16. Fanning, K.A., Pilson, M.E.Q., 1973. On the spectrophotometric determination of dissolved silica in natural waters. Analytical Chemistry, 45, 136-141. Fitzsimmons, J.N., John, S.G., Marsay, C.M., Hoffman, C.L., Nicholas, S.L., Toner, B.M., German, C.R., Sherrell, R.M., 2017. Iron persistence in a distal hydrothermal plume supported by dissolved-particulate exchange. Nature Geoscience, 10, 195-201. Freeman, K.H., Hayes, J.M., 1992. Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels. Global Biogeochemical Cycles, 6, 185-198. Fry, B., 1996. 13C/12C fractionation by marine diatoms. Marine Ecology Progress Series, 134, 283-294. Gaudin, A.M., 1957. Flotation. McGraw-Hill Book Company, Inc., 573 pp. Georicke, R., Fry, B., 1994. Veriations of marine plankton δ13C with latitude, temperature, and dissolved CO2 in the world ocean. Global Biogeochemical Cycles, 8, 85-90. Gomez-Saez, G. V., Ristova, P. P., Sievert, S. M., Elvert, M., Hinrichs, K. U., Bühring, S. I., 2017. Relative importance of chemoautotrophy for primary production in a light exposed marine shallow hydrothermal system. Frontiers in Microbiology, 8, 702. doi: 10.3389/fmicb.2017.00702. Gong, G.C., Shiah, F.K., Liu, K.K., Wen, Y.H., Liang, M.H., 2000. Spatial and temporal variation of chlorophyll a, primary productivity and chemical hydrography in the southern East China Sea. Continental Shelf Research, 20, 411-436. Guo, W., Ye, F., Xu, S., Jia, G., 2015. Seasonal variation in sources and processing of particulate organic carbon in the Pearl River estuary, South China. Estuarine, Coastal and Shelf Science, 167, Part B, 540-548. Hall-Spencer, J.M., Rodolfo-Metalpa, R., Martin, S., Ransome, E., Fine, M., Turner, S.M., Rowley, S.J., Tedesco, D., Buia, M., 2008. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature, 454, 96-99.

Page 34 of 42

Journal Pre-proof

Jo

ur

na

lP

re

-p

ro

of

Han, C., Ye, Y., Pan, Y., Qin, H., Wu, G., Chen, C.T.A., 2014. Spatial distribution pattern of seafloor hydrothermal vents to the southeastern Kueishan Tao offshore Taiwan Island. Acta Oceanologica Sinica, 33, 37-44. Hinga, K.R., Arthur, M.A., Pilson, M.E.Q., Whitaker, D., 1994. Carbon isotope fractionation by marine phytoplankton in culture: The effects of CO2 concentration, pH, temperature, and species. Global Biogeochemical Cycles, 8, 91-102. House, C.H., Schopf, J.W., Stetter, K.O., 2003. Carbon isotopic fractionation by Archaeans and other thermophilic prokaryotes. Organic Geochemistry, 34, 345-356. Hu, C.K., Chiu, C.T., Chen, S.H., Kuo, J.Y., Jan, S., Tseng, Y.H., 2010. Numerical simulation of barotrophic tides around Taiwan. Terrestrial, Atmospheric, and Oceanic Sciences, 21, 71-84. Hung, J.J., Yeh, H.Y., Peng, S.H., Chen, C.T.A., 2018. Influence of submarine hydrothermalism on sulfur and metal accumulation in surface sediments in the Kueishantao venting field off northeastern Taiwan. Marine Chemistry, 198, 88-96. Jing, Z., Qi, Y., Du, Y., 2012. Persistent upwelling and front over the Sulu Ridge and their variations. Journal of Geophysical Research, 117, C11011, doi:10.1029/2012JC008355. Juniper, S.K., Bird, D.F., Summit, M., Vong, M.P., Baker, E.T., 1998. Bacterial and viral abundances in hydrothermal event plumes over northern Gorda Ridge. Deep-Sea Research II, 45, 2739-2749. Kâ, S., Hwang, J.S., 2011. Mesozooplankton distribution and composition on the northeastern coast of Taiwan during autumn: effects of the Kuroshio Current and hydrothermal vents. Zoological Studies, 50, 155-163. Lee, I.H., Hu, J.H., 1998. The relation between the I-Lan Bight Water and the shelf water northeast of Taiwan. Acta Oceanographica Taiwanica, 37, 89-103. (in Chinese with English abstract) Lee, I.H., Ko, D.S., Wang, Y.H., Centurioni, L., Wang, D.P., 2013. The mesoscale eddies and Kuroshio transport in the western North Pacific east of Taiwan from 8-year (2003-2010) model reanalysis. Ocean Dynamics, 63, 1027-1040. Li, Y., Tang, K., Zhang, L., Zhao, Z., Xie, X., Chen, C.T.A., Wang, D., Jiao, N., Zhang, Y., 2018. Coupled carbon, sulfur, and nitrogen cycles mediated by microorganisms in the water column of a shallow-water hydrothermal ecosystem. Frontiers in Microbiology, 9, 2718. doi:10.3389/fmicb.2018.02718. Lin, Y.S., Lui, H.K., Lee, J, Chen, C.T.A., Burr, G.S., Chou, W.C., Kuo, F.W., 2019. Fates of vent CO2 and its impact on carbonate chemistry in the shallow-water hydrothermal field offshore Kueishantao Islet, NE Taiwan. Marine Chemistry, 210, 1-12. Lupton, J.E., Baker, E.T., Garfield, N., Massoth, G.J., Feely, R.A., Cowen, J.P., Greene, R.R., Rago, T.A., 1998. Tracking the evolution of a hydrothermal event plume with a RAFOS neutrally buoyant drifter. Science, 280, 1052-1055.

Page 35 of 42

Journal Pre-proof

Jo

ur

na

lP

re

-p

ro

of

Lupton, J.E., Craig, H., 1981. A major helium-3 source at 15°S on the East Pacific Rise. Science, 214, 13-18. Mantha, G., Awasthi, A.K., Al-Aidaroos, A.M., Hwang, J.S., 2013. Diversity and abnormalities of cyclopoids around hydrothermal vent fluids, Kueishantao Island, north-eastern Taiwan. Journal of Natural History, 47, 685-697. Maruyama, A., Mita, N., Higashihara, T., 1993. Particulate materials and microbial assemblages around the Izena black smoking vent in the Okinawa Trough. Journal of Oceanography, 49, 353-367. Monsen, N.E., Cloern, J.E., Lucas, L.V., 2002. A comment on the use of flushing time, residence time, and age as transport time scales. Limnology and Oceanography, 47, 1545-1553. Mottl, M.J., McConachy, T.F., 1990. Chemical processes in buoyant hydrothermal plumes on the East Pacific Rise near 21° N. Geochimica et Cosmochimica Acta, 54, 1911-1927. Ogawa, N., Ogura, N., 1997. Dynamics of particulate organic matter in the Tamagawa Estuary and inner Tokyo Bay. Estuarine, Coastal and Shelf Science, 44, 263-273. Pereira, A.F., Belém, A.L., Castro, B.M., Geremias, R., 2005. Tide-topography interaction along the eastern Brazilian shelf. Continental Shelf Research, 25, 15211539. Pichler, T., Veizer, J., Hall, G.E.M., 1999. The chemical composition of shallow-water hydrothermal fluids in Tutum Bay, Ambitle Island, Papua New Guinea and their effect on ambient seawater. Marine Chemistry, 64, 229-252. Pyke, B., Fornasiero, D., Ralston, J., 2003. Bubble particle heterocoagulation under turbulent conditions. Journal of Colloid and Interface Science, 265, 141-151. Reed, D.C., Breier, J.A., Jiang, H., Anantharaman, K., Klausmeier, C.A., Toner, B.M., Hancock, C., Speer, K., Thurnherr, A.M., Dick, G.J., 2015. Predicting the response of the deep-ocean microbiome to geochemical perturbations by hydrothermal vents. The ISME Journal, 9, 1857-1869. Robinson, C., 2000. Plankton gross production and respiration in the shallow water hydrothermal systems of Milos, Aegean Sea. Journal of Plankton Research, 22, 887906. Roth, S.E., Dymond, J., 1989. Transport and settling of organic material in a deep-sea hydrothermal plume: evidence from particle flux measurements. Deep-Sea Research, 36, 1237-1254. Sheik, C.S., Anantharaman, K., Breier, J.A., Sylvan, J.B., Edwards, K.J., Dick, G.J., 2015. Spatially resolved sampling reveals dynamic microbial communities in rising hydrothermal plumes across a back-arc basin. The ISME Journal, 9, 1434-1445. Sorokin, Y.I., Sorokin, P.Y., Zakuskina, O.Y., 1998. Microplankton and its functional activity in zones of shallow hydrotherms in the Western Pacific. Journal of Plankton Research, 20, 1015-1031.

Page 36 of 42

Journal Pre-proof

Jo

ur

na

lP

re

-p

ro

of

Sorokin, Y.I., Sorokin, P.Y., Zakuskina, O.Y., 2003. Microplankton and its function in a zone of shallow hydrothermal activity: the Craternaya Bay, Kurile Islands. Journal of Plankton Research, 25, 495-506. Soulsby, R. L., 1997. Dynamics of Marine Sands. Thomas Telford, London. Speer, K., Thurnherr, A.M., 2012. The Lau Basin Float Experiment (LAUB-FLEX). Oceanography, 25, 284-285. Tang, K., Liu, K., Jiao, N., Zhang, Y., Chen, C.T.A., 2013. Functional metagenomics investigations of microbial communities in a shallow-sea hydrothermal system. PLoS ONE, 8, e72958. doi:10.1371/journal.pone.0072958. Tang, K., Zhang, Y., Lin, D., Chen, C.T.A., Wang, D., Lin, Y.S., Sun, J., Zheng, Q., Jiao, N., 2018. Cultivation-independent and cultivation-dependent analysis of microbes in the shallow-sea hydrothermal system off Kueishantao Island, Taiwan: Unmasking heterotrophic bacterial diversity and functional capacity. Frontiers in Microbiology, 9, 279. doi:10.3389/fmicb.2018.00279. Tarasov, V.G., Gebruk, A.V., Shulkin, V.M., Kamenev, G.M., Fadeev, V.I., Kosmynin, V.N., Malakhov, V.V., Starynin, D.A., Obzhirov, A.I., 1999. Effect of shallowwater hydrothermal venting on the biota of Matupi Harbour (Rabaul Caldera, New Britain Island, Papua New Guinea). Continental Shelf Research, 19, 79-116. Tarasov, V.G., 2006. Effects of shallow-water hydrothermal venting on biological communities of coastal marine ecosystems of the Western Pacific. Advances in Marine Biology, 50, 267-410. Tarasov, V.G., Gebruk, A.V., Mironov, A.N., Moskalev, L.I., 2005. Deep-sea and shallow-water hydrothermal vent communities: Two different phenomena? Chemical Geology, 224, 5-39. Tudino, T., Bortoluzzi, G., Aliani, S., 2014. Shallow-water gaseohydrothermal plume studies after massive eruption at Panarea, Aeolian Islands, Italy. Journal of Marine Systems, 131, 1-9. Vargas-Yáñez, M., Viola, T.S., Jorge, F.P., Rubín, J.P., García-Martínez, M.C., 2002. The influence of tide-topography interaction on low-frequency heat and nutrient fluxes. Application to Cape Trafalgar. Continental Shelf Research, 22, 115-139. Von Damm, K.L., Edmond, J.M., Grant, B., Measures, C.I., Walden, B., Weiss, R.F., 1985. Chemistry of submarine hydrothermal solutions at 21°N, East Pacific Rise. Geochimica et Cosmochimica Acta, 49, 2197-2220. Wegener, G., Bausch, M., Holler, T., Thang, N.M., Prieto Mollar, M., Kellermann, M.Y., Hinrichs, K.U., Boetius, A., 2012. Assessing sub-seafloor microbial activity by combined stable isotope probing with deuterated water and 13C-bicarbonate. Environmental Microbiology, 14, 1517-1527. Winn, C.D., Karl, D.M., 1986. Microorganisms in deep-sea hydrothermal plumes. Nature, 320, 744-746.

Page 37 of 42

Journal Pre-proof

Jo

ur

na

lP

re

-p

ro

of

Yang, L., Hong, H., Guo, W., Chen, C.T.A., Pan, P.I., Feng, C.C., 2012. Absorption and fluorescence of dissolved organic matter in submarine hydrothermal vents off NE Taiwan. Marine Chemistry, 128-129, 64-71. Yang, T.F., Lan, T.F., Lee, H.F., Fu, C.C., Chuang, P.C., Lo, C.H., Chen, C.H., Chen, C.T.A., Lee, C.S., 2005. Gas compositions and helium isotopic ratios of fluid samples around Kueishantao, NE offshore Taiwan and its tectonic implications. Geochemical Journal, 39, 469-480. Yoon, R.H., 2000. The role of hydrodynamic and surface forces in bubble-particle interaction. International Journal of Mineral Processing, 58, 129-143. Yu, M.Z., Chen, X.G., Garbe-Schönberg, D., Ye, Y., Chen, C.T.A., 2019. Volatile chalcophile elements in native sulfur from a submarine hydrothermal system at Kueishantao, offshore NE Taiwan. Minerals, 9, 245. doi:10.3390/min9040245. Zhang, Y., Zhao, Z., Chen, C.T.A., Tang, K., Su, J., Jiao, N., 2012. Sulfur metabolizing microbes dominate microbial communities in Andesite-hosted shallow-sea hydrothermal systems. PLoS ONE, 7, e44593. doi:10.1371/journal.pone.0044593.

Page 38 of 42

Journal Pre-proof Figure captions Figure 1. (a) Location of the Kueishantao Islet. The islet is located in the Ilan Bight, offshore NE Taiwan. The Ilan Bight abuts the Okinawa Trough, where the main stream of the Kuroshio passes. (b) Location of the sampling sites. The region near the vents is enlarged in the inset. Series Mw and My both include three sites, with a horizontal distance of 6 (sites Mw6 and My6), 14 (Mw14 and My14) and 20 (Mw20 and My20) m

of

from the vents. The green diamond denotes the location where the acoustic Doppler

ro

current profiler (ADCP) and moorings were deployed. (c) Design of the mooring

re

pressure (TP) and temperature (T) loggers.

-p

instrument set, including a bottom-mounted ADCP and a T-string with temperature-

lP

Figure 2. Vertical distribution of Si(OH)4 and δ13CDIC in the vent fluid, vertical plume,

comparison.

na

and near-vent waters of the (a) YV and (b) WV. The background waters were plotted for

ur

Figure 3. Vertical distribution of solid-phase properties in the vent fluid, vertical plume,

comparison.

Jo

and near-vent waters of the (a) YV and (b) WV. The background waters were plotted for

Figure 4. Modeled versus measured values of solid-phase parameters of the vertical plumes (Sites My0 and Mw0). Figure 5. (a) δ13CDIC, (b) TSM, (c) POC, (d) C/N ratio of particulate organic matter, and (e) δ13CPOC versus Si(OH)4 in the surface water (0 and 5 m water depth) of Transect B and the buoyant plumes. The mixing lines (mean ± SD) were calculated using the

Page 39 of 42

Journal Pre-proof conservative mixing models (Eqns. 1–3). Numbers next to the symbols denote the Δ values of marked outliers. Figure 6. (a) Observations of sea level (blue line) and wind (vectors) from 10:00 of 8 Aug to 14:00 of 9 Aug, 2017, recorded respectively at the Central Weather Bureau tidal station Wushi and weather station Kueishantao. (b) The time series of horizontal current

of

vector plotted over temperature variation recorded by the ADCP and T-string moorings. (c) The vertical current component (W, with positive values indicating upward current)

ro

recorded by the ADCP. The four gray bars in each panel denote the periods when the

-p

drifter deployments were carried out.

re

Figure 7. Tracks of the drifters during the deployment (a) F1-1, (b) F1-2, (c) E2-1, and (d)

lP

E2-2 (cf. Fig. 6a). Start and end times of each track were written in legends with (start, end) after each track (trk) number. The open circles denote the start location of each track,

na

the dots the location at the four quarters of an hour, and the open diamonds the location

ur

on the hour. The mooring site was marked with a triangle. The gray tracks in (d) are

Jo

tracks in (a), (b), and (c).

Figure 8. (a) εPOC/DIC versus the partial pressure of CO2 (pCO2) of the lateral plume waters. The data of cultured marine phytoplankton (Hinga et al., 1994) were also plotted for comparison. The original εPOC/CO2 values of Hinga et al. (1994) were corrected to εPOC/DIC assuming an isotopic difference of 7‰ between dissolved CO2 and DIC (House et al., 2003). (b) δ13CPOC versus δ13CDIC values of lateral plume waters. The data of an estuarine study (Ogawa and Ogura, 1997) were plotted for comparison.

Page 40 of 42

Journal Pre-proof Table 1. Results (p values) of the two-tailed t tests. * denotes parameters that are significantly different (α = 0.05) between the tested samples.

Si(OH)4 δ13CDIC TSM POC C/N ratio δ13CPOC Cell counts Chl a

Vertical plume vs. near-vent water Series My 0.1326 0.0812 0.1554 0.5712 0.9696 0.7057 0.1979 0.3651

Near-vent vs. background water

Series Mw 0.3829 0.2710 0.3671 0.2489 0.3270 0.8638 0.1321 0.1550

Series My 0.0019* 0.0007* 0.0076* 0.0011* 0.0000* 0.0000* 0.2080 NAa

of

Parameters

Series Mw 0.0006* 0.0035* 0.3777 0.4832 0.0000* 0.0001* 0.0219* NA

Jo

ur

na

lP

re

-p

ro

a. NA, not applicable because the background water had only one single measurement.

Page 41 of 42

Journal Pre-proof Highlights Mixing and sorting shape particle chemistry in the plumes.



Physical processes cause POC enrichment in the vertical plumes.



Eddies extend plume water retention time to 1‒2 h in near-vent regions.



Primary production was intensified locally in plume waters near the vents.

Jo

ur

na

lP

re

-p

ro

of



Page 42 of 42

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8