Characterizing marine particles and their impact on biogeochemical cycles in the GEOTRACES program

Accepted Manuscript Preface Characterizing marine particles and their impact on biogeochemical cycles in the GEOTRACES program Robert F. Anderson, Christopher T. Hayes PII: DOI: Reference:

S0079-6611(14)00199-2 http://dx.doi.org/10.1016/j.pocean.2014.11.010 PROOCE 1497

To appear in:

Progress in Oceanography

Please cite this article as: Anderson, R.F., Hayes, C.T., Characterizing marine particles and their impact on biogeochemical cycles in the GEOTRACES program, Progress in Oceanography (2014), doi: http://dx.doi.org/ 10.1016/j.pocean.2014.11.010

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.

Characterizing marine particles and their impact on biogeochemical cycles in the GEOTRACES program Robert F. Anderson 1,2* and Christopher T. Hayes 3

(1) Lamont-Doherty Earth Observatory of Columbia University, P.O. Box 1000, Palisades, NY, USA 10964

(2) Department of Earth & Environmental Sciences, Columbia University, New York, NY, USA *Corresponding author Email address: [email protected] Phone: +1-845-365-8508 (3) Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

No abstract since this is an introductory chapter to a special volume

Keywords: GEOTRACES, marine particles, trace elements

1

Trace elements and their isotopes (TEIs) are of priority interest in several subdisciplines of oceanography. For example, the vital role of trace element micronutrients in regulating the growth of marine organisms, which, in turn, may influence the structure and composition of marine ecosystems, is now well established (Morel & Price, 2003; Twining & Baines, 2013). Natural distributions of some TEIs have been severely impacted by anthropogenic emissions, leading to substantial perturbations of natural ocean inventories. Pb and Hg, for example, (Lamborg et al., 2002; Schaule & Patterson, 1981), may represent a significant threat to human food supply. Furthermore, much of our knowledge of past variability in the ocean environment, including the ocean’s role in climate change, has been developed using TEI proxies archived in marine substrates such as sediments, corals and microfossils. Research in each of these areas relies on a comprehensive knowledge of the distributions of TEIs in the ocean, and on the sensitivity of these distributions to changing environmental conditions. With numerous processes affecting the regional supply and removal of TEIs in the ocean, a comprehensive understanding of the marine biogeochemical cycles of TEIs can be attained only by a global, coordinated, international effort. GEOTRACES, an international program designed to study the marine biogeochemical cycles of trace elements and their isotopes (Anderson et al., 2014; Henderson et al., 2007), aims to achieve these goals. Particles play several critical roles in the marine biogeochemical cycles of TEIs. Many of the TEIs delivered to the ocean by continental weathering are transported in association with particles, either via the atmosphere as dust (e.g., Jickells et al., 2005) or as river-derived suspended load (e.g., Oelkers et al., 2011). If the concept of particles is

2

expanded to include microscopic organisms, then particles also influence the chemical and physical speciation of TEIs in the ocean. Key aspects of speciation include oxidation state, organic complexation, and components of cellular organic tissue and of inorganic mineral structures. Particles may be best known as agents in the removal of TEIs from seawater. The principal removal process for many TEIs involves sorption to particles and sedimentation, a process commonly referred to as “scavenging”. Scavenging often leaves concentrations of dissolved TEIs in seawater orders of magnitude below those that would be expected if controlled by the thermodynamic solubility of pure inorganic solids. This key role for particles in the marine biogeochemical cycles of TEIs was recognized as early as the 1950’s (Goldberg, 1954; Krauskopf, 1956). Particles gained the spotlight in marine geochemistry in the 1970’s as a consequence of an intensive investigation of scavenging processes by GEOSECS and contemporary programs, relying heavily on naturally occurring uranium-series radionuclides to define rates of TEI removal from the ocean (Lal, 1977; Turekian, 1977). Shortly thereafter, Lal (1980) posited that much of the downward flux of particles, including adsorbed TEIs, was mediated by large, but rare, particles with relatively high sinking rates (up to hundreds of meters per day). Small particles (order microns), which are much more abundant and to which most TEI sorption occurs because of their high surface-to-volume ratio, do not sink at appreciable rates on their own. Instead, their sedimentation occurs primarily by coagulation with large particles and transport in “piggy back” mode.

3

Large volume sampling by in situ filtration during GEOSECS provided sufficient quantities of particulate material from open-ocean regions to permit the measurement of the concentrations of several natural and anthropogenic radionuclides. Krishnaswami et al. (1976) modeled these results to constrain the average sinking rate of the particles responsible for TEI scavenging to fall between 0.2 and 2.0 m d-1, much less than the inferred sinking rates of large (order millimeter) aggregates (100 - 300 m d-1, Berelson, 2002). To be clear, these rates derived by modeling radionuclide distributions are not intended to be representative of the large work-horse aggregates that are responsible for most of the sedimentation of particle mass (Lal, 1980). Rather they reflect the average sinking rate of particulate TEIs, and thus they are dominated by the preponderance of small particles that sink very slowly if at all. Building on the pioneering work of Krishnaswami et al. (1976), subsequent studies modeled the measured partitioning between particles and solution of three different thorium isotopes to demonstrate that scavenging is a reversible process (Bacon & Anderson, 1982; Nozaki et al., 1981), as expected for solutes interacting with reactive functional groups on the surfaces of minerals and organic matter (Balistrieri et al., 1981; Schindler, 1975). Expanding the analysis to include thorium results from particles collected by sediment traps, Bacon et al. (1985) combined the concept of reversible scavenging with the reversible aggregation and disaggregation of particles from different size classes (piggy backing of Lal, 1980) to develop a conceptual model that continues to be widely used (e.g., Anderson, 2003; Jeandel et al., this volume). By the late 1980’s the important role of particles in marine biogeochemical cycles was generally recognized, as were the many challenges inherent in the collection and

4

analysis of marine particulates. In an effort to advance the field, a large international group of experts met for a week-long workshop to summarize the state of the art and make recommendations for future improvements (Hurd & Spencer, 1991). Assessing the impact of any workshop is a daunting task, fraught with sensitivities. Nevertheless, the senior author of this paper (RFA), who served as a member of the organizing committee for that workshop, has long felt that the products of the workshop failed to generate the impact that they deserved. The workshop volume (Hurd & Spencer, 1991) contained 57 papers, consisting of working group reports and individual contributions describing the state of knowledge about marine particle biogeochemistry as well as the state of the art in the collection and analysis of marine particulate matter. Although these papers contain a wealth of information, they have been cited only sparingly. According to the Web of Science in October 2013, only seven of the 57 papers had 30 or more citations. Thirtyeight papers had less than six citations. In our opinion, this measure of impact reflects not so much the quality of the papers, which was generally high, representing the best available information in the field at the time, as the inaccessibility of the volume in which they were published. The volume was not available electronically until March 2013, more than 20 years after publication. In a world of constantly evolving publishing practices, this anecdote illustrates the value of the electronic availability of research publications. A second factor that limited the advancement of research on marine particles is the fact that the development, testing and intercalibration of new methods was not a priority for any major program in the 1990’s. Although particulate material was sampled widely by the Joint Global Ocean Flux Study (Fasham et al., 2001), most of the work was

5

confined to a limited number of established techniques, including sediment traps, in situ pumps and transmissometers. As described in this volume, a wealth of new technologies for observing, sampling and analyzing marine particles is now available, including optical methods to characterize the abundance, distribution and first-order composition of particles, devices to collect particles in their in situ shape and structure, and instrumentation that can define elemental relationships within the structure of individual particles. GEOTRACES seeks to exploit many of these newer technologies to assess the distribution and dynamics of marine particles, and thereby gain a more quantitative knowledge of their role in the biogeochemical cycles of TEIs. In light of the important role of particles in TEI biogeochemistry, described above, GEOTRACES places a high priority on: 1) examining the influence of particles in TEI biogeochemistry in contrasting oceanic regimes, 2) developing, testing and applying new technologies for the collection, analysis and characterization of marine particulate material, and 3) nurturing the synthesis of this information, including the development of models that simulate the role of particles in TEI biogeochemistry. Sampling regions that represent the full spectrum of particle abundance, composition and dynamics was a guiding criterion in the design of the GEOTRACES global survey (an updated map can be found on the web site, http://www.geotraces.org). Ocean sections and process studies have examined regions of intense dust deposition (e.g., the tropical Atlantic, downwind of Saharan dust sources) and regions under the influence of major rivers (e.g., the Amazon and Ganges-Brahmaputra), where particles serve as an important source of TEIs. GEOTRACES sections cover nearly the full range

6

of open-ocean biological productivity, from oligotrophic subtropical gyres to highly productive eastern boundary current upwelling systems. This strategy enables investigators to explore the sensitivity of TEI biogeochemistry to the structure of marine ecosystems as well as the related abundance and flux of biogenic particles. Several particle-related objectives were afforded high priority during the planning and implementation of GEOTRACES. Cruises in 2008 and 2009 were dedicated to the intercalibration of sampling and analytical methods and these cruises provided opportunities for extensive testing of different types of filter material and filtration systems. Concentrations of particulate TEIs collected by different in situ filtration systems were compared against one another, as well as against results obtained by shipboard filtration of water collected in sampling bottles. In the course of this work a flaw was discovered in the design of a filter holder that was commonly used with in situ pumps, frequently causing 75 to 90% of the large (operationally defined as >51 µm) particles to be lost from prefilters. Increasing the baffling of the filter holder inlet, and reducing the face velocity of water passing through filters, eliminated the systematic differences between filter holder designs, a feature that has recently been placed into routine operation. Detailed results from these tests, as well as recommendations for future work, have now been published (Bishop et al., 2012; Planquette & Sherrell, 2012). Development, testing and intercalibration of methods for the collection and analysis of marine particles is an ongoing effort. For example, a recent workshop under the direction of P. J. Lam (24-25 March 2013, Honolulu USA), the lead author of the fifth paper in this volume, initiated a new round of intercalibration among labs measuring (1) total digests of particles for trace elements, and (2) major particle composition

7

(particulate organic carbon, particulate inorganic carbon, biogenic silicon, lithogenic phases). Additional information about this intercalibration can be found on the GEOTRACES web site < http://www.geotraces.org/news-50/news/116-news/535workshop-particulate-intercalibration>. Concurrently with method development, GEOTRACES has promoted the interpretation, synthesis and modeling of the distribution and dynamics of marine particles, as well as their roles in the biogeochemical cycles of TEIs. In this context, GEOTRACES hosted three Model-Data Synergy workshops (Delmenhorst Germany, September 2007; Paris France December 2009; Barcelona Spain November 2011) with an increasing focus on the importance of particles in TEI cycling leading to the third meeting being dedicated explicitly to this question. Papers in this volume are a product of the workshop in Barcelona. Each paper in this volume represents the synthesis of a workshop theme, the ensemble of which was selected to guide future research on marine particles and their role in TEI biogeochemistry. Jeandel et al. (this volume) provides a historical foundation for future research by reviewing key particle-related studies from the 1970’s through the 1990’s, with particular attention to the GEOSECS program (see also above). Jeandel et al. emphasize the analytical challenges associated with reliable measurement of particulate TEI concentrations at mid depth in open-ocean regions, arguably the “cleanest” water on Earth, where total particle concentrations often fall below 10 µg per kg of seawater. For many TEIs, present in particulate matter at ppm levels, analytical methods must be capable of reliable, contamination-free detection of concentrations that are frequently below 10-12 moles kg-1 seawater.

8

The remaining papers in this volume describe the detection, collection, analysis and modeling of particles. Boss et al. (this volume) review the basic physics inherent in the interaction of light with particles, and the sensor systems that have been designed to exploit these principles to determine in situ the distribution, abundance, size and/or composition of particles. Most attention is given to commercially available instruments, but emerging technologies and prospects for their future applications are described as well. McDonnell et al. (this volume) summarize the advantages and limitations of different technologies used to collect particulate material in the ocean, including in situ pumps, sediment traps, bottles, towed devices and marine snow collectors (large volume water samplers). The paper also describes results from the GEOTRACES intercalibration initiative, new technologies to capture intact large marine particles (fecal pellets and aggregates), and steps that have been taken to collect contamination-free TEI samples from sediment traps. Lam et al. (this volume) describe a broad array of methods used to determine TEI concentrations in particles. These can be divided operationally into methods for dissolution of marine particles for subsequent analysis (both total dissolution and selective leaching), and instrumental methods for determining TEI concentrations either after, or without, sample dissolution. In particular, the paper describes methods using Xrays to determine TEI concentrations in particles without dissolution. These include established methods such as X-Ray Fluorescence as well as more novel techniques that exploit high-intensity synchrotron X-rays to determine the speciation of TEIs within the environment of their individual particle carriers.

9

Dutay et al. (this volume) describe modeling strategies to simulate the role of particles in the biogeochemical cycles of TEIs at basin to global scales. For the most part, these strategies begin with models designed to simulate ocean circulation, to which biologically mediated production or transformation of particles as well as TEI interaction with particles have been incorporated. Within this general strategy there exists substantial variability of approaches, which are compared and contrasted by Dutay et al. Jackson and Burd (this volume) describe coagulation theory and the related sorption of TEIs to a continuous size spectrum of interacting particles in the ocean. The current generation of global models, which typically include at most two size classes of particles, are compared with models that encompass a more detailed representation of the actual size spectrum of particles. Challenges faced when incorporating computationally demanding coagulation processes into global biogeochemical models are described, together with recommendations for progress toward this goal. Henderson and Marchal (this volume) conclude the volume by presenting a series of recommendations from the workshop, including areas in need of development. Success will be measured by how well the themes represented here are integrated to achieve the shared goal of defining the role of particles in the marine biogeochemical cycles of TEIs. Fortunately, nature assists us in these efforts by providing tracers that are sensitive to the supply and removal of TEIs by particles. For example, the combined use of primordial 232Th and radiogenic 230Th has created a new strategy to evaluate the rate of TEI supply by dust (Hayes et al., 2013; Hsieh et al., 2011). Modeling the distribution of Nd and its isotopic composition in the Bay of Bengal has revealed a large source of TEIs

10

derived from dissolution of river-derived particles (Singh et al., 2012), as inferred from earlier studies (Jeandel et al., 2011). Thorium-230 is a particularly sensitive tracer for characterizing the removal of TEIs from the ocean by scavenging. Thorium-230 is produced uniformly throughout the ocean by radioactive decay of dissolved 234U, and it is removed by reversible sorption onto particles. To a first approximation, and neglecting net lateral transport by ocean dispersion, the radioactive disequilibrium between 230Th and 234U provides a quantitative measure of the intensity of TEI removal by scavenging. Thus, fields of relative scavenging intensity can be mapped throughout the ocean by measuring dissolved 230Th concentrations. Early GEOTRACES results are proving to be particularly rewarding in this regard. For example, a section through the high productivity region off NW Africa (GA03 in Figure 1) provides unambiguous evidence for boundary scavenging of 230Th (Figure 2B, see also Hayes et al., in press). Boundary scavenging, the intensification of scavenging in particle-rich ocean margin regions, was predicted by Bacon et al. (1976), and subsequently modeled (Bacon, 1988), but 230Th data of sufficient quality and spatial resolution to test this prediction were unavailable until the advancements facilitated by GEOTRACES. Similarly, regions of intensified scavenging of 230Th have been observed in association with nepheloid layers, zones of resuspended sediments rising as much as 1000 m above the sea floor (Biscaye & Eittreim, 1977; Brewer et al., 1976) along GEOTRACES Atlantic sections (Figure 1) GA02 (Deng et al., 2014) and GA03 (Figure 2). The close correspondence between the presence of nepheloid layers, indicated by

11

transmissometer readings (Figure 2A), and deficits in the concentration of dissolved 230Th compared to surrounding regions lacking nepheloid layers (cf. panels A and B in Figure 2) leave little doubt that these features are widespread and, therefore, may have a significant impact on the biogeochemical cycles of TEIs. Enhanced scavenging near the sea bed was discovered more than three decades ago during early studies of uraniumseries disequilibria (Bacon & Anderson, 1982; Craig et al., 1973; Nozaki et al., 1980), but the process has not, to our knowledge, been simulated in large-scale models of marine biogeochemical cycles. The mounting evidence for enhanced near-bottom scavenging from GEOTRACES (Deng et al., 2014; Hayes et al., in press) and from related studies (Okubo et al., 2012) should motivate the marine geochemical community to examine these processes in greater detail. Future studies of nepheloid layers provide just one illustration of the potential benefits to be derived by integrating the various themes described in this volume. Most TEIs have residence times in the ocean much greater than that of 230Th. Consequently, the impact of nepheloid layers on TEI biogeochemistry must be assessed indirectly, in most cases, rather than by direct measurement as can be done with 230Th. An integrated assessment would include routine deployment of optical sensors (Boss et al., this volume) to define the spatial dimensions and intensity of nepheloid layers. Careful sampling of particles from throughout the water column (McDonnell et al., this volume) and analysis of a broad suite of TEIs (Lam et al., this volume), including 230Th, can be exploited to determine the relative affinity of individual TEIs for each major particulate phase (aluminosilicates, biogenic opal, CaCO3, organic matter, authigenic Fe and Mn oxides). By integrating these observations with models that incorporate coagulation theory

12

(Jackson & Burd, this volume) as well as global ocean circulation and biogeochemistry (Dutay et al., this volume), the marine science community will be equipped to realize not only the global marine biogeochemical cycles of TEIs, but also the sensitivity of these cycles to changing environmental conditions, and the implications for marine ecosystems that rely on many TEIs as essential nutrients.

Acknowledgements: This paper arose from a workshop that was co-sponsored by European Science Foundation COST Action ES0801, "The ocean chemistry of bioactive trace elements and paleoproxies," by the Scientific Committee on Oceanic Research, through support to SCOR from the U.S. National Science Foundation (Grant OCE0938349 and OCE-1243377), and from a US NSF grant to the US GEOTRACES Project Office (OCE - 0850963).

13

References Anderson, R.F., 2003. Chemical tracers of particle transport. In H. Elderfield (Ed.), The Oceans and Marine Geochemistry (pp. 247-273). Oxford: Elsevier-Pergamon. Anderson, R.F., Mawji, E., Cutter, G.A., Measures, C.I., Jeandel, C., 2014. GEOTRACES: Changing the way we explore ocean chemistry. Oceanography, 27, 50 - 61. Bacon, M.P., 1988. Tracers of chemical scavenging in the ocean - Boundary effects and large-scale chemical fractionation. Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 325, 147160. Bacon, M.P., Anderson, R.F., 1982. Distribution of thorium isotopes between dissolved and particulate forms in the deep-sea. Journal of Geophysical Research-Oceans and Atmospheres, 87, 2045-2056. Bacon, M.P., Huh, C.A., Fleer, A.P., Deuser, W.G., 1985. Seasonality in the flux of natural radionuclides and plutonium in the deep Sargasso Sea. Deep-Sea Research Part a-Oceanographic Research Papers, 32, 273-286. Bacon, M.P., Spencer, D.W., Brewer, P.G., 1976. 210Pb-226Ra and 210Po-210Pb disequilibria in seawater and suspended particulate matter. Earth and Planetary Science Letters, 32, 277-296. Balistrieri, L.S., Brewer, P.G., Murray, J.W., 1981. Scavenging residence times of trace metals and surface chemistry of sinking particles in the deep ocean. Deep-Sea Research, 28A, 101-121. Berelson, W., 2002. Particle settling rates increase with depth in the ocean. Deep-Sea Research- Part II, Topical Studies in Oceanography, 49, 237-251. Biscaye, P.E., Eittreim, S.L., 1977. Suspended particulate loads and transports in the nepheloid layer of the abyssal Atlantic Ocean Marine Geology, 23, 155-172. Bishop, J.K.B., Lam, P.J., Wood, T.J., 2012. Getting good particles: Accurate sampling of particles by large volume in-situ filtration. Limnology and Oceanography: Methods, 10, 681-710. Boss, E., Guidi, L., Richardson, M.J., Stemmann, L., Gardner, W., Bishop, J.K.B., Anderson, R.F., Sherrell, R.M., this volume. Optical techniques for in-situ characterization of particles pertinent to GEOTRACES. Progress In Oceanography. Brewer, P.G., Spencer, D.W., Biscaye, P.E., Hanley, A., Sachs, P.L., Smith, C.L., Kadar, S., Fredericks, J., 1976. Distribution of particulate matter in the Atlantic Ocean. Earth and Planetary Science Letters, 32, 393-402. Craig, H., Krishnaswami, S., Somayajulu, B.L.K., 1973. 210Pb - 226Ra radioactive disequilibrium in deep-sea. Earth and Planetary Science Letters, 17, 295-305. Deng, F., Thomas, A.L., Rijkenberg, M.J.A., Henderson, G.M., 2014. Controls on seawater 231Pa, 230Th and 232Th concentrations along the flow paths of deep waters in the Southwest Atlantic. Earth and Planetary Science Letters, 390, 93-102. Dutay, J.C., Tagliabue, A., Kriest, I., van Hulten, M.M.P., this volume. Large scale modeling of oceanic trace element distributions. Progress In Oceanography. Fasham, M.J.R., Balino, B.M., Bowles, M.C., Anderson, R., Archer, D., Bathmann, U., Boyd, P., Buesseler, K., Burkill, P., Bychkov, A., Carlson, C., Chen, C.T.A., Doney, S., Ducklow, H., Emerson, S., Feely, R., Feldman, G., Garcon, V., Hansell,

14

D., Hanson, R., Harrison, P., Honjo, S., Jeandel, C., Karl, D., Le Borgne, R., Liu, K.K., Lochte, K., Louanchi, F., Lowry, R., Michaels, A., Monfray, P., Murray, J., Oschlies, A., Platt, T., Priddle, J., Quinones, R., Ruiz-Pino, D., Saino, T., Sakshaug, E., Shimmield, G., Smith, S., Smith, W., Takahashi, T., Treguer, P., Wallace, D., Wanninkhof, R., Watson, A., Willebrand, J., Wong, C.S., 2001. A new vision of ocean biogeochemistry after a decade of the Joint Global Ocean Flux Study (JGOFS). Ambio, 4-31. Goldberg, E.D., 1954. Marine geochemistry, 1., Chemical scavengers of the sea. Journal of Geology, 62, 249-265. Hayes, C.T., Anderson, R.F., Fleisher, M.Q., Huang, K.F., Robinson, L.F., Lu, Y., Cheng, H., Edwards, R.L., Moran, S.B., in press. 230Th and 231Pa on GEOTRACES GA03, the U.S. GEOTRACES North Atlantic transect, and implications for modern and paleoceanographic chemical fluxes. Deep Sea Research Part II: Topical Studies in Oceanography, http://dx.doi.org/10.1016/j.dsr2.2014.07.007. Hayes, C.T., Anderson, R.F., Fleisher, M.Q., Serno, S., Winckler, G., Gersonde, R., 2013. Quantifying lithogenic inputs to the North Pacific Ocean using the long-lived thorium isotopes. Earth and Planetary Science Letters, 383, 16-25. Henderson, G.M., Anderson, R.F., Adkins, J., Andersson, P., Boyle, E.A., Cutter, G., de Baar, H., Eisenhauer, A., Frank, M., Francois, R., Orians, K., Gamo, T., German, C., Jenkins, W., Moffett, J., Jeandel, C., Jickells, T., Krishnaswami, S., Mackey, D., Measures, C.I., Moore, J.K., Oschlies, A., Pollard, R., van der Loeff, M.R.D., Schlitzer, R., Sharma, M., von Damm, K., Zhang, J., Masque, P., 2007. GEOTRACES - An international study of the global marine biogeochemical cycles of trace elements and their isotopes. Chemie Der Erde-Geochemistry, 67, 85-131. Henderson, G.M., Marchal, O., this volume. Recommendations for future measurement and modelling of particles in GEOTRACES and other biogeochemistry programmes. Progress In Oceanography. Hsieh, Y.-T., Henderson, G.M., Thomas, A.L., 2011. Combining seawater 232Th and 230 Th concentrations to determine dust fluxes to the surface ocean. Earth and Planetary Science Letters, 312, 280-290. Hurd, D., Spencer, D.W., (Eds.), 1991. Marine Particles: Analysis and Characterization. Washington, DC: American Geophysical Union. Jackson, G.A., Burd, A.B., this volume. Simulating particle dynamics in ocean biogeochemical models. Progress In Oceanography. Jeandel, C., Peucker-Ehrenbrink, B., Jones, M.T., Pearce, C.R., Oelkers, E.H., Godderis, Y., Lacan, F., Aumont, O., Arsouze, T., 2011. Ocean margins: The missing term in oceanic element budgets? EOS, Transactions of the American Geophysical Union, 92 (26), 217–224. Jeandel, C., Rutgers van der Loeff, M., Kretschmer, S., Lam, P.J., Sherrell, R.M., RoyBarman, M., German, C.R., Dehairs, F., this volume. What did we learn on the oceanic particle dynamic from the GEOSECS-JGOFS times? Progress In Oceanography. Jickells, T.D., An, Z.S., Andersen, K.K., Baker, A.R., Bergametti, G., Brooks, N., Cao, J.J., Boyd, P.W., Duce, R.A., Hunter, K.A., Kawahata, H., Kubilay, N., laRoche, J., Liss, P.S., Mahowald, N., Prospero, J.M., Ridgwell, A.J., Tegen, I., Torres, R.,

15

2005. Global iron connections between desert dust, ocean biogeochemistry, and climate. Science, 308, 67-71. Krauskopf, K.B., 1956. Factors controlling the concentrations of 13 rare metals in seawater. Geochimica et Cosmochimica Acta, 9, 1-32B. Krishnaswami, S., Lal, D., Somayajulu, B.L.K., Weiss, R.F., Craig, H., 1976. Large volume in situ filtration of deep Pacific waters: mineralogical and radioisotope studies. Earth and Planetary Science Letters, 32, 420-429. Lal, D., 1977. Oceanic microcosm of particles. Science, 198, 997-1009. Lal, D., 1980. Comments on some aspects of particulate transposrt in the oceans. Earth and Planetary Science Letters, 49, 520-527. Lam, P.J., Twining, B.S., Jeandel, C., Roychoudhury, A.N., Resing, J., Geibert, W., Santschi, P., Anderson, R.F., this volume. Methods for analyzing the concentration and speciation of major and trace elements in marine particles Progress In Oceanography. Lamborg, C.H., Fitzgerald, W.F., O'Donnell, J., Torgersen, T., 2002. A non-steady-state compartmental model of global-scale mercury biogeochemistry with interhemispheric atmospheric gradients. Geochimica et Cosmochimica Acta, 66, 1105-1118. McDonnell, A.M.P., Lamborg, C.H., Buesseler, K.O., Lam, P.J., Sanders, R., Smith, H., Sargent, E.C., Riley, J.S., Lampitt, R.S., Marsay, C., Bishop, J.K.B., this volume. A summary of techniques for the collection of marine particles. Progress In Oceanography. Morel, F.M.M., Price, N.M., 2003. The biogeochemical cycles of trace metals in the oceans. Science, 300, 944-947. Nozaki, Y., Horibe, Y., Tsubota, H., 1981. The water column distribution of thorium isotopes in the western North Pacific. Earth and Planetary Science Letters, 54, 203216. Nozaki, Y., Turekian, K.K., Vondamm, K., 1980. 210Pb in GEOSECS water profiles from the North Pacific. Earth and Planetary Science Letters, 49, 393-400. 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. Applied Geochemistry, 26, S365-S369. Okubo, A., Obata, H., Gamo, T., Yamada, M., 2012. 230Th and 232Th distributions in midlatitudes of the North Pacific Ocean: Effect of bottom scavenging. Earth and Planetary Science Letters, 339-340, 139-150. Planquette, H., Sherrell, R.M., 2012. Sampling for particulate trace element determination using water sampling bottles: methodology and comparison to in situ pumps. Limnology and Oceanography: Methods, 10, 367-388. Schaule, B.K., Patterson, C.C., 1981. Lead concentrations in the Northeast Pacific Evidence for global anthropogenic perturbations. Earth and Planetary Science Letters, 54, 97-116. Schindler, P.W., 1975. Removal of trace metals from the oceans: a zero order model. Thalassia Jugoslavica, 11, 101-111. Singh, S.P., Singh, S.K., Goswami, Bhushan, R., Rai, V.K., 2012. Spatial distribution of dissolved neodymium and εNd in the Bay of Bengal: Role of particulate matter and mixing of water masses. Geochimica et Cosmochimica Acta, 94, 38-56.

16

Turekian, K.K., 1977. The fate of metals in the ocean. Geochimica et Cosmochimica Acta, 41, 1139-1144. Twining, B.S., Baines, S.B., 2013. The Trace Metal Composition of Marine Phytoplankton. Annual Review of Marine Science, 5, 191-215.

17

Figure 1. Map of the Atlantic Ocean showing both planned and completed GEOTRACES sections in red. Black lines indicate sections completed during the International Polar Year, prior to the main GEOTRACES field program. Black dots indicate locations of historical time series stations, the data from which provide a measure of time-varying ocean conditions as a context in which GEOTRACES results can be interpreted. Updated information about GEOTRACES cruises can be found at: , , and .

18

Figure 2. (A) Particle beam attenuation coefficient, Cp, determined by transmissometer along GEOTRACES Section GA03 (Figure 1). CTD casts are marked in black. The section begins (left hand side) off the NE U.S. and tracks southeast to Mauritania (labeled Africa) before turning north toward Portugal (right hand side of section). Pronounced nepheloid layers are observed below 3.5 km depth in the western North Atlantic. Higher particle concentrations throughout the water column off NW Africa reflect the combined influence of high biological productivity in the region as well as the supply of particles as Saharan dust. (B) Distribution of dissolved (<0.45 µm) excess 230Th along the section. Black dots indicate location of samples. Relatively low concentrations are observed below 3.5 km in the western portion of the section, reflecting enhanced scavenging by nepheloid layer particles, and throughout the water column off NW Africa, reflecting boundary scavenging. Measured concentrations of 230Th were corrected for 230Th derived by dissolution of lithogenic material using measured 232Th concentrations and assuming congruent dissolution of both Th isotopes. See Hayes et al. (in press) for details regarding the calculation of excess 230Th. Figure redrafted from Hayes et al. (in press) using Ocean Data View (Schlitzer, R., http://odv.awi.de, 2013).

19

Science Highlights_Anderson_Hayes • Role of particles in marine trace element biogeochemistry reviewed. • New technologies to define particle distributions and dynamics in the ocean. • Particle biogeochemistry framework for papers in this volume.