Comparison of particulate trace element concentrations in the North Atlantic Ocean as determined with discrete bottle sampling and in situ pumping

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 116 (2015): 272-282, doi:10.1016/j.dsr2.2014.11.005.The oceanic geochemical cycles of many metals are controlled, at least in part, by interactions with particulate matter, and measurements of particulate trace metals are a core component of the international GEOTRACES program. Particles can be collected by several methods, including in-line filtration from sample bottles and in situ pumping. Both approaches were used to collect particles from the water column on the U.S. GEOTRACES North Atlantic Zonal Transect cruises. Statistical comparison of 91 paired samples collected at matching stations and depths indicate mean concentrations within 5% for Fe and Ti, within 10% for Cd, Mn and Co, and within 15% for Al. Particulate concentrations were higher in bottle samples for Cd, Mn and Co but lower in bottle samples for Fe, Al and Ti, suggesting that large lithogenic particles may be undersampled by bottles in near-shelf environments. In contrast, P was 58% higher on average in bottle samples. This is likely due to a combination of analytical offsets between lab groups, differences in filter pore size, and potential loss of labile P from pump samples following misting with deionized water. Comparable depth profiles were produced by the methods across a range of conditions in the North Atlantic.This work was funded by grants from the US National Science Foundation to BST (OCE-0928289) and PJL (OCE-0963026) as part of the US GEOTRACES North Atlantic Zonal Transect program

A dissolved cobalt plume in the oxygen minimum zone of the eastern tropical South Pacific

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 13 (2016): 5697-5717, doi:10.5194/bg-13-5697-2016.Cobalt is a nutrient to phytoplankton, but knowledge about its biogeochemical cycling is limited, especially in the Pacific Ocean. Here, we report sections of dissolved cobalt and labile dissolved cobalt from the US GEOTRACES GP16 transect in the South Pacific. The cobalt distribution is closely tied to the extent and intensity of the oxygen minimum zone in the eastern South Pacific with highest concentrations measured at the oxycline near the Peru margin. Below 200 m, remineralization and circulation produce an inverse relationship between cobalt and dissolved oxygen that extends throughout the basin. Within the oxygen minimum zone, elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low O2. As these high cobalt waters are upwelled and advected offshore, phytoplankton export returns cobalt to low-oxygen water masses underneath. West of the Peru upwelling region, dissolved cobalt is less than 10 pM in the euphotic zone and strongly bound by organic ligands. Because the cobalt nutricline within the South Pacific gyre is deeper than in oligotrophic regions in the North and South Atlantic, cobalt involved in sustaining phytoplankton productivity in the gyre is heavily recycled and ultimately arrives from lateral transport of upwelled waters from the eastern margin. In contrast to large coastal inputs, atmospheric deposition and hydrothermal vents along the East Pacific Rise appear to be minor sources of cobalt. Overall, these results demonstrate that oxygen biogeochemistry exerts a strong influence on cobalt cycling.This work was funded by NSF awards OCE-1233733 to MAS, OCE-1232814 to BST, and OCE-1237011 to JAR

Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 14 (2017): 2715-2739, doi:10.5194/bg-14-2715-2017.Cobalt is the scarcest of metallic micronutrients and displays a complex biogeochemical cycle. This study examines the distribution, chemical speciation, and biogeochemistry of dissolved cobalt during the US North Atlantic GEOTRACES transect expeditions (GA03/3_e), which took place in the fall of 2010 and 2011. Two major subsurface sources of cobalt to the North Atlantic were identified. The more prominent of the two was a large plume of cobalt emanating from the African coast off the eastern tropical North Atlantic coincident with the oxygen minimum zone (OMZ) likely due to reductive dissolution, biouptake and remineralization, and aeolian dust deposition. The occurrence of this plume in an OMZ with oxygen above suboxic levels implies a high threshold for persistence of dissolved cobalt plumes. The other major subsurface source came from Upper Labrador Seawater, which may carry high cobalt concentrations due to the interaction of this water mass with resuspended sediment at the western margin or from transport further upstream. Minor sources of cobalt came from dust, coastal surface waters and hydrothermal systems along the Mid-Atlantic Ridge. The full depth section of cobalt chemical speciation revealed near-complete complexation in surface waters, even within regions of high dust deposition. However, labile cobalt observed below the euphotic zone demonstrated that strong cobalt-binding ligands were not present in excess of the total cobalt concentration there, implying that mesopelagic labile cobalt was sourced from the remineralization of sinking organic matter. In the upper water column, correlations were observed between total cobalt and phosphate, and between labile cobalt and phosphate, demonstrating a strong biological influence on cobalt cycling. Along the western margin off the North American coast, this correlation with phosphate was no longer observed and instead a relationship between cobalt and salinity was observed, reflecting the importance of coastal input processes on cobalt distributions. In deep waters, both total and labile cobalt concentrations were lower than in intermediate depth waters, demonstrating that scavenging may remove labile cobalt from the water column. Total and labile cobalt distributions were also compared to a previously published South Atlantic GEOTRACES-compliant zonal transect (CoFeMUG, GAc01) to discern regional biogeochemical differences. Together, these Atlantic sectional studies highlight the dynamic ecological stoichiometry of total and labile cobalt. As increasing anthropogenic use and subsequent release of cobalt poses the potential to overpower natural cobalt signals in the oceans, it is more important than ever to establish a baseline understanding of cobalt distributions in the ocean.We also gratefully acknowledge support of funding agencies on the following grants: the US National Science Foundation (NSF-OCE 0928414, 1233261, 1435056) and the Gordon and Betty Moore Foundation (grant 3738)

Size-fractionated major particle composition and concentrations from the US GEOTRACES North Atlantic Zonal Transect

AbstractThe concentration and the major phase composition (particulate organic matter, CaCO3, opal, lithogenic matter, and iron and manganese oxyhydroxides) of marine particles is thought to determine the scavenging removal of particle-reactive TEIs. Particles are also the vector for transferring carbon from the atmosphere to the deep ocean via the biological carbon pump, and their composition may determine the efficiency and strength of this transfer. Here, we present the first full ocean depth section of size-fractionated (1–51µm, >51µm) suspended particulate matter (SPM) concentration and major phase composition from the US GEOTRACES North Atlantic Zonal Transect between Woods Hole, MA and Lisbon, Portugal conducted in 2010 and 2011. Several major particle features are notable in the section: intense benthic nepheloid layers were observed in the western North American margin with concentrations of SPM of up to 1648µg/L, two to three orders of magnitude higher than surrounding waters, that were dominated by lithogenic material. A more moderate benthic nepheloid layer was also observed in the eastern Mauritanian margin (44µg/L) that had a lower lithogenic content and, notably, significant concentrations of iron and manganese oxyhydroxides (2.5% each). An intermediate nepheloid layer reaching 102µg/L, an order of magnitude above surrounding waters, was observed associated with the Mediterranean Outflow. Finally, there was a factor of two enhancement in SPM at the TAG hydrothermal plume due almost entirely to the addition of iron oxyhydroxides from the hydrothermal vent. We observe correlations between POC and CaCO3 in large (>51µm) particles in the upper 2000m, but not deeper than 2000m, and no correlations between POC and CaCO3 at any depth in small (<51µm) particles. There were also no correlations between POC and lithogenic material in large particles. Overall, there were very large uncertainties associated with all regression coefficients for mineral ballast (“carrying coefficients”), suggesting that mineral ballast was not a strong predictor for POC in this section

Elevated Trace Metal Content of Prokaryotic Communities Associated with Marine Oxygen Deficient Zones

Little is known about the trace metal content of marine prokaryotes, in part due to their co-occurrence with more abundant particulate phases in the upper ocean, such as phytoplankton and biogenic detritus, lithogenic minerals, and authigenic Mn and Fe oxyhydroxides. We attempt to isolate these biomass signals in particulate data from the US GEOTRACES Eastern Pacific Zonal Transect (cruise GP16) in the Eastern Tropical South Pacific (ETSP), which exhibited consistent maxima in P and other bioactive trace metals, and minima in particulate Mn, in the oxygen deficient zones (ODZs) of 13 stations. Nitrite maxima and nitrate deficits indicated the presence of denitrifying prokaryotic biomass within ETSP ODZs, and deep secondary fluorescence maxima at the upper ODZ boundaries of 10 stations also suggested the presence of low-light, autotrophic communities. ODZs were observed as far west as 99 degrees W, more than 2300 km from the South American coast, where eolian lithogenic and lateral/resuspended sedimentary inputs were negligible, presenting a unique opportunity to examine prokaryotic metal stoichiometries. ODZ particulate P maxima can rival gyre mixed layer biomass concentrations, are highly sensitive to oxygen, and are in excess of amounts scavengable by local Fe oxyhydroxides and acid-volatile sulfides. Even after correction for lithogenic and ferruginous-scavenged metals, ODZ P-maxima are often enriched in Cd, Co, Cu, Ni, V, and Zn, exhibiting particulate trace metal ratios to P that exceed mixed layer biomass ratios by factors of 2-9. ODZ prokaryotic communities may be largely hidden, TM-rich pools involved in the marine cycles of these bioactive trace metals

Coastal sources, sinks and strong organic complexation of dissolved cobalt within the US North Atlantic GEOTRACES transect GA03

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 14 (2017): 2715-2739, doi:10.5194/bg-14-2715-2017.Cobalt is the scarcest of metallic micronutrients and displays a complex biogeochemical cycle. This study examines the distribution, chemical speciation, and biogeochemistry of dissolved cobalt during the US North Atlantic GEOTRACES transect expeditions (GA03/3_e), which took place in the fall of 2010 and 2011. Two major subsurface sources of cobalt to the North Atlantic were identified. The more prominent of the two was a large plume of cobalt emanating from the African coast off the eastern tropical North Atlantic coincident with the oxygen minimum zone (OMZ) likely due to reductive dissolution, biouptake and remineralization, and aeolian dust deposition. The occurrence of this plume in an OMZ with oxygen above suboxic levels implies a high threshold for persistence of dissolved cobalt plumes. The other major subsurface source came from Upper Labrador Seawater, which may carry high cobalt concentrations due to the interaction of this water mass with resuspended sediment at the western margin or from transport further upstream. Minor sources of cobalt came from dust, coastal surface waters and hydrothermal systems along the Mid-Atlantic Ridge. The full depth section of cobalt chemical speciation revealed near-complete complexation in surface waters, even within regions of high dust deposition. However, labile cobalt observed below the euphotic zone demonstrated that strong cobalt-binding ligands were not present in excess of the total cobalt concentration there, implying that mesopelagic labile cobalt was sourced from the remineralization of sinking organic matter. In the upper water column, correlations were observed between total cobalt and phosphate, and between labile cobalt and phosphate, demonstrating a strong biological influence on cobalt cycling. Along the western margin off the North American coast, this correlation with phosphate was no longer observed and instead a relationship between cobalt and salinity was observed, reflecting the importance of coastal input processes on cobalt distributions. In deep waters, both total and labile cobalt concentrations were lower than in intermediate depth waters, demonstrating that scavenging may remove labile cobalt from the water column. Total and labile cobalt distributions were also compared to a previously published South Atlantic GEOTRACES-compliant zonal transect (CoFeMUG, GAc01) to discern regional biogeochemical differences. Together, these Atlantic sectional studies highlight the dynamic ecological stoichiometry of total and labile cobalt. As increasing anthropogenic use and subsequent release of cobalt poses the potential to overpower natural cobalt signals in the oceans, it is more important than ever to establish a baseline understanding of cobalt distributions in the ocean.We also gratefully acknowledge support of funding agencies on the following grants: the US National Science Foundation (NSF-OCE 0928414, 1233261, 1435056) and the Gordon and Betty Moore Foundation (grant 3738)

Basin-scale inputs of cobalt, iron, and manganese from the Benguela-Angola front to the South Atlantic Ocean

Author Posting. © Association for the Sciences of Limnology and Oceanography, 2012. This article is posted here by permission of Association for the Sciences of Limnology and Oceanography for personal use, not for redistribution. The definitive version was published in Limnology and Oceanography 57 (2012): 989-1010, doi:10.4319/lo.2012.57.4.0989.We present full-depth zonal sections of total dissolved cobalt, iron, manganese, and labile cobalt from the South Atlantic Ocean. A basin-scale plume from the African coast appeared to be a major source of dissolved metals to this region, with high cobalt concentrations in the oxygen minimum zone of the Angola Dome and extending 2500 km into the subtropical gyre. Metal concentrations were elevated along the coastal shelf, likely due to reductive dissolution and resuspension of particulate matter. Linear relationships between cobalt, N2O, and O2, as well as low surface aluminum supported a coastal rather than atmospheric cobalt source. Lateral advection coupled with upwelling, biological uptake, and remineralization delivered these metals to the basin, as evident in two zonal transects with distinct physical processes that exhibited different metal distributions. Scavenging rates within the coastal plume differed for the three metals; iron was removed fastest, manganese removal was 2.5 times slower, and cobalt scavenging could not be discerned from water mass mixing. Because scavenging, biological utilization, and export constantly deplete the oceanic inventories of these three hybrid-type metals, point sources of the scale observed here likely serve as vital drivers of their oceanic cycles. Manganese concentrations were elevated in surface waters across the basin, likely due to coupled redox processes acting to concentrate the dissolved species there. These observations of basin-scale hybrid metal plumes combined with the recent projections of expanding oxygen minimum zones suggest a potential mechanism for effects on ocean primary production and nitrogen fixation via increases in trace metal source inputs.This research was supported US National Science Foundation Chemical Oceanography (Division of Ocean Sciences OCE-0452883, OCE-0752291, OCE-0928414, OCE-1031271), the Center for Microbial Research and Education, the Gordon and Betty Moore Foundation, the WHOI Coastal Ocean Institute, and the WHOI Ocean Life Institute

Near-field iron and carbon chemistry of non-buoyant hydrothermal plume particles, Southern East Pacific Rise 15°S

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Chemistry 201 (2018): 183-197, doi:10.1016/j.marchem.2018.01.011.Iron (Fe)-poor surface waters limit phytoplankton growth and their ability to remove carbon (C) from the atmosphere and surface ocean. Over the past few decades, research has focused on constraining the global Fe cycle and its impacts on the global C cycle. Hydrothermal vents have become a highly debated potential source of Fe to the surface ocean. Two main mechanisms for transport of Fe over long distances have been proposed: Fe-bearing nanoparticles and organic C complexation with Fe in the dissolved (dFe) and particulate (pFe) pools. However, the ubiquity and importance of these processes is unknown at present, and very few vents have been investigated for Fe-Corg interactions or the transport of such materials away from the vent. Here we describe the near-field contributions (first ~100 km from ridge) of pFe and Corg to the Southern East Pacific Rise (SEPR) plume, one of the largest known hydrothermal plume features in the global ocean. Plume particles (> 0.2 μm) were collected as part of the U.S. GEOTRACES Eastern Pacific Zonal Transect cruise (GP16) by in-situ filtration. Sediment cores were also collected to investigate the properties of settling particles. In this study, X-ray absorption near edge structure (XANES) spectroscopy was used in two complementary X-ray synchrotron approaches, scanning transmission X-ray microscopy (STXM) and X-ray microprobe, to investigate the Fe and C speciation of particles within the near-field non-buoyant SEPR plume. When used in concert, STXM and X-ray microprobe provide fine-scale and representative information on particle morphology, elemental co-location, and chemical speciation. Bulk chemistry depth profiles for particulate Corg (POC), particulate manganese (pMn), and pFe indicated that the source of these materials to the non-buoyant plume is hydrothermal in origin. The plume particles at stations within the first ~100 km down-stream of the ridge were composites of mineral (oxidized Fe) and biological materials (organic C, Corg). Iron chemistry in the plume and in the core-top suspended sediment fluff layer were both dominated by Fe(III) phases, such as Fe(III) oxyhydroxides and Fe(III) phyllosilicates. Particulate sulfur (pS) was a rare component of our plume and sediment samples. When pS was detected, it was in the form of an Fe sulfide mineral phase, composing ≤ 0.4% of the Fe on a per atom basis. The resuspended sediment fluff layer contained a mixture of inorganic (coccolith fragments) and Corg bearing (lipid-rich biofilm-like) materials. The particle morphology and co-location of C and Fe in the sediment was different from that in plume particles. This indicates that if the Fe-Corg composite particles settle rapidly to the sediments, then they experience strong alteration during settling and/or within the sediments. Overall, our observations indicate that the particles within the first ~ 100 km of the laterally advected plume are S-depleted, Fe(III)-Corg composites indicative of a chemically oxidizing plume with strong biological modification. These findings confirm that the Fe-Corg relationships observed for non-buoyant plume particles within ~ 100 m of the vent site are representative of particles within this region of the non-buoyant plume (~100 km). These findings also point to dynamic alteration of Fe-Corg bearing particles during transport and settling. The specific biogeochemical processes at play, and the implications for nutrient cycling in the ocean are currently unknown and represent an area of future investigation

Dissolved and particulate barium distributions along the US GEOTRACES North Atlantic and East Pacific zonal transects (GA03 and GP16): global implications for the marine barium cycle

Author Posting. © American Geophysical Union, 2022. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 36(6), (2022): e2022GB007330, https://doi.org/10.1029/2022gb007330.Processes controlling dissolved barium (dBa) were investigated along the GEOTRACES GA03 North Atlantic and GP16 Eastern Tropical Pacific transects, which traversed similar physical and biogeochemical provinces. Dissolved Ba concentrations are lowest in surface waters (∼35–50 nmol kg−1) and increase to 70–80 and 140–150 nmol kg−1 in deep waters of the Atlantic and Pacific transects, respectively. Using water mass mixing models, we estimate conservative mixing that accounts for most of dBa variability in both transects. To examine nonconservative processes, particulate excess Ba (pBaxs) formation and dissolution rates were tracked by normalizing particulate excess 230Th activities. Th-normalized pBaxs fluxes, with barite as the likely phase, have subsurface maxima in the top 1,000 m (∼100–200 μmol m−2 year−1 average) in both basins. Barite precipitation depletes dBa within oxygen minimum zones from concentrations predicted by water mass mixing, whereas inputs from continental margins, particle dissolution in the water column, and benthic diffusive flux raise dBa above predications. Average pBaxs burial efficiencies along GA03 and GP16 are ∼37% and 17%–100%, respectively, and do not seem to be predicated on barite saturation indices in the overlying water column. Using published values, we reevaluate the global freshwater dBa river input as 6.6 ± 3.9 Gmol year−1. Estuarine mixing processes may add another 3–13 Gmol year−1. Dissolved Ba inputs from broad shallow continental margins, previously unaccounted for in global marine summaries, are substantial (∼17 Gmol year−1), exceeding terrestrial freshwater inputs. Revising river and shelf dBa inputs may help bring the marine Ba isotope budget more into balance.The International GEOTRACES Programme is possible in part thanks to the support from the U.S. National Science Foundation (Grant OCE-1840868) to the Scientific Committee on Oceanic Research (SCOR). This research was supported by the National Science Foundation under Grant No. NSF OCE-0927951, NSF OCE-1137851, NSF OCE-1261214, and NSF OCE-1925503 to A. M. Shiller; NSF OCE-1829563 to R. F. Anderson; NSF OCE-0927064 and NSF OCE-1233688 to R. F. Anderson and M. Q. Fleisher; NSF OCE-0927754 to R. Lawrence Edwards; NSF OCE-1233903 to R. Lawrence Edwards and H. Cheng; NSF OCE-0926860 to L. F. Robinson; NSF OCE-0963026 and NSF OCE-1518110 to P. J. Lam; and NSF OCE-1232814 to B. S. Twining

Intensity of Th and Pa scavenging partitioned by particle chemistry in the North Atlantic Ocean

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Marine Chemistry 170 (2015): 49-60, doi:10.1016/j.marchem.2015.01.006.The natural radionuclides 231Pa and 230Th are incorporated into the marine sediment record by scavenging, or adsorption to various particle types, via chemical reactions that are not fully understood. Because these isotopes have potential value in tracing several oceanographic processes, we investigate the nature of scavenging using trans-Atlantic measurements of dissolved (<0.45 μm) and particulate (0.8-51 μm) 231Pa and 230Th, together with major particle composition. We find widespread impact of intense scavenging by authigenic Fe/Mn (hydr)oxides, in the form of hydrothermal particles emanating from the Mid-Atlantic ridge and particles resuspended from reducing conditions near the seafloor off the coast of West Africa. Biogenic opal was not found to be a significant scavenging phase for either element in this sample set, essentially because of its low abundance and small dynamic range at the studied sites. Distribution coefficients in shallow (< 200 m) depths are anomalously low which suggests either the unexpected result of a low scavenging intensity for organic matter or that, in water masses containing abundant organic-rich particles, a greater percentage of radionuclides exist in the colloidal or complexed phase. In addition to particle concentration, the oceanic distribution of particle types likely plays a significant role in the ultimate distribution of sedimentary 230Th and 231Pa.Cruise management for GA03 was funded by the U. S. National Science Foundation to W. Jenkins (OCE-0926423), E. Boyle (OCE-0926204), and G. Cutter (OCE-0926092). Radionuclide studies were supported by NSF (OCE-0927064 to LDEO, OCE-0926860 to WHOI, OCE- 0927757 to URI, and OCE-0927754 to UMN). Additional support came from the European Research Council (278705) to LFR and the Ford Foundation Predoctoral Fellowship to SMV. Particle studies were supported by NSF OCE-0963026 to PJL