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

Hawco, Nicholas J.; Ohnemus, Daniel C.; Resing, J. A.; Twining, Benjamin S.; Saito, Mak A.

doi:10.5194/bg-13-5697-2016

Cited by 61 publications

(110 citation statements)

References 90 publications

(178 reference statements)

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“…In particular, the Co* deficit observed within the subsurface represents a useful indicator for the integrated influence of cobalt scavenging. One can consider that during periods of ocean anoxia or suboxia, these negative Co* regions in the ocean interior would likely be replaced by higher dCo inventories and associated positive Co* values as the Co scavenging process is diminished due to lack of oxygen, as has been predicted for the Neoproterozoic era and observed in modern OMZs (Hawco et al, 2016;Noble et al, 2012Noble et al, , 2017. The selection of this moderate Q value results in Co* values that were considerably in excess of unity in the upper water column.…”

Section: Ocean Sections Of Co* and Dco : P Slopesmentioning

confidence: 95%

“…The balancing act between these two major processes is apparent in the variability of individual profiles, demonstrating the complex hybrid nature of the dissolved cobalt profile. Scavenging of dCo appears to be a critical process in controlling the inventory of cobalt in the oceans, and this topic, including the estimate of overall scavenging influences during horizontal advection through ocean basins, is further explored in Hawco et al (2016).…”

Section: Evidence For Mesopelagic Scavenging Of Cobalt In the Atlantimentioning

confidence: 99%

“…Improved analytical methods for the determination of dissolved Co, and the resulting recent production of large GEO-TRACES datasets (Geotraces Group, 2015), provide new opportunities to explore the variability in Co stoichiometry and the processes that create this range (Baars and Croot, 2015;Bown et al, 2011Bown et al, , 2012Dulaquais et al, 2014a, b;Hawco et al, 2016;Noble et al, 2012Noble et al, , 2008Saito et al, 2010;Shelley et al, 2012). Here we examine and compare two zonal full depth sections of total dissolved cobalt and labile cobalt from the North and South Atlantic Ocean to examine the tug-ofwar among competing processes affecting cobalt cycling in the oceanic water column.…”

Section: Introductionmentioning

confidence: 99%

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The acceleration of dissolved cobalt's ecological stoichiometry due to biological uptake, remineralization, and scavenging in the Atlantic Ocean

et al. 2017

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Abstract. The stoichiometry of biological components and their influence on dissolved distributions have long been of interest in the study of the oceans. Cobalt has the smallest oceanic inventory of inorganic micronutrients and hence is particularly vulnerable to influence by internal oceanic processes including euphotic zone uptake, remineralization, and scavenging. Here we observe not only large variations in dCo : P stoichiometry but also the acceleration of those dCo : P ratios in the upper water column in response to several environmental processes. The ecological stoichiometry of total dissolved cobalt (dCo) was examined using data from a US North Atlantic GEOTRACES transect and from a zonal South Atlantic GEOTRACES-compliant transect (GA03/3_e and GAc01) by Redfieldian analysis of its statistical relationships with the macronutrient phosphate. Trends in the dissolved cobalt to phosphate (dCo : P) stoichiometric relationships were evident in the basin-scale vertical structure of cobalt, with positive dCo : P slopes in the euphotic zone and negative slopes found in the ocean interior and in coastal environments. The euphotic positive slopes were often found to accelerate towards the surface and this was interpreted as being due to the combined influence of depleted phosphate, phosphorus-sparing (conserving) mechanisms, increased alkaline phosphatase metalloenzyme production (a zinc or perhaps cobalt enzyme), and biochemical substitution of Co for depleted Zn. Consistent with this, dissolved Zn (dZn) was found to be drawn down to only 2-fold more than dCo, despite being more than 18-fold more abundant in the ocean interior. Particulate cobalt concentrations increased in abundance from the base of the euphotic zone to become ∼ 10 % of the overall cobalt inventory in the upper euphotic zone with high stoichiometric values of ∼ 400 µmol Co mol −1 P. Metaproteomic results from the Bermuda Atlantic Timeseries Study (BATS) station found cyanobacterial isoforms of the alkaline phosphatase enzyme to be prevalent in the upper water column, as well as a sulfolipid biosynthesis protein indicative of P sparing. The negative dCo : P relationships in the ocean interior became increasingly vertical with depth, and were consistent with the sum of scavenging and remineralization processes (as shown by their dCo : P vector sums). Attenuation of the remineralization with depth resulted in the increasingly vertical dCo : P relationships. Analysis of particulate Co with particulate Mn and particulate phosphate also showed positive linear relationships below the euphotic zone, consistent with the presence and increased relative influence of Mn oxide particles involved in scavenging. Visualization of dCo : P slopes across an ocean section revealed hotspots of scavenging and remineralization, such as at the hydrothermal vents and below the oxygen minimum zone (OMZ) region, respectively, while that of an estimate of Co* illustrated stoPublished by Copernicus Publications on behalf of the European Geosciences Union. ichiometrically ...

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Section: Ocean Sections Of Co* and Dco : P Slopesmentioning

confidence: 95%

Section: Evidence For Mesopelagic Scavenging Of Cobalt In the Atlantimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The acceleration of dissolved cobalt's ecological stoichiometry due to biological uptake, remineralization, and scavenging in the Atlantic Ocean

et al. 2017

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“…This Northwest African/Mauritanian Upwelling region contains the smallest of five major marine OMZs in the oceans, with the others located in the eastern tropical North and South Pacific, the eastern South Atlantic, and the Arabian Sea (Keeling et al, 2010). Previous cobalt studies have shown that the South Atlantic OMZ and the two Pacific OMZs all harbor high concentrations of cobalt (Ahlgren et al, 2014;Hawco et al, 2016;Noble et al, 2012;Saito et al, 2004Saito et al, , 2005. The current study confirms high cobalt concentrations in the North Atlantic OMZ as well, despite this OMZ having higher O 2 concentrations and lacking the substantial suboxic and anoxic waters found in other OMZs.…”

Section: Major Sources Of Cobalt To the North Atlantic Oceanmentioning

confidence: 98%

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

et al. 2017

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Abstract. 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.

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“…The estimated dust input was 0.4 nmol m -2 d -1 , which would still be of little consequence (<15% of export) in the Gyre. Long term sources of the dissolved pool most likely originate from coastal shelf fluxes and upwelling (Hawco et al, 2016;Saito et al, 2004;. Ra-based estimates suggest that 59 nmolCo m -2 d -1 is being supplied from the Shelf to the Gyre.…”

Section: Comentioning

confidence: 99%

An investigation of basin-scale controls on upper ocean export and remineralization

Black¹

2018

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The biological carbon pump (BCP) helps to moderate atmospheric carbon dioxide levels by bringing carbon to the deep ocean, where it can be sequestered on timescales of centuries to millennia. Climate change is predicted to decrease the efficiency of the global BCP, however, the magnitude and timescale of this shift is largely uncertain and will likely impact some areas of the global ocean more significantly than others. Therefore, it is imperative that we (1) accurately quantify surface export and remineralization of particulate organic carbon (POC) via the BCP over large regions of the global ocean, (2) examine the factors controlling these POC fluxes and their variability, which includes the cycling of biologically-relevant trace metals, and (3) establish if and how the BCP is changing over time.This thesis focuses on addressing various aspects of these objectives using the 234 Th-238 U method across basin-scale GEOTRACES transects. First, the export and remineralization of POC were examined across large gradients in productivity, upwelling, community structure, and dissolved oxygen in the southeastern tropical Pacific Ocean. Although low oxygen zones are traditionally thought to have decreased POC flux attenuation relative to other regions of the global ocean and the low oxygen Pacific locations followed this pattern, regions that were functionally anoxic had enhanced attenuation in the upper 400 m. Second, trace metal export and remineralization were quantified across the Pacific transect. Because many trace metals are necessary for the metabolic functions of marine organisms and can co-limit marine productivity, the controls on the cycling of trace metals in the upper ocean were examined. Lastly, POC export was determined across two transects in the Western Arctic Ocean, where light and nutrient availability drive the biological pump. Upper ocean export estimates in the central basin did not reflect a substantial change in the biological pump compared to studies from the last three decades, however, an extensive maximum in 234 Th relative to 238 U deeper in the water column indicated that rapid vertical transport had occurred, which could suggest a more efficient biological pump in the Arctic Ocean.

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

Cited by 61 publications

References 90 publications

The acceleration of dissolved cobalt's ecological stoichiometry due to biological uptake, remineralization, and scavenging in the Atlantic Ocean

The acceleration of dissolved cobalt's ecological stoichiometry due to biological uptake, remineralization, and scavenging in the Atlantic Ocean

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

An investigation of basin-scale controls on upper ocean export and remineralization

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