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  • 1
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    Non-Rayleigh control of upper-ocean Cd isotope fractionation in the western South Atlantic (2017)
    Elsevier
    In:  Earth and Planetary Science Letters, 471 . pp. 94-103.
    Details
    Publication Date: 2020-02-06
    Description: We present seawater Cd isotopic compositions in five depth profiles and a continuous surface water transect, from 50 degrees S to the Equator, in the western South Atlantic, sampled during GEOTRACES cruise 74JC057 (GA02 section, Leg 3), and investigate the mechanisms governing Cd isotope cycling in the upper and deep ocean. The depth profiles generally display high epsilon Cd-112/110 at the surface and decrease with increasing depth toward values typical of Antarctic Bottom Water (AABW). However, at stations north of the Subantarctic Front, the decrease in epsilon Cd-112/110 is interrupted by a shift to values intermediate between those of surface and bottom waters, which occurs at depths occupied by North Atlantic Deep Water (NADW). This pattern is associated with variations in Cd concentration from low surface values to a maximum at mid-depths and is attributed to preferential utilization of light Cd by phytoplankton in the surface ocean. Our new results show that in this region Cd-deficient waters do not display the extreme, highly fractionated epsilon Cd-112/110 reported in some earlier studies from other oceanic regions. Instead, in the surface and subsurface southwest (SW) Atlantic, when [Cd] drops below 0.1 nmol kg(-1), epsilon Cd-112/110 are relatively homogeneous and cluster around a value of +3.7, in agreement with the mean value of 3.8 +/- 3.3 (2SD, n = 164) obtained from a statistical evaluation of the global ocean Cd isotope dataset. We suggest that Cd-deficient surface waters may acquire their Cd isotope signature via sorption of Cd onto organic ligands, colloids or bacteriallpicoplankton extracellular functional groups. Alternatively, we show that an open system, steady-state model is in good accord with the observed Cd isotope systematics in the upper ocean north of the Southern Ocean. The distribution of epsilon Cd-112/110 in intermediate and deep waters is consistent with the water mass distribution, with the north-south variations reflecting changes in the mixing proportion of NADW and either AABW or AAIW depending on the depth. Overall, the SW Atlantic Cd isotope dataset demonstrates that the large-scale ocean circulation exerts the primary control on epsilon(112/110) Cd cycling in the global deep ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
    Format: other
    DOI: 10.1016/j.epsl.2017.04.024
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The cadmium–phosphate relationship in the western South Atlantic — The importance of mode and intermediate waters on the global systematics (2015)
    Elsevier
    In:  Marine Chemistry, 177 . pp. 110-123.
    Details
    Publication Date: 2018-09-12
    Description: The correlation between dissolved cadmium (Cd) and phosphate (PO4) in the modern ocean has been extensively studied. However, factors that cause the non-linearity in this global correlation are still largely debated and poorly constrained. In this study, we present vertical and meridional distributions of Cd concentrations along the GEOTRACES GA02 Leg 3 transect (53°S to 0°S) in the western South Atlantic. The vertical profiles of dissolved Cd show typical nutrient-like distributions, matching those of the macronutrient PO4. In the surface ocean, low Cd concentrations of 0.34–45 pmol kg− 1 are measured at all stations sampled. Below the fluorescence maxima, Cd concentrations increase with depth, reaching maxima at the depths of, or slightly below, the oxygen minimum. Similarly, surface waters have very low dissolved Cd/PO4 ratios, followed by a sudden decrease at depths corresponding to the fluorescence maxima, below which the Cd/PO4 ratios increase with depth. These variations in Cd and Cd/PO4 ratios are consistent with phytoplankton uptake in the surface ocean at higher Cd/PO4 ratios compared to deep water Redfield Cd/PO4 ratios, and remineralization of high Cd/PO4 organic particles as they sink to depth. In addition, a comparison of Cd and PO4 distributions in waters within the depth range of Subantarctic Mode Water (SAMW) in our study and those in the source regions suggests that SAMW plays an important role in the non-linearity of the Cd–PO4 correlation in the global ocean. On the other hand, intermediate waters at the equatorial stations display significantly lower Cd compared to the southern stations in this study. We attribute this to the influence of low-Cd waters originating in the oxygen-depleted zone (ODZ) of the Angola Basin that are brought in via the Benguela and Equatorial Currents. In the deep ocean (〉 1000 m), the meridional distributions of dissolved Cd concentrations and Cd/PO4 ratios reflect mixing between North Atlantic Deep Water (NADW) (low nutrients, low Cd/PO4 ratios) and Antarctic Bottom Water (AABW) (high nutrients, high Cd/PO4 ratios), showing that dissolved Cd and PO4 can reliably trace deep ocean circulation in the modern ocean.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.marchem.2015.06.011
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Responses of marine phytoplankton in iron enrichment experiments in the northern North Sea and northeast Atlantic Ocean (1998)
    Elsevier
    In:  Marine Chemistry, 61 (3-4). pp. 229-242.
    Details
    Publication Date: 2017-05-30
    Description: Short-term iron enrichment experiments were carried out with samples collected in areas with different phytoplankton activity in the northern North Sea and northeast Atlantic Ocean in the summer of 1993. The research area was dominated by high numbers of pico-phytoplankton, up to 70,000 ml−1. Maximum chlorophyll a concentrations varied from about 1.0 μg l−1 in a high-reflectance zone (caused by loose coccoliths, remnants from a bloom of Emiliania huxleyi) and about 3.5 μg l−1 in a zone in which the phytoplankton were growing, to about 0.5 μg l−1 in the northeast Atlantic Ocean. From the high-reflectance zone to the northeast Atlantic Ocean, nitrate concentrations increased from 0.5 μM to 6.0 μM. Concentrations of reactive iron in surface water showed an opposite trend and decreased from about 2.6 nM in the high-reflectance zone to 〈1.0 nM in the northeast Atlantic Ocean. In the research area, no signs of true iron deficiency were found, but iron enrichments in the high-reflectance zone, numerically dominated by Synechococcus sp., resulted in increased nitrate uptake. Ammonium uptake was hardly affected. Strong support for the effect of Fe on cell physiology is given by the increase in the f-ratio. Net growth rates of the phytoplankton (changes in cell numbers over 24 h) were almost unchanged. Phytoplankton collected from the northeast Atlantic Ocean, did not show changes in the nitrogen metabolism upon addition of iron. Net growth rates in these incubations were low or negative, with only slightly higher values with additional iron.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0304-4203(97)00110-2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Mesoscale features create hotspots of carbon uptake in the Antarctic Circumpolar Current (2017)
    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 138 . pp. 39-51.
    Details
    Publication Date: 2020-02-06
    Description: The influence of eddy structures on the seasonal depletion of dissolved inorganic carbon (DIC) and carbon dioxide (CO2) disequilibrium was investigated during a trans-Atlantic crossing of the Antarctic Circumpolar Current (ACC) in austral summer 2012. The Georgia Basin, downstream of the island of South Georgia (54-55°S, 36-38°W) is a highly dynamic region due to the mesoscale activity associated with the flow of the Subantarctic Front (SAF) and Polar Front (PF). Satellite sea-surface height and chlorophyll-a anomalies revealed a cyclonic cold core that dominated the northern Georgia Basin that was formed from a large meander of the PF. Warmer waters influenced by the SAF formed a smaller anticyclonic structure to the east of the basin. Both the cold core and warm core eddy structures were hotspots of carbon uptake relative to the rest of the ACC section during austral summer. This was most amplified in the cold core where greatest CO2 undersaturation (−78 μatm) and substantial surface ocean DIC deficit (5.1 mol m−2) occurred. In the presence of high wind speeds, the cold core eddy acted as a strong sink for atmospheric CO2 of 25.5 mmol m−2 day−1. Waters of the warm core displayed characteristics of the Polar Frontal Zone (PFZ), with warmer upper ocean waters and enhanced CO2 undersaturation (−59 μatm) and depletion of DIC (4.9mol m−2). A proposed mechanism for the enhanced carbon uptake across both eddy structures is based on the Ekman eddy pumping theory: (i) the cold core is seeded with productive (high chlorophyll-a) waters from the Antarctic Zone and sustained biological productivity through upwelled nutrient supply that counteracts DIC inputs from deep waters; (ii) horizontal entrainment of low-DIC surface waters (biological uptake) from the PFZ downwell within the warm core and cause relative DIC-depletion in the upper water column. The observations suggest that the formation and northward propagation of cold core eddies in the region of the PF could project low-DIC waters towards the site of Antarctic Intermediate Water formation and enhance CO2 drawdown into the deep ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1016/j.dsr2.2015.10.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The GEOTRACES Intermediate Data Product 2014 (2015)
    In:  EPIC3Marine Chemistry, 177, pp. 1-8, ISSN: 03044203
    Details
    Publication Date: 2018-03-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Distributions, trends and inter-annual variability of nutrients along a repeat section through the Weddell Sea (1996–2011) (2015)
    Elsevier
    In:  EPIC3Marine Chemistry, Elsevier, 177, pp. 545-553, ISSN: 03044203
    Details
    Publication Date: 2015-12-01
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
    Format: application/pdf
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  • 7
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    The {GEOTRACES} Intermediate Data Product 2014 (2015)
    In:  EPIC3Marine Chemistry, 177, P, pp. 1 - 8
    Details
    Publication Date: 2016-02-29
    Description: Abstract The {GEOTRACES} Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international {GEOTRACES} programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The {IDP2014} covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The {TEI} data in the {IDP2014} are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including {ASCII} spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the {IDP2014} also contains data quality flags and 1-� data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the {IDP2014} data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 8
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    Calcium carbonate saturation states along the West Antarctic Peninsula (2021)
    Cambridge University Press
    In:  EPIC3Antarctic Science, Cambridge University Press, 33(6), pp. 575-595, ISSN: 0954-1020
    Details
    Publication Date: 2022-01-13
    Description: The waters along the West Antarctic Peninsula (WAP) have experienced warming and increased freshwater inputs from melting sea ice and glaciers in recent decades. Challenges exist in understanding the consequences of these changes on the inorganic carbon system in this ecologically important and highly productive ecosystem. Distributions of dissolved inorganic carbon (CT), total alkalinity (AT) and nutrients revealed key physical, biological and biogeochemical controls of the calcium carbonate saturation state (Ωaragonite) in different water masses across the WAP shelf during the summer. Biological production in spring and summer dominated changes in surface water Ωaragonite (ΔΩaragonite up to +1.39; ∼90%) relative to underlying Winter Water. Sea-ice and glacial meltwater constituted a minor source of AT that increased surface water Ωaragonite (ΔΩaragonite up to +0.07; ∼13%). Remineralization of organic matter and an influx of carbon-rich brines led to cross-shelf decreases in Ωaragonite in Winter Water and Circumpolar Deep Water. A strong biological carbon pump over the shelf created Ωaragonite oversaturation in surface waters and suppression of Ωaragonite in subsurface waters. Undersaturation of aragonite occurred at 〈 ∼1000 m. Ongoing changes along the WAP will impact the biologically driven and meltwater-driven processes that influence the vulnerability of shelf waters to calcium carbonate undersaturation in the future.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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