Beschreibung: The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 22 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017.

Beschreibung: 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.

Beschreibung: 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.

Beschreibung: Highlights: • We measured the speciation of iron and copper in an estuarine sample at pHs between 6.8 and 8.2. • We use measured complexation parameters to optimize the NICA-Donnan model for Fe and Cu complexation in estuarine samples. • We examine the impact of increased pCO2 on iron and copper complexation by dissolved organic matter in our estuarine sample. • We found that inorganic copper and iron concentrations increase as carbonate ion concentrations and pH decrease. Abstract: The uptake of anthropogenic atmospheric CO2 by the oceans causes a shift in the carbonate chemistry system which includes a lowering of pH; this process has been termed ocean acidification. Our understanding of the specific effects of ocean acidification on chemical speciation of trace metals, in particular on organic–metal interactions, is limited. In this study we have experimentally determined the effects of changing pH from 8.3 to 6.8 (on the NBS scale) on the speciation of iron and copper in estuarine waters. Our experimental results indicated that complexation of iron and copper would decrease and inorganic iron and copper concentrations increase, as pH decreased, although it was not possible to confidently quantify changes in speciation at lower pH due to constraints of the analytical technique. In addition to our experimental approach, we used a non-ideal competitive adsorption (NICA)–Donnan model to determine the chemical speciation of iron and copper as a function of pH. The NICA–Donnan model was optimised in order to produce similar metal binding characteristics to those observed in our sample across the pH range examined in our study. The model allowed for simultaneous modelling of solubility and organic complexation. Model results indicated that a decrease in iron and copper binding by organic matter at lower pH, coupled with increased solubility (for iron), resulted in a 3 fold increase in inorganic iron concentration and a 6 fold increase in inorganic copper concentration at pH of 7.41 compared to a pH of 8.18 (expressed on the total scale). This compared to a 10 fold increase in inorganic iron concentration, and a 5 fold increase in inorganic copper concentration, obtained at pH 8.18, when the dissolved organic carbon (DOC) concentration was halved. Variability in DOC might thus be expected to have a greater impact on metal speciation in seawater, than projected variability in pH resulting from increases in atmospheric CO2. Our study therefore suggests that increases in the concentrations of the more bioavailable inorganic iron and copper species in estuarine waters resulting from increased pCO2 are likely to occur, but that such changes will be moderate in magnitude.

Beschreibung: A major surface circulation feature of the Arctic Ocean is the Transpolar Drift (TPD), a current that transports river‐influenced shelf water from the Laptev and East Siberian Seas toward the center of the basin and Fram Strait. In 2015, the international GEOTRACES program included a high‐resolution pan‐Arctic survey of carbon, nutrients, and a suite of trace elements and isotopes (TEIs). The cruises bisected the TPD at two locations in the central basin, which were defined by maxima in meteoric water and dissolved organic carbon concentrations that spanned 600 km horizontally and ~25‐50 m vertically. Dissolved TEIs such as Fe, Co, Ni, Cu, Hg, Nd, and Th, which are generally particle‐reactive but can be complexed by organic matter, were observed at concentrations much higher than expected for the open ocean setting. Other trace element concentrations such as Al, V, Ga, and Pb were lower than expected due to scavenging over the productive East Siberian and Laptev shelf seas. Using a combination of radionuclide tracers and ice drift modeling, the transport rate for the core of the TPD was estimated at 0.9 ± 0.4 Sv (106 m3 s‐1). This rate was used to derive the mass flux for TEIs that were enriched in the TPD, revealing the importance of lateral transport in supplying materials beneath the ice to the central Arctic Ocean and potentially to the North Atlantic Ocean via Fram Strait. Continued intensification of the Arctic hydrologic cycle and permafrost degradation will likely lead to an increase in the flux of TEIs into the Arctic Ocean.

Beschreibung: The neodymium isotopic composition (εNd) of seawater is one of the most important geochemical tracers to investigate water mass provenance, which can also serve as a proxy to reconstruct past variations in ocean circulation. Nd isotopes have recently also been used to reconstruct past circulation changes in the Mediterranean Sea on different time scales. However, the modern seawater εNd dataset for the Mediterranean Sea, which these reconstructions are based on, is limited and up to now only 160 isotopic measurements are available for the entire basin. The lack of present-day data also limits our understanding of the processes controlling the Nd cycle and Nd isotopic distribution in this semi-enclosed basin. Here we present new εNd data from 24 depth profiles covering all Mediterranean sub-basins, which significantly increases the available dataset in the Mediterranean Sea. The main goal of our study is to better characterize the relationship between the dissolved Nd isotope distributions and major water masses in the Mediterranean Sea and to investigate the impact and relative importance of local non-conservative modifications, which include input of riverine particles and waters, aeolian-derived material and exchange with the sediments at continental margins. This comprehensive εNd dataset reveals a clear εNd – salinity correlation and a zonal and depth gradient with εNd systematically increasing from the western to the eastern Mediterranean basin (average εNd = −8.8 ± 0.8 and −6.7 ± 1 for the entire water column, respectively), reflecting the large-scale basin circulation. We have evaluated the conservative εNd behaviour in the Mediterranean Sea and quantified the non-conservative components of the εNd signatures by applying an Optimum Multiparameter (OMP) analysis and results from the Parametric Optimum Multiparameter (POMP) analysis of Jullion et al. (2017). The results of the present study combined with previously published Nd isotope values indicate that dissolved εNd behaves overall conservatively in the open Mediterranean Sea and show that its water masses are clearly distinguishable by their Nd isotope signature. However, misfits between measured and OMP- and POMP-derived εNd values exist in almost all sub-basins, especially in the eastern Levantine Basin and Alboran Sea at intermediate-deep depths, which can be explained by the influence of detrital lithogenic εNd signatures through interaction with highly radiogenic Nile sourced volcanic fractions and unradiogenic sediments, respectively. The radiogenic signature acquired in the eastern Levantine Basin is carried by the Levantine Intermediate Water and transferred conservatively to the entire Mediterranean at intermediate depths. Our measured εNd values and OMP- and POMP-derived results indicate that non-conservative contributions originating from sediment sources are then propagated by water mass circulation (with distinct preformed εNd) along the Mediterranean Sea through advection and conservative mixing. Mediterranean εNd effectively traces the mixing between the different water masses in this semi-enclosed basin and is a suitable water mass tracer.

Beschreibung: The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Beschreibung: In this study we present dissolved and particulate 230Th and 232Th results, as well as particulate 234Th data, obtained as part of the GEOTRACES central Arctic Ocean sections GN04 (2015) and IPY11 (2007). Samples were analyzed following GEOTRACES methods, and compared to previous results from 1991. We observe significant decreases in 230Th concentrations in the deep waters of the Nansen Basin. We ascribe this non-steady state removal process to a variable release and scavenging of trace metals near an ultra-slow spreading ridge. This finding demonstrates that hydrothermal scavenging in the deep-sea may vary on annual time scales and highlights the importance of repeated GEOTRACES sections

Beschreibung: 230Th and 231Pa are produced in sea water by radioactive decay of Uranium isotopes (234U, 235U). Both are particle reactive and are scavenged onto settling particles. As 230Th is more particle reactive than 231Pa, their distribution in the water column and activity ratio give information about particle fluxes and circulation patterns and –intensities. Both particle fluxes and deep water circulation may respond to climatic changes in the Arctic Ocean. This study discusses temporal changes in radionuclide concentration in the context of climate change. We compare results from 1991 [1] 2007 and 2015. We present results of dissolved 231Pa and 230Th activities of samples collected in the Nansen-, Amundsenand Makarov Basins during GEOTRACES sections GIPY11 (2007, 4 stations), GN04 (2015, 10 stations) aboard RV Polarstern. Our discussion of factors controlling the 230Th and 231Pa distribution is supported by, dissolved CFC, dissolved iron and particulate 230Th and 231Pa (3 stations) collected during GEOTRACES section GN04. We find that distributions and concentrations of dissolved 231Pa and 230Th in the central Arctic Ocean have changed significantly since 1991. Dissolved 231Pa concentrations in the Makarov basin decreased by half within less than 20 years. These changes are discussed in the context of environmental changes, such as declining sea ice cover and related increase of particle fluxes or changing deep water circulation. [1] Scholten, J. C., et al. (1995). Deep-Sea Research II 42: 1519- 1531