The GEOTRACES Intermediate Data Product 2014

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

Gelöstes Barium und partikuläre Seltenerdmetalle als Tracer für Interaktion der Schelfmeere und Becken im Arktischen Ozean

This study gives an outlook on the usability of dissolved Ba and particulate rare earth elements as oceanographical tracers in the Arctic Ocean. It is integrated into a sub-project focussing on tracers for the identification of freshwater sources of the European integrated project DAMOCLES (Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies). From Polarstern expedition ARK-XXII/2 in summer 2007, dissolved Ba and particulate REE were analyzed in the Barents, Kara, Laptev seas, the Eurasian Basins and the Makarov Basin up to and beyond the Alpha and Mendeleyev Ridges. In chapter 2 I discuss Ba as a tracer in discerning Eurasian from North American runoff together with well established water mass tracers (salinity, d18O, nutrients). In chapter 3 I investigate how dissolved Ba of intermediate and deep waters may be used together with Al and silicate to describe exchange of waters from the shelf seas with the interior basins. In chapter 4 I describe REE patterns in suspended particulate matter from surface water in a wider context illustrating the contrast between the remote Southern Ocean and the nearly land locked Arctic Ocean

Dissolved Barium and particulate Rare Earth Elements as tracers for shelf-basin interaction in the Arctic Ocean

This study gives an outlook on the usability of dissolved Ba and particulate REE as oceanographical tracers in the Arctic Ocean. From Polarstern expedition ARK-XXII/2 in summer 2007, dissolved Ba and particulate rare earth elements (REE) were analyzed in the Barents, Kara, Laptev seas, and the Eurasian Basins as well as the Makarov Basin up to and beyond the Alpha and Mendeleyev Ridges. Data on particulate REE from the Arctic Ocean are discussed in a wider context including samples from the East Atlantic and the Atlantic sector of the Southern Ocean. In chapter 2 I discuss Ba as a tracer in discerning Eurasian from North American runoff together with well established water mass tracers (salinity, δ18O, nutrients). Prolonged ice-free conditions promote phytoplankton growth and thereby are influencing microbiogeochemical cycling of trace elements in the water column. Changing climate is expected to have an impact on trace element distributions in the Arctic Ocean. It has to be questioned to what extent tracers like Ba involved in biological cycles can be used in the future dependent on those changes. In the light of this question, it is shown in chapter 2 that in the Arctic Ocean Ba is involved in microbiogeochemical cycling. Ba is removed from surface waters and released to deep waters. This process masks the presence of North American runoff in surface waters and leads to an overestimation of these waters in sub-surface layers of the Makarov Basin. In chapter 3 I investigate how dissolved Ba of intermediate and deep waters may be used together with Al and silicate to describe exchange of waters from the shelf seas with the interior basins. The vast Arctic shelves are the main source of these elements to the central Arctic Ocean. Distribution of these elements indicates deep shelf convection into the Nansen Basin north of Severnaya Zemlya. Moreover in the Makarov Basin, inflow from the Canadian Basin and overflow from the Amundsen Basin at 2000 m depth at the Lomonosov Ridge are required to explain the composition of bottom waters. This supports previous studies on the renewal of bottom waters in the Arctic basins. Furthermore, in chapter 4 I describe REE patterns in suspended particulate matter (SPM) from surface water. REE patterns are supposed to help understanding the transport ways of particles to the water column. Input of terrigenous particles plays an important role in contributing (micro-)nutrients to the oceans and in this way is controlling biological productivity. A unique set of particulate REE from different oceanographic regimes between 88°N and 72°S has been sampled following the same sampling protocol so that comparison of REE patterns becomes possible. In the East Atlantic Ocean a clear transition can be seen from strong inputs from Saharan dust in the north of the intertropical convergence zone (ITCZ) to low terrigenous supply in the south. In the Southern Ocean, a much stronger impact of exchange with seawater can be seen. This illustrates the contrast between the remote Southern Ocean where REE patterns are dominated by adsorption from seawater and the nearly land locked Arctic Ocean where REE patterns are fully terrigenous. The homogeneity of REE patterns in SPM from the Arctic Ocean leads to the conclusion that sources other than continental runoff, i.e., dissolved REE from seawater or REE resuspended from shelf sediments, are of minor importance regarding surface water SPM

Deep water circulation and composition in the Arctic Ocean by dissolved barium, aluminium and silicate

As part of the ARK-XXII/2 Polarstern expedition in summer 2007, dissolved Ba was analyzed in the Eurasian Basins and the Makarov Basin including the Alpha and Mendeleyev Ridges as well as on the adjacent shelves. The data was compared with data of dissolved Al and Si from the same cruise. Superimposed on the gradual increase of concentration with depth by dissolution of the particle rain, we observe different flow patterns in intermediate waters along the track. In the Atlantic and Intermediate Depth Water (AIDW) in the Amundsen Basin the influence from Eurasian shelf water can be seen in slightly enhanced concentrations of dissolved Ba compared with Al and Si. At the same time Al concentrations decrease with distance from the Eurasian shelves. Source waters to the Atlantic Layer Water (ALW) in the Makarov Basin have the same background Ba concentrations as the Nansen AIDW. We describe the distributions of the elements in the Deep Eurasian and Bottom Water (DEBW) by deep shelf convection as well as diffusion from sediments controlling concentrations in the Nansen DEBW while in the Amundsen DEBW diffusion from sediments appears to be more important. In the Makarov Basin inflow from the Canadian Basin and overflow from the Amundsen Basin at 2000 m depth at the Lomonosov Ridge are required to explain the composition of bottom waters

Barium measured on water bottle samples during POLARSTERN cruise ARK-XXII/2 (SPACE)

Dissolved barium has been shown to have the potential to distinguish Eurasian from North American (NA) river runoff. As part of the ARK-XXII/2 Polarstern expedition in summer 2007, Ba was analyzed in the Barents, Kara, Laptev seas, and the Eurasian Basins as well as the Makarov Basin up to the Alpha and Mendeleyev Ridges. By combining salinity, d18O and initial phosphate corrected for mineralization with oxygen (PO4*) or N/P ratios we identified the water mass fractions of meteoric water, sea ice meltwater, and marine waters of Atlantic as well as Pacific origin in the upper water column. In all basins inside the lower halocline layer and the Arctic intermediate waters we find Ba concentrations close to those of the Fram Strait branch of the lower halocline (41-45 nM), reflecting the composition of the incoming Atlantic water. A layer of upper halocline water (UHW) with higher Ba concentrations (45-55 nM) is identified in the Makarov Basin. Atop of the UHW, the Surface Mixed Layer (SML), including the summer and winter mixed layers, has high concentrations of Ba (58-67 nM). In the SML of the investigated area of the central Arctic the meteoric fraction can be identified by assuming a conservative behavior of Ba to be primarily of Eurasian river origin. However, in productive coastal regions biological removal compromises the use of Ba to distinguish between Eurasian and NA rivers. As a consequence, the NA river water fraction is underestimated in productive surface waters or waters that have passed a productive region, whereas this fraction is overestimated in subsurface waters containing remineralised Ba, particularly when these waters have passed productive shelf regions. Especially in the Laptev Sea and small regions in the Barents Sea, Ba concentrations are low in surface waters. In the Laptev Sea exceptionally high Ba concentrations in shelf bottom waters indicate that Ba is removed from surface waters to deep waters by biological activity enhanced by increasing ice-free conditions as well as by scavenging by organic matter of terrestrial origin. We interpret high Ba concentrations in the UHW of the Makarov Basin to result from enrichment by remineralisation in bottom waters on the shelf of the Chukchi Sea and therefore the calculated NA runoff is an artefact. We conclude that no NA runoff can be demonstrated unequivocally anywhere during our expedition with the set of tracers considered here. Small contributions of NA runoff may have been masked by Ba depletion and could only be resolved by supportive tracers on the uptake history. We thus suggest that Ba has to be used with care as it can put limits but not yield quantitative water mass distributions. Only if the extra Ba inputs exceed the cumulative biological uptake the signal can be unequivocally attributed to NA runoff

Radium in Arctic surface water

The transpolar drift is strongly enriched in 228Ra accumulated on the wide Arctic shelves with subsequent rapid offshore transport. We present new data of Polarstern expeditions to the central Arctic and to the Kara and Laptev seas. Because 226Ra activities in Pacific waters are 30% higher than in Atlantic waters, we correct 226Ra for the Pacific admixture when normalizing 228Ra with 226Ra. The use of 228Ra decay as age marker critically depends on the constancy in space and time of the source activity, a condition that has not yet adequately been tested. While 228Ra decays during transit over the central basin, ingrowth of 228Th could provide an alternative age marker. The high 228Th/228Ra activity ratio (AR = 0.8-1.0) in the central basins is incompatible with a mixing model based on horizontal eddy diffusion. An advective model predicts that 228Th grows to an equilibrium AR, the value of which depends on the scavenging regime. The low AR over the Lomonosov Ridge (AR = 0.5) can be due to either rapid transport (minimum age without scavenging 1.1 year) or enhanced scavenging. Suspended particulate matter load (derived from beam transmission and particulate 234Th) and total 234Th depletion data show that scavenging, although extremely low in the central Arctic, is enhanced over the Lomonosov Ridge, making an age of 3 years more likely. The combined data of 228Ra decay and 228Th ingrowth confirm the existence of a recirculating gyre in the surface water of the eastern Eurasian Basin with a river water residence time of at least 3 years