Description: Measuring temperature and salinity profiles in the world's oceans is crucial to understanding ocean dynamics and its influence on the heat budget, the water cycle, the marine environment and on our climate. Since 1983 the German research vessel and icebreaker Polarstern has been the platform of numerous CTD (conductivity, temperature, depth instrument) deployments in the Arctic and the Antarctic. We report on a unique data collection spanning 33 years of polar CTD data. In total 131 data sets (1 data set per cruise leg) containing data from 10 063 CTD casts are now freely available at doi:10.1594/PANGAEA.860066. During this long period five CTD types with different characteristics and accuracies have been used. Therefore the instruments and processing procedures (sensor calibration, data validation, etc.) are described in detail. This compilation is special not only with regard to the quantity but also the quality of the data – the latter indicated for each data set using defined quality codes. The complete data collection includes a number of repeated sections for which the quality code can be used to investigate and evaluate long-term changes. Beginning with 2010, the salinity measurements presented here are of the highest quality possible in this field owing to the introduction of the OPTIMARE Precision Salinometer.

Description: A prominent two-step rise in atmospheric CO2 marked the end of the last glacial. The steps coincided with climatic intervals Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). Records of 231Pa/230Th on sediment cores bathed by NADW, revealed a rapid reduction of the Atlantic Meridional Overturning Circulation (AMOC), during these intervals. It was argued that a weakened AMOC would have significantly reduced the efficiency of the biological pump and thus might have contributed to the rise in atmospheric CO2. Despite playing an important role, this process fails to account for the enigmatic drop in atmospheric Δ14C and δ13C during HS1 that marks the first step of the CO2-rise. Increasing CO2-concentrations with a simultaneous drop in their Δ14C, call for the ventilation of an old and 14C-depleted carbon reservoir. In this respect, several studies point to the presence of very old, 14C-depleted deep-waters in the glacial Southern Ocean, which rejuvenated during the last deglaciation. However, the accumulation of 14C-depleted, carbon-rich waters in the deep Southern Ocean requires circulation patterns that significantly differ from todays. Here we present a combined set of 231Pa/230Th-, Rare Earth Element- and XRF-proxy records to understand the evolution of the South Pacific Overturning Circulation (SPOC) over the last 35,000 years. Our reconstructions are based on a transect of five sediment cores from the Southwest Pacific, covering the AAIW as well as the UCDW and LCDW. Our data show that throughout the last glacial the SPOC was significantly weakened. This reduction favored the observed accumulation of 14C-depleted CO2 in Circumpolar Deep Waters (CDW). Parallel to the HS1 increase of atmospheric CO2, the deep circulation picked up its pace and recovered toward the Holocene. This trend is in remarkable agreement with water mass radiocarbon reconstructions from the very same area, as well as with atmospherical changes in CO2, Δ14C and δ13C. Hence, we are confident that the Southern Ocean – represented here by the South Pacific – played the dominant role in the first rise in atmospheric CO2. In addition the observed deglacial SPOC strengthening may have supported the transport of warm CDW onto the shelf areas since the timing of retreating West Antarctic ice sheets is in good agreement with recent reconstructions.

Description: We extended the 224Ra/228Th disequilibrium approach to examine benthic fluxes of a variety of metals, ranging from alkaline earth (Ba) to redox sensitive elements (U, Mn, and Fe), into the Pearl River Estuary (PRE), China. Depth profiles of 224Ra and 228Th in bulk sediment, as well as dissolved 224Ra and trace metals in porewater were measured along a transect within the estuary in July 2015. Significant deficit of 224Ra relative to 228Th was commonly observed in the upper 0–15 cm sediment. We took advantage of the 224Ra/228Th disequilibrium in the bottom sediments to construct a full mass balance of 224Ra in the overlying water column. We demonstrated that porewater exchange (PEX) processes with scale lengths of several centimeters are the predominant mechanism for solute transport between sediments and overlying waters in the PRE. In contrast, deep porewater flow or submarine groundwater discharge (SGD) with scale lengths of “meters to kilometers” are a negligible component in the water column budget of 224Ra. Strong correlations between dissolved 224Ra and trace metals (Ba, U, Mn, and Fe) in porewater were frequently observed in the study region. This likely reflects a fact that geochemical cycling of alkaline earth elements (e.g., Ra and Ba) and redox sensitive elements (like U) in sediments was closely linked to diagenetic reactions of manganese and iron oxides. This linkage makes it possible to quantify benthic fluxes of alkaline earth and redox sensitive metals using 224Ra/228Th disequilibrium in sediments. Benthic Ba fluxes based on 224Ra/228Th disequilibrium were found to vary from virtually nil to 320 μmol m−2 d−1 within the PRE. The highest flux was identified at salinity = 3.0–7.8 and could lead to an elevation of 54 nmol Ba l−1 in the water column, which well reproduced the Ba excess frequently observed in the low salinity domain of the estuary. Benthic fluxes of redox sensitive U ranged from −0.42 (“−” denotes flux into sediment) to 1.3 μmol m−2 d−1. This could only cause a change of −0.1 to 0.3 nmol U l−1 in the water column, which is very small when compared to the U concentration of 13–14 nmol l−1 in the northern South China Sea. We therefore predicted that water column U in the PRE must behave conservatively during mixing. This prediction is consistent with historical measurements of water column U concentration within the PRE. Large benthic fluxes of Mn and Fe were generally acquired with the 224Ra/228Th disequilibrium method. They varied from virtually nil up to 97 mmol m−2 d−1, and from zero to 27 mmol m−2 d−1, respectively. These estimates are 1–2 orders of magnitude higher than historical measurements based on the traditional incubation method in other coastal settings. Nonetheless, they are in agreement with a simple consideration of Mn and Fe mass balances in the sediment. An important implication of this study is that the role of coastal sediments in estuarine geochemistry of trace metals may need to be re-evaluated.

Description: 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.

Description: Unravelling inputs of multiple air pollution sources and reconstructing their historic contribution can be a difficult task. Here, new trace metal concentrations and Pb isotope data were combined for a radionuclide (210Pb-241Am) dated peat core from the Liffey Head bog (LHB) in eastern Ireland in order to reconstruct how different sources contributed to the atmospheric pollution over the past century. Highest enrichments in the heavy metals Pb, Cu, Ag, Sn, and Sb, together with a Pb isotope composition (206Pb/204Pb: 18.351 ± 0.013; 206Pb/207Pb: 1.174 ± 0.012) close to that of the Wicklow mineralisation demonstrates significant aerial influx of heavy metals from local mining and smelting activities during the 19th century until ca. 1940s. A dramatic compositional shift defined by elevated Co, Cr, Ni, Mo, Zn, and V enrichments and a sharp transition towards unradiogenic 206Pb values (206Pb/204Pb: 18.271 ± 0.013–17.678 ± 0.006; 206Pb/207Pb: 1.170 ± 0.012–1.135 ± 0.007) is documented from the 1940s until ca. 2000. These are attributed to the atmospheric impact of fossil fuels and especially leaded petrol, modelled to have contributed between 6 and 78% to the total Pb pollution at this site. The subsequent turn to a more radiogenic Pb isotope signature since 2000 in Ireland is clearly documented in the investigated archive (206Pb/204Pb: 17.930 ± 0.006; 206Pb/207Pb: 1.148 ± 0.007) and reflects the abolishment of leaded petrol. However, there remains a persisting and even increasing pollution in Ni, Mo, Cu, and especially Zn, collectively originating from countrywide use of fossil fuels(peat, coal, heating oil, and unleaded vehicle fuels) for domestic and industrial purposes. This illustrates the continued anthropogenic influence on important natural archives such as bogs in Ireland despite the phase-out of leaded petrol.

Description: The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide and global modeling efforts – thereby enhancing predictions of the WG in global ocean circulation and climate.

Description: We present a dating method for deep-sea sediments that is independent from the presence of microfossils, carbonates or ash layers. In analogy to the constant-rate-of-supply (CRS) model for excess 210Pb, we use the natural radionuclide 230Th (half-life 75,380 years) as an absolute age marker. Using a sediment core from the Western Indian Sector of the Southern Ocean (PS63/146-2), we evaluate how a set of values of 230Th, 232Th and U isotopes concentrations can be used to derive age information for the last ~450,000 years for a continuously deposited sediment if the precision, resolution and depth/age coverage of the analytical data is sufficient. We also assess the age uncertainties resulting from analytical errors using a Monte-Carlo approach as well as an analytical solution for error propagation. These methods show good agreement. In addition, we evaluate deviations due to a violation of model assumptions, e.g. by variable focusing of deep-sea sediments, using a simulated core. The results show that the sensitivity of dates to these effects is quantifiable, and smallest in the central part of the record. The obtained ages also allow calculating 230Th-normalized preserved vertical rain rates of various sedimentary compounds. Our example for a 230Th CRS dated record of lithogenic fluxes in the Southern Ocean agrees exceptionally well with the timing of the completely independent global oxygen isotope record of foraminifera in marine sediments. 230Thex-CRS-dating therefore adds an important tool for dating marine records irrespective of their composition, and for quantifying elemental fluxes in a broad range of deep-sea sediments.

Description: The Western Antarctic Peninsula is an exceptionally climate-sensitive area and investigations into its environmental response to recent and past climate changes may support our understanding of the complex interactions in the ice-ocean-atmosphere system. Organic geochemical and micropaleontological analyses of a 210Pb-dated sediment core from the Bransfield Strait (located between the Antarctic Peninsula and the South Shetland Islands) reveal highly variable sea ice conditions over the past 200 years and increased phytoplankton productivity since the 1930s. Concentrations of biomarker lipids (highly branched isoprenoids (IPSO25), phytosterols) and diatom-based sea ice estimates are compared to satellite data and further environmental information derived from Antarctic Peninsula ice cores extending back in time beyond instrumental records. Fluctuations in the sedimentary abundance of the sea ice biomarker IPSO25 (Belt et al., 2016) and sea ice-associated diatom assemblages seem to be linked to changes in atmospheric (ENSO, SAM) and oceanic circulation patterns. Interestingly, both IPSO25- and diatom-based sea ice reconstructions for the spring and winter season, respectively, do not reflect the overall warming trend and sea ice decline observed in the study area over past decades (e.g., Stammerjohn et al., 2008). This observation may highlight the need for an improved understanding and more reasoned interpretations of proxy archives.