Description: The eastern equatorial Pacific (EEP) is one of the key areas for studying oceanic processes that control atmospheric CO2 concentrations. Southern-sourced water masses (SOIW) are thought to stimulate the biological pump in the EEP and hence contributed to the CO2 drawdown during glacial times. Orbital forcing in combination with local feedback mechanisms are assumed to be the main driver for this water mass advection. Newest studies, however, question the capability of SOIW to stimulate primary productivity during Marine Isotope Stage 2 (MIS2), as nutrients are rather utilized in the Southern Ocean. Instead, nutrient-rich Glacial North Pacific Intermediate Waters (GNPIW) seem to be a major component of water masses upwelled in the EEP to enhance productivity in the EEP during MIS2. We present changes in biological productivity in the EEP over the last 190 ka derived from surface-dwelling planktic foraminifera Globigerinoides ruber and deep-dwelling planktic foraminifera Globorotaloides hexagonus (ODP Site 1240). The δ13C gradient between surface and sub-thermocline (Δδ13Crub-hex) has been used to assess export production in that area. We compare this with variations in the nutrient gradient (Δδ13Chex-SOIW) between sub-thermocline equatorial waters (~350 m) and SOIW. The Δδ13Chex-SOIW variability is dominated by 100 kyr and 23 kyr cycles. This implies a strong response to changes in orbital precession and internal climate forcing related to major changes in ice volume. At times of low precession the difference between the nutrient concentrations of EEP waters and nutrients delivered via SOIW differ substantially, thus indicating that SOIW is not providing sufficient nutrients to stimulate productivity in the EEP. This scenario is most prominent during MIS2 and MIS6. Following the interpretation by Max et al. (submitted) we speculate that similar to MIS2, nutrients were trapped in the Southern Ocean also during MIS6 leaving northward-advected SOIW rather nutrient-depleted. Similar to MIS 2, we assume a greater contribution and hence, influence of nutrients from GNPIW on the productivity of the EEP during MIS6. A switch from GNPIW to SOIW influence of water masses upwelled in the EEP is recorded during glacial terminations.

Description: Future climate change will have significant effects on ecosystems worldwide and on polar regions in particular. Hence, palaeo-environmental studies focussing on the last warmer-than-today phase (i.e. the early Holocene) in higher latitudes are of particular importance to understand climate development and its potential impact in polar systems. Molluscan bivalve shells constitute suitable bio-archives for high-resolution palaeo-environmental reconstructions. Here, we present a first reconstruction of early Holocene seasonal water temperature cycle in an Arctic fjord based on stable oxygen isotope (δ18Oshell) profiles in shells of Arctica islandica (Bivalvia) from raised beach deposits in Dicksonfjorden, Svalbard, dated at 9954–9782 cal. yr BP. Reconstructed maximum and minimum bottom water temperatures for the assumed shell growth period between April and August of 15.2°C and 2.8°C imply a seasonality of about 12.4°C for the early Holocene. In comparison to modern temperatures, this indicates that average temperature declined by 6°C and seasonality narrowed by 50%. This first palaeo-environmental description of a fjord setting during the Holocene Climate Optimum at Spitsbergen exceeds most previous global estimates (+1–3°C) but confirms studies indicating an amplified effect (+4–6°C) at high northern latitudes.

Description: Shells of the bivalve Arctica islandica serve as high-resolution archive of past environmental conditions. Stable oxygen isotopes (δ18O) values from wellpreserved A. islandica shells are frequently used as a proxy for water temperature (and salinity). Hence, this species may improve distinctly our understanding of seasonal temperature dynamics in the past. We present the first stable isotope (δ18O & δ13C) analysis on a fossil semi-recrystallized A. islandica shell from the Tjörnes Beds of Iceland (Pliocene). Confocal Raman microscopy is used to identify areas of pristine aragonite and recrystallized calcite shell, which were then sampled by highresolution micro-milling. We compare paleo-water temperatures inferred from stable oxygen isotope ratios of both recrystallized and non-recrystallized portions of the shell to highlight and discuss the impacts of taphonomic alterations on a micro-scale and its implications for paleo-environmental reconstructions. Our findings emphasize the need for careful interpretation of carbonate-based water temperature reconstructions, because small-scale diagenesis can significantly modify the original stable oxygen isotope signature and substantially distort the paleoclimatic or paleoenvironmental signals inferred thereof.

Description: The West Antarctic Ice Sheet (WAIS) is considered the most unstable part of the Antarctic Ice Sheet. As the WAIS is mostly grounded below sea level, its stability is of great concern. A collapse of large parts of the WAIS would result in a significant global sea-level rise. At present, the WAIS shows dramatic ice loss in its Amundsen Sea sector, especially in Pine Island Bay. Pine Island Glacier (PIG) is characterised by fast flow, major thinning and rapid grounding-line retreat. Its mass los over recent decades is generally attributed to melting caused by the inflow of warm Circumpolar Deep Water (CDW). Future melting of PIG may result in a sea level tipping point, because it could trigger widespread collapse of the WAIS, especially when considering ongoing climate change. Our research project aims to establish proxies (integration of foraminifera, sediment properties and oceanographic data) for modern environmental conditions by analysing seafloor surface sediments along a transect from the glacier proximal settings to the middle-outer shelf in the eastern Amundsen Sea Embayment. These proxies will then be applied on sediment records spanning the Holocene back to the Last Glacial Maximum for reconstructing spatial and temporal variations of CDW upwelling and ice-ocean interactions during the past c. 23,000 years. We will present preliminary results from the analyses of ten short marine sediment cores (multi and box cores) collected during expeditions JR179 (2008) and ANT-XXVI/3 (2010) along a transect from inner Pine Island Bay to the middle-outer shelf part of the Abbot Palaeo-Ice Stream Trough at water depths ranging from 458 m (middle shelf) to 1444 m (inner shelf). The sediment cores are currently investigated for distribution patterns of planktonic and benthic foraminifera and grain-size distribution at 1 cm resolution. Core tops (0-10 cm) were stained with Rose Bengal for living benthic foraminifera investigations. The chronology of the cores will be based on 210Pb and calibrated 14C dates. First results reveal the presence of living benthic foraminifera in surface sediments of all investigated cores suggesting that modern seabed surfaces were recovered. Moreover, a core retrieved from a water depth of 793 m in the Abbot Palaeo-Ice Stream Trough shows particularly high abundances of planktonic foraminifera Neogloboquadrina pachyderma.