Description: A marine sediment record from the central Bering Sea, spanning the last 20 thousand years (ka), was studied to unravel the depositional history with regard to terrigenous sediment supply and biogenic sedimentation. Methodic approaches comprised the inference of accumulation rates of siliciclastic and biogenic components, grain-size analysis, and (clay) mineralogy, as well as paleoclimatic modelling. Changes in the depositional history provides insight into land-ocean linkages of paleoenvironmental changes. During the finale of the Last Glacial Maximum, the depositional environment was characterized by hemipelagic background sedimentation. A marked change in the terrigenous sediment provenance during the late Heinrich 1 Stadial (15.7–14.5 ka), indicated by increases in kaolinite and a high glaciofluvial influx of clay, gives evidence of the deglaciation of the Brooks Range in the hinterland of Alaska. This meltwater pulse also stimulated the postglacial onset of biological productivity. Glacial melt implies regional climate warming during a time of widespread cooling on the northern hemisphere. Our simulation experiment with a coupled climate model suggests atmospheric teleconnections to the North Atlantic, with impacts on the dynamics of the Aleutian Low system that gave rise to warmer winters and an early onset of spring during that time. The late deglacial period between 14.5 and 11.0 ka was characterized by enhanced fluvial runoff and biological productivity in the course of climate amelioration, sea-level rise, seasonal sea-ice retreat, and permafrost thaw in the hinterland. The latter processes temporarily stalled during the Younger Dryas stadial (12.9-11.7 ka) and commenced again during the Preboreal (earliest Holocene), after 11.7 ka. High river runoff might have fertilized the Bering Sea and contributed to enhanced upper ocean stratification. Since 11.0 ka, advanced transgression has shifted the coast line and fluvial influence of the Yukon River away from the study site. The opening of the Bering Strait strengthened contour currents along the continental slope, leaving behind winnowed sand-rich sediments through the early to mid-Holocene, with non-deposition occurring since about 6.0 ka.

Description: The Southern Ocean has the potential to regulate climate via changes in its productivity and circulation regimes. We therefore investigated the glacial/interglacial variability of bioproductivity in the upper water column and the bottom water ventilation in the Subantarctic and Antarctic zones at two sediment core locations, covering the last 150,000 years, in the eastern Atlantic sector of the Southern Ocean. We used a combined approach, and integrated information derived from two major plankton groups, diatoms and organic-walled cysts of dinoflagellates (dinocysts):- The diatom group Chaetoceros reflects high-carbon/low-silica export regimes, the abundance of Fragilariopsis kerguelensis frustules indicates low-carbon/high-silica export regimes. Changes in relative abundance of these two types of diatoms in the sedimentary record reflect past changes/shifts in productivity regimes.- The cyst-forming dinoflagellate genus Protoperidinium, the only heterotrophic dinoflagellate taxon to be found as fossil cysts in the study area, feeds predominantly on diatoms such as Chaetoceros, and thus high accumulation rates of Protoperidinium cysts in the sediment might reflect high Chaetoceros production.- Protoperidinium cysts are highly sensitive to pore water oxygen concentrations in the sediments in which they become embedded, and well preserved Protoperidinium cysts are used as an indicator for a low oxygen sedimentation environment.The direct comparison between Chaetoceros and sensitive dinocyst abundance in the sediment record thus provides information on past primary production and pore water oxygenation, which can be integrated to results derived by other proxies for export productivity (the deep-dwelling radiolarian Cycladophora davisiana), pore water oxygen (authigenic uranium) and bottom current velocity (percentage of sortable silt). Our study provides an excellent opportunity to assess the causal relationship between upper-ocean regimes (temperature, nutrient gradients, sea-ice extent) and changes in bottom water formation, and suggests higher glacial bioproductivity in both the Subantarctic and Antarctic zones synchronously to the formation of less ventilated bottom water.

Description: The Southern Ocean has the potential to regulate climate via changes in its productivity and circulation regimes. We therefore investigated the glacial/interglacial variability of bioproductivity in the upper water column and bottom water ventilation in the Subantarctic and Antarctic zones at two sediment core locations, covering the last 150,000 years, in the eastern Atlantic sector of the Southern Ocean. We used a combined approach, and integrated information derived from two major plankton groups, diatoms and organic-walled cysts of dinoflagellates (dinocysts):- The diatom group Chaetoceros reflects high-carbon/low silica export regimes, the abundance of Fragilariopsis kerguelensis frustules indicates low-carbon/high-silica regimes (Abelmann et al., 2006). Changes in relative abundance of these two types of diatoms in the sedimentary record reflect past changes/shifts in productivity regimes.- The cyst-forming dinoflagellate genus Protoperidinium, the only heterotrophic dinoflagellate to be found as fossil cysts in the study area, feeds predominantly on diatoms such as Chaetoceros (Jacobson and Anderson, 1986), and thus high accumulation rates of Protoperidinium cysts in the sediment might reflect high Chaetoceros production.- Protoperidinioid cysts are highly sensitive to pore water oxygen concentrations in the sediments in which they become embedded, and are used as proxies for a low oxygen sedimentation environment (Zonneveld et al., in press).The direct comparison between Chaetoceros and sensitive dinocyst abundance in the sediment record thus provides information on past primary production and pore water oxygenation, which can be integrated to results derived by other proxies for export productivity (the deep-dwelling radiolarian Cycladophora davisiana), pore water oxygen (authigenic Uranium) and bottom current velocity (percentage of sortable silt).Our study provides an excellent opportunity to assess the causal relationship between upper-ocean regimes (temperature, nutrient gradients, sea-ice extent) and changes in bottom water formation, and suggests higher glacial productivity in both the Subantarctic and Antarctic zones synchronously to the production of less ventilated bottom water.References: Abelmann, A., Gersonde, R., Cortese, G., Kuhn, G. and Smetacek, V., 2006. Paleoceanography 21, PA1013, doi: 10.1029/2005PA001199; Jacobson D. and Anderson, D.M., 1986. Journal of Phycology 22, 249-258; Zonneveld, K.A.F., Bockelmann, F. and Holzwarth, U., in press. Marine Geology.

Description: The European Project for Ice Coring in Antarctica (EPICA) aims at reconstructing past climate and environmental conditions from two deep ice cores in Antarctica (EDML and EDC). We present concentration and size distribution data of aeolian dust from the EDML core over the last 150 kyr and compare it to the dust data from EDC.Owing to highly synchronized time scales it can be seen that all mayor climatic changes lead to synchronous changes of dust flux for the two sites, which indicates a common source or a common variation of the respective sources. The ratio of dust concentration at EDML and EDC is found to be moderately variable (factor ~3); probably caused by variable efficiency of atmospheric transport from the source to the two sites.During Termination I a regime shift at the onset of the ACR can be observed in both cores: The time before (older than) the ACR is characterized by a high correlation between dust concentration, mean particle size and isotopic temperature, while the period after shows no or weak correlations, respectively. This can be observed also in other parts of the record, e.g. during MIS5. At DML, periods of weak correlations show frequent occurrence of large particles in the core, indicating that dust storms were able to penetrate directly into DML during these times. These periods coincide with minimum sea ice in the Atlantic sector of the Southern Ocean as inferred from marine sediment cores. Thus, the sea ice extent in the Atlantic sector may have had an important influence on atmospheric transport patterns around Antarctica as well as on the connection of temperature with wind speed and aridity in the source areas.

Description: Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations1. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was developed by the Climate Long-Range Investigation, Mapping and Prediction (CLIMAP) project in the 1970s and 1980s (refs 2, 3). Since that time, several shortcomings of that earlier effort have become apparent4. Here we present an updated synthesis of sea surface temperatures during the Last Glacial Maximum, rigorously defined as the period between 23 and 19 thousand years before present, from the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface (MARGO) project5. We integrate microfossil and geochemical reconstructions of surface temperatures and include assessments of the reliability of individual records. Our reconstruction reveals the presence of large longitudinal gradients in sea surface temperature in all of the ocean basins, in contrast to the simulations of the Last Glacial Maximum climate available at present