ALBERT

Description: Sedimentation and the early diagenetic processes have been studied in surface sediments from the NE-Greenland shelf and continental slope. I have used these data together with geochemical and sedimentological investigations from seven long sediment cores from the NE- and E-Greenland continental margin between 80' and 72' N for reconstructing the paleoenvironmental history of the East- Greenland-Current (ff).

Description: Detailed sedimentological and geochemical analyses were performed on sediments taken from two gravity cores (PS2118-2 and PS2121-4) and one surface sample (PS2121-2) from the eastern Fram Strait at 79°N to get informations about the paleoclimatic and paleoceanographic conditions through the last 35.000 years. The analyses comprise sand/silt/clay distribution, content of ice rafted debris, clay mineralogy, and measurements of carbonate, organic carbon, and nitrogen. The stratigraphy is based on oxygen isotope stages, 14C-dating, and correlation with other sediment cores from the eastern Fram Strait. The sediments from core PS2118-2 represent the time interval from middle isotope stage 3 to recent. The results can be summarized as follows: (1) During isotope stage 3 the Eastspitsbergen Current transports sediment-loaded icebergs in a seasonally open Fram Strait (SPIELHAGEN 1991). Because of a high content of smectite the source of these icebergs probably is Franz Josef Land. At the end of stage 3 HEBBELN (1991) supposes an influence of Atlantic water masses which might be connected with a maximum carbonate content. (2) At the beginning of isotope stage 2, a high content of ice-rafted debris as well as a high content of terrigenous organic carbon were recorded. This verifies the extension of the glaciers of Spitsbergen onto the continental shelf (HEBBELN 1991) and a maximum growth of the Barents Sea Icesheet (ELVERH01 et al., in press). During the last glacial maximum the high content of carbonate resulted from high aboundances of detrital fragments (limestone and dolomite) probably derived from Spitsbergen. The retreat of the glaciers at the end of stage 2 causes an increase in the content of ice rafted debris. At about 15.000 years B.P. a district melt-water signal appears and indicates the onset of deglaciation. This transition from the last glacial maximum to the recent interglacial (Termination I) is documented in decreasing values of d18O. (3) At least since the beginning of isotope stage 1 the inflow of warmer Atlantic water becomes important.

Description: In a sediment core from the Pacific sector of the Antarctic Zone (AZ) of the Southern Ocean, we report diatom-bound N isotope (d15Ndb) records for total recoverable diatoms and two distinct diatom assemblages (pennate and centric rich). These data indicate tight coupling between the degree of nitrate consumption and Antarctic climate across the last two glacial cycles, with d15Ndb (and thus the degree of nitrate consumption) increasing at each major Antarctic cooling event. Coupled with evidence from opal- and barium-based proxies for reduced export production during ice ages, the d15Ndb increases point to ice age reductions in the supply of deep ocean-sourced nitrate to the AZ surface. The two diatom assemblages and species abundance data indicate that the d15Ndb changes are not the result of changing species composition. The pennate and centric assemblage d15Ndb records indicate similar changes but with a significant decline in their difference during peak ice ages. A tentative seasonality-based interpretation of the centric-to-pennate d15Ndb difference suggests that late summer surface waters became nitrate free during the peak glacials.

Description: We present a new record of eolian dust flux to the western Subarctic North Pacific (SNP) covering the past 27000 years based on a core from the Detroit Seamount. Comparing the SNP dust record to the NGRIP ice core record shows significant differences in the amplitude of dust changes to the two regions during the last deglaciation, while the timing of abrupt changes is synchronous. If dust deposition in the SNP faithfully records its mobilization in East Asian source regions, then the difference in the relative amplitude must reflect climate-related changes in atmospheric dust transport to Greenland. Based on the synchronicity in the timing of dust changes in the SNP and Greenland, we tie abrupt deglacial transitions in the 230Th-normalized 4He flux record to corresponding transitions in the well-dated NGRIP dust flux record to provide a new chronostratigraphic technique for marine sediments from the SNP. Results from this technique are complemented by radiocarbon dating, which allows us to independently constrain radiocarbon paleoreservoir ages. We find paleoreservoir ages of 745 ± 140 yr at 11653 yr BP, 680 ± 228 yr at 14630 yr BP and 790 ± 498 yr at 23290 yr BP. Our reconstructed paleoreservoir ages are consistent with modern surface water reservoir ages in the western SNP. Good temporal synchronicity between eolian dust records from the Subantarctic Atlantic and equatorial Pacific and the ice core record from Antarctica supports the reliability of the proposed dust tuning method to be used more widely in other global ocean regions.