Benthic foraminifera abundance data of sediment core GeoB7926-2

We present a high resolution, multiproxy study of the relationship between pelagic and benthic environments of a coastal upwelling system in the subtropical NE Atlantic Ocean. Marine sediments corresponding to late MIS3 to the Holocene in the radiocarbon dated core GeoB7926, retrieved off Mauritania (21°N) were analysed to reconstruct productivity in surface waters and its linkage to deep waters during the last 35 ka BP. High latitude cold events and changes in atmospheric and oceanographic dynamics influenced upwelling intensity over this time period. Subsequently, this caused changes in primary productivity off this low-latitude coastal upwelling locality. The benthic foraminiferal fauna displays four main community shifts corresponding to fundamental climatic events, first of all during late MIS3 (35-28 ka BP), secondly from 28 to 19 ka BP (including Heinrich event 2 and the LGM), thirdly within Heinrich event 1, the Bølling Allerød and the Younger Dryas (18-11.5 ka BP) and finally during the Holocene (11.5-0 ka BP). In particular, strong pelagic-benthic coupling is apparent in MIS 3, as demonstrated by increased primary productivity, indicated by moderate DAR and the dominance of benthic foraminiferal species which prefer fresh phytodetritus. A decline in upwelling intensity and nutrient availability follows, which resulted in a proportionately larger amount of older, degraded matter, provoking a shift in the benthic foraminifera fauna composition. This rapid response of the benthic environment continues with a progressive increase in upwelling intensity due to sea level and oceanographic changes and according high surface production during the LGM. During Heinrich event 1 and the Younger Dryas, extreme levels of primary production actually hindered benthic environment through the development of low oxygen conditions. After this period, a final change in benthic foraminiferal community composition occurs which indicates a return to more oxygenated conditions during the Holocene.

(Table 1) Gas tie points used to correlate NorthGRIP and Vostol records

North Atlantic sediment records (MD95-2042), Greenland (Greenland Ice Core Project (GRIP)) and Antarctica (Byrd and Vostok) ice core climate records have been synchronized over marine isotopic stage 3 (MIS 3) (64 to 24 kyr B.P.) (Shackleton et al., 2000). The resulting common timescale suggested that MD95-2042 d18Obenthic fluctuations were synchronous with temperature changes in Antarctica (dDice or d18Oice records). In order to assess the persistency of this result we have used here the recent Greenland NorthGRIP ice core covering the last glacial inception. We transfer the Antarctic Vostok GT4 timescale to NorthGRIP d18Oice and MD95-2042 d18Oplanktonic records and precisely quantify all the relative timing uncertainties. During the rapid warming of Dansgaard-Oeschger 24, MD95-2042 d18Obenthic decrease is in phase with d18Oplanktonic decrease and therefore with NorthGRIP temperature increase, but it takes place 1700 ± 1100 years after the Antarctic warming. Thus the present study reveals that the results obtained previously for MIS 3 cannot be generalized and demonstrates the need to improve common chronologies for marine and polar archives.