Age determination and planktonic foraminifera og ODP Site 159-958

Site 958 was drilled to monitor the late Neogene history of both continental aridity in northwestern Africa and the Canary Current distant from nearshore upwelling. Based on magnetostratigraphy, biostratigraphic datums, variations in carbonate, coarse fraction components, and the species composition of planktonic foraminifers, as well as using the d18O records of Globigerinoides ruber (white), we established a splice between Holes 958A and 958B and a stratigraphic age scale deciphering Milankovitch cycles. Over the last 630 k.y., sedimentation rates amount to 2.9 cm/k.y., and to 2.05-2.53 cm/k.y. back to the base of the Pleistocene. Extremely low rates of 0.4 cm/k.y. and a reworking of fossils mark the late Pliocene. The first continuous, long, sea-surface temperature (SST) record from the center of the Canary Current, which is based on foraminifer species census data, depicts a general temperature decrease in the late Pliocene, lower SST and high seasonalities of up to 6°C ~2.0-1.6 Ma, a warmer interval from 1.6 Ma to ~0.85 Ma, again lower SST and higher seasonalities until 0.33 or 0.26 Ma, and a final warmer interval, lasting until at least 50 ka, possibly reflecting the attenuated dynamics of the Canary Current. Especially over the last 400 k.y., since Stage 11, glacial stages are hardly reflected by cold SST cycles, except for various abrupt and extremely short cooling events amounting to D6°C, which possibly result from North Atlantic Heinrich events. Similar, but not necessarily synchronous, events of short-term, extremely high values occur in the paleoproductivity and (d13Cbased) paleonutrient records, which indicate a generally low primary production averaging to 180 g C m**-2 yr**-1 at 50-330 ka and about 300 g C m**-2 yr**-1 back to the base of the Pleistocene. Near 1.2-1.6 Ma, the grain-size and magnetic susceptibility records document a significant increase in the discharge of south Saharan/Sahelian dust, possibly linked to increasing aridity.

Os isotope record of ODP Site 159-959

The known temporal relationship between the benthic foraminiferal d18O record and the marine Os isotope record is used to reinterpret the absolute chronology and paleoceanographic context of an episode of organic carbon burial on the West African margin Ocean Drilling Program (ODP) Site 959. Although organic-rich sediments require significant corrections for in situ decay of 187Re to 187Os, these results demonstrate the utility of the marine Os isotope record for chemostratigraphic correlation of organic-rich sediments that are devoid of age diagnostic microfossils with pelagic carbonate sequences. Revision of the ODP Site 959 chronology shifts the age assignment of an interval of biosiliceous, organic-rich sediment deposition from the Oligocene to the late Eocene and earliest Oligocene, likely culminating with the first major glaciation of the Oligocene (Oi1). We speculate that enhanced organic carbon burial over much of the West African margin may have contributed to drawdown of atmospheric carbon dioxide before and during the Oi1 event and suggest that Os isotope chemostratigraphy provides a valuable tool for further exploring this possibility.