Stable isotope record during the past 1 Myr of ODP Site 162-980 in the subpolar North Atlantic

Benthic foraminiferal carbon isotope records from a suite of drill sites in the North Atlantic are used to trace variations in the relative strengths of Lower North Atlantic Deep Water (LNADW), Upper North Atlantic Deep Water (UNADW), and Southern Ocean Water (SOW) over the past 1 Myr. During glacial intervals, significant increases in intermediate-to-deep delta13C gradients (commonly reaching >1.2?) are consistent with changes in deep water circulation and associated chemical stratification. Bathymetric delta13C gradients covary with benthic foraminiferal delta18O and covary inversely with Vostok CO2, in agreement with chemical stratification as a driver of atmospheric CO2 changes. Three deep circulation indices based on delta13C show a phasing similar to North Atlantic sea surface temperatures, consistent with a Northern Hemisphere control of NADW/SOW variations. However, lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band.

(Table 2) Stratigraphic marker taxa in ODP Hole 162-985A sediments

The rich and diverse dinocyst assemblages in Cores 162-985A-32X through 62X confirm the importance of these microfossils in unraveling the evolution of the Norwegian Sea. Cosmopolitan taxa, with well-documented stratigraphic ranges in northwest Europe, indicate the following ages: Sections 162-985A-62X-1 through 51X-2, Rupelian (early Oligocene); 50X-5, Oligocene, possibly Chattian; 48X-6, Aquitanian? (early Miocene); 48X-4 through 37X-5, Aquitanian (early Miocene); and 36X-5 through 32X-1, Burdigalian (early Miocene). This stratigraphic interpretation suggests that a major hiatus, which can be correlated with an apparently coeval hiatus at Site 643, occurs within the Chattian at Site 985. Several endemic dinocyst taxa with unusual morphology and restricted stratigraphic occurrences are present in Hole 985A and other Norwegian Sea sites, especially Site 643. By using Hole 985A data for control, the Oligocene-Miocene sediments can be correlated with some degree of confidence in the Norwegian Basin.

Stable carbon and oxygen isotope ratios of planktonic and benthic foraminifera from ODP Site 162-982 in the North Atlantic

Changes in the intermediate water structure of the North Atlantic were reconstructed using benthic foraminiferal delta13C at Ocean Drilling Program (ODP) site 982 for the past 1.0 Myr. During most terminations of the late Pleistocene, melting of icebergs and low-salinity surface waters caused production of Glacial North Atlantic Intermediate Water to cease, resulting in decreased ventilation of the middepth North Atlantic. Poor ventilation of intermediate water masses lasted well into some interglacial stages until upper North Atlantic Deep Water (NADW) production resumed under full interglacial conditions. The magnitude of benthic delta13C minima and ice-rafted debris maxima at terminations at site 982 generally match the degree of glacial suppression of NADW inferred from site 607. These processes may be related and controlled by the spatial and seasonal extent of sea ice cover during glaciations in the Nordic Seas.