Abstract:
Site 162-982 is at 57 degrees N, 16 degrees W on the Rockall Plateau in the North Atlantic. At 1133 m water depth, the site was located to study the behavior of North Atlantic Intermediate Water on glacial-interglacial time scales. Because of the elevation of the plateau above the surrounding sea floor, the site is well suited to study the history of delivery of coarse-grained ice-rafted debris (IRD). We have completed a combined record of stable-isotopic variation and IRD fluctuations, carried out on the same samples, and extending over the last 2 million years. The record of the last 1 million years is in print (Venz et al., Paleoceanography). Here, we concentrate on the 1-2 million year interval, when climate variations were dominated by the 41 kyr period of orbital obliquity, and atmospheric carbon dioxide concentrations may have been higher than during the late Pleistocene (Raymo et al., 1998, Nature). Sample spacing for our record is about 1.5 to 3 kyr. The time span studied shows quite steady delivery of IRD to the site, albeit interrupted by several periods of about 10,000 yrs without any IRD. The IRD pulses quite faithfully reflect the 41-kyr dominance, and are generally much smaller than the Terminal Ice Rafting Events associated with the Terminations of the last 1 million years. IRD peaks correlate more with benthic oxygen-isotope peaks, and less with glacial-interglacial transitions, compared to the late Pleistocene record, perhaps reflecting migrations of the IRD belt. Most IRD peaks are also associated with negative excursions in the benthic carbon-isotopic record, suggesting that already in this time slice, iceberg fluxes and melt water discharges influenced thermohaline circulation.