Abstract:
It is now clear that millennial scale oscillations appear globally in geological archives of Pleistocene climate change. The same instabilities, although of lower magnitudes, have been identified within the Holocene from continental sediments, ice cores and a few marine sediment cores. One of the areas more sensitive to climatic changes is the North Atlantic since the formation rate of deep-water in the Nordic seas, and regional air temperatures are tightly linked via modulation of the meridional transport of ocean heat. Yet, paleoceanographic reconstructions, which rely on geochemical proxies, have yet to definitively resolve the precise relationship between past changes in meridional overturning rate and North Atlantic climate. One possible reason for this is that geochemical proxies are unable to differentiate between changes in the preformed chemistry and variations in the ventilation rate of deep waters. Here we use a multi-proxy approach to delineate surface ocean climate, deep-water hydrography and the intensity of deep-water overflow from the Nordic Seas during the Holocene. Our core, ODP Site 983, is located near the head of the Gardar Drift (60 degrees 24'N, 23 degrees 38'W, 1983 m water depth), which extends along the eastern flank of the Reykjanes Ridge, following the main pathway of Iceland-Scotland Overflow Water (ISOW), a major precursor of North Atlantic Deep Water. We present results of the isotopic composition of benthic and planktonic foraminifers, ice-rafted abundances and sortable silt mean grain size. Our deep-water proxies suggest that the overflow of ISOW increased gradually between 11.0 and 7 BP. From 7 BP to the present, the strength of the overflow decreased steadily. These long-term increases and decreases in ISOW flow strength exhibit distinct millennial-scale pacing throughout the Holocene interval. The vigor of overflow parallel marine and terrestrial paleotemperature reconstructions from the Norwegian Sea and northern Europe. Overall, our results demonstrate a close coupling between the production rate of cold, dense water across the Iceland-Scotland ridge and the inflow of warm, saline waters into the Nordic seas.