Norwegian Sea overflow variability and NE Atlantic surface hydrography during the past 150,000 years

Abstract

The long-term variability of Norwegian Sea Overflow through the Faeroe Bank Channel and its relation to NE Atlantic surface hydrography is reconstructed based on sedimentological, micropalaeontological and stable isotope analysis, as well as AMS 14C dating, of a sediment core (ENAM-33) retrieved near the outlet of the channel. Additional palaeoceanographic information has been obtained from three nearby sediment cores (ENAM-30, -32, 94-13). Our results demonstrate enhanced circulation of Norwegian Sea Overflow Water (NSOW) at times of increased Sea Surface Temperature (SST), and a reduction or cessation of NSOW flow at times of low SST. During the Last Glacial Maximum (LGM), NSOW activity was at a minimum from about 22 ka to 16 ka. After the LGM, NSOW circulation was weak until a major flow pulse of NSOW occurred, dated at between 13.4 ka and 12.0 ka. Thereafter, NSOW flow was once again reduced. Renewed intensification of NSOW flow did not occur until after 9.8 ka, whereas a further increase in NSOW activity is observed after the early Holocene. The timing of both glacial–interglacial and deglacial NSOW variability is similar to the timing of changes in deep-water circulation reconstructed from cores from the open North Atlantic in previous studies. Whereas most of these studies involve the reconstruction of changes in the proportion of North Atlantic Deep Water (NADW) relative to southern-source deep waters, the lithology of the cores from near the Faeroe Bank Channel outlet provides a qualitative but direct indication of the strength of NSOW currents. This study confirms that the NADW changes observed in the North Atlantic are due to a reduction in NSOW, and cannot be attributed only to an increase in southern-source deep waters. Furthermore, our results indicate that NSOW flow through the Faeroe Bank Channel was not a source of Glacial North Atlantic Intermediate Water (GNAIW), and that a subpolar source for this water mass is likely.