Depositional regimes in the Norwegian-Greenland Sea: the last two glacial to interglacial transitions

Abstract

Various models of surface and deep-water circulation in the Norwegian-Greenland Sea (NGS) have been proposed for the last two glacial to interglacial transitions. Although much progress has been made in understanding the sedimentary response to climatic and oceanographic changes, conflicting interpretations have been developed. To clarify some of these discrepancies and to test or modify the existing circulation concepts, a multiparameter approach is applied, combining sedimentological, micropaleontological, organic-geochemical and isotopic methods. On the basis of indicative properties a combined litho-and organofacies concept is developed and calibrated with modern depositional settings beneath different surface water masses. Sedimentary regimes are then derived for glacial and deglacial settings.Atlantic water intrusions in the NGS reveal complex and highly dynamic patterns for the last two glacial and interglacial periods, with repetitive inflows during Isotope Stage 6 and a high variability in Isotope Stage 5. Specific facies patterns show maximum extensions of Atlantic Water intrusions during the climatic highstands 5.5.1, 5.3 and 5.1 and narrowest intrusions in the cool phases 5.4 and most pronounced in 5.2. In contrast, different glacio-marine depositional regimes depict variable sea ice coverage and supply of ice-rafted debris. Most conspicuous are short-term depositional events marked by diamictons, which are related to the high instabilities of continental ice sheets. Some of the diamictons seem to occur contemporaneously with Heinrich layers H1 and H2. The probable temporal and obvious phenomenological concidence of Heinrich layers and NGS diamictons suggests a common trigger mechanism which caused an almost simultaneous disin-R. Henrich (1~) -T. Wagner tegration of huge continental ice masses along the shelves of North America and the eastern margin of the NGS.A previous estuarine circulation model claims regional upwelling along the eastern margin of the NGS for specific periods of the last deglaciation. The organic character of sediments covering the same time intervals show a clear predominance of reworked fossil organic matter and thus does not support the estuarine model.

Late Quaternary paleoceanography in the Fram Strait

“…Of special interest is substage 5.5, which in all data sets from the Fram Strait looks like an interstadial rather than an interglacial (Figures 7 and 8). The cold conditions in the Fram Strait during substage 5.5, as indicated by the low carbonate and coccolith accumulation, are rather unexpected, as in the Nordic Seas this period is indicated as comparable to the Holocene and distinctly warmer than substage 5.1 [Kellogg, 1980;Belanger, 1982;Haake and Pflaumann, 1989;Henrich et al, 1989Henrich et al, , 1995. A plausible explanation for this discrepancy has been offered by Bauch [1993].…”

Recent distribution and accumulation of organic carbon on the continental margin west off Spitsbergen

“…If admixed in minor proportions as erosional debris to the marine sediment flux, the geochemical and isotopic signatures of modern sediments may be changed. Indeed, Rock Eval Tmax values in these selected samples are generally higher (>435°C) than in all other samples (Table 3) pointing to an admixture of fossil organic carbon as frequently observed in glacial and deglacial sediments from the eastern Norwegian‐Greenland Sea [ Wagner and Henrich , 1994; Henrich et al , 1995; Wagner and Hölemann , 1995]. This is consistent with the geochemical characterization of these Mesozoic, TOC‐rich shales and siltstones exemplary collected in Pleistocene morainic material from the northwestern Barents Sea where Rock Eval Tmax and vitrinite reflection (Ro) values vary between ∼450–485°C and 0.5–1.0%, respectively [ Bjorøy and Vigran , 1980].…”

Sediment reworking on high-latitude continental margins and its implications for palaeoceanographic studies: insights from the Norwegian-Greenland Sea

“…Heinrich 1988;Bond et al 1992;Henrich et al 1995;Bischoff 2000;Grousset et al 2001). A key premise of this work is that the IRD layers result from episodes of intense rain-out of iceberg-rafted debris coupled to background hemipelagic sedimentation and are linked to large-scale ice-sheet dynamics.…”