Interglacial conditions of the Iceland Sea (ICIS)
Zusammenfassung der Projektergebnisse
Sediment cores from across the western Iceland Sea were studied for their last interglacial (Marine Isotope Stage or MIS 5e) and Holocene dinoflagellate cyst (dinocyst) content in combination with planktic foraminiferal, ice rafted detritus (IRD), and stable isotope analysis, in order to reconstruct and compare the climatic evolution of both interglacial intervals. This showed that the Holocene and MIS 5e evolved quite differently, and illustrated varying degrees of decoupling between the uppermost ocean and subsurface water masses, proving the usefulness of a multi-proxy approach for refined paleoceanographic reconstructions. Intensive investigation of samples from the final phases of the Saalian deglaciation (Termination II) has confirmed the enigmatic co-occurrence of the warm-temperate dinocyst species Lingulodinium machaerophorum and the subtropical-temperate planktic foraminifer Beella megastoma. This phenomenon had also been observed for Termination II in the eastern Nordic seas during phases of specific IRD deposition and enhanced meltwater input. The fact that this feature is thus also observed in the western Nordic seas underlines its probable significance in terms of basin-wide ocean circulation during deglacial times, and is therefore currently being further investigated. Directly after the cessation of major IRD input that characterizes Termination I and II, the earliest phase of both interglacials shows a marked decoupling of the surface and subsurface waters. Holocene primary productivity increased directly around 11 ka BP, possibly in reaction to high growing-season solar irradiation, albeit that the dominance of the polar dinocyst species Impagidinium pallidum reveals that relatively cold conditions continued to prevail in the upper ocean until ~6.5 ka BP. By contrast, subpolar planktic foraminifer species only start to appear at about 1000 years into the Holocene, implying that warm Atlantic water masses did not affect the subsurface water masses at the Iceland Plateau during the earliest Holocene. Inversely, the earliest phase of MIS 5e is marked by a gradual warming of the subsurface waters, while surface water conditions appear to have remained unfavourable for primary productivity. The Holocene upper ocean decoupling persisted after the earliest interglacial interval: the planktic foraminiferal data show a gradual warming of the subsurface waters from ~9.5 ka onwards and peaking around 7.5 ka BP, but the dinocyst assemblages remain dominated by the cold species I. pallidum during that time and suggest that warmest and most saline conditions occurred in the uppermost ocean layer between 6.5 and 5 ka BP. These discrepancies reflect the proxy-specific response to changes in their respective habitat depth, steered by subsurface advection of Atlantic water on the one hand, and surface advection of polar water masses on the other hand. By contrast, both fossil groups react in a similar manner for MIS 5e after the initial phase of subsurface warming, indicating the existence of optimal interglacial conditions with a clear “Atlantic signature” between 122 and 120 ka, followed by a general cooling towards the end of MIS 5e at ~117 ka. The timing of the optimum in the Iceland Sea, during the first half of MIS 5e, opposes our and others’ previous observations of a late MIS 5e optimum in the eastern Nordic seas. Our new data support a major repositioning of the oceanographic fronts in the Nordic seas around 120.5 ka, which allowed the northward flow of the Norwegian Atlantic Current to intensify, in turn strengthening the East Greenland Current and thus the advection of cold waters towards the Iceland Plateau. Overall, a higher share of “Atlantic” elements can be observed in the planktic assemblages from MIS 5e with respect to the Holocene. This implies a quite different upper ocean circulation pattern for both interglacial intervals, with more intense advection of warm Atlantic waters towards the western Nordic seas, possibly in part due to a more northward expansion of the Irminger Current under weakened East Greenland/East Icelandic currents. Such a scenario is in line with other evidence for relatively warm conditions around southwestern Greenland during MIS 5e.
Projektbezogene Publikationen (Auswahl)
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Spherical brown spinous cysts from last interglacial (MIS 5e) sediments from the Norwegian Sea. International Workshop on Pacific Dinoflagellate Cysts: Morphology, Taxonomy, Distribution, and Ecology of Late Quaternary Dinoflagellate Cysts. Victoria, Canada, 07.05.2009
Van Nieuwenhove, N., Matthiessen, J.
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A dinoflagellate cyst perspective on the last interglacial (MIS 5e) surface circulation in the Atlantic and Arctic Domain of the Nordic seas. APEX Fourth International Conference and Workshop: Arctic paleoclimate proxies and chronologies. Höfn, Iceland, 29.05.2010
Van Nieuwenhove, N., Bauch, H.A., Kandiano, E.
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2011. Evidence for delayed poleward expansion of North Atlantic surface waters during the last interglacial (MIS 5e). Quaternary Science Reviews 30, 934-946
Van Nieuwenhove, N., Bauch, H.A., Eynaud, F., Kandiano, E., Cortijo, E., Turon, J.-L.
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Holocene versus last interglacial (MIS 5e) surface ocean conditions in the Nordic seas and northern North Atlantic. Dino 9 – 9th International Conference on Modern and Fossil Dinoflagellates. Liverpool, U.K., 30.08.2011
Van Nieuwenhove, N., Bonnet, S., Eynaud, F., de Vernal, A., Bauch, H.A.
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Last interglacial (MIS 5e) surface circulation in the North Atlantic and Nordic seas, based on dinoflagellate cysts. The XVIII INQUA Congress. Bern, Switzerland, 25.07.2011
Van Nieuwenhove, N., Bauch, H.A., de Vernal, A., Eynaud, F., Kandiano, E., Fréchette, B.
