Wechselwirkung zwischen marinem Antrieb, Klimaänderung und westgrönländischem Eisschild während des Mittel- bis Spätholozäns
Zusammenfassung der Projektergebnisse
The project focused on West Greenland waters and dealt with the reconstruction of mid- to late Holocene regional sea surface and bottom (subsurface) water conditions with the main objective to investigate the possible role of ocean forcing on ice-stream behavior. High resolution sediment cores, taken during RV Maria S. Merian cruise MSM05/03, were studied applying a multi-proxy approach in collaboration with national and international partners. Backed up by a sound chronology these cores allowed reconstructions of changes in bottom (West Greenland Current WGC signal) and surface water properties at centennial to decadal timescales, which where compared with published records of ice-stream retreat and re-advances in the Disko Bugt region, in particular of the Jakobshavn Isbræ. Between c. 7 and 6.3 ka BP, the influx of a warm WGC caused via subsurface ice melting increased meltwater production in Disko Bugt area and forced a south-to-north displacement of the Arctic sea-ice edge. The ice retreat led to the opening of the Vaigat Strait a new passage for icebergs exiting Disko Bugt after 6 ka BP. In the eastern Disko Bugt area the ice sheet was largely land-based and reduced meltwater runoff from the Greenland Ice sheet occurred after c. 6 ka BP. A prolonged warm phase reflecting ‘thermal optimum-like’ conditions off West Greenland is linked to a stable and warm WGC from 5.5 to 3.5 ka BP. From 3.5 ka BP the long-term late Holocene cooling of the bottom waters is associated with the onset of the Neoglacial. The deterioration of oceanographic conditions favoured the ice sheet re-advance in the Disko area. Superimposed on the cooling trend is marked multi-centennial scale variability within the WGC: i) a cooling related to the known ´2.7 ka BP cooling event’; ii) a warm phase corresponding to the Roman Warm Period; iii) only a slight warming linked to the Medieval Climatic Anomaly and; iv) a strong cooling from c. 0.9 ka BP culminating in the Little Ice Age. According to time series analyses of proxy data from sediment cores a pronounced correlation with major cold events can be recorded. In contrast to terrestrial observations, post Little Ice Age oceanic conditions remain cool, likely caused by a continued strong contribution of cold/fresher waters from the East Greenland Current to the WGC. However, low amplitude changes in ocean temperature show some similarities with changes in the ice margin position of Jakobshavn Isbræ and the Atlantic Multidecadal Oscillation during the last 100 years. Cold ocean temperatures from 1910 to c. 1925 and from late 1940s to late 1980s coincide with stabilization and/or re-advance of Jakobshavn Isbræ. Warmer ocean temperatures recognized from c. 1925 to late 1940s and since mid-1990s correlate with ice margin retreat phases. Our paleoceanographic reconstructions highlight the strong control of ocean temperatures on ice margin stability/position on a range of time scales form the mid Holocene to the present day. Thus, warm ocean temperatures influence marine based ice sheets, by enhancing basal melting, leading to increased glacier acceleration and meltwater production, and thus triggering ice retreat. As for the mid Holocene (8-6 ka BP) and also for the most recent past of the last few decades, ice retreat in Disko Bugt, West Greenland, occurred in response to warming’s of the WGC and not exclusively in response to increasing atmospheric temperatures. Therefore, ocean forcing displays an important mechanism influencing ice sheet behavior. The comparison of proxy time series studied here and major Holocene climatic (cold) events recorded for the North Atlantic realm suggests a clear correlation in periodicities and supports the hypothesis that the Atlantic climate and oceanographic dynamics plays an important role controlling the Disko Bugt’s depositional environment during the mid- to late Holocene. The interaction between ice and ocean needs to be considered in future projection of ice sheet behavior (e.g. calving rates, flow activity, meltwater production) and the sea level change involved.
Projektbezogene Publikationen (Auswahl)
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(2010) Late-Holocene diatom inferred reconstruction of temperature variations of the West Greenland Current from Disko Bugt, central West Greenland. The Holocene 20 (5): 659-666
Krawczyk D., Witkowski A., Moros M., Lloyd J., Kuijpers A., Kierzek A.
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(2011) A 100 year record of ocean temperature control on the stability of Jakobshavn Isbrae, West Greenland. Geology 39: 867-870
Lloyd J.M., Moros M., Perner K., Telford R., Kuijpers A., Jansen E., McCarthy D.J.
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(2011) Centennial scale benthic foraminiferal record of late Holocene oceanographic variability in Disko Bugt, West Greenland. Quaternary Science Reviews 30: 2815-2826
Perner K., Moros M., Lloyd J.M., Kuijpers A., Telford R.J., Harff J.
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(2012) Climate variability in West Greenland during the past 1500 years: evidence from a high-resolution marine palynological record from Disko Bay. Boreas 41: 68-83
Ribeiro S., Moros M., Ellegaard M., Kuijpers A.
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(2012) Holocene palaeoceanographic evolution off West Greenland. The Holocene
Perner K., Moros M., Jennings A.E., Lloyd J.M., Knudsen K.L.
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(2012) Hydrological consequences of the reinterpretation of two diatom species from the West Greenland margin – Thalassiosirakushirensis and Thalassiosiraantarctica var. borealis. Marine Micropaleontology 88-89: 1-14
Krawczyk D., Witkowski A., Wroniecki M., Waniek J., Kurzydłowski K.J., Płociński T.
