Reconstruction of the Atlantic paleocirculation back to the Last Interglacial by a combined proxy approach from ODP Leg 172 Site 1063 sediments.
Final Report Abstract
Extreme and abrupt Northern Hemisphere climate oscillations during the last glacial cycle were modulated by changes in ocean circulation and atmospheric forcing. However, the variability of the Atlantic Meridional Overturning Circulation (AMOC) that has controlled heat transport from low to high latitudes and ocean CO2 storage is still poorly constrained beyond the Last Glacial Maximum. We reconstruct both the strength and direction of the AMOC during the last glacial cycle (150 ka to present) based on a highly resolved marine sedimentary record from the deep northwestern Atlantic Ocean. Measurements of two independent chemical water mass tracers obtained from the very same samples (231Pa/230Th and εNd), that are not directly affected by changes of the global carbon cycle, reveal consistent responses of the AMOC during the last two glacial Terminations. Here we show that a deep and vigorous overturning circulation mode persisted throughout most of the last glacial cycle, while a shallower glacial mode with Southern Source Waters filling the deep western North Atlantic only occurred during the Glacial Maxima. Any significant deviations from this configuration resulting in slow-downs of the AMOC were restricted to centennial-scale excursions during catastrophic iceberg discharges of the Heinrich Stadials (HS). It was, however, only during those Heinrich Stadials close to glacial maxima (HS 1, 2 and 11) when elevated fresh water input resulted in severely weakened North Atlantic deep water formation lasting several hundred years, suggesting that AMOC stability was relatively insensitive to sub-millennial meltwater pulses during warmer climate states. In contrast, a pronounced active AMOC prevailed during the Dansgaard-Oeschger Interstadials (Greenland warm periods).
Publications
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2014, Strong and deep Atlantic meridional overturning circulation during the last glacial cycle. Nature
Böhm, E., J. Lippold, M. Gutjahr, M. Frank, P. Blaser, B. Antz, J. Fohlmeister, N. Frank, M. Andersen, M. Deininger
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2014. Rekonstruktion der Atlantischen Zirkulation innerhalb des letzten Glazialen Zyklus, PhD thesis, Institute of Environmental Physics. University of Heidelberg
Böhm, E.
