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OC3 webinar: Insights into deglacial AMOC changes - a summary of the PAGES OC3 stable isotope compilation data from the North Atlantic

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Ning Zhao
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OC3 webinar: Insights into deglacial AMOC changes - a summary of the PAGES OC3 stable isotope compilation data from the North Atlantic


Date: Tuesday 5 April
Time: 15:00 UTC
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Speaker: Janne Repschläger
Contributors: Ning Zhao, Devin Rand, Lorraine Lisiecki, Juan Muglia, Stefan Mulitza, Andreas Schmittner, Olivier Cartapanis, Henning A. Bauch, Ralf Schiebel, Gerald H. Haug

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Please register by 3 April.


The Atlantic Meridional Overturning Circulation (AMOC) during the last glacial interval was considerably different from modern ocean circulation, including changes in deepwater formation, position of convection sites, depth of overturning, deepwater flow strength and stratification. Deepwater circulation significantly changed during the last deglaciation from a shallow to a deep-reaching overturning cell. This change went along with a drawdown of isotopically light waters into the abyss and a deep ocean warming that changed deep ocean stratification from a salinity- to a temperature-controlled mode.

Yet, the exact mechanisms causing these changes are still unknown. Furthermore, the long-standing ideas of a northward extension of Southern Ocean water during the Last Glacial Maximum (LGM) and a complete shutdown of North Atlantic deepwater formation during Heinrich Stadial 1 (HS1) (17.5-14.6 kyr BP) remains prevalent.

For a better understanding of the glacial and deglacial deepwater circulation changes, a compilation of published and unpublished benthic δ13C and δ18O data is established within the framework of the PAGES OC3 working group.

Here, we present the extensive compilation data from the North Atlantic Ocean with 105 sediment cores. The combined benthic δ13C and δ18O indicate the existence of a 13C-depleted and 18O-enriched North Atlantic deepwater mass traceable at depths between 4000 and 3000 m and between 50 and 20°N during the Last Glacial Maximum and into Heinrich Stadial 1 (HS1). Benthic 14C ages in the deep North Atlantic younger than the Southern Ocean and a barrier of 13C-enriched and 18O-depleted water in the deep equatorial Atlantic exclude a southern origin of this water mass. Instead, transects across the subpolar and polar North Atlantic point toward an active deepwater formation in the Irminger Sea and/or Labrador Sea region. During HS1 a δ18O-depleted, δ13C-enriched, young water mass is apparent at latitudes between 40 and 50°N in the western North Atlantic Basin that reached a depth of 4000 m.

The abrupt occurrence of the δ18O depleted signature in the western Atlantic Basin indicate either two different deepwater sources during HS1 or an alteration of the deepwater on its southward pathway. Based on these results, we discuss concepts of deepwater formation in the North Atlantic that help to explain the deglacial change from a salinity-driven to a temperature-driven circulation mode from the LGM to the Late Holocene.

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