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Impacts of the North Atlantic gyre circulation on Holocene climate off northwest Africa

Jung-Hyun Kim^*,,1, Helge Meggers^*,1, Norel Rimbu^*,2, Gerrit Lohmann^*,2, Tim Freudenthal^*,3, Peter J. Müller^*,4 and Ralph R. Schneider^*,5

¹ Universität Bremen, FB 5 Geowissenschaften, Klagenfurter Straße, D-28359 Bremen, Germany
² Alfred Wegener Institute for Polar and Marine Research, Bussestrasse 24, D-27570 Bremerhaven, Germany
³ Universität Bremen, Marum, Leobener Strasse, D-28359 Bremen, Germany
⁴ Universität Bremen, FB 5 Geowissenschaften, Klagenfurter Straße, D-28359 Bremen, Germany
⁵ Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften, Ludewig-Meyn-Strasse 10, D-24118 Kiel, Germany

We present well-dated high-resolution Holocene records of sea-surface temperature (SST) and upwelling intensity off northwest (NW) Africa. We identify long-term cooling trends over the Holocene in the subtropical North Atlantic in response to boreal summer insolation. A pronounced cooling event of 1 °C ca. 8.5 cal ka indicates a large-scale reorganization of the ocean current system possibly induced by melt-water from the northern North Atlantic. Our alkenone SST record off Cape Ghir provides strong evidence for the impact of ocean circulation changes on subtropical North Atlantic SSTs. It is likely that cold waters were propagated to the subtropics via the Canary Current in a way similar to Heinrich events and the Younger Dryas off Cape Blanc. We find 2–3 k.y. periodic variations in SST and upwelling intensity off NW Africa superimposed on the cooling trend. Such a cycle has been documented in various paleoclimate archives in phase with solar forcing. We show that these variations on millennial time scales are linked to the North Atlantic subtropical gyre circulation and the Northern Hemisphere atmospheric circulation, and in particular to changes in the pressure gradient between the Icelandic Low and the Azores High. This suggests that oceanic circulation, in response to solar forcing, played a more important role in the generation of 2–3 k.y. cyclicity than has been previously considered.

Key Words: alkenone sea-surface temperature • Holocene • North Atlantic subtropical gyre circulation • upwelling intensity • trade winds

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