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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 11 | Copyright
Clim. Past, 14, 1639-1651, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Nov 2018

Research article | 07 Nov 2018

Change in the North Atlantic circulation associated with the mid-Pleistocene transition

Gloria M. Martin-Garcia1, Francisco J. Sierro1, José A. Flores1, and Fátima Abrantes2,3 Gloria M. Martin-Garcia et al.
  • 1Department of Geology, University of Salamanca, Salamanca, Spain
  • 2Marine Geology and Georesources (DivGM), Portuguese Institute for the Sea and Atmosphere, Lisbon, Portugal
  • 3Centre for Marine Sciences at University of Algarve, Faro, Portugal

Abstract. The southwestern Iberian margin is highly sensitive to changes in the distribution of North Atlantic currents and to the position of oceanic fronts. In this work, the evolution of oceanographic parameters from 812 to 530ka (MIS20–MIS14) is studied based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37°34.285′N, 10°7.562′W; 2585mb.s.l.). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55°N, basin-wide paleoceanographic conditions are reconstructed. Variations of assemblages dwelling in different water masses indicate a major change in the general North Atlantic circulation during MIS16, coinciding with the definite establishment of the 100ky cyclicity associated with the mid-Pleistocene transition. At the surface, this change consisted in the redistribution of water masses, with the subsequent thermal variation, and occurred linked to the northwestward migration of the Arctic Front (AF), and the increase in the North Atlantic Deep Water (NADW) formation with respect to previous glacials. During glacials prior to MIS16, the NADW formation was very weak, which drastically slowed down the surface circulation; the AF was at a southerly position and the North Atlantic Current (NAC) diverted southeastwards, developing steep south–north, and east–west, thermal gradients and blocking the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the increase in the meridional overturning circulation, in combination with the northwestward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheet growth, which could have worked as a positive feedback to prolong the glacials towards 100ky cycles.

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Short summary
This work documents major oceanographic changes that occurred in the N. Atlantic from 812 to 530 ka and were related to the mid-Pleistocene transition. Since ~ 650 ka, glacials were more prolonged and intense than before. Larger ice sheets may have worked as a positive feedback mechanism to prolong the duration of glacials. We explore the connection between the change in the N. Atlantic oceanography and the enhanced ice-sheet growth, which contributed to the change of cyclicity in climate.
This work documents major oceanographic changes that occurred in the N. Atlantic from 812 to...