Role of the North Atlantic circulation in the mid-Pleistocene transition

  • Martin-Garcia G
  • Sierro F
  • Flores J
  • et al.
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Abstract

<p><strong>Abstract.</strong> 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 530<span class="thinspace"></span>ka (MIS20-MIS14) is reconstructed, based on the analysis of planktonic foraminifer assemblages from site IODP-U1385 (37&amp;deg;34.285&amp;apos;<span class="thinspace"></span>N, 10&amp;deg;7.562&amp;apos;<span class="thinspace"></span>W; 2585<span class="thinspace"></span>m<span class="thinspace"></span>bsl). By comparing the obtained results with published records from other North Atlantic sites between 41 and 55&amp;deg;<span class="thinspace"></span>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 100-ky cyclicity associated to the Mid-Pleistocene Transition. In surface, this change consisted in the re-distribution 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. During glacials prior to MIS 16, 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 blockading the arrival of warm water, with associated moisture, to high latitudes. During MIS16, the important increase in the meridional overturning circulation, in combination with the north-westward AF shift, allowed the arrival of the NAC to subpolar latitudes, multiplying the moisture availability for ice-sheets growth, which worked as a positive feedback to prolong the glacials towards 100-ky cycles.</p>

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Martin-Garcia, G. M., Sierro, F. J., Flores, J. A., & Abrantes, F. (2018). Role of the North Atlantic circulation in the mid-Pleistocene transition. Climate of the Past Discussions, 1–20. https://doi.org/10.5194/cp-2018-30

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