Paleoceanographic and climatic implications of a new Mediterranean Outflow branch in the southern Gulf of Cadiz

QUATERNARY SCIENCE REVIEWS

卷:197

Article

Lebreiro, S. M.¹  Anton, L.²  Reguera, M., I¹  Marzocchi, A.³ 

[1] IGME Geol Survey Spain, Madrid 28003, Spain

[2] IGME Geol Survey Spain, Tres Cantos 28760, Spain

[3] Natl Oceanog Ctr, Southampton, Hants, England

关键词: Quaternary;    Paleoceanography;    Climate modelling;    North Atlantic;    Foraminifers;    Stable isotopes;    Sortable silt;    Mediterranean outflow;    Morocco contourite drift;   

DOI  :  10.1016/j.quascirev.2018.07.036

来源: Elsevier

【 摘 要 】

The presence of contourite drifts in the southern Gulf of Cadiz (GoC) along the Moroccan margin raises questions about the (re)circulation of Mediterranean Outflow Water (MOW) in the GoC and the origin of the currents depositing them. Here, we compare two cores representative of Iberian and Moroccan contourite drifts, covering the last 22 kyr. Although the whole sequence is contouritic in character, it reflects the interaction of distinctive silty-contourite facies (high flow velocity periods) imbedded in muddy-contourite fades (low flow velocity periods). Evidence from benthic foraminifera delta C-13, sortable silt grain-size, oceanographic CTD profiles and numerical simulations, indicate the Mediterranean water mass as the source of the southern contourite deposits. Our data, therefore, suggests an additional branch of upper-MOW veering southwards off the Straits of Gibraltar along the Moroccan margin. During MIS(Marine Isotope Stage) 2, upper-MOW was a sluggish current while in the Holocene upper-MOW dominated as a fast, semi-steady flow. Throughout the deglaciation, silty contourites associated with higher flow speeds were deposited in the northern and southern GoC during cold events such as Heinrich Stadial 1 (HSI) and the Younger Dryas, forced by global millennial-scale climate variability. Millennial variability also appears to drive the deposition of silty-contourites in the Holocene. We estimated an average duration of 1 ka for the process of depositing a fast contourite unit. The case of silty-contourite 16 (within HSI) allows us to illustrate with extremely high resolution a rapid sequential change in circulation, with gradual slow-down of dense Mediterranean water while surface was freshening (HSI), provoking injection of high-salinity intermediate waters (via contour-currents) into the GoC, and hence the North Atlantic. The subsequent brief collapse of dense water formation in the Mediterranean Sea triggered a major increase in sea surface temperatures (10 degrees C/ka) in the GoC, developing into the next interstadial (Bolling/Allerod). The impact of Mediterranean intermediate waters is manifested here by triggering a substantial rearrangement of intermediate and deep circulation in the North Atlantic, which would have further impacted the Atlantic Meridional Overturning Circulation (AMOC). (C) 2018 Elsevier Ltd. All rights reserved.

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