Upper Water Column Variability During Marine Isotope Stages (MIS) 10 to 17 on the Western Iberian Margin
Abstract
Calypso core MD03-2699 (39 deg N; 10.7 deg W) was retrieved from the Estremadura spur north of Lisbon. Modern hydrographic conditions in this area are defined by the seasonal changes in the surface and subsurface currents. During summer, the area is influenced by the southward flowing Portugal current and the upwelling filament off Cape Roca. During winter, the Iberian poleward current brings subtropical surface and subsurface waters originating from the Azores front to the site, while the Portugal current is displaced further offshore. To study paleo-changes in the surface water hydrography from 336 to 703 ka BP we are using stable isotope data of two planktonic foraminifera species, namely Orbulina universa as the surface dwelling species and Globorotalia inflata as deep-dweller, the amount of lithic fragments as indicator for ice-rafted debris, and an alkenone sea surface temperature (SST) record. Sample resolution is 2 to 1 cm, equal to a temporal resolution of generally 210 to 625 years, but reaching values of 1240 to 1370 years in MIS 12.2 and MIS 15.4, respectively. Both planktonic oxygen isotope records show millennial-scale variability overprinting the orbital-scale variations. Lightest isotope values, especially for O. universa, are associated with MIS 11.3, heaviest with glacial stages MIS 12.2, 14.2 and 16.4. With the exception of MIS 12, the delta 18O difference between both species varies between 0.2 and 1 permil, equal to a temperature gradient in the surface mixed layer of 0.9 to 3.4 degrees C, that is in the range of the modern gradient in the upper 300 m. During MIS 11.3 and 13.3, the steeper gradient is observed nearly consistently hinting to a stable thermal gradient in the upper water column over long periods of time, i.e. in the case of MIS 11.3 for nearly 20 ka. During most of MIS 12, on the other hand, the gradient was consistently small. Biomarker SST varied between 10 and nearly 18 degrees C. They indicate fairly stable warm conditions from 480 to 620 ka in the surface layer, while the winter mixed layer (G. inflata) experienced short-termed cooling events, which during MIS 15.2 and 14.2 were associated with minor IRD amounts. Major increases in IRD deposition only occurred during Termination V and MIS 10 and were contemporary with cooling in the surface and subsurface layers. The existence of a modern-type temperature gradient in the upper water column during most of the studied interval indicates a persistent influence of the Iberian poleward current, while the cooling events are more likely linked to the Portugal current.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMPP23C1778V
- Keywords:
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- 4901 Abrupt/rapid climate change (1605);
- 4926 Glacial;
- 4936 Interglacial;
- 4954 Sea surface temperature;
- 4962 Thermohaline