Changes in paleotemperature and paleoproductivity over the last 40,000 years: NW Iberian Continental Margin

Abstract

This work aims to identify changes in paleoceanographic conditions on the NW Iberian Continental Margin during the last ~40 ka BP. Paleotemperatures expressed as mean annual Sea Surface Temperature (SSTma) and paleoproductivities expressed as Export Productivity (Pexpma) were evaluated using the modern analog technique SIMMAX 28, based on planktonic foraminifera census counts. The study took into account the results of 180 samples collected along the core KC024-19 (sampled at 1-cm interval), recovered from the Galician (NW Spain) continental slope (42°08’98’’N, 10°29´96’’W, and 2765 m). The chronology was based on eight radiocarbon dates (in foraminifera by AMS), in δ18O stratigraphy and in the record of the four last Heinrich Events (HEs). Variations in the supply of phytodetritus to the sea floor were assessed by using the total percentage of phytodetrital-dependent benthic foraminifera species (PhyBF). Results give variations of SSTma between 0.9-20.2 ºC and Pexpma between 12.6-108 gC/m2/y. The lowest values of SSTma were recorded during the HEs, which agree with the southward migration of the glacial polar front. Significant decreases of Pexpma and PhyBF values are recorded during the HEs, but mostly in HE1. During the HEs Globigerina bulloides and Neogloboquadrina (dextral), the most important species related to the upwelling system, are largely replaced by Neogloboquadrina pachyderma (sinistral); in benthic foraminifera assemblages the deep endofaunal species were able to consume degraded organic of lower quality and tolerate low oxic condition increase. These results suggest the occurrence of significant changes in the hydrographic conditions on the Iberian Continental Margin during these HEs (but mostly in HE1) both in surface and deep-water masses circulation.