Iberian Margin Sea Surface Temperature during MIS 15 to 9 (580-300 ka): Glacial suborbital variability vs interglacial stability

Past sea surface water conditions of south-western Iberian margin were reconstructed based on biomarker analysis of a marine deep sea core MD03-2699 from the Estremadura Spur north off Lisbon, providing new insights into orbital and suborbital-scale climate variability between Marine Isotope Stage (MIS) 15 to MIS 9 (580 to 300 ka). We use biomarker based proxy records such as the alkenone unsaturated index to estimate sea surface temperature (SST), the total alkenone concentration to reconstruct phytoplankton productivity and terrestrial biomarkers to evaluate the continental input. The results extend the existing biomarker record namely the sea surface temperature (SST) based on alkenone unsaturated index for the Iberian Margin back to the 6th climatic cycle (580 ka). A general trend of warmth is detected since MIS 15 to MIS 9 in western Iberia. Most of these interglacials are considered to be very stable in this region with the exception of MIS 9.3 which is unstable. The interglacial MIS 11.3 SST remained relative stable for 30 ka and the MIS 13 even for 61 ka. The composed Iberian SST record (core MD03-2444 and core MD03-2699), reflecting the last 580 ka shows that both the SST values and patterns of MIS 11.3 are similar to the present interglacial (Holocene). The interglacials stability contrasts with glacial periods and glacial inceptions which are marked by high-frequency variability. Thus, several short-lived climatic coolings were identified by huge SST decreases, the occurrence of ice-rafted detritus (IRD) and high percentages of the tetra-unsaturated alkenone C37:4. Five stadial-type oscillations were detected from MIS 15.1 to MIS 14, and eight between MIS 13.1 and MIS 12 and among MIS 11.3 and MIS 10. Some of these events were extremely cold and similar in their general trends to the well known Heinrich events of the last glaciation. The first Heinrich-type events (Ht) 1 was detected during MIS10.2; which was followed by Ht2 and Ht3 during MIS 11.24 and 11.23; Ht4 at the onset of termination V; Ht5 during MIS 12.2; Ht6 and Ht7 during the glacial inception of MIS 12; and finally Ht8 during the glacial inception of MIS 14. The general deglaciation pattern detected between MIS 15 and MIS 9 is similar in their general trends to that characterizing the more recent climatic cycles, i.e. marked by two coolings separated by a short warming episode which can be associated with the southward, north- and southward migration of the Polar Front.