MEDIUM AND LOW LATITUDE ALKENONE PALAEOTHERMOMETRY RECORDS OF SUBMILLENNIAL-SCALE VARIABILITY OVER THE LAST TWO-THREE CLIMATIC CYCLES

The submillenial sea surface temperature changes (SST) in cores ODP977 (Alboran Sea, 36º1.907'N 1º57.319'W) and MD98-2165 (Tropical Indian Ocean, 9°38'96 S, 118°20'31 E, 2100 m) have been studied using the C37 alkenone derived method. Abrupt and intensive SST changes have been identified in the Alboran Sea record. The changes between MIS1-3 parallel those already observed in a previous Alboran core MD952043 (Cacho et al., 1999) exhibiting about the same variability and intensity. Thus, the SST pattern is similar to the Dansgaard-Oeschger (D/O) events in the 18O record of the Greenland ice cores (D/O1-14) and the Heinrich events (H1-5) in the North Atlantic sediments, involving abrupt changes of 2.5-5ºC in MIS 3-4. However, the intensities of abrupt SST change in the interglacial periods may be larger, representing oscillations in the order of 2.4-10ºC in MIS 5. The intensity spans of these abrupt oscillations are comparable to the glacial/interglacial SST shifts that involve a maximum difference of 14.5ºC in the two climatic cycles studied. The SST minima that are concurrent with the H and the D/O episodes and exhibit increases in the relative proportion of the tetraunsaturated alkenone (%C37:4). In contrast, the Tropical Indian Ocean records exhibit rather smooth SST variation, in the order of 0.5ºC or even less when considering submillenial variation. In this case, the maximum glacial/interglacial transitions of the last three climatic cycles involve SST ranges of 5.5ºC. Whereas the SST changes in the Alboran Sea reflect the abrupt high latitude climatic events in the Northern Hemisphere the smoother SST profile in the Tropical Indian Ocean shows no influence of submillennial-scale climatic forcing from these high latitudes. Insight into the climatic aspects determining submillenial SST variability in this core is obtained by comparison to the ice records of Antarctica and nearby SST profiles.