Evolution of Mediterranean sea surface temperature: Evidence for an intensification of European glaciation at the Pliocene-Pleistocene boundary?

As the most “continental” of the ocean basins, the Mediterranean provides a unique climate archive for monitoring the history of the climate of southern Europe and northern Africa over time. It also lies in a strategic position to trace the evolution of the northern edge of the African monsoonal regime and the southward extent of glaciation during the Plio-Pleistocene ice ages. We report here results on sea surface temperature (SST) over the critical time of initial growth of the northern hemisphere ice sheets (3.3-2.7 Ma) and into the heart of the late Pliocene and early Pleistocene 41 kyr ice age regime. We present a continuous record of SST from 3.3-1.6 Ma, sampled at orbital resolution, from a composite of marine sections outcropping on land and from ODP Site 964, based on the alkenone unsaturation proxy. We find that SSTs are quite decoupled from the amount of alkenones in the sediment (“C37 total”). The C37 total record is paced throughout by the precessional cycle that determines the well-known episodes of sapropel formation in the eastern Mediterranean. In contrast, the SST record traces a larger-scale evolution in northern hemisphere climate. Prior to ~2.7 Ma, SST fluctuated predominantly at the precessional time scale. After the advent of northern hemisphere glaciation, SST followed a 41 kyr rhythm, in conjunction with the waxing and waning of northern hemisphere ice sheets during late Pliocene and early Pleistocene time. However, we detected a major increase in the amplitude of SST change at the Pliocene-Pleistocene boundary. Glacial coolings increase by 2-3oC at this time. As this change is not reflected in the marine oxygen isotope record, it seems to shed light on a regional increase in the influence of ice sheets on the glacial climate of the Mediterranean. We hypothesize that the extent of glaciation in northern and central Europe increased significantly at approximately the dawn of the Pleistocene.