39. PLANKTONIC δ 18 O AND U k '37 TEMPERATURE ESTIMATES FROM ORGANIC-RICH SEDIMENTS AT SITES 974 AND 975, TYRRHENIAN SEA AND BALEARIC RISE 1

Sapropels at Sites 974 and 975 as well as sediment samples from immediately below and above sapropels were analyzed for alkenone concentrations. Paleo‐sea-surface temperatures (SSTs) were inferred from the U k′37 unsaturation index in Pleistocene sapropel sequences. These SST estimates vary between 13° and 25°C. The upper range of SST estimates is distinctly warmer than modern mean annual SST at both sites and closely groups around the modern summer SST. The cold end of the inferred SST range is still warmer than the mean glacial winter SSTs from the Climate Long-Range Investigation Mapping and Prediction Project (CLIMAP) planktonic foraminifer census counts (Thiede, 1978). We infer, therefore, that sapropel formation at both sites was coeval with warm climates. Using planktonic δ18O and Uk′37 SST estimates as input into an oxygen isotope paleotemperature equation, we can deduce seawater δ18O which, in turn, we can use to infer the paleosalinity for two Pleistocene sapropels at Site 975. These paleosalinity estimates are between 32 and 34, considerably lower than the modern salinity of 37.5 at this location. If we use more negative freshwater δw values in the equation, then the salinity offsets are reduced by 2‐4 units. Depleted salinities, whatever their true values might have been, in conjunction with increased SSTs, imply that sapropel formation in the western Mediterranean occurred during warm and moist climates. This agrees with the idea that sapropel formation in the eastern Mediterranean is a result of enhanced northern hemisphere insolation. Whether or not climatic forcing caused similar marine environmental responses (such as enhanced biological productivity and/or reduced deep-water circulation) in both the eastern and western Mediterranean remains to be determined.