High-resolution temperature and evaporation changes during the late Holocene in the northeastern Arabian Sea

In order to reconstruct the monsoonal variability during the late Holocene we investigated a complete, annually laminated sediment record from the oxy gen minimum zone (OMZ) off Pakistan for oxygen isotopes of planktic foramin ifera and alkenone-derived sea surface temperatures (SST). Significant SST changes of up to 3 degreesC which cannot be explained by changes in the alk enone-producing coccolithophorid species (inferred from the Gephyrocapsa oc eanica / Emiliania huxleyi ratio) suggest that SST changes are driven by ch anges in the monsoon strength. Our high-(decadal)-resolution data indicate that the late Holocene in the northeastern Arabian Sea was not characterize d by a stable uniform climate, as inferred from the Greenland ice cores, bu t by variations in the dominance of the SW monsoon conditions with signific ant effects on temperatures. Highest SST fluctuations of up to 3.0 degreesC and 2.5 degreesC were observed for the time interval from 4600 to 3300 yea rs B.P. and during the past 500 years. The significant, short-term SST chan ges during the past 500 years might be related to climatic instabilities kn own from the northern latitudes ("Little Ice Age") and confirm global effec ts. Surface salinity values, reconstructed from delta O-18 records after co rrection for temperature-related oxygen isotope fractionation, suggest that in general, the past 5000 years were characterized by higher-than-recent e vaporation and more intense SW monsoon conditions. However, between 4600 an d 3700 years B.P., evaporation dropped, SW monsoon weakened, and NE monsoon conditions were comparatively enhanced. For the past 1500 years we infer s trongly fluctuating monsoon conditions. Comparisons of reconstructed salini ty records with ice accumulation data from published Tibetan ice core and T ibetan tree ring width data reveal that during the past 2000 years, enhance d evaporation in the northeastern Arabian Sea correlates with periods of in creased ice accumulation in Tibet, and vice versa. This suggests a strong c limatic relationship between both monsoon-controlled areas.