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Arabian Sea sediments record changes in the upwelling system off Arabia, which is driven by the monsoon circulation system over the NW Indian Ocean. In accordance with climate models, and differing from other large upwelling areas of the tropical ocean, a 500,000-yr record of productivity at ODP Site 723 shows consistently stronger upwelling during interglaciations than during glaciations. Sea-surface temperatures (SSTs) reconstructed from the alkenone unsaturation index (UK′37) are high (up to 27°C) during interglaciations and low (22-24°C) during glaciations, indicating a glacial-interglacial temperature change of >3°C in spite of the dampening effect of enhanced or weakened upwelling. The increased productivity is attributed to stronger monsoon winds during interglacial times relative to glacial times, whereas the difference in SSTs must be unrelated to upwelling and to the summer monsoon intensity. The winter (NE) monsoon was more effective in cooling the Arabian Sea during glaciations then it is now.

Abstract. Sea stYace temperature (SST) estimates were made using data for C37.39 alkenones analyzed in modem and glacial-age intervals of sediment cores collected along an east-west (~42 ø N from 125 ø to 132 ø W) and a north-south (41 ø-33 øN) transect of the California Current system (CCS). The prymnesiophyte biomarker results suggest that surface waters warrned significantly throughout this region since the last glacial maximum (LGM) but the magnitude of warrning varied spatially. Stratigraphic profiles from four sediment cores along the north-south transect indicate the warming period was confined to the glacial/interglacial transition (15-10 ka), with SST reaching a maximum value at ~ 10 ka and maintaining a uniformly high value throughout the Holocene. Comparison of estimates derived from analysis of modem and LGM sediment intervals indicates the magnitude of the SST change was minimal for locations south of about 36øN (< 1 ø-2øC) and increased significantly (3 ø-5øC) north of this latitude. Using a simple heat balance model, we calculate from the latitudinal gradient in SST that southward flow in the California Current system during the LGM was about 60% of that measured today at 36 øN. Our findings support the conclusion of others based on pollen data that coastal upwelling in the region of the northeast Pacific off northern California was significantly reduced or even completely shutdown during the LGM.

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We analyzed the unsaturation ratio (U k) of long-chain ketones-a molecular sea-surface temperature (SST) indicator-concentrations of carbonate and organic carbon in sediments from Site 846 in the eastern equatorial Pacific Ocean. Based on an isotopic age model for the composite depth section of 0-46 m below seafloor and on estimates of sediment density, accumulation rates of these biogenic compounds were calculated. Our combined temperature and biogenic flux record traces conditions at the origin of the South Equatorial Current over the last 1.3 m.y. S STs have fluctuated considerably over the interval studied. A long trend of gradual decrease from 24°C at 1.3 Ma ends between 500 and 400 Ka, when lowest values of 19°C were reached. Since this time, the temperature data indicate a warming trend to the Holocene modulated by high-amplitude variation (19° to 27°C). The inversion of the trend between 400 and 500 Ka coincides with maximal accumulation rates of carbonate, which since then have decreased. In contrast, organic carbon accumulation since then has increased in variability and in absolute values. On shorter time scales, the records show a strong link to the global climatic background. Since 1.3 Ma, carbonate (0.2-3 g/cm 2 k.y.~1) and organic carbon accumulation rates (2-30 mg/cm 2 k.y.~1) were consistently high (more than twice their modern values and those of interglacials) during glacial maxima in the benthic isotope record, when temperatures were low. However, cross-spectral analyses with the δ 18 θ record suggest that variation in organic carbon flux is not linked directly to variations in SST. Temperature maxima in our record led interglacial events by 7 k.y. in the 100-k.y. eccentricity cycle and by 5 k.y. in the 41-k.y. obliquity cycle. In contrast, maxima in organic carbon accumulation lag behind glacial maxima and low temperatures by 14 k.y. in the eccentricity cycle. On glacial/interglacial time scales, a prominent influence on SST-but not on organic carbon burial-at Site 846 appears to be the advection of cold water into the South Equatorial Current.

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