Generation, Transport, and Preservation of the Alkenone-Based U-37(K ') Sea Surface Temperature Index in the Water Column and Sediments of the Cariaco Basin (Venezuela)

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alkenones, U-37(K ') index, SST, sediment traps, marine Sediments, Cariaco Basin, (10 degrees 30 ' N, 64 degrees 40 ' W)

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Alkenone fluxes in the water column of the Cariaco Basin ranged from 12 to 20 mg m(-2) d(-1) and were inversely related to upwelling strength. The U-37(K') ratios of sinking particles varied from 0.78 to 0.96 and exhibited seasonal changes that were coherent with a 7degreesC variation in sea surface temperature (SST). The correlation between SST and U-37(K') ratios closely overlapped with the calibration of Prahl et al. [1988]. Alkenone burial fluxes in Cariaco Basin sediments varied markedly over the past similar to6000 years, ranging from 0.2 to 5 mug m(-2) d(-1). The U-37(K') ratios of surface sediments indicate SST was higher (26.3degreesC) during the last 50 years of deposition than in the previous 300 years (similar to25degreesC), signaling an upwelling decrease in the latter part of the twentieth century. The lowest U-37(K')-derived temperatures (similar to25degreesC) were measured in sediments deposited during the little ice age (LIA). These compositions, coupled with relatively low alkenone fluxes (less than or equal to2 mug m(-2) d(-1)), are consistent with conditions of enhanced upwelling, decreased SST and reduced haptophyte production. The highest U-37(K')-derived SST estimates (over 26.5degreesC) were measured during the Medieval Warm Period (MWP) and suggest reduced upwelling at this time. Prior to the MWP, the alkenone record indicates temperatures of similar to26degreesC and burial fluxes of similar to2 mug m(-2) d(-1). These compositions indicate stronger upwelling conditions during the Holocene relative to the last 50 years and the MWP but annual SSTs above those estimated for the LIA.

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Global Biogeochemical Cycles, v. 18, no. 2, article GB2001.