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alkenones, U37K' 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 μg m−2 d−1 and were inversely related to upwelling strength. The U37K′ ratios of sinking particles varied from 0.78 to 0.96 and exhibited seasonal changes that were coherent with a 7°C variation in sea surface temperature (SST). The correlation between SST and U37K′ ratios closely overlapped with the calibration of Prahl et al. [1988]. Alkenone burial fluxes in Cariaco Basin sediments varied markedly over the past ∼6000 years, ranging from 0.2 to 5 μg m−2 d−1. The U37K′ ratios of surface sediments indicate SST was higher (26.3°C) during the last 50 years of deposition than in the previous 300 years (∼25°C), signaling an upwelling decrease in the latter part of the twentieth century. The lowest U37K′‐derived temperatures (∼25°C) were measured in sediments deposited during the little ice age (LIA). These compositions, coupled with relatively low alkenone fluxes (≤2 μg m−2 d−1), are consistent with conditions of enhanced upwelling, decreased SST and reduced haptophyte production. The highest U37K′‐derived SST estimates (over 26.5°C) 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 ∼26°C and burial fluxes of ∼2 μg 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, issue 2, art. GB2001

Copyright 2004 by the American Geophysical Union.