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 U ₃₇ ^K′ 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 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 ∼6000 years, ranging from 0.2 to 5 μg m⁻² d⁻¹. The U ₃₇ ^K′ 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 U ₃₇ ^K′ -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 U ₃₇ ^K′ -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.