Abstract
<p> Alkenone fluxes in the water column of the Cariaco Basin ranged from 12 to 20 μg m <sup> −2 </sup> d <sup> −1 </sup> and were inversely related to upwelling strength. The <strong> U </strong> <sub> <strong> 37 </strong> </sub> <sup> <strong> K′ </strong> </sup> 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 <strong> U </strong> <sub> <strong> 37 </strong> </sub> <sup> <strong> K′ </strong> </sup> ratios closely overlapped with the calibration of <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2003GB002132#gbc1043-bib-0047"> <em> Prahl et al. </em> [1988] </a> . Alkenone burial fluxes in Cariaco Basin sediments varied markedly over the past ∼6000 years, ranging from 0.2 to 5 μg m <sup> −2 </sup> d <sup> −1 </sup> . The <strong> U </strong> <sub> <strong> 37 </strong> </sub> <sup> <strong> K′ </strong> </sup> 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 <strong> U </strong> <sub> <strong> 37 </strong> </sub> <sup> <strong> K′ </strong> </sup> ‐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 <sup> −2 </sup> d <sup> −1 </sup> ), are consistent with conditions of enhanced upwelling, decreased SST and reduced haptophyte production. The highest <strong> U </strong> <sub> <strong> 37 </strong> </sub> <sup> <strong> K′ </strong> </sup> ‐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 <sup> −2 </sup> d <sup> −1 </sup> . 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.</p>
Original language | American English |
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Journal | Global Biogeochemical Cycles |
Volume | 18 |
DOIs | |
State | Published - Jun 1 2004 |
Keywords
- alkenones
- U37K' Index
- SST
- sediment traps
- marine Sediments
- Cariaco Basin
- (10 degrees 30 ' N
- 64 degrees 40 ' W)
Disciplines
- Life Sciences
- Marine Biology