Distinct year-to-year particle flux variations off Cape Blanc during 1988–1991: Relation to δ18O-deduced sea-surface temperatures and trade winds
Particle fluxes measured from 1988 to 1991 adjacent to a coastal upwelling site off Cape Blanc showed significant interannual variability of fluxes and sea-surface temperatures (SST) deduced from stable oxygen isotope analysis of the planktonic foraminifera Globigerinoides ruber and, partly, of the pteropod Limacina inflata. For the duration of the study period, a decrease in the seasonality of SST's was observed, as well as a significant decrease in the average annual SST from 24.4° to 20.8°C. This cooling trend was mainly the effect of a drastic decrease in the summer to fall SST (from 27.2° to 21.8°C). In comparison, the winter-spring SST decreased only slightly from 20.3° in 1988 to 19.8°C in 1991. Concomitantly, we measured decreasing annual total, carbonate, biogenic opal and lithogenic fluxes and, in contrast, increasing marine organic carbon fluxes. During 1991, when cold SST's prevailed and the trade winds were rather high throughout, annual biogenic and lithogenic fluxes (except organic carbon) were lower by approximately a factor of two compared to the other years. Colder SST's, generally corresponding to stronger trade winds and upwelling intensity, did not result in increased biogenic opal and lithogenic matter sedimentation; but higher marine organic carbon fluxes were recorded. Decreasing summer-fall SST from 1988 to 1991 coincided with decreased carbonate sedimentation maxima which generally occurred during the warm summer season. In the summer of 1989, when SST's were the highest of the four-year sampling period and upwelling was less intense due to weak spring-summer trades, a large sedimentation pulse of pteropod shells was observed. Our data set does not yet provide conclusive evidence that the observed year-to-year flux and SST variations represent larger-scale, periodically occurring climatic variations in the eastern Atlantic but it offers insight into the prevailing large variability in biochemical cycles and processes in the eastern Atlantic.
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Document Type: Research Article
Publication date: 01 January 1996
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