Trends in primary production, sea surface temperature and wind in upwelling systems (1998–2007)

Abstract

We take advantage of the longest high quality single-sensor global data set of ocean color available today to explore recent trends in the primary productivity of the main eastern boundary upwelling systems (EBUEs): California, Canary, Humboldt and Benguela. The chlorophyll- a concentration is used as a proxy for primary production. SST data from AVHRR and wind speed data from QuikSCAT are used in conjunction with this data set to analyse forcing mechanisms explaining the chlorophyll biomass. Whereas the worldwide primary-production biomass shows on average decreasing trends, as already observed in the stratified part of the worldwide ocean, the productivity of most EBUEs increases during the study period. These contrasting trends are both significant, at least for the mid latitude range of 50°S–50°N, where the data coverage is sufficient for accurate estimation. Probably due to the large scale atmospheric forcing, trends in sea surface temperature (SST) show non-significant relationships with the trends in biomass within upwelling systems, suggesting that SST anomalies cannot be used as an indicator of change in upwelling intensity in a continuous warming context. On the other hand, upwelling favourable equatorward winds show a significant correlation with the observed trends in biomass, suggesting that the trends in the trade winds are probably linked to an increase in the intensity of the Hadley cell circulation observed during the last several decades.