Is the trend in chlorophyll-a in the Arabian Sea decreasing?

Abstract

Recent studies of satellite-derived Chlorophyll concentrations (Chl-a) in the western Arabian Sea (AS) have suggested an increasing temporal trend, but the length of the records used have typically been too short to resolve longer-term trends, if any. Our analysis of a long term satellite ocean color data shows a change of trend in the summer chlorophyll for the western AS before and after 2003; Chl-aconcentration was indeed increasing till 2003, but appears to be declining since then, indicating a secular multi-year trend in Chl-avariability. However, this trend is not uniform over the entire region. Analysis of wind, sea surface temperature (SST), Sea Level Anomaly (SLA) and thermocline depth, suggests that the declining summer monsoon chlorophyll-a(Chl-a) concentration may be due to increasing SLA in this region. The earlier observed biological changes in the western AS could be an artifact of the change in local winds and ocean dynamics, which may be a part of the natural long-term variability.