[Show abstract][Hide abstract] ABSTRACT: The seasonal variability of phytoplankton biomass in the Arabian Sea, though a well researched topic, its inter-annual variability is less explored and understood. Analysis of the satellite-derived chlorophyll pigment concentration in the Arabian Sea during 1997-2007 showed a weak increasing trend. Contrary to the earlier hypothesis, our analysis showed that this increased phytoplankton biomass was not driven by the strengthening winds during summer monsoon. In fact, the basin-averaged chlorophyll concentrations during summer monsoon tend to decline, whereas those in September-October and during the winter monsoon showed an increasing trend. Based on the analysis of wind and aerosol optical thickness data, we attribute the increased phytoplankton biomass during September-October to dust-induced iron fertilization when there is sufficient buildup of nitrate in the upper ocean. During winter, the enhanced evaporative cooling under the strengthening winds led to the increased convective mixing. Subsequent supply of subsurface nutrients to the euphotic zone coupled with the increased dust delivery support the observed increase in phytoplankton biomass during winter
[Show abstract][Hide abstract] ABSTRACT: The response of the Arabian Sea to global warming is the disruption in the natural decadal cycle in the sea surface temperature (SST) after 1995, followed by a secular warming. The Arabian Sea is experiencing a regional climate-shift after 1995, which is accompanied by a five fold increase in the occurrence of "most intense cyclones". Signatures of this climate-shift are also perceptible over the adjacent landmass of India as: (1) progressively warmer winters, and (2) decreased decadal monsoon rainfall. The warmer winters are associated with a 16-fold decrease in the decadal wheat production after 1995, while the decreased decadal rainfall was accompanied by a decline of vegetation cover and increased occurrence of heat spells. We propose that in addition to the oceanic thermal inertia, the upwelling-driven cooling provided a mechanism that offset the CO(2)-driven SST increase in the Arabian Sea until 1995.
Marine environmental research 07/2009; 68(5):217-22. · 2.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The impact of global warming in the recent decade is shown by the disruption in the natural decadal cycle in the sea surface temperature (SST) of the Arabian Sea after 1995. We propose a regional climate shift after 1995, the signature of which is perceptible over the adjacent landmass of India, as decreased decadal monsoon rainfall and in the Arabian Sea as increase in phytoplankton biomass. The decrease in rainfall after 1995 was linked to the increase in the Eurasian winter snow cover. The increased phytoplankton biomass during fall and winter is attributed to the iron-fertilization driven by enhanced dust-delivery under this regional climate shift. Finally, it is shown that the increased fish (oil-sardine) catch in the eastern and western Arabian Sea after 1995 is also tightly coupled to the increased phytoplankton biomass.