The Arabian Sea (AS) has undergone a regime shift after 1995, manifesting the disruption of its natural decadal cycle over-riding a secular rise in its sea-surface temperature (SST). Using a suite of in situ and remote sensing data, we show that the rate of post-1995 accelerated warming is spatially different, due to regionally and seasonally differing oceanographic processes. Along parts of the western boundary, the accelerated warming was mediated by a reduction in the post-1995 linear trend of wind speed during summer monsoon leading to reduced upwelling and also reduced evaporation trend. In the northeast AS, post-1995 increase in specific humidity during late winter, lead to a decrease in the evaporative cooling and subsequent convective mixing resulting in the increased rate of warming. The continued warming seen in the northeast AS until spring inter-monsoon was due to the increasing net heat flux trend into the ocean along with reducing trend in evaporation. The accelerated warming in the central AS was linked to the reduced wind speed trend.

The eastern Arabian Sea (EAS) is a region of complex interplay between several spatially and temporally varying oceanographic processes. Using two sets of in situ data collected from the same stations, separated by a decade, we show that warming and cooling in the EAS were linked to the long‐term variability of this region. Though the warming in the southern part of EAS was consistent with the basin‐wide rise in sea surface temperature in the Arabian Sea (AS), the enhanced freshening was a remote response to episodic events mediated by the strengthening of interbasin exchange between Bay of Bengal and AS through East India Coastal Current and West India Coastal Current. The increased stratification in the southern part of EAS led to the decline in the chlorophyll over the decade. In contrast, enhanced chlorophyll in the northern part of the EAS over the decade was linked to the increased wind speed.

ABSTRACT:The sea surface temperature (SST) in the Bay of Bengal (BoB) during the period 1960-1995 showed a decadal cycle, riding over a warming trend. The disruption of the decadal cycle was noticed post-1995 and was followed by a slowdown in the sea surface warming. The cause for the disruption of the SST decadal cycle was the weakening of the link between SST and sunspot number. The rising trend in the SST is due to the increasing atmospheric CO 2 concentration. The post-1995 SST slowdown was due to the increasing influence of the number of depressions, cyclones and severe cyclones in the BoB, the occurrence of which showed an upward trend. Using Price-Weller-Pinkel model we show that cyclonic systems deepen the mixed-layer through enhanced mechanical-mixing with cooler sub-surface waters, thereby reducing the mixed-layer temperature and consequently the SST. This process opposes the SST rise due to increasing atmospheric CO 2 concentration. The net effect of the wind-mixing caused by the increased number of depressions, cyclones and severe cyclones and the increased CO 2 concentration is a SST slowdown in the BoB. This mechanism differs from the SST slowdown mechanisms suggested for the Atlantic and the Pacific.