Why is the Bay of Bengal experiencing a reduced rate of sea surface warming?

Abstract

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.

A bio-physicochemical perspective of the Bay of Bengal

“…Studies found that the entire Indian Ocean has been warming over the past half-century (Chambers et al ., 1999; Alory et al ., 2007; Du & Xie, 2008; Rao et al ., 2012; Dong et al ., 2014). A significant increase of water temperature in the BoB, as noted in this study, is supported by the findings of D'Mello & Prasanna Kumar (2016), who claimed an increase in SST at a rate of 0.014°C per year over the period of 1960–2011. Adding to that, the sunspot cycle was partially controlling the rising trend of temperature in the BoB (White et al ., 1997).…”

Processes controlling the accelerated warming of the Arabian Sea

“…Such a link between the decadal cycle and SST is also seen in the eastern part of the North Indian Ocean, i.e. the Bay of Bengal, from 1960 to 1995 (D'Mello and Prasanna Kumar, ). However, this decadal relation between AS SST and sunspot number cycle is disrupted post‐1995, as can be seen in Figure .…”