Trend and interannual variability of the Arabian Sea heat content

Abstract

Long-term trend and interannual variability of heat content down to 300 m in the Arabian Sea during the period 2000–2017 are analyzed to understand the physical forcings that lead to the significant warming of the Arabian sea. The warming trend during spring and summer are primarily due to heat accumulated below the mixed layer (ML) while the heat accumulated in the ML contributes to the warming during the fall and winter. The study reveals that the combined effect of El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) drives the interannual variability of heat content below the ML and the corresponding thermocline variability during spring. During summer, advection of heat plays a key role. Air-sea fluxes mainly drive the variability of heat content in the ML. However, ENSO and IOD also add to the variability during fall and winter. This study indicates that the warming over the upper 300 m in the Arabian Sea is influenced by the number of positive IOD and El Niño years during the study period, while the air-sea fluxes are responsible for the warming of the surface ML. This analysis sheds new light on the Arabian Sea seasonal heat content trends, and underscores the need for evaluation of their implications for the regional climate variability, trend and extremes. The findings have implications for process understanding needed to better predict impacts on marine heatwaves, cyclones and the regional climate.