Causes for the reversal of North Indian Ocean decadal sea level trend in recent two decades

Abstract

Using satellite and in-situ observations, ocean reanalysis products and model simulations, we show a distinct reversal of the North Indian Ocean (NIO, north of 5°S) sea level decadal trend between 1993–2003 and 2004–3013, after the global mean sea level rise is removed. Sea level falls from 1993 to 2003 (Period I) but rises sharply from 2004 to 2013 (Period II). Steric height, which is dominated by thermosteric sea level of the upper 700 m, explains most of the observed reversal, including the spatial patterns of sea level change. The decadal change of surface turbulent heat flux acts in concert with the change of meridional heat transport at 5°S, with both being driven by decadal change of surface winds over the Indian Ocean, to cause sea level fall during Period I and rise during Period II. While the effect of surface net heat flux is consistent among various data sets, the uncertainty is larger for meridional heat transport, which shows both qualitative and quantitative differences amongst different reanalyses. The effect of the Indonesian Throughflow on heat content and thus thermosteric sea level is limited to the South Indian Ocean, and has little influence on the NIO. Our new results point to the importance of surface winds in causing decadal sea level change of the NIO.