Global thermosteric sea level change contributed by the deep ocean below 2000 m estimated by Argo and CTD data

Abstract

Due to an insufficient amount of observational data, little is known about the temperature variation in the global abyssal ocean and its contribution to sea level change. In this study, we estimated the monthly seawater temperature below 2000 m from 2005–2015 by combining Array for Real-time Geostrophic Oceanography (Argo) and conductivity-temperature-depth (CTD) data. For this purpose, we divided the global ocean into 38 regions according to the CTD temperature profile properties. For each region, we used CTD data to construct a mathematical model to describe the relation of temperatures between 1000–2000 m and those below 2000 m. We then used this mathematical model and the Argo data to reconstruct the temperature profile below 2000 m and evaluate its thermostatic contribution to sea level change. We discovered that the deep ocean below 2000 m contributed 0.12 ± 0.03 mm/yr to the mean global thermosteric sea level rise from 2005–2015. Our result was confirmed by geodetic observations, i.e., the rate of thermosteric sea level rise calculated using altimeter, Gravity Recovery and Climate Experiment (GRACE), and Argo data was approximately 0.15 ± 0.41 mm/yr. The contribution of each ocean layer generally decreased with depth, and there was an obvious fluctuation between approximately 4000–5000 m, interpreted as being caused by geothermal heating of the ocean floor.