Future dynamic sea level change in the western subtropical North Pacific associated with ocean heat uptake and heat redistribution by ocean circulation under global warming

Hiroaki Tatebe,Tatsuo Suzuki

doi:10.1186/s40645-020-00381-9

Abstract

In the present study, the relative importance of ocean heat uptake and heat redistribution on future sea level changes in the western North Pacific has been reconciled based on a set of climate model experiments in which anomalous surface fluxes of wind stress, heat, and freshwater in a warmed climate are separately given to those fluxes in a pre-industrial control simulation. Our findings suggest that the basin-wide ocean heat uptake and resultant heat accumulation by the climatological-mean advection are required to explain the future dynamic sea level (DSL) rise in the western subtropical North Pacific caused by the thermal expansion of subtropical mode water (STMW). At the same time, it has been recognized that the localized heat uptake in association with the wintertime mixed-layer formation around the Kuroshio Extension can be solely attributed to the future STMW change. The thermally induced component is a dominant contribution to the future DSL rise in the western subtropical North Pacific compared to the contributions of wind-induced and halosteric components, which, especially the former, have been reported as a dominant factor resulting from a linear response of the ocean to the northward shift and strengthening of the mid-latitude westerly over the North Pacific in a warmed climate.

Highlights

The global ocean stores more than 90% of the heat energy accumulated in the climate system of the Earth during recent decades (e.g., Levitus et al 2012; Church et al 2013a, b)
We focus on the contributions of the ocean heat uptake and heat redistribution by ocean circulation on the dynamic sea level (DSL) change in order to understand the physical nature of the relative sea level rise in the Kuroshio Extension (KE) recirculation
3.1 Regional sea level response to surface flux perturbations In order to find the spatial pattern in the North Pacific, we illustrate the regional changes in DSL as deviations from the basin average in the upper panels of Fig. 2

Summary

Introduction

The global ocean stores more than 90% of the heat energy accumulated in the climate system of the Earth during recent decades (e.g., Levitus et al 2012; Church et al 2013a, b). The DSL changes in the western North Pacific are characterized by a northward shift of the Kuroshio Extension (KE) path and strengthening of the Kuroshio and the KE recirculation gyre. These characteristic patterns are observed in the multi-model ensemble mean of the Coupled Model Intercomparison Project (CMIP) models (e.g., Sueyoshi and Yasuda 2012; Zhang et al 2014; Yin 2012; Church et al 2013a, b; Terada and Minobe 2018). Changes in the surface wind stress alone cannot fully explain the strengthening of the KE recirculation

Methods

Results

Conclusion