Dynamic sea level change and ocean heat uptake in the North Pacific under global warming in MIROC6

Tatsuo Suzuki and Hiroaki Tatebe, JAMSTEC Japan Agency for Marine-Earth Science and Technology, Research Center for Environmental Modeling and Application, Yokohama, Japan
The Dynamical sea-level changes in the 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 seen in the multi-model ensemble mean of the CMIP5 models (e.g., Yin 2012; Church et al. 2013; Terada and Minobe 2018). Analyzing CMIP5 models, Terada and Minobe (2018) suggested that the intensification of the KE is related to a warming of the subtropical mode water (STMW) which induces the thermosteric sea level rise in the Kuroshio and the KE recirculation regions. Furthermore, they inferred that the decrease of the STMW density is influenced by the downward heat flux anomaly related to the northward shift of the KE, which is caused by the wind stress change. However, the relationship between the ocean heat uptake and the DSL rise in the Kuroshio and the KE recirculation gyre is still unclear. In the present study, we conducted a series of model experiments for the detailed analysis of the DSL change and ocean heatuptake in the North Pacific, following a procedure provided by the Flux-anomaly-forced model inter-comparison project (FAFMIP), which is an AOGCM inter-comparison project of CMIP6 proposed by Gregory et al. (2016). Changes in wind stress under global warming (faf-stress) contribute to the north of KE. However, the heat flux change south of the KE did not fully explain the sea level rise due to STMW water mass alteration (high temperature, low salinity) as noted by Terada and Minobe (2018). On the other hand, the experiment that added the heat flux change (faf-heat) under global warming could explain the sea level rise in the Kuroshio recirculation region due to the high temperature of STMW. Heat transport to the subsurface of the Kuroshio recirculation region during this warming is determined by climatological mean flow.