Future changes of the Seychelles-Chagos Thermocline Ridge in the Southwestern Indian Ocean under global warming scenario projected in the CMIP6 models
Saat Mubarrok (a*), Fuad Azminuddin (b), Heesok Jung (b), Chan Joo Jang (b)

a) Program Study Of Oceanography, Bandung Institute of Technology
Jalan Ganesha 10, Bandung 40132, Indonesia
*saatmubarrok[at]gmail.com

b) Ocean Circulation & Climate Research Department, Korea Institute of Ocean Science and Technology, South Korea

Abstract

The Seychelles-Chagos Thermocline Ridge (SCTR, 5oS-10oS, 50oE-80oE) is a unique open-ocean upwelling region in the southwestern Indian Ocean. Due to the negative wind stress curl between the equatorial westerlies and southeasterly trade winds, SCTR is known as a strong upwelling region with high biological productivity, providing a primary fishing zone for the surrounding countries. This study evaluates future changes in the SCTR using outputs from ten models of the Coupled Model Intercomparison Project Phase 6 (CMIP6). The thermocline depth, indicated by the depth of maximum temperature gradient (DTmax), shows a significant deepening trend across Shared Socio-economic Pathways (SSPs) scenarios (2015-2100), with deeper DTmax in SSPs compared to the CMIP6 historical simulations (1980-2014). Additionally, the analysis of Ekman pumping velocity in both historical simulations and SSPs future projection scenarios reveals a notable reduction in the SSPs scenarios, particularly evident in the equatorial region, attributed to a prevailing easterly wind bias common in climate models. This study suggests a connection between the bias in CMIP6 models^ thermocline depth and an easterly wind bias in the Indian Ocean in SSPs scenarios, as observed in the historical simulation. Investigating this bias reveals a diminished SST difference between the eastern and western Indian Ocean, notably during summer in SSPs scenarios, likely attributed to global warming leading to warmer conditions in the western Indian Ocean. The findings highlight the substantial impact of projected warming trends on Indian Ocean wind patterns and their critical role in altering thermocline depth in the SCTR region.

Keywords: thermocline, SCTR, CMIP6, Ekman pumping velocity

Topic: Ocean Sciences