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Fast and slow responses of the Subantarctic Mode Water in the South Indian Ocean to global warming in CMIP5 extended RCP4.5 simulations

Abstract

The present study examines the long-term evolution of the Subantarctic Mode Water (SAMW) in the south Indian Ocean (SIO) based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) extended simulations through 2300 under Representative Concentration Pathways 4.5 (RCP4.5). The SAMW in the SIO shrinks and thins rapidly during the fast radiative forcing increasing period between 2000 and 2100. After 2100, when the radiative forcing stabilizes, the SAMW expands and thickens slowly. The response of SAMW is dependent both on the evolution of surface buoyancy forcing and overlying westerly wind stress. During year 2000–2100, the surface heat flux dominates the net buoyancy gain over the SAMW formation region, whereas the enhanced westerly wind contributes to a lesser extent due to its poleward shift. As the radiative forcing increases rapidly from 2000 to 2100, the buoyancy gain over the SAMW formation region results in a fast shoaling mixed layer and a reduction in the SAMW subduction rate. The surface intensified warming enhances stratification and reduces the SAMW that is quantified by the volume of low potential vorticity (PV) water. Consequently, the SAMW shrinks and thins fastly. When the radiative forcing stabilizes after 2100, the warming is greater in the subsurface than the surface, and the associated slow destratification gradually increases the low PV water volume. Hence, the SAMW expands and thickens slowly. The distinct fast and slow responses of SAMW have implications for the heat uptake and circulation of the SIO.

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Acknowledgements

We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling institutions (listed in Table 1) for producing and making available their model output. For CMIP the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led the development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. All the model outputs used in this study are downloaded from http://www.ipcc-data.org/sim/gcm_monthly/AR5/Reference-Archive.html. We also acknowledge the NASA Physical Oceanography Distributed Active Archive Center for making the CCMP dataset freely available (http://www.remss.com/measurements/ccmp/). The HadISST datasets are provided by the Hadley Centre (https://www.metoffice.gov.uk/hadobs/hadisst/). And World Ocean Atlas (WOA18) offers temperature and salinity (https://www.nodc.noaa.gov/cgi-bin/OC5/woa18/woa18.pl?parameter=t). This work is supported by the National Key R&D Program of China (2018YFA0605700), the National Natural Science Foundation of China (41906180, 41830538, 41525019, 41876006), the Chinese Academy of Sciences (XDA15020901, 133244KYSB20190031, ZDRW-XH-2019-2), and the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (GML2019ZD0303, 2019BT2H594).

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Correspondence to Yan Du.

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Xia, X., Xu, L., Xie, SP. et al. Fast and slow responses of the Subantarctic Mode Water in the South Indian Ocean to global warming in CMIP5 extended RCP4.5 simulations. Clim Dyn 56, 3157–3171 (2021). https://doi.org/10.1007/s00382-021-05635-w

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  • DOI: https://doi.org/10.1007/s00382-021-05635-w

Keywords

  • Subantarctic Mode Water (SAMW)
  • Fast and slow responses
  • Global warming
  • CMIP5
  • Subduction