Preprints
https://doi.org/10.5194/os-2021-97
https://doi.org/10.5194/os-2021-97

  11 Oct 2021

11 Oct 2021

Review status: this preprint is currently under review for the journal OS.

Interannual variability of sea level in the South Indian Ocean: Local versus remote forcing mechanisms

Marion Kersalé1,2, Denis L. Volkov1,2, Kandaga Pujiana1,2, and Hong Zhang3 Marion Kersalé et al.
  • 1Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, USA
  • 2NOAA Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
  • 3Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Abstract. The subtropical South Indian Ocean (SIO) has been described as one of the world's largest heat accumulators due to its remarkable warming during the past two decades. However, the relative contributions of the remote (of Pacific origin) forcing and local wind forcing to the variability of heat content and sea level in the SIO have not been fully attributed. Here, we combine a general circulation model, an analytic linear reduced gravity model, and observations to disentangle the spatial and temporal inputs of each forcing component on interannual to decadal timescales. A sensitivity experiment is conducted with artificially closed Indonesian straits to physically isolate the Indian and Pacific Oceans, thus, intentionally removing the Indonesian throughflow (ITF) influence on the Indian Ocean heat content and sea level variability. We show that the relative contribution of the signals originating in the equatorial Pacific versus signals caused by local wind forcing to the interannual variability of sea level and heat content in the SIO is dependent on location within the basin (low vs. mid latitude; western vs. eastern side of the basin). The closure of the ITF in the numerical experiment reduces the amplitude of interannual-to-decadal sea level changes compared to the simulation with a realistic ITF. However, the spatial and temporal evolution of sea level patterns in the two simulations remain similar and correlated with El Nino Southern Oscillation (ENSO). This suggests that these patterns are mostly determined by local wind forcing and oceanic processes, linked to ENSO via the ‘atmospheric bridge’ effect. We conclude that local wind forcing is an important driver for the interannual changes of sea level, heat content, and meridional transports in the SIO subtropical gyre, while oceanic signals originating in the Pacific amplify locally-forced signals.

Marion Kersalé et al.

Status: open (until 06 Dec 2021)

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Marion Kersalé et al.

Marion Kersalé et al.

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Short summary
The South Indian Ocean is one of the major basins for regional heat accumulation and sea level rise. The year-to-year changes of regional sea level are influenced by water exchange with the Pacific Ocean via the Indonesian Throughflow. Using a general circulation model, we show that the spatio-temporal pattern of these changes is primarily set by local wind forcing modulated by El Nino Southern Oscillation, while oceanic signals originating in the Pacific can amplify locally-forced signals.