Poster Presentation AMOS Annual Meeting and International Conference on Tropical Meteorology and Oceanography

Projected changes of ocean gyre circulation and related sea level patterns (#1012)

Xuebin Zhang 1 , John Church 2 , Kewei Lyu 1
  1. CSIRO, Hobart, TAS, Australia
  2. Climate Change Research Centre, UNSW, Sydney, NSW, Australia

Regional sea levels exhibits significant deviations from the global mean, induced by several factors such as ocean density and circulation change, land ice melting and Glacial Isostatic Adjustment. This study examines the connection between ocean gyre circulation and dynamical sea levels (DSL) in historical and future climates simulated by the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. It’s found that horizontal ocean gyre circulation plays significant roles in determining DSL distribution. In the present mean, anticyclonic (cyclonic) ocean gyres generally correspond to high (low) DSLs. In the future climate, ocean gyre circulation, as indicated by the barotropic stream function, is projected to show some common features among ~20 CMIP5 under both medium and strong emission scenarios (RCP4.5 and RCP8.5), including spin-up of the “super-gyre” in the Southern Ocean, and spin-down of both subtropical and subpolar gyres in the North Atlantic, which can be favourably explained by wind-driven Sverdrup-type response. Consistency can be found in the future projections of ocean gyre circulation and DSL, in particular in the Southern Ocean and North Atlantic, but it doesn’t hold everywhere. The spin-up of super-gyre in response to poleward shifting and strengthening of westerlies in the Southern Hemisphere have quite consistent impacts in three ocean basins in both gyre circulation and sea level. High sea levels show up along the poleward edge of subtropical gyres. However, North Pacific displays large sea level changes but not much streamfuntion changes, which are associated with different responses in upper and lower depths, possibly due to the stronger stratification there in the future. Unlikely the other basins, both thermo- and halo-steric effects need to be considered to explain circulation changes at different depths in the North Atlantic. Moreover, weakening of Atlantic Meridional Overturning Circulation also influences, or even dominates, sea level changes in some regions.