Asymmetric Changes of the Subtropical Gyre Circulation and Associated Sea Level Over 1960–2018 in the Pacific Ocean

Abstract

Ocean circulations and sea level are undergoing long-term changes as part of anthropogenic global warming. Understanding these changes through the water column is important for comprehending the ocean's response to climate change. This study employs regional dynamic height (RDH) referenced to a no-motion layer (2,000 m) as a proxy to diagnose ocean circulations and sea levels using four observation-based datasets and 11 Ocean Model Intercomparison Project Phase 2 model simulations spanning from 1960 to 2018. Ocean Model Intercomparison Project Phase 2 simulations reproduce the major changes in ocean circulation indicated by observations, although regional differences are present, with certain regions exhibiting higher or lower RDH trends. North Pacific subtropical gyre shows positive RDH trends in the upper 400 m without a clear poleward shift but negative trends (spins down) below ∼400 m, while the South Pacific subtropical gyre shows positive RDH trends from surface to the no-motion layer and undergoes a poleward shift. These asymmetrical RDH trends between the North and South Pacific, are dominated by thermosteric components. The wind stress curl trends drive most changes of ocean circulations, resulting in asymmetric dynamic topography rise. Continued global warming in the 21st century is anticipated to intensify the asymmetric development of subtropical gyre circulations and associated sea levels in the Pacific Ocean.