Response of Pacific subtropical‐tropical thermocline water pathways and transports to global warming

Abstract

Global warming may change the thermocline water pathways and transports from the subtropics to the tropics in the Pacific Ocean, which are known to have profound implications for the El Niño‐Southern Oscillation (ENSO) and thereby global climate. This study investigates the changes by comparing solutions between a present‐day climate and a future, warmer climate from a set of Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) models. As the climate warms, although the total transport from the subtropics to the tropics exhibits no significant change, transport via western boundary pathways increases and via interior pathways decreases. This shift is due to high potential vorticity (PV) zones that extend further westward, thus dynamically guiding thermocline water away from interior pathways to prefer western boundary pathways from the subtropics to the tropics. Additionally, a warmer climate induces a large temperature increase near the sea surface in the eastern tropics and a significantly enhanced Equatorial Undercurrent (EUC) in the western and central Pacific; the former is related to the decreased transport through interior pathways and the latter is linked to the increased transport through western boundary pathways. Implications of the results of this study are also discussed.