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Global ocean heat content redistribution during the 1998–2012 Interdecadal Pacific Oscillation negative phase

Gastineau, Guillaume, Friedman, Andrew R., Khodri, Myriam, Vialard, Jérôme
Climate dynamics 2019 v.53 no.1-2 pp. 1187-1208
basins, climate, cold, heat transfer, latitude, models, oceans, phase transition, sea level, surface temperature, wind, wind stress, Indian Ocean, Pacific Ocean
Previous studies have linked the slowdown in global surface temperature warming during the 1998–2012 period to a negative Interdecadal Pacific Oscillation (IPO) phase. Here, we investigate the changes in ocean heat content (OHC) during this period. We compare two ensembles of coupled model experiments with either zero or observed prescribed tropical Pacific wind stress interannual anomalies. This successfully constrains the global surface temperature, sea level pressure and OHC patterns associated with the IPO phase transition around 1998. The negative IPO phase (1998–2012) is associated with a global ocean heat redistribution. The anomalously cold tropical Pacific Ocean leads to an increased oceanic uptake in this region, and a global OHC increase of 4 × 10²² J. The cold equatorial Pacific also forces mid-latitude wind changes through atmospheric teleconnections, leading to an enhanced wind-driven heat transport convergence at 40°N and 40°S. Enhanced Pacific easterlies also yield an enhanced heat transport to the Indian Ocean via the Indonesian throughflow. As a result, the anomalous Pacific heat uptake is entirely exported towards the North Pacific (~ 50%), Indian (~ 30%) and Southern (~ 20%) Oceans. A significant fraction of this heat is released back to the atmosphere in the North Pacific and Indian basins, and transported across 31°S in the Indian Ocean. Overall, OHC increases most in the Southern Ocean (~ 60% of global changes) and northern Pacific (~ 40%), with negligible changes in the Indian and Atlantic basins. These results point to the major importance of oceanic circulation in re-distributing the Pacific heat uptake globally during negative IPO phases.