Modulation of global-scale warming of the atmosphere and subsurface ocean by diathermal heat transport in the equatorial Pacific’s cold tongue

Abstract

Significant heat is transported from the atmosphere through the upper ocean in the equatorial Pacific’s cold tongue (PCT), primarily a result of turbulence-enhanced mixing, but with a significant contribution from penetrating solar radiation in especially the eastern extent of the PCT. We consider whether diathermal heat transport in the PCT is sufficiently large to influence global-scale heating from Earth’s energy imbalance by evaluating its magnitude and variability through the 21.5°C isotherm. Here, multiyear observations of mixing at 0°, 140°W are augmented by neural network predictions to fill in data gaps and extend the existing record of mixing to a 30-year period. Spatial extrapolation of these estimates to a larger area is guided by a high-resolution model. We find that the average heat transport through 21.5°C in the PCT, which comprises 0.2% to 0.6% of the world ocean’s surface area, is many times larger than the global atmosphere’s heating rate, 24 to 116% of the global ocean’s heating rate between 100 and 300 m depth and 7.9 to 24% of the global ocean’s heating rate below 100 m. Further, decadal variations of mixing in the PCT, driven by changes in ENSO phase, are large enough and of the correct sign to account for transient global-scale variations in atmosphere and subsurface ocean heating during and after the 1998–2012 atmospheric warming slowdown. These results provide observation-based evidence that the PCT is a globally-significant pathway for heat transport from the atmosphere through to the subsurface ocean.