Simulated Warming Hole in Paleo-Pacific Oceans

Abstract

Abstract Both observations and simulations show that under global warming, there exists a warming deficit in the North Atlantic, known as the North Atlantic warming hole (NAWH). Here, we show that a similar warming hole occurs in the subpolar Pacific Ocean of paleoclimate simulations. As the solar constant is increased, the local surface becomes substantially cooler rather than warmer in the subpolar paleo-Pacific Ocean under the land–sea configurations of 70, 90, and 150 million years ago (Ma). The warming hole has a magnitude of ≈3°C and is located in the Northern Hemisphere in 70 and 90 Ma. The warming hole in 150 Ma has a magnitude of ≈1°C and is located in the Southern Hemisphere. Both atmospheric and oceanic processes contribute to trigger the warming hole. For 70- and 90-Ma experiments, atmospheric teleconnection along a great circle from tropics to extratropics intensifies surface winds over subpolar ocean and thereby increases relatively cool seawater transport from high to low latitudes. Meanwhile, global meridional overturning circulation (GMOC) becomes weaker, causing a divergence of the meridional ocean heat transport in the warming hole region. An increasing regional cloud shortwave cooling effect acts to further enhance the warming hole. For 150-Ma experiments, the warming hole is related to the meridional shift of midlatitude jet stream and the weakening of GMOC in the Southern Hemisphere. The strength and phase of the atmospheric teleconnection and the response of GMOC strongly depend on land–sea configuration, resulting in the paleo-Pacific warming hole to occur in special periods only.