Simulated Warming Hole in Paleo-Pacific Oceans

Abstract Both observations and simulations show that under global warming there exists warming deficit in the North Atlantic, known as the North Atlantic warming hole (NAWH). Here we show that similar warming hole occurs in the sub-polar Pacific ocean of paleo-climate simulations. As solar constant is increased, local surface becomes substantially cooler rather than warmer in the sub-polar 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 locates in the Northern Hemisphere in 70Ma and 90Ma. The warming hole in 150Ma has a magnitude of ≈1 °C and locates in the Southern Hemisphere. Both atmospheric and oceanic processes contribute to trigger the warming hole. For 70Ma and 90Ma experiments, atmospheric teleconnection along a great circle from tropics to extratropics intensifies surface winds over sub-polar 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 of regional cloud shortwave cooling effect acts to further enhance the warming hole. For 150Ma experiments, the warming hole is related to the meridional shift of mid-latitude 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 to the paleo-Pacific warming hole to occur in special periods only.