| Superimposed on the long-term early Paleogene greenhouse climate, an episode of widespread extreme greenhouse warming named the Paleocene-Eocene thermal maximum (PETM), occurred ~55 Ma ago. We identify the PETM in a recently recovered (Arctic Coring Expedition, IODP Expedition 302) marine sedimentary sequence deposited near the North Pole and examine the pattern of Arctic climate change during this extreme climate anomaly. We show that during the PETM the tropical dinoflagellate Apectodinium inhabited the Arctic Ocean, when TEX86-derived surface temperatures rose from 18ºC to over 23ºC. Concomitantly, sea level rose and photic zone euxinia developed. Arctic surface temperatures before, during and after the PETM were at least 10°C warmer than predicted by paleoclimate model simulations with 2000 ppmv CO2. Moreover, our data confirm previously-noted significantly reduced pole-to-equator temperature gradients that cannot be reproduced by the current generation of fully coupled climate models. This suggests that feedback mechanisms that are unimplemented in the models played a crucial role in the polar-amplified warmth of early Paleogene climates, in conjunction with elevated greenhouse gas concentrations. Finally, our results show that the pole-to-equator temperature gradient remained similar during the PETM, suggesting that the mechanism that caused early Paleogene reduced gradients was largely saturated at this event. |
