An altered Atlantic atmospheric circulation regime during Last Glacial Maximum: 1. Evidence from a coupled climate model

The Last Glacial Maximum (LGM), 21 thousand years before present, was the time of maximum land ice extent during the last ice age. A recent simulation of LGM climate by a state-ofthe-art fully coupled global climate model is shown to exhibit strong, steady atmospheric jets and weak transient eddy activity in the Atlantic sector compared to today’s climate. In contrast, previous work based on uncoupled atmospheric model simulations has shown that the LGM jets and eddy activity in the Atlantic sector are similar to those observed today, with the main difference being a northeastward extension of their maxima. The coupled model simulation is shown to agree better with paleoclimate proxy records, and thus, is taken as the more reliable representation of LGM climate. The existence of this altered atmospheric circulation state during LGM in the model has implications for our understanding of the stability of glacial climates, for the possibility of multiple atmospheric circulation regimes, and for the interpretation of paleoclimate proxy records.