A multi-centennial mode of North Atlantic climate variability throughout the Last Glacial Maximum

Paleoclimate proxy records from the North Atlantic region reveal substantially greater multi-centennial temperature variability during the Last Glacial Maximum (LGM) compared to the current interglacial. As there was no obvious change in external forcing, causes for the increased variability remain unknown. Here we provide a mechanism for enhanced multi-centennial North Atlantic climate variability during the LGM based on experiments with the coupled climate model CESM. The model simulates an internal mode of multi-centennial variability, which is associated with variations in the Atlantic meridional overturning circulation. In accordance with high-resolution proxy records from the glacial North Atlantic, this mode induces highest surface temperature variability in subpolar and mid latitudes and almost no variance in low latitudes. Greenland surface air temperature varies by up to 4°C, which is in line with multi-centennial variability reconstructed from ice cores. We show that this mode is based on a salt-oscillator mechanism and emerges only under full LGM climate forcing. Moderate deviations from full-glacial boundary conditions lead to its disappearance. We further argue that the multi-centennial mode has to be distinguished from millennial-scale Dansgaard-Oeschger oscillations.