GLACIER MAXIMA IN BAFFIN BAY DURING THE MEDIEVAL WARM PERIOD

In the Northern Hemisphere, moraines deposited by mountain glaciers during the Little Ice Age typically represent the largest extent of glaciers during the late Holocene. In some settings, however, moraines that predate Little Ice Age moraines are preserved on the landscape, offering a unique opportunity to develop longer chronologies of late Holocene glacier change. In turn these chronologies can be used to assess spatio-temporal patterns of glaciation and their associated climatic driving mechanisms. Although fresh moraines deposited in front of modern glacier snouts were undoubtedly deposited sometime during the last few hundred years, direct and precise ages for these moraines are scarce. Recent advancements in low-level ¹⁰Be surface exposure dating now allow for robust late Holocene glacier chronologies in some Arctic settings. Here, we present a sub-centennial and well-resolved ¹⁰Be-based record of late Holocene glaciation from north-central Baffin Island. Over the last ~1,000 years, we are able to resolve the culmination of 5 distinct glacier advances and find that, remarkably, glaciers were at their maximum Little Ice Age configurations throughout the Medieval Warm Period. When our new record is combined with complimentary data, we find that the western North Atlantic region remained cool, whereas the eastern North Atlantic region was comparatively warmer during the Medieval Warm Period – a dipole pattern consistent with a persistent positive phase of the North Atlantic Oscillation. Finally, these results open the door for developing robust ¹⁰Be-based records of Arctic glacier change from young surfaces located near sea level.