DECIPHERING GLACIER ACTIVITY ON BAFFIN ISLAND DURING DEGLACIATION WITH RADIOCARBON ARCHIVES

Reconstructing complex glacier histories, even over the relatively recent Last Glacial Maximum (LGM) deglaciation, is notoriously difficult due to the preservation bias of glacial landforms as well as the ability to securely date those landforms. However, chronicling glacier behavior during deglaciation is important for understanding past climate variability and to contextualize recent anthropogenic warming. We present results of ongoing studies from Baffin Island, Arctic Canada, that combine in situ cosmogenic ¹⁴C from rock surfaces and conventional ¹⁴C dating of long-entombed vegetation to provide a more complete picture of climate trends during deglaciation and subsequent Holocene glacier expansion. Many glaciers and ice caps on Baffin Island are wholly or in part cold based. This leads to preservation of the subglacial landscape, including tundra plants killed by advancing ice and preserved in growth position until re-exposed as a result of modern warming. Because recently exposed plants are efficiently removed from the landscape (or regrow), their ¹⁴C ages record the most recent time that ice advanced over (and remained over) the sample location until modern exposure. Large populations of plant ¹⁴C ages have been used to show that glacier regrowth during the Holocene began ~5ka and continued episodically until the Little Ice Age. In addition, a transect of plant ¹⁴C ages was used to reconstruct the advance and retreat of an individual ice cap over the past ~2,000 years. While plant ages generally record only the most recent ice advance, the balance between in situ ¹⁴C production and decay in adjacent rock surfaces is modulated by ice cover, such that the inventory of in situ ¹⁴C provides a measure of the integrated ice cover history. Thus, the use of both plant and in situ ¹⁴C to constrain forward models of in situ production narrows substantially the set of plausible ice-cover scenarios compared to what is possible using each method alone. With this approach, we have shown that peak Baffin Island warmth occurred early in the Holocene in conjunction with peak summer insolation and that summer temperatures are only now reaching similar levels. We have also found that many locations on Baffin Island have likely been continuously ice-covered since the end of the last interglacial. Their recent exposure indicates that current summer temperatures are likely warmer than at any time in the past ~120ka.