Early Holocene evolution of the western Greenland Ice Sheet and Baffin Island mountain glaciers

Reconstructing the behavior of extant and defunct ice-sheets can provide novel insights into the forcing mechanisms that drive short-term ice-sheet change. Here, I reconstruct the early Holocene (∼11,700-7,000 yr ago) behavior of the western Greenland Ice Sheet (GrIS) margin in Disko Bugt, and the early Holocene behavior of northeastern outlets of the Laurentide Ice Sheet (LIS) and independent mountain glaciers on eastern Baffin Island. A suite of 10Be surface exposure ages, combined with radiocarbon-dated lake sediments, indicate that abrupt cooling ca. 8,200 and 9,300 yr ago, recorded in central Greenland ice cores, triggered advances of the western GrIS margin in Disko Bugt, including the marine-terminating Jakobshavn Isbræ. Although the magnitude of ice-margin change differed between marine- and land-terminating sectors of the western GrIS, this chronology indicates that 8.2 and 9.3 ka cooling was of sufficient magnitude and duration to prompt a clear response from both types of ice margins. In addition, I use these results to resolve a long-standing debate regarding the origin of an extensive moraine system deposited along the ice-free fringe of western Greenland; moraines were deposited at the culminations of climate-driven advances of the western GrIS and not deposited strictly by topographical control on ice-sheet behavior. On eastern Baffin Island, new and pre-existing 10Be and radiocarbon ages demonstrate that the 8.2 ka event triggered the synchronous advance of Laurentide Ice Sheet outlet glaciers and independent mountain glaciers. Combined with the western GrIS chronology, these data reveal that marine- and land-terminating ice margins respond to warming and cooling with relatively short lag times between initial climate forcing and ice-margin response. The rapid, dynamically aided retreat of outlet glaciers in response to warming is well documented; however, results presented here suggest that marine-terminating outlet glaciers can also advance quickly in response to cooling, challenging the notion that outlet-glacier decay occurs much faster than growth.