Substantial agreement on the timing and magnitude of Late Holocene ice cap expansion between East Greenland and the Eastern Canadian Arctic: A commentary on Lowell etal., 2013

摘要

Lowell et al. (2013) present a large series of radiocarbon dates on tundra plants preserved beneath ice caps and cosmogenic nuclide exposure ages on moraine boulders and bedrock that document changes in the dimensions of Istorvet, an independent coastal ice cap on East Greenland. They argue that their reconstruction of Istorvet advances during the Late Holocene is inconsistent with the reconstructions of Miller et al. (2012) for Arctic Canada. Here we show that a careful interpretation of their data reveals a remarkable similarity with the compilation of radiocarbon dates on rooted tundra plants long-entombed beneath over 50 different ice masses in a 1000 km transect along Baffin Island, Arctic Canada and with the high-resolution record from an Icelandic ice cap (Miller et al., 2012). Collectively, these results suggest synchronous responses of ice masses across the northwestern sector of the North Atlantic Arctic during recent millennia. We also emphasize that the interpretation of radiocarbon ages of rooted plants exposed by receding ice depends to a large extent on the collection protocols employed. The sampling protocols outlined below maximize the value of these key new datasets to provide unambiguous constraints on past climates and changes in glacier dimensions. Examples of settings that meet these criteria are shown in Figs. 1 and 2.