Thursday, September 22, 2016, 12:30PM - 1:30PM
Constraining latest Holocene expansion and 20th century retreat of a small Canadian Arctic ice cap using entombed vegetation
Records of Holocene glacier activity in the Arctic are often incomplete due to discontinuous moraine records. Glaciers can overrun and obliterate previous moraines that also only record the culmination of an advance. However, recent warming at high latitudes has caused extensive retreat of ice caps and glaciers in the Arctic over the past few decades. These cold-based ice caps, having preserved the underlying landscape, are now exposing preserved landscapes complete with in situ, intact tundra plants previously entombed by ice. The plants were most likely killed by advancing ice, and their radiocarbon ages correlate with the timing of snowline depression a period of local cooling. In rare instances, rapid ice margin retreat can expose hundreds of meters of preserved land surface from which a transect of plant radiocarbon ages can be obtained and used to construct a near-continuous chronology of past ice margin advance for one ice cap. Here we present radiocarbon results from the first such transect on Baffin Island, which directly dates ice margin history over the past two millennium. Initially, ice began expanding at or prior to ~20 CE. Ice expanded episodically from 1000 CE until it reached its Holocene maximum extent at ~1600 CE, where it remained until rapidly retreating toward its current position beginning ~1910 CE. We employ a two-dimensional numerical glacier model to explore of the sensitivity of the ice cap to temperature change. Model experiments show that a minimum of 0.5°C of cooling is required at or before ~20 CE to drive ice expansion to the Holocene maximum extent. Simulations also show that ~3°C of cumulative warming is necessary to shrink ice back to its modern position, and continuation of this warming will cause the disappearance of the ice cap before 2100 CE.