ABSTRACT: Ice cap retreat in northern Baffin Island: providing a context for current Arctic warming.

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Abstract

Instrumental records show that the Earth has warmed ca. 0.7 °C over the past century, with the most dramatic increase in the decades since the 1960s. The Arctic has experienced a similar pattern, but the magnitude is greater, with average annual temperature increases of 2 to 5 °C across portions of the Arctic since the 1960s. The short time span of direct observations makes it difficult to evaluate the roles of natural climate variability and greenhouse gas forcing in explaining these observations, but the pattern of change is consistent with GCM simulations of the consequences of increased greenhouse gases. This project is designed to provide a Holocene context for 20th century Arctic warming. How unusual is the rate and magnitude of this warming? When was the Arctic last as warm as it is now? Is this degree of warmth within the range of natural variability or is it unprecedented? The Arctic instrumental record is limited in time and space, so natural archives of proxy climate data must be used to address these questions. Extensive, thin, cold-based ice caps mantling the north-central plateau of Baffin Island, Arctic Canada, have receded by 97% in area since their Little Ice Age (LIA) maxima. One ice cap studied in the 1960s and early 1980s has now completely melted (Tiger Ice Cap, Fig. 1); many others are predicted to vanish in the next 5 to 10 years, and all are expected to vanish before 2050. This project contains four techniques by which these ice caps can contribute to the Arctic warming debate: 1) Plant remains preserved beneath extant plateau ice caps will be collected by boring through the ice along transects from the ice margin to the ice divide. Radiocarbon ages of the entombed vegetation define the last time the Arctic was warm enough to completely melt these ice caps. 2) Cosmogenic in situ 14C produced in quartz collected along transects from the current ice margins to beyond the edge of the LIA margin will define exposure histories across the plateau. The duration of surface exposure defines what proportion of the Holocene the plateaus have been ice-free since regional deglaciation, providing a longer-term perspective on current warming. 3) Lakes in the immediate vicinity of the ice caps that have emerged as the ice has melted back will be cored and plant macrofossils within the sediment cores will be 14C-dated to establish the number and timing of deglacial episodes during the Holocene. When used in concert, these methods should give a clearer picture of the history of Arctic climate throughout the Holocene, specifically when and for how long this area was as warm as it is at present. 4) Lastly, aerial rates of ice-cap retreat over the past 50 years will be defined from air photo and satellite imagery, from which their final disappearance can be predicted. First-order estimates on the magnitude of LIA-to-present climate change can be derived from the integration of satellite imagery and digital elevation models.

Bibliography of Canadian Geomorphology