A HISTORY OF SEA-ICE IN THE CANADIAN ARCTIC ARCHIPELAGO BASED ON POSTGLACIAL REMAINS OF THE BOWHEAD WHALE (BALAENA-MYSTICETUS)

The bowhead whale (Balaena mysticetus) is a planktivore of the baleen group of whales adapted to live in the lease edges of the north polar sea ice. Its annual migrations roughly track the advance and retreat o f the flee edge. The distribution and radiocarbon ages of bowhead subf ossils in the Canadian Arctic Archipelago show that the range of the w hale has expanded and contracted abruptly several times over the last 10.5 thousand years (ka). Each expansion or contraction was followed b y nearly stable conditions that persisted for millennia.These changes in the geographic range of the bowhead are defined by > 400 radiocarbo n dates. The paleo-ranges are the basis for reconstructing summer sea- ice minima. Using this criterion, postglacial time is divided into fou r intervals: (1) 10.5-8.5 ka B.P.-A large bowhead population extended in the summer all the way to retreating glacier margins and ultimately from the Beaufort Sea to Baffin Bay; meltwater-driven outflows probab ly cleared the inter-island channels of sea ice; this interval termina ted when the present interglacial circulation pattern was established; (2) 8.5-5 ka B.P.-Bowheads were excluded from most of the archipelago because the channels failed to clear of sea ice; summer sea-ice condi tions for most of this time were more severe than during historical ti mes; (3) 5-3 ka B.P.-Bowheads reoccupied the central channels of the A rctic Islands, and their range extended beyond historical limits; and (4) 3-0 ka B.P.-Sea ice excluded whales from the central channels, as it does today. This paleoenvironmental record based on bowhead whale d istributions is more complex than that revealed in the delta(18)O, con ductivity or the percent-melt records of the Devon and Agassiz ice cor es. A reconciliation of the two data sets may indicate the following g eneral summer climatic conditions: 10-8 ka B.P.-warm summers with maxi mum postglacial warmth; 8-5 ka B.P.-cool, dry summers; 5-3 ka B.P.-coo l, wet summers; 3-0 ka B.P.-cold, dry summers.