A History of Sea Ice in the Canadian Arctic Archipelago Based on Postglacial Remains of the Bowhead Whale (<i>Balaena Mysticetus</i>)
The bowhead whale (Balaena mysticetus) is a planktivore of the baleen group of whales adapted to live in the loose edges of the north polar sea ice. Its annual migrations roughly track the advance and retreat of the floe edge. The distribution and radiocarbon ages of bowhead subfossils in the Canadian Arctic Archipelago show that the range of the whale has expanded and contracted abruptly several times over the last 10.5 thousand years (ka). Each expansion or contraction was followed by nearly stable conditions that persisted for millennia. These changes in the geographic range of the bowhead are defined by >400 radiocarbon dates. The paleo-ranges are the basis for reconstructing summer sea-ice minima. Using this criterion, postglacial time is divided into four 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 probably cleared the inter-island channels of sea ice; this interval terminated 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 conditions for most of this time were more severe than during historical times; (3) 5-3 ka B.P. - Bowheads reoccupied the central channels of the Arctic 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 distributions is more complex than that revealed in the delta 18O, conductivity or the percent-melt records of the Devon and Agassiz ice cores. A reconciliation of the two data sets may indicate the following general summer climatic conditions: 10-8 ka B.P. - warm summers with maximum postglacial warmth; 8-5 ka B.P. - cool, dry summers; 5-3 ka B.P. - cool, wet summers; 3-0 ka B.P. - cold, dry summers.