HOLOCENE GLACIER FLUCTUATIONS IN THE CARIBOO MOUNTAINS, BRITISH COLUMBIA, CANADA

We use terrestrial and lacustrine evidence to reconstruct Holocene glacier fluctuations in the Cariboo Mountains of British Columbia. Onoff Lake only receives glacigenic sediments from Castle Creek Glacier when the glacier is downvalley of its AD 1946 position, which is ca. 300 m from its terminal moraine and 1500 m inside of its present terminus. Times when Castle Creek and other glaciers in the Cariboo Mountains advanced are constrained by seventeen ¹⁴C ages obtained from wood and plant material recovered from glacier forefields, six AMS ¹⁴C ages on terrestrial macrofossils collected from lake sediments, and tephras. The data indicate that glaciers were no more extensive 9200 ¹⁴C yr BP [10,490-10,250 cal yr BP] than in AD 1946. This age was obtained on macrofossils collected 0.5 m above basal lake sediments from Onoff Lake and thus is a minimum limiting age for terminal Pleistocene deglaciation of the Cariboo Mountains. A single piece of detrital wood yielded an age of 7915±25 ¹⁴C yr BP [8970-8610 cal yr BP], so the evidence for glacier activity during the early Holocene remains equivocal. Two detrital logs returned ages of ca. 4700 ¹⁴C yr BP, suggesting that Neoglacial expansion was underway by 5580-5330 cal yr BP. Eleven ¹⁴C ages on detrital wood and stumps and alpine vegetation in growth position indicate that glaciers advanced about 4900 and 4200 cal yr BP. The latter age coincides with rapid and significant climate deterioration recognized throughout the Northern Hemisphere. Based on the sediment record from Onoff Lake, Castle Creek Glacier first achieved a downvalley position greater than in AD 1946 between 2500 ¹⁴C and 2400 ¹⁴C yr BP [2720-2350 cal yr BP]. The glacier then retreated, but it advanced again ca. 1860 ¹⁴C yr BP [1870-1720 cal yr BP] and 1610 ¹⁴C yr BP [1540-1420 cal yr BP]. For the next 1500 years, Castle Creek Glacier terminated downvalley of its AD 1946 position. An age of 930±15 ¹⁴C yr BP obtained from wood below till 200 m upvalley from the outermost Little Ice Age moraine sugests that an early Little Ice Age advance was undeway by AD 1140-1260. Holocene glacier fluctuations in the Cariboo Mountains are broadly similar to those documented in the Coast and Rocky mountains, and our data also indicate that the First Millennium Advance was comparable in magnitude to advances of the Little Ice Age.