TWO PROXIES ARE BETTER THAN ONE: THE LACUSTRINE AND TERRESTRIAL EVIDENCE OF HOLOCENE GLACIER FLUCTUATIONS IN THE SOUTHERN COAST MOUNTAINS, BRITISH COLUMBIA, CANADA

Terrestrial and lake-based records have been widely used in North America and elsewhere to reconstruct Holocene glacier fluctuations. But there have been few studies that have exploited the strengths inherent in each type of record to supplement weaknesses present in the other. We utilize both methods to reconstruct the behavior of alpine glaciers in the southern Coast Mountains of British Columbia during the Holocene. Terrestrial proxies include moraines and radiocarbon ages from sheared and detrital wood collected in glacier forefields. This direct yet temporally incomplete evidence is supplemented with proglacial lake-sediment records from six lake basins that register continuous changes in clastic sedimentation through time. Trends in glacigenic sedimentation are constrained with radiocarbon ages and volcanic tephras, and by varve counting. Taken together, the terrestrial and lake-sediment records indicate: a) an advance of at least one cirque glacier prior to 9680 14C yr BP that was slightly more extensive than advances of the Little Ice Age; b) a minor advance of glaciers that coincides with the 8200-yr cold event; c) growth of glaciers at ca. 3200 14C yr BP to lengths comparable to LIA extents; and d) advance of some glaciers to their maximum downvalley positions at ca. 2700-2300 14C yr BP and 1600-1900 AD. The correspondence between these proxies is less certain for the interval 6000-5000 14C yr BP given the lack of suitable dating control in the lake-sediment cores.

The terrestrial and lake-sediment records indicate glaciers fluctuated on century time scales through the Holocene. This variability, however, is superimposed on a long-term trend of glacier expansion from early Holocene to present.

The advantage afforded by the tandem use of both proxies is the ability to infer changes in glacier extent as well as reconstruct the frequency or timing of glacier advances.