PALEOECOLOGY OF A HOLOCENE BOG NEAR TIEDEMANN GLACIER, COAST MOUNTAINS, BRITISH COLUMBIA

Palynology, sedimentology, moraine stratigraphy, and radiocarbon ages are used to (1) reconstruct changes in Holocene vegetation and inferred climate at Tiedemann Glacier and (2) infer the extent, timing, and nature of the Tiedemann advance at its type locality. Moraine Bog is situated in the southern Coast Mountains at the transition between the Englemann Spruce Subalpine Fir (ESSF) and Mountain Hemlock (MH) biogeoclimatic zones. The bog is at the distal margin of the outermost Holocene lateral moraine of Tiedemann Glacier and contains a continuous sediment record extending back to the early Holocene. Three pollen zones span the period of interest in this study, from about 4500 ¹⁴C yr BP to present in Moraine Bog. The lowest of the three zones (ca.4500-3300 ¹⁴C yr BP) records a subalpine forest adjusting to a gradual cooling climate. Pollen of shrub alder (Alnus viridis) and other plants that inhabit disturbed landscapes become more abundant during the Tiedemann phase (ca. 3300-1900 ¹⁴C yr BP). This change likely records increasing moisture, decreasing temperature, and episodic landscape instability related to advances of Tiedemann Glacier. A modern subalpine plant assemblage, including spruce (Picea engelmanni), became established about 900 ¹⁴C yr BP. The Tiedemann glacial phase comprises at least three separate advances separated by intervals of less extensive ice cover. The first phase occurred before 2600 ¹⁴C yr BP. The second and most extensive advance occurred between about 2500 and 2300 ¹⁴C yr BP. The final advance happened after 1900 ¹⁴C yr BP. Sediments in Moraine Bog are dominantly peat, but include limnic gyttja as well as a silt layer deposited during the second Tiedemann advance when Tiedemann Glacier constructed its outermost moraine. The basal sediment in Moraine Bog is sand and silt deposited shortly after deglaciation ca.10,000 ¹⁴C yr BP. Tiedemann Glacier is the only glacier in the Coast Mountains that is known to have achieved its maximum Holocene extent during the Tiedemann advance.