Late Quaternary Vegetation Dynamics of the Queen Charlotte Islands, Northern Vancouver Island, and the Continental Shelf of British Columbia

Paleoecological analyses and radiocarbon dating of late-Quaternary sediments from the Queen Charlotte Islands (QCI), northern Vancouver Island, and the continental shelf along the coast of British Columbia reveal substantial changes in vegetation and climate over the last 14,000 [superscript]14C yr (17,000 cal yr). Extensive portions of the shelf were subaerially exposed at the end of the last glaciation due to lowering of relative sea level by as much as 150 m. AMS radiocarbon ages indicate that the shelf in Hecate Strait was exposed between at least 14,330 and 12,860 [superscript]14C yr BP. Cyperaceae were locally abundant on the exposed shelf, and fossil Pediastrum algae indicate the presence of freshwater. Interpretation of pollen from late-glacial lake sediments in the southern QCI suggest a succession from herb tundra dominated by Cyperaceae to dwarf shrub tundra including Salix and Empetrum before the development of Pinus contorta woodland. Fossil stomata suggest that Pinus contorta grew locally by 13,040 +/- 305 [superscript]14Cyr BPI and an in situ Pinus stump and associated plant macrofossils demonstrate that forests grew on the adjacent shelf 12,200 [superscript]14C yr BP. Submerged lake sediments in Logan Inlet record the transition from Pinus contorta woodland to Picea forests about 11,200 [superscript]14C yr BP. Northern Vancouver Island also supported Pinus contorta woodland during the late-glacial period. Mixed coniferous forests dominated by Pinus contorta with Alnus and pteridophytes occupied the shelf north of Vancouver Island 10,500 [superscript]14C yr BP. Warming in the early Holocene allowed the northward extension of Pseudoiwga menziesiii, although Picea, Tsuga heterophylla, and Alnus rubra dominated regional forests. By 7500 [superscript]14C yr BPI shade-tolerant Tsuga heterophylla was the dominant forest tree. A cooler and wetter climate in the late Holocene facilitated development of temperate coniferous rainforest. This research, in combination with earlier studies, demonstrates that portions of the continental shelf were ice-free and vegetated between 14,300 and 9,500 [superscript]14C yr BP; moderate climatic conditions supported diverse and productive vegetation while adjacent mainland areas remained glaciated. Stratigraphic sequences spanning the last glaciation are still required to confirm the existence of continuous late Pleistocene glacial refugia in the QCI region.