Advance of alpine glaciers during final retreat of the Cordilleran ice sheet in the Finlay River area, northern British Columbia, Canada

Abstract

Sharp-crested moraines, up to 120 m high and 9 km beyond Little Ice Age glacier limits, record a late Pleistocene advance of alpine glaciers in the Finlay River area in northern British Columbia. The moraines are regional in extent and record climatic deterioration near the end of the last glaciation. Several lateral moraines are crosscut by meltwater channels that record downwasting of trunk valley ice of the northern Cordilleran ice sheet. Other lateral moraines merge with ice-stagnation deposits in trunk valleys. These relationships confirm the interaction of advancing alpine glaciers with the regionally decaying Cordilleran ice sheet and verify a late-glacial age for the moraines. Sediment cores were collected from eight lakes dammed by the moraines. Two tephras occur in basal sediments of five lakes, demonstrating that the moraines are the same age. Plant macrofossils from sediment cores provide a minimum limiting age of 10,550–10,250 cal yr BP (9230±5014C yr BP) for abandonment of the moraines. The advance that left the moraines may date to the Younger Dryas period. The Finlay moraines demonstrate that the timing and style of regional deglaciation was important in determining the magnitude of late-glacial glacier advances.

Numerical simulations of the Cordilleran ice sheet through the last glacial cycle

“…Secondly, latent warming of the moisture-depleted air parcels flowing over this enhanced topography could have resulted in an inflow of potentially warmer air over the eastern flank of the ice sheet, thereby counterbalancing the potential continentality gradient discussed above through increasing melt along the advancing margin (cf. Langen et al, 2012). Because these two processes, both with a tendency to limit ice-sheet growth, are absent from our model, the eastern margin of the ice sheet and the position of the main meridional ice divide are certainly biased towards the east in our simulations (Seguinot et al, 2014).…”

Western Canadian glaciers advance in concert with climate change circa 4.2 ka

“…Radiocarbon ages from glacier forefields are supplemented with data gathered from proglacial Green, Lower Joffre, Diamond, and Red Barrel lakes (Figure 1), sites that we have studied in detail in the past [ Filippelli et al , 2006; Lakeman et al , 2008]. Glaciers today cover, respectively, 7%, 25%, 0%, and 5% of these four lakes’ watersheds.…”

“…Glaciers today cover, respectively, 7%, 25%, 0%, and 5% of these four lakes’ watersheds. At the peak of the Little Ice Age, glacier cover in the four watersheds was 12%, 30%, 16%, and 14% [ Filippelli et al , 2006; Osborn et al , 2007; Lakeman et al , 2008]. Sediment cores retrieved from the four lakes were analyzed for particle size, magnetic susceptibility, density, and water and organic matter content.…”

Deglaciation of the Cordillera of Western Canada at the end of the Pleistocene

“…Active ice probably persisted longest in high mountain valleys, but these remnant glaciers may have coexisted with large masses of dead ice in some areas of the British Columbia interior. Fulton, 1969 Disintegration of the Cordilleran Ice Sheet was interrupted repeatedly by glacier readvances (Alley and Chatwin, 1979;Clague, 1984Clague, , 1989Clague et al, 1997;Clague, 2002a, 2002b;Kovanen, 2002;Lakeman et al, 2008). Most re-advances affected relatively small areas and may not have been synchronous from one region to another.…”

“…Lakeman et al (2008) presented evidence that the Cordilleran Ice Sheet in north-central British Columbia thinned and in some areas transformed into a labyrinth of dead or dying ice tongues in valleys. During the Younger Dryas, however, alpine glaciers advanced downvalley and built moraines or coalesced with dead ice masses at lower elevations.…”