Possible refugia in the Alexander Archipelago of southeastern Alaska during the late Wisconsin glaciation

Abstract

The interpretation of the extent of late Wisconsin glaciation in southeastern Alaska has varied between geologists and biologists. Maps and reports of the region prepared by geologists commonly indicated that late Wisconsin ice extended as a large uniform front west to the edge of the continental shelf. However, the distribution of plants and animals in the region has led many biologists to suggest that there may have been ice-free areas that served as refugia during the late Wisconsin. Based on analyses of aerial photographs, topographic maps, and bathymetric charts, in conjunction with a review of previous literature and reconnaissance fieldwork throughout the region, this study presents data supporting a limited ice extent in the Alexander Archipelago during the late Wisconsin and identifies possible ice-free areas that may have served as refugia. These areas include (1) the Fairweather Ground, (2) the Herbert Graves Island area, (3) the western coast of southern Baranof Island and adjacent continental shelf, (4) Coronation Island and the adjacent continental shelf, (5) the Warren Island area, (6) the continental shelf from west of Heceta Island to Forrester Island in the south, (7) parts of the west coast of southern Dall Island, and (8) lowland areas in southern Prince of Wales Island. The identification of these possible refugia has bearing on the recolonization of the Alexander Archipelago, as they could have served as centers of biotic dispersal upon regional deglaciation and as stepping stones for early humans with a maritime tradition entering the western hemisphere from Asia.

Deciphering translocations from relicts in Baranof Island mountain goats: is an endemic genetic lineage at risk?

“…In our opinion, the distribution of the SNP is best explained by island-to-mainland dispersal during the initial glacial retreat when sea levels were lower (Josenhans et al 1995) and glaciers bridged islands. Portions of Baranof Island were ice-free during the last glacial maximum (Carrara et al 2007) and the area near Haines is recognized as a contact zone among biogeographic regions (Swenson and Howard 2005), including mountain goats (Shafer et al 2011). If the C haplotype arose prior to 1923 in a small, isolated population on the island, drift would have facilitated its fixation.…”

The Role of Temperature in the Distribution of the Glacier Ice Worm,Mesenchytraeus solifugus(Annelida: Oligochaeta: Enchytraeidae)

“…), 500-km-long Alexander Archipelago. The archipelago supports few, small alpine glaciers on only two of its 2000 islands (Carrara et al, 2007). The absence of ice worms on the well-studied Juneau Icefield (Miller and Pelto, 1999) at the northern end of the Boundary Range has long been puzzling, considering that available habitat is within the ice worm's temperature envelope.…”

“…We propose the following historical explanation. During prior glacial maxima, the Boundary Range was not coastal (Carrara et al, 2007), but separated from tidewater by 100 km of mountains consisting of the Alexander Archipelago embedded in the Cordilleran Ice Sheet (Fig. 1).…”

The last deglaciation of Alaska

“…1). Parts of the continental shelf were exposed by lower eustatic sea level (Carrara et al, 2007), and much of the evidence for LGM ice extent is now submerged due to postglacial sea level rise. It is thought that some portions of the continental shelf now submerged likely were ice free during the LGM (Carrara et al, 2003(Carrara et al, , 2007.…”