Map of glacial limits and possible refugia in the southern Alexander Archipelago, Alaska, during the late Wisconsin glaciation

During the late Wisconsin glaciation (circa 26,000-13,000 carbon-14 yr
BP) the Cordilleran glacier complex formed vast ice fields and large
glaciers along the crest of the Coast Mountains. As these glaciers
flowed west to the Pacific Ocean, they were joined by local glaciers
originating on the higher reaches of the Alexander Archipelago (Mann
and Hamiltion, 1995). This extensive volume of ice was channeled into
deep troughs (present-day fiords) that formed major outlet glaciers,
such as the glaciers that occupied Chatham Strait and Dixon Entrance.
In several places along the coast, deep glacially scoured submarine
troughs indicate that glaciers reached to the edge of the continental
shelf. For instance, the glacier that extended into the Dixon Entrance
trough is known to have extended to the edge of the continental shelf.
Its retreat began sometime after 16,000-15,000 carbon-14 yr BP (Barrie
and Conway, 1999).
The exact extent of late Wisconsin cordilleran ice in southeastern
Alaska is poorly known. Small-scale maps and reports of the region
commonly show or imply ice extending west to the edge of the
continental shelf (Capps, 1931; Coulter and others, 1965; Flint, 1971;
Pewe, 1975; Denton and Hughes, 1981; and Prest, 1984). These maps
relied heavily on earlier work, much of it of a reconnaissance nature.
The map shows our interpretation of the limit of the Cordilleran ice
sheet, which is more restricted than previous estimates, and possible
refugium (an area that escaped the extensive glaciation of the late
Wisconsin and so provided a suitable habitat for relict species) in the
southern Alexander Archipelago during the late Wisconsin glaciation.
In addition to the analysis of the bathymetric map, the limits of the
Cordilleran ice sheet and possible refugia were also identified by
analyses of aerial photographs, USGS topographic maps (1:63,360 and
1:250,000 scales), NOAA bathymetric charts (1:20,000 and 1:40,000
scales), previous literature, and reconnaissance fieldwork throughout
the region. Ice-free areas that may have served as refugia include (1)
high mountain nunataks (too small to show at map scale), (2)
unglaciated ocean-facing slopes and forelands (Dahl, 1946), (3) the
outer islands of the Alexander Archipelago (Worley, 1980), and (4)
parts of the inner continental shelf exposed by the lowering of sea
level during the late Wisconsin by an estimated 125 m (Bard and others,
1990).