RELATIVE SEA LEVEL AND GLACIATION ALONG THE GULF OF ALASKA MARGIN

People may have first entered low latitude North America along the Pacific coast, but we still know little about the feasibility of this Northwest Coast Route at various times in the past. In the western Gulf of Alaska, glaciers advanced down Shelikof Strait to reach the outer continental shelf after 26.4 cal ka BP, and deglaciation occurred 17.6-18.2 BP. Near the tip of the Alaska Peninsula, deglaciation occurred before 16.5 BP. A post-glacial marine limit of ~25 m occurred on the Alaska Peninsula where LGM ice thickness had been 500-600 m. The absence of raised marine deposits on southwest Kodiak suggests sea level was never higher than today. A 1500-km gap in our understanding of glacial and RSL history extends from Kodiak to the Alexander Archipelago. At the northern end of the Alexander Archipelago, an outlet glacier terminated at the outer shelf edge during the LGM. North of there, along the outer coast of Glacier Bay National Park, glaciers terminated near the present coastline and retreated by 15 BP. Further south, LGM glaciers probably reached the outer shelf edge at major fjord mouths in the Alexander Archipelago but may not have covered intervening areas. The middle fjord zone was deglaciated by 13.8 BP, and inner fjords before 12.9 BP. On the outer coast, the post-glacial marine limit was near the level of today's high tide. In Icy Strait 130 km east of the outer shelf edge, RSL was 55 m above its present level at the time of deglaciation ca. 14 cal ka BP, but then fell rapidly and passed below present sea level before 13.5 cal ka BP. Further south, RSL more closely resembled the pattern at Haida Gwaii in northern British Columbia, where an isostatic crustal forebulge raised the land relative to the sea. In Sitka Sound, RSL was below -122 m prior to about 12.5 cal ka BP, while west of Prince of Wales Island, a transgression reached the present shoreline around 10.5 cal ka BP, and a highstand of about 16 m between 9.5 and 7.6 cal ka BP. In summary, continental shelves in the western Gulf of Alaska were probably ice-free and emergent by 17,000 BP. Timing may have been similar on the coast of Southeast Alaska. This is good news for the opening of a feasible coastal route early in postglacial times; however, the intervening 1500 km of coastline in the northern Gulf of Alaska remain terra incognita.