SEDIMENT ACCUMULATION ALONG A GLACIALLY IMPACTED MOUNTAINOUS COASTLINE - NORTHEAST GULF OF ALASKA

Tectonically active coastal regions of the world recently have been su ggested to supply the bulk of sediment from land to the oceans. Seabed sampling on the continental shelf and in coastal embayments of the no rth-east Gulf of Alaska (Alsek River to Prince William Sound) was perf ormed to examine the temporal and spatial variability of sediment accu mulation in a mountainous coastal setting. Cores of varying lengths (3 0-300 cm) were collected at 84 stations to provide information on sedi mentary processes using radiochemical (Pb-210 and Cs-137) techniques. Four types of Pb-210 activity profiles were observed, dominantly refle cting steady-state sediment accumulation. However, nonsteady-state pro files also were measured, resulting in part from episodic deposition n ear glacier-fed rivers and on the Copper River Delta. Sediment accumul ation rates in the eastern half of the study area are highest at midsh elf depths (approximate to 100 m) (greater than or equal to 10 mm yr(- 1)) and near rivers draining the Bering Glacier (approximate to 20 mm yr(-1)). On the Copper River Delta, sediment accumulation rates are hi ghest for the delta front (> 20 mm yr(-1)) and decrease westward along the sediment dispersal route. Total annual sediment accumulation is 9 0-140 x 10(6) tons yr(-1) on the shelf in the study area. Annual sedim ent accumulation for the total marine environment in the study area (i ncluding Icy and Yakutat Bays) exceeds 250 x 10(6) tons yr(-1), potent ially making this region the largest sink for sediment in North Americ a. Spatial patterns in sediment accumulation on the shelf are similar between centennial and Holocene time-scales, reflecting the dominance of the Copper River and Bering and Malaspina glaciers as sediment sour ces. Temporal variability in accumulation rates between centennial and Holocene time-scales exists for portions of the study area near hoods and demonstrates the considerable changes that occur in sediment supp ly during glacial advances and retreats.