Abstract:
The Gulf of Alaska is a climatically sensitive and tectonically active region that also hosts one of the world’s most productive salmon fisheries. However, due to its remoteness and harsh climate, there are few long-term historical records of changing environmental conditions in this area. An extraordinarily thick sedimentary deposit (>150 m) in Prince William Sound offers the potential to preserve high-resolution paleorecords of these conditions. A suite of 11 gravity cores was collected within the Sound in order to determine the modern day sediment depositional trends and to develop elemental proxies for earthquakes and seasonal sedimentation using core scanning XRF elemental analysis in conjunction with geochronological, sedimentological and physical oceanographic studies. 210Pb/137Cs-derived sedimentation rates grain size trends indicate that there are two distinct sediment sources to the Sound; an allochthonous source of sediment that is advected into the Sound through Hinchinbrook Entrance, and an autochthonous source of sediment from the Columbia Glacier region of the northern Sound. Cyclic variations in grain size were identified in Hinchinbrook Entrance sediments using the XRF Sr/Pb ratio and were interpreted to be the result of seasonal sedimentation; with coarse-grained sediments deposited during the winter when storm-driven wave and currents in the nearshore region are high, and fine-grained sediments deposited during the summer when costal conditions are less energetic and when the discharge and transport of sediments from the Copper River is high. Gravity flow deposits from the northern Sound were identified as having a source from the Columbia Glacier region using the XRF K/Ca ratio. The gravity flows that caused these deposits were identified as being triggered by historically recorded earthquakes, which likely remobilized sediment on the steep slopes of the northern channel and which then flowed downslope to the south.
