• 60,000 year climate and vegetation history of Southeast Alaska

      Wilcox, Paul S.; Fowell, Sarah; Bigelow, Nancy; Mann, Daniel; Dorale, Jeffrey (2017-08)
      Sedimentological and palynological analyses of lacustrine cores from Baker Island, located in Southeast Alaska's Alexander Archipelago, indicate that glaciers persisted on the island until ~14,500 cal yr. BP. However, the appearance of tree pollen, including Pinus cf. contorta ssp. contorta (shore pine) and Tsuga mertensiana (mountain hemlock) immediately following deglaciation suggests that a forest refugium may have been present on ice-free portions of neighboring islands or the adjacent continental shelf. Sedimentological and palynological analyses indicate a variable climate during the Younger Dryas interval between ~13,000 and ~11,500 cal yr. BP, with a cold and dry onset followed by ameliorating conditions during the latter half of the interval. An eight cm-thick black tephra dated to 13,500 ± 250 cal yr. BP is geochemically distinct from the Mt. Edgecumbe tephra and thus derived from a different volcano. Based on overall thickness, multiple normally graded beds, and grain size, I infer that the black tephra was emplaced by a large strombolian-style paroxysm. Because the dominant wind direction along this coast is from the west, the Addington Volcanic Field on the continental shelf, which would have been subaerially exposed during the eruption, is a potential source. The similarity in timing between this eruption and the Mt. Edgecumbe eruption suggests a shared trigger, possibly a response to unloading as the Cordilleran Ice Sheet retreated. To complement the Baker Island lacustrine record, a speleothem paleoclimate record based on δ¹³C and δ¹⁸O values spanning the interval from ~60,000 yr. BP to ~11,150 yr. BP was recovered from El Capitan Cave on neighboring Prince of Wales Island. More negative δ¹³C values are attributed to predominance of angiosperms in the vegetation above the cave at ~22,000 yr. BP and between ~53,000 and ~46,000 yr. BP while more positive δ¹³C values in speleothem EC-16-5-F indicate the presence of gymnosperms. These data suggest limited or no ice cover above El Capitan Cave for the duration of the record, possibly indicating that this region was a nunatak during glacial periods.
    • Sand dune field paleoenvironment, paleoecology, and human environmental interaction in the middle Tanana River Valley near the Gerstle River, subarctic Alaska: the late glacial to the middle Holocene

      Bowman, Robert C.; Reuther, Joshua D.; Potter, Ben A.; Clark, Jamie L. (2017-08)
      This study was conducted to explore paleoenvironmental change within the Gerstle-Sawmill Dune Field (GSDF), located just west of the Gerstle River in the middle Tanana River valley, Interior Alaska from the late Glacial to the middle Holocene. Specifically, this study was undertaken to document human-environment interaction on the landscape. Geoarchaeological methods were used in order to determine the history of sand dune development across the area, how the local ecological systems changed through time, and determine prehistoric human use of environment and response to environmental and ecological change. The data collected from these locations was used to create a model for sand dunes and human land use regarding local ecological stability and dynamic sand dune deposition. Patterns of human land use within the GSDF were then compared with data collected from sites in proximity to the GSDF to determine how this portion of the environment operated within the larger geographic area. This geoarchaeological research aids in understanding ecological patterning within terrestrial lowland systems from the Late Glacial to the Middle Holocene, with regard to human land use dynamics within a changing geomorphological system.