Eolian Response to Little Ice Age Climate Change, Tana Dunes, Chugach Mountains, Alaska, U.S.A.

AbstractThe late Holocene history of eolian activity in a parabolic dune complex in the northern Chugach Mountains, Alaska, is reconstructed using 80 tree-ring dates and 5 radiocarbon ages. A radiocarbon age on detrital organics shows mobilization of sands about cal yr A.D. 1260. General forest growth over the dune field area indicates that this active interval was followed by dune stabilization by A.D. 1500. The present interval of dune migration activity, reconstructed from calendar dates and radiocarbon ages on buried trees, began as early as the late A.D. 1600s, was well under way by the mid–A.D. 1700s, and continues today at a diminishing rate. Intervals of increased eolian activity correspond with pulses of the Little Ice Age as reconstructed from a well-established glacial history for the region over the last 1000 yr. Century-scale cooling in climate appears to have forced dune activity through general geomorphic instabilities of nearby glacial and fluvial-lacustrine systems. Geomorphic activity includes a combination of dynamic fluvial incision of cutbanks and release of dormant dune sands, increased wind intensity, as well as internal feedback mechanisms associated with parabolic and blowout dune dynamics. Over the past 200 yr, average rates of dune migration between 1 to 3 m yr−1are estimated using tree-ring dating. Observations and tree ages along the dune margins suggest that vegetative cover may now be increasing and dune stabilization may be under way.