HOLOCENE GLACIATION OF ALASKA: 20 YEARS ON

It has been 20 years since publication of Parker Calkin's comprehensive review of Holocene glaciation in Alaska. Since then, multiple studies have reinforced his conclusion that fluctuations of land-terminating glaciers were broadly synchronous across this region. Glacier margins were largely retracted through much of the Holocene with major advances restricted to the last 3000 years. In southern Alaska, recent development of master tree-ring chronologies spanning the past two thousand years has enabled four distinct expansions to be distinguished, respectively culminating in the 6th to early 8th, late 13th, 15th to early 18th, and late 19th centuries AD. Tidewater termini in southern Alaska show a somewhat different picture, with expansions often out of phase with each other and with those of nearby land-terminating glaciers. This asynchronous response reflects non-climatic factors such as iceberg calving, sediment supply, fiord geometry and area-altitude feedbacks. Nonetheless, major tidewater glacier systems show progressively larger expansions in the late Holocene and retreats have largely been initiated during regionally recognized warm intervals, suggesting that climate is a significant control on the dynamics of these large ice masses.