AN ABRUPT AND SEA-ICE DRIVEN LIA EXPANSION OF DRANGAJÖKULL, VESTFIRÐIR, ICELAND
We illustrate Drangajökull’s LIA aerial extent from 1) sediment fill of threshold lake cores and 2) moraines identified in a newly constructed DEM of the southern margin. Lake cores with pre-LIA sediment were measured for magnetic susceptibility (MS), density and organic proxies (TOC, TN, ∂13C, ∂15N, C/N). Abrupt increases in MS, decreased %TOC and increased C/N signify entrance of the ice cap into lake catchments under a cooling climate. These interpretations are supported by correlations to remotely sensed moraines identified in our DEM of the south margin. Secondly, we derive temporal constraint from 1) tephrochronology and 14C-dated macrofossils in the lake cores and 2) 14C-dating of dead vegetation revealed from beneath the receding ice margin. The latter defines past episodes of persistently cooler summer temperatures that favored ice cap expansion until modern warmth forced marginal recession. Our results suggest regional cooling and subsequent ice cap expansion occurred initially at ~150 AD with intensification at ~1250 and ~1550 AD, culminating in the 19th century. Marine sea ice reconstructions and documentary evidence from the north shelf show increased presence of sea ice coincident with our LIA reconstructions, suggesting sea ice played a role in this particular cooling event.