2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 283-4
Presentation Time: 8:55 AM


HARNING, David, Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík, 101, Iceland; INSTAAR, University of Colorado, Boulder, CO 80303, GEIRSDÓTTIR, Áslaug, Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík, 101, Iceland, MILLER, Gifford H., INSTAAR and Geological Sciences, University of Colorado, Boulder, CO 80309-0450 and BELART, Joaquín M.C., Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavík, 101, Iceland; Laboratoire d'Etudes en Géophysique et Océanographique Spatiales, Université de Toulouse, Toulouse, 31400, France, dharning@gmail.com

In light of the Arctic’s sensitivity to recent warming, understanding the mechanisms behind natural and abrupt climate change remains a concern for future modeling projections. Here we focus on NW Iceland and the region’s largest ice cap, Drangajökull, to assess the nature of abrupt climate transitions in the northern North Atlantic. Holocene reconstructions from marine and terrestrial sites around Iceland demonstrate the sensitivity of the North Atlantic to both internal and external modes of climate variability however exact forcings remain debated. In this study, we use multiple and independent proxies to constrain the spatio-temporal extent of Drangajökull during the Little Ice Age (LIA), the most severe climate event of the Late Holocene. The ice cap’s coastal proximity and location between competing Atlantic and Arctic ocean masses also makes it an ideal target to investigate the role of dynamic ocean currents and sea ice export on abrupt cooling events.

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.