Háskóli Íslands

Darren Larsen will give a lecture about his doctoral thesis in Geology on Monday 16th of September at 11:00. The thesis is titled: Holocene Climate Evolution and Glacier Fluctuations Inferred from Proglacial Lake Sediments at Hvítárvatn, Central Iceland.
This is a joint Ph.D. degree from the University of Iceland and the University of Colorado Boulder, with main defense taking place in Boulder, CO USA.
Instructors are Dr. Áslaug Geirsdóttir and Dr. Gifford H. Miller.

About the Doctoral Candidate:
Darren Jon Larsen grew up in southern New York State and received a B.A. degree from Colby College, Maine where he studied Geology and Biology. Following graduation, he worked for two years as an environmental educator and field instructor at the Teton Science Schools, Wyoming, where he taught field courses in Grand Teton and Yellowstone National Parks. Darren began is graduate studies in 2007 and is currently enrolled in a dual PhD program at the University of Colorado and the University of Iceland. His thesis research has been focused on Holocene paleoclimate and ice cap reconstructions in Iceland, working primarily with proglacial lake sediments to provide a framework for assessing current and future impacts of modern climate change occurring in the Arctic. During the course of his dissertation, Darren also completed a Masters degree in Hydrology, Water Resource Engineering, and Environmental Fluid Mechanics at the University of Colorado, as well as a graduate certificate in Hydrologic Sciences.

Abstract
Understanding the character and expression of past climate changes in response to discrete forcing mechanisms is prerequisite to a critical assessment of modern climate variability and to anticipating future changes to Earth’s climate system. In this dissertation, Holocene paleoclimate and glacier fluctuations in central Iceland are reconstructed using the varved sediment archive preserved in proglacial lake Hvítárvatn. Sediment cores retrieved from >35 locations throughout Hvítárvatn’s main basin are used in conjunction with seismic reflection profiles and multibeam bathymetric data to construct a detailed record of environmental conditions and the changing dimensions of the adjacent Langjökull ice cap (925 km2) for the past 10.2 ka.

Spatial and temporal changes in varve thickness reflect variations in the production and delivery of erosional products related to Langjökull fluctuations. A suite of environmental and glacier proxies reveal a dynamic Holocene terrestrial climate with abrupt and high magnitude changes in Langjökull size and landscape stability. All sedimentary proxies indicate glacier ice was absent from the catchment during the Holocene Thermal Maximum, between 7.9 and 5.5 ka. Neoglaciation is recorded as a step-like transition toward cooler summers, landscape destabilization, and the inception and expansion of Langjökull beginning ~5.5 ka, with notable increases in ice cap size and landscape instability at 4.2, 3.0, 1.4, and 0.7 ka.

Langjökull’s maximum Holocene extent occurred during the Little Ice Age (LIA), the most recent and severe climate anomaly of the Neoglacial period. Sediment yield calculated from decadal average varve thickness patterns reveals two main phases of Langjökull growth during the LIA, ca. 1400 to 1550 AD and ca. 1680 to 1890 AD. During Langjökull’s second and ultimate LIA advance, outlet glaciers Norðurjökull and Suðurjökull advanced into the lake and maintained calving margins. Sediment stratigraphy and physical characteristics indicate that while Norðurjökull advanced into the basin stably, Suðurjökull experienced a quasi-periodic series of eight surges, each of which resulted in fragmentation of the glacier terminus and advances of up to ~1.6 km in less than 2 years.

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