The goal of this collaborative project to reconstruct late Quaternary climate and glacier change in Arctic Alaska, one of few regions in the Arctic where mountain glaciers have left physical records of their former extent, making it valuable for comparing the timing and extent of mountain glacier variability between the lower latitudes and the Arctic. Several features of the climate and glacier history of the Brooks Range contrast with those from the North Atlantic region (which is often taken to represent the entire Northern Hemisphere in records of climate change) and currently available evidence indicates that the history of the Brooks Range more closely resembles glacier records from the southern Hemisphere. The investigators propose to develop records of climate change from lake sediments and records of glacier fluctuations using proglacial lake sediments and beryllium-10 dating of glacial features to address questions centered around four intervals of pronounced global change: (1) Last Glacial Maximum: Did glaciers retreat and temperatures increase in Arctic Alaska during the global LGM, as has been simulated by climate models? (2) Deglaciation: To what extent did climate change in Arctic Alaska coincide with North Atlantic climate fluctuations during deglaciation? (3) Holocene Glaciation: What was the extent of glaciers during (a) the Holocene thermal maximum, and (b) Neoglaciation? (4) Little Ice Age: Was it wetter or drier in the Brooks Range? The research will take place in suitable valleys (floatplane accessible valley with extant glaciers) in the north­central Brooks Range. The project has several educational components, including support four graduate students and several undergraduate students and visits to the community of Anaktuvuk Pass to deliver presentations on climate research and the Brooks Range. The proposed research aims to produce well-dated and quantitative records of glacier and climate variability in the northernmost glaciated region of the U.S. Documenting the past behavior of arctic glaciers when subject to extreme climate events during the late glacial period and warm intervals like the Holocene can provide valuable insight to help better predict responses to future change.

Project Report

The main goal of the project is to reconstruct Pleistocene and Holocene alpine glacier activity in two valleys of the northern Brooks Range, Alaska. My role in this project was to coordinate the collection and interpretation of acoustic profile data in several proglacial lakes in the field area: Cascade Lake, Karupa Lake, Shannin Lake and Shannin Pond. The acoustic profiling was conducted in July 2012 to document overall basin bathymetry, to document total sediment thickness and to assess the lateral continuity of specific stratigraphic units in each of the four lakes studied. The ultimate goal of the acoustic seismic research was to facilitate selection of the optimum core sites based on bathymetry and the completeness of the stratigraphic record. A Knudsen dual frequency (12 and 200 khz) echosounder was used for the data collection deployed on a surfboard and towed alongside an inflatable boat. A series of longitudinal and transverse transects were made across each of the four basins. The position of each transect was recorded with GPS tracking software using an iPad. We commonly documented greater than 14 meters of layered lacustrine sediment in the proglacial lakes (see figures) and at least three meters in Shainin Pond. The acoustic signal typically thinned over bathymetric highs (affording a compressed stratigraphic record) and thickened in the bathymetric basins (affording an expanded stratigraphic record ). The acoustic record was generally lost as we approached the delta front (probably a function of textural changes) and periodically the records would "wash-out" due to interstitial gas in the sediment. In this way, the acoustic profiling will be used to avoid gas charged sediment and thereby core deformation associated with core recovery in these areas. In one lake basin (Karupa) we documented what appears to be evidence of lake level lowering – inclined layers are truncated by horizontally layered mud at a stratigraphic depth of 2 meters and a 6m depth below the present lake-level. We plan to test this hypothesis by recovering a transect of core to document textural changes that may represent lake level lowering. Lower lake levels would indicate dryer than present conditions during the Holocene and would be an exciting contribution to our understanding of Holocene climate variability. The acoustic seismic transects were utilized in the subsequent spring coring season (April 2013) by collaborating PI’s Jason Briner (U Buffalo), Darrell Kaufman (Northern Arizona Univ.) , and Billy D’Andrea (Lamont Doherty Geological Observatory) and graduate students to determine sediment coring sites.

National Science Foundation (NSF)
Division of Polar Programs (PLR)
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Henrietta N. Edmonds
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Bates College
United States
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