Collaborative Research: Establishing Marine Varve Thickness as a Proxy for Annual Alaska Climate Variability and PDO Oscillations, Hubbard Glacier Field Study

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ABSTRACTCowanOPP-0327106Powell OPP-0327107 JaegerOPP-: 0326926 This is a collaborative proposal by Principal Investigators at the Appalachian State University, Northern Illinois University (NIU), and the University of Florida (UF). A major goal of Arctic science is to quantify the impact of recent climate change on threatened ecosystems and native cultures. In Alaska, this climate forcing by North Pacific (Pacific Decadal Oscillation (PDO); Aleutian Low Pressure (ALPI), and Arctic Oscillation (AO) climate systems is most strongly manifested in decadal-long shifts in Arctic (60degrees-90degreesN) air temperature and precipitation. This has led to pronounced changes in regional oceanography and noticeably in the accelerated melting of Alaskan glaciers, which has been shown to have a global impact on sea-level rise and perhaps on regional freshwater input to the Bering Sea from the Gulf of Alaska. However, the timing and forcing of glacial melting cannot be established, because there are few annual records of meltwater discharge directly from large cliff-calving glaciers to test how glacier melt varies in response to high-frequency climate change over the last two decades.Intellectual Merit: This research will generate annually-resolved climate records in an area where forcing by the PDO and ALPI is strongest and the impact is likely to affect threatened Arctic ecosystems by establishing a correlation between marine varve thickness and local meteorological forcing. Analysis of the proxy climate record at Hubbard Glacier, the largest tidewater glacier in North America, will allow evaluation of what climate variables or indices most closely correlate with annual release of sediment and meltwater. The Hubbard is an ideal glacier for a field study because it is relatively stable, is located in a climatically sensitive region, and there is a long (50+ year) monthly record of local climatology in Yakutat, AK. Annual varves form in proglacial basins adjacent to large tidewater glacier systems along the Gulf of Alaska coast and consist of summer deposition of meltwater-produced laminated mud following winter deposition of a diamicton produced by iceberg rafting. The hypothesis to be tested is that the thickness of the laminated unit is a proxy for summer meltwater discharge from Hubbard Glacier. Preliminary analysis of varve thickness shows a correlation between PDO, ALPI, and sedimentation rate, such that the negative (cold-phase) PDO index correlates with higher winter snowfall leading to increased meltwater discharge later in the summer melt season. After a 1989 regime shift, the varve record also correlates with higher summer precipitation, a characteristic of the post-1989 ALP index. By using these relationships, a 20-year long hypothetical varve record has been produced for testing by collecting ~30 piston cores from Disenchantment Bay. Sedimentological and radiochemical techniques will establish varve thickness and chronology. High resolution seismic reflection profiles will be collected to increase spatial coverage and correlation, which will address how varve thickness varies as a function of distance from the sediment source. The Broader Impacts will include improved understanding of the role of glacial melting in influencing the freshwater discharge to the Gulf of Alaska, which plays a critical role in the health of fisheries within the Gulf of Alaska and Bering Sea. This proposal also emphasizes collaboration among researchers at various stages of their careers, including five undergraduate students, and several graduate students at UF and NIU, to train students in the earth sciences. This project will also contribute to citizen outreach by establishing a partnership with a regional science center in Western North Carolina to produce a photographic display and a lecture series to communicate Arctic climate change as well as methods used to study tidewater glaciers to an adult audience. Two of the reviewers are not convinced that the results of this project will be of large scale significance. They realize that understanding the recent record of meltwater discharge as a function of specific environmental variables is important, as described on page C-10 for example, but this just does not seem important enough. They think that a longer term perspective should have been a stronger and more prominent element of this proposal - with perhaps a smaller effort on the short record and a greater effort on longer records. While the short record is critical for developing the tools to interpret older records, they recommend that this be taken into consideration should this project be funded for only a single field season. Perhaps this should have been written as a three year project, with two field seasons, and more discussion of why and how a longer term data set would help us put modern day glacial retreat into perspective.