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Thesis Defense

Biogeochemistry of a glaciated fjord ecosystem: Glacier Bay National Park, Alaska

Monday, 17 November, 3:30 pm
Stacey Reisdorph, MS Oceanography Candidate
Faculty Advisor: Dr. Jeremy Mathis

Fairbanks—201 O'Neill • Juneau—103 Lena Point bldg.

Thesis Defense
Biogeochemistry of a glaciated fjord ecosystem: Glacier Bay National Park, Alaska
Monday, 17 November, 3:30 pm
Stacey Reisdorph, MS Oceanography Candidate
Faculty Advisor: Dr. Jeremy Mathis
Fairbanks—201 O'Neill • Juneau—103 Lena Point bldg.

Glacier Bay (GLBA) contains a pristine, glacially influenced ecosystem in Southeast Alaska that was carved out by the rapid retreat of the Glacier Bay Icefield thousands of years ago and the remaining glaciers continue to melt with their stores of freshwater draining into the bay. The runoff, especially that of tidewater glaciers, is low in total alkalinity (TA), which buffers seawater against decreases in pH. However, the influence of tidewater glaciers is not limited to just TA, as runoff is also low in macronutrients. This has the potential to impact the efficiency and structure of the marine food web within GLBA, which can be estimated using net community production (NCP). This is evident in the substantial spatial and temporal variability in our NCP estimates within GLBA and the varying uptake rates of carbon dioxide (CO2) from the atmosphere.
The burning of fossil fuels, coupled with land use and deforestation practices, has resulted in CO2 being emitted into the atmosphere and has led to increases in marine dissolved inorganic carbon (DIC) concentrations and a decrease in ocean pH, a process referred to as ocean acidification (OA). Increased concentrations of DIC can reduce saturation states (omega) with respect to biologically important calcium carbonate minerals, such as calcite and aragonite. The uptake of atmospheric CO2, coupled with the influx of low-TA glacial runoff presents potential hazards for calcifying organisms in GLBA. Although CO2 is currently thought to be the primary driver of omega and OA in the global ocean, we found that glacial runoff, especially that of tidewater glaciers, heavily impacts aragonite saturation states, with the main drivers of omega (DIC and TA) varying seasonally. The low-TA discharge reduces the buffering capacity of surface waters, enhancing the vulnerability of the estuary to further reductions in pH. Corresponding reductions in omega may cause these waters to become corrosive to shell-building organisms. In GLBA low omega values were well correlated with the timing of maximum glacial discharge events and most prominent within the two regions where tidewater glacial discharge was highest. This interplay between low TA glacier runoff and DIC concentrations, controlled largely by plankton populations, will be critical for determining the extent, duration and intensity of OA events in the future.