Monday, September 30, 2019,
Lovejoy / 100 Kassman Auditorium

The Arctic and subarctic oceans are experiencing rapid change as a result of climate warming and associated feedbacks. High latitude ecosystems are especially vulnerable to climate warming due to sea ice loss and related polar temperature amplification. Climate change may also impact nutrient cycling by impacting the sources and availability of iron and macronutrients to pelagic phytoplankton and their productivity.

For example, the North Pacific Ocean and the Bering Sea are characterized as a high nutrient, low chlorophyll (HNLC) regions due to limited iron inputs. Terrestrial iron sources include fresh and weathered volcanic ash as well as dust from both Asian deserts and regional glaciated catchments. To estimate the relative impact of these aerosol sources on ecosystems, we performed a suite of geochemical assessments following established protocols. We found that glacier-derived sediments have higher total iron content as well as three times higher easily-reducible iron than desert-derived dust samples. Results support previous work suggesting that mechanical weathering by glaciers produces iron that is more soluble and bioavailable than chemically-altered material from arid regions. In addition, we found that fractional iron solubility was higher in glacial sediment than volcanic ash. Despite well-documented evidence of phytoplankton blooms triggered by ash deposition, we found that volcanic ash contributed substantially less soluble and easily-reducible Fe, and contained a larger fraction of refractory Fe, than other aerosol sources. Together these results suggest that glacier-derived dust may provide the northeastern subarctic Pacific with more bioavailable iron per unit mass than either volcanic ash or desert-derived dust. As climate change continues to impact glaciers in the North Pacific region, we may expect to see changes in the supply of terrestrial nutrients delivered to the ocean ecosystem.

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