Evaluating the Iron Geochemistry of Terrestrial Aerosol Sources to the Subarctic Pacific Ocean
Date of Award
Honors Thesis (Open Access)
Colby College. Geology Dept.
Bess G. Koffman
Walter A. Sullivan
Wind-blown dust and volcanic ash deposited in high nutrient, low chlorophyll (HNLC) regions can fertilize phytoplankton by providing iron and other trace nutrients, in turn impacting ecosystems as well as the global carbon and nitrogen cycles. The second largest HNLC region in the world is the northeastern subarctic Pacific. Aeolian transport to this region deposits lithogenic material including desert-derived dust from Asia, glacier-derived dust from Alaska and northwestern Canada, and volcanic ash from Eurasia and North America.
This research aims to assess the geochemistry of aerosol sources to the northeastern subarctic Pacific in relation to the biological availability of iron. The samples are glacier-derived sediment and volcanic ash from Alaska, which are compared to existing published data on desert-derived sediment from Asia. The total iron content determined by complete acid digestion is compared to the iron content by chemical species determined through sequential iron extractions. The geochemistry of these samples was investigated through mineralogy using X-ray diffraction, and iron solubility assessed in Milli-Q leaching experiments.
The glacier-derived sediments have higher total iron content (average 10.9 wt. % compared to 7.46 wt. %) as well as three times higher easily reducible iron (average 2.55 wt. % compared to 0.81 wt. %) than desert-derived dust samples. Fractional iron solubility was higher in glacial sediment (average cumulative 0.261 % FeS) than volcanic ash (cumulative 0.060 % FeS). 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.
iron, aerosols, HNLC, phytoplankton fertilization, volcanic ash
Recommended CitationYoder, Meg, "Evaluating the Iron Geochemistry of Terrestrial Aerosol Sources to the Subarctic Pacific Ocean" (2019). Honors Theses. Paper 919.