Atmospheric mineral dust can be a significant source of iron for oceanic phytoplankton. Iron is essential for the fixation of nitrogen, a vital nutrient for primary productivity. However, many areas of the ocean, especially the open ocean, are labeled as high nutrient, low chlorophyll (HNLC) areas. It is believed that these regions have plenty of nutrients, but lack iron to facilitate primary production. We have designed experiments with the aim of understanding how atmospheric mineral dust, a major source of iron to the remote oceans, affects phytoplankton growth in both iron-enriched and iron-deficient environments.  Additionally, as nitrogen is a key nutrient for growth, we have also analyzed the effects of additional nitrates; both free and mineral-bound nitrates.  These studies are significant in understanding the source of micronutrients to HNLC regions as well as the effects of atmospheric heterogeneous chemistry, which commonly results in nitrated-coated mineral surfaces due to nitric acid uptake during atmospheric transport.               Experimental phytoplankton growth studies were performed under controlled growth conditions such that each culture was exposed to different environments, including the variability of nitrate sources and the presence of Fe-containing clay minerals commonly found in atmospheric mineral dust.  UV-Vis spectrometry was used to analyze the chlorophyll A concentrations using the trichromatic method over a period of approximately 50 days. Our results suggest that, in an iron-deficient environment, the dust provides a significant amount of iron for the phytoplankton to undergo primary production similar to what would be found in Fe-rich environments. In the iron-enriched environment, the iron contribution from mineral dust has little effect on the growth of the phytoplankton. Finally, the addition of free nitrates beyond the concentration found in the standard L-1 media resulted in depreciated growth rates.

Effects of Fe-containing clay mineral deposition on primary production

247th National Meeting (2014)

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