The impact of dissolved organic matter photochemistry on the carbon and nutrient cycling in arctic and subarctic marine ecosystems

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The Arctic Ocean receives the largest input of terrestrially derived dissolved organic matter (DOM) on a per unit volume basis. Currently, little is known of the processes controlling the transformation and fate of this DOM pool. Mid- and low-latitude studies suggest that sunlight-initiated photochemistry in the surface ocean likely play an important role in processing terrestrial dissolved organic carbon (DOC) by directly oxidizing DOM to small inorganic carbon molecules (e.g., CO2 and CO) and by labilizing biologically refractory DOM to bacterial metabolic attack. Phototransformation of DOM may also affect the nitrogen cycling by directly converting biologically resistant dissolved organic nitrogen (DON) to bioavailable inorganic nitrogen (e.g., ammonium, nitrite) and/or through enhancing bacterial demand for inorganic nutrients. The impact of photochemistry on terrestrial DOM cycling in Arctic and subarctic oceans has been assumed to be insignificant due to low solar angles and extensive seasonal and year-round ice cover. However, this may change as a consequence of climate warming and stratospheric ozone reduction that are possible already occurring over the high northern latitudes. Climate warming reduces ice cover extent and ice thickness while stratospheric ozone reduction increases the ultraviolet radiation reaching the sea surface; the combination of the two hence augments the solar radiation penetrating into the water column. By conducting three field surveys in Arctic (Mackenzie Shelf and Lena Delta) and subarcitc (Hudson Bay) seas, this proposed research is aimed at (1) quantitatively evaluating the impacts of photochemistry on the fate of terrestrial DOC and on inorganic nitrogen cycling in Arctic and subarctic marine ecosystems, and (2) predicting how climate warming and stratospheric ozone reduction over these regions affect these impacts.