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

北冰洋每单位体积接收的陆源溶解有机物（DOM）最多。目前，我们对控制这个DOM池的转换和命运的过程知之甚少。中低纬度研究表明，海洋表面阳光引发的光化学可能在处理陆地溶解有机碳（DOC）中发挥重要作用，直接将DOM氧化为小无机碳分子（例如，CO2和CO），并通过使生物学上难降解的DOM对细菌代谢攻击不稳定。DOM的光转化也可以通过直接将生物抗性溶解有机氮（DON）转化为生物可利用的无机氮（例如，铵、亚硝酸盐）和/或通过增强细菌对无机营养物的需求。在北极和亚北极海洋的陆地DOM循环的光化学的影响被认为是微不足道的，由于低太阳角和广泛的季节性和全年的冰盖。然而，由于北方高纬度地区可能已经出现气候变暖和平流层臭氧减少的情况，这一情况可能会发生变化。气候变暖减少了冰盖范围和冰层厚度，而平流层臭氧减少增加了到达海面的紫外线辐射;这两者的结合增加了穿透水柱的太阳辐射。通过在北极（麦肯齐陆架和勒拿河三角洲）和亚北极（哈德逊湾）海域进行三次实地调查，本研究旨在（1）定量评估光化学对北极和亚北极海洋生态系统中陆地DOC归宿和无机氮循环的影响，（2）预测气候变暖和平流层臭氧减少对这些影响的影响。

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.