Doctoral Dissertation Research: Sunlight stimulates a spectrum of microbial CO2 production from permafrost carbon

我们需要更好地了解和减少温室气体排放，以实现《巴黎协定》将全球变暖控制在1.5摄氏度以内的目标。储存在北极永久冻土中的有机碳融化最终会产生二氧化碳(一种温室气体)。此外，据预测，随着全球变暖的加剧，这一过程将放大到未知的程度。因此，我们需要量化永久冻土融化释放的二氧化碳将在多大程度上放大全球变暖；这是北极科学家必须回答的最紧迫的问题之一。为了解决这一问题，该项目将进行测量，以量化融化的永久冻土中的有机碳流入阳光充足的北极地表水域时产生多少二氧化碳。该项目还将利用密歇根大学现有的一个名为地球营的项目，通过实践体验和户外活动让高中生了解环境科学。当水在融化的土壤中流动时，它会溶解有机碳。这些溶解的有机碳(DOC)然后流入溪流、池塘和湖泊。一旦进入地表水，微生物和阳光都会将DOC氧化成二氧化碳。与置于黑暗中的DOC相比，暴露在阳光下的DOC更容易被微生物氧化成二氧化碳。然而，到达地表水域的阳光跨越了从高能紫外线(UV)到低能可见光的各种波长。一个关键的未知因素是，从紫外线到可见光的哪些波长的阳光在帮助微生物将DOC氧化为二氧化碳方面最有效。如果可见光帮助微生物将更多的DOC氧化为二氧化碳，那么这一过程产生的二氧化碳可能是目前估计的两倍，因为到达地表水域的可见光比紫外线更多。此外，不同波长的阳光可能有助于微生物氧化一部分DOC，在没有阳光的情况下，微生物无法将其氧化为二氧化碳。这部分DOC很难氧化，可能是冻土中冻结了数千年的最古老的碳。该项目将通过测量在紫外线和可见光下微生物氧化永冻土DOC所产生的二氧化碳的量和放射性碳年龄，来测试阳光帮助微生物氧化古代永冻土DOC的效率。该项目的结果将能够预测古代永久冻土有机碳融化并输出到阳光充足的地表水域产生的二氧化碳，这是量化北极对全球变暖放大所需的关键知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

We need to better understand and reduce greenhouse-gas emissions to meet the Paris Agreement goal of limiting global warming to a 1.5 ºC increase. The thawing of organic carbon stored in Arctic permafrost soils ultimately creates carbon dioxide (a greenhouse gas). Further, this process is predicted to amplify with additional global warming, however, to an unknown extent. Therefore, we need to quantify the extent to which carbon dioxide released from thawing permafrost will amplify global warming; this is one of the most urgent questions that Arctic scientists must answer. To address this, this project will make measurements to quantify how much carbon dioxide is produced when organic carbon from thawing permafrost soils flows into sunlit arctic surface waters. The project will also leverage an existing University of Michigan program called Earth Camp to engage high school students about environmental sciences through hands-on experiences and outdoor activities.As water moves through thawed soil it dissolves organic carbon. This dissolved organic carbon (DOC) then flows into streams, ponds, and lakes. Once in surface waters, both microbes and sunlight oxidize DOC to CO2. DOC exposed to sunlight is easier for microbes to oxidize to CO2 compared to the same DOC kept in the dark. However, the sunlight reaching surface waters spans a spectrum of wavelengths, from the high-energy ultraviolet (UV) to the lower-energy visible light. A critical unknown is which wavelengths of sunlight from the UV to the visible are most efficient at helping microbes to oxidize DOC to CO2. If visible light helps microbes oxidize more DOC to CO2 than currently assumed, the CO2 produced from this process could be double the current estimate because there is more visible light reaching surface waters than UV light. In addition, different wavelengths of sunlight may help microbes oxidize a fraction of DOC that, in the absence of sunlight, microbes would not be able to oxidize to CO2. This fraction of DOC that is difficult to oxidize may be some of the oldest carbon that has been frozen for thousands of years in permafrost soils. This project will test how efficiently sunlight helps microbes oxidize ancient permafrost DOC by measuring the amount and radiocarbon age of the CO2 produced from microbial oxidation of permafrost DOC exposed to UV and visible sunlight. Results from this project will enable predictions of the CO2 produced from ancient permafrost organic carbon thawed and exported to sunlit surface waters, which is critical knowledge needed to quantify arctic amplification of global warming.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.