Impact of Photochemistry on Carbon Cycling in the Sea

物理和生物过程历来被认为是影响海洋碳循环的最重要因素。具体的过程包括气-海CO2交换、表面混合、深层沃茨排放、碳固定、呼吸作用、碳酸钙形成和沉积作用。最近 研究表明， 光引发的（光化学）过程也强烈地影响海洋表面的碳循环，特别是关于溶解有机碳（DOC）的光降解和细菌底物的产生。 老化的、生物难降解的DOC的光化学氧化的重要性的证据包括：1）无菌过滤的海水的照射导致CO2、CO和生物可利用的基质的高生产率，2）低生产率的中心环流似乎是净异养的（即，细菌C利用率通常超过初级生产率），3）细菌C利用率估计与开阔海洋表面沃茨中DOM光降解产生的生物不稳定底物的生产率大致相同，以及4）在表面沃茨中被开阔海洋细菌同化的碳的显著部分是同位素老化的。尽管有这些强有力的证据，光化学在海洋碳循环中的定量重要性仍然是未知的。 研究将侧重于：（1）海洋DOM光化学产生CO2和CO，（2）DOC的光化学损失，（3）微生物对光氧化DOM的吸收和再矿化。结果将评估光化学对碳通量和有机碳质量平衡的影响 在 的 水柱，包括初级 和 细菌生产力， 微生物呼吸， BATS站，微粒 碳 剂. 我们预计 细菌对光氧化老化DOM的利用可以在很大程度上解释高细菌C利用率和低初级生产率之间的显著差异，这种差异在低生产力沃茨中经常观察到。这项研究的另一个重要目标是开发基于行动的算法 光谱、DOM吸收和表面辐照度，以预测表面沃茨的光化学速率。这些算法结合遥感DOM荧光预测CO2和CO的光化学生产和DOC的光降解率在大面积的海洋。 以往在研究各种海洋环境中的光化学过程方面取得的成功为评估这些过程在海洋碳循环中的重要性奠定了坚实的基础。

Physical and biological processes are historically considered to be the most important factors affecting the carbon cycle in the ocean. Specific processes include air- sea CO2 exchange, surface mixing, venting of deep waters, carbon fixation, respiration, calcium carbonate formation and sedimentation. Recent studies now suggest that light- initiated (photochemical) processes also strongly impact carbon cycling at the sea surface, particularly with respect to the photodegradation of dissolved organic carbon (DOC) and the production of bacterial substrates. The evidence for the importance of photochemical oxidation of aged, biologically refractory DOC includes: 1) irradiation of sterile-filtered seawater results in high production rates of COz, CO and biologically utilizable substrates, 2) low productivity central gyres appear to be net heterotrophic (i.e., bacterial C utilization rates often exceed primary productivity rates), 3) bacterial C utilization rates are estimated to be about the same as the production rate of biologically labile substrates from DOM photodegradation in open oceanic surface waters, and 4) a significant fraction of the carbon assimilated by open ocean bacteria in surfaces waters is isotonically old. Despite this strong evidence the quantitative importance of photochemistry in the oceanic carbon cycle is still unknown. Studies will focus on: (1) the photochemical production of CO2 and CO from marine DOM, (2) the photochemical loss of DOC, and (3) the microbial uptake and remineralization of photooxidized DOM. Results will assess the impact of photochemistry on carbon fluxes and organic carbon mass balances in the water column, including primary and bacterial productivities, microbial respiration and, at the BATS station, particulate carbon fluxes. We expect Bacterial utilization of photooxidized, aged DOM may largely explain the appare nt discrepancy between high bacterial C utilization rates and low primary productivity rates that have been frequently observed for low productivity waters. Another important goal of this study is to develop algorithms, based on action spectra, DOM absorbance and surface irradiance, to predict photochemical rates in surface waters. These algorithms in combination with remotely sensed DOM fluorescence to Predict CO2 and CO photochemical production and DOC photodegradation rates over large areas of the ocean. Previous successes in studying photochemical processes in a variety of marine environments gives a strong foundation for assessing the importance of these processes in the oceanic carbon cycle.