Arctic biogeochemical and optical properties of dissolved organic matter across river to sea gradients
Arctic biogeochemical and optical properties of dissolved organic matter across river to sea gradients
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DOI：
10.3389/fmars.2022.949034
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
M. Novak;A. Mannino;J. B. Clark;P. Hernes;M. Tzortziou;R. Spencer;A. Kellerman;Brice K. Grunert
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文献类型：
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作者：
M. Novak;A. Mannino;J. B. Clark;P. Hernes;M. Tzortziou;R. Spencer;A. Kellerman;Brice K. Grunert
由于降水和融雪时间的变化，北极景观正在变暖和变得更加湿润，从而改变了季节性径流和河流流量模式。这些水文变化导致陆地溶解有机物 (DOM) 向北极沿岸海域的动员和运输增加，从而对生物地球化学循环产生重大影响。在这里，我们展示了育空河至白令海系统中溶解有机碳 (DOC) 和发色 DOM (CDOM) 以及阿拉斯加北坡流入波弗特海的两条河流羽流的测量结果。我们的采样表征了育空河-白令海系统在河流高流量和低流量期间 DOM 的光学和生物地球化学特性。育空河多个河口的平均 DOC 浓度范围为 2019 年淡水上升肢期间（5 月下旬）的最高值 10.36 mg C L-1，2019 年淡水下降肢期间（6 月下旬）的 6.4 mg C L-1，以及 2018 年 8 月河流流量低时的最低值 3.86 mg C L-1。 412 nm 处的 CDOM 吸收系数（a CDOM(412)) 平均分别为 8.23 m-1、5.07 m-1 和 1.9 m-1。尽管从育空河下游到北白令海以及北坡系统的 DOC 浓度下降了一个数量级，但基于 DOC 与 CDOM 特性关系的几种模拟 DOC 浓度的方法证明了这些北极沿海系统的跨系统季节和空间鲁棒性。从育空河三角洲到诺顿湾的 DOC 和 CDOM 的“快照”通量是根据我们的测量值计算出来的，并根据上游 USGS 河流测量数据模拟了水通量。我们的研究结果表明，在河流高流量期间，DOM 到达三角洲时基本上没有受到输入或物理和生物地球化学处理的改变，并且育空河 DOM 的转化主要发生在羽流中。然而，在夏季流量较少期间，包括局部降水事件、微生物分解、光化学和其他可能的过程在内的多种过程可能会在流入诺顿湾之前改变育空河下游和三角洲内的 DOM 特性。
Arctic landscapes are warming and becoming wetter due to changes in precipitation and the timing of snowmelt which consequently alters seasonal runoff and river discharge patterns. These changes in hydrology lead to increased mobilization and transport of terrestrial dissolved organic matter (DOM) to Arctic coastal seas where significant impacts on biogeochemical cycling can occur. Here, we present measurements of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) in the Yukon River-to-Bering Sea system and two river plumes on the Alaska North Slope which flow into the Beaufort Sea. Our sampling characterized optical and biogeochemical properties of DOM during high and low river discharge periods for the Yukon River-Bering Sea system. The average DOC concentration at the multiple Yukon River mouths ranged from a high of 10.36 mg C L-1 during the ascending limb of the 2019 freshet (late May), 6.4 mg C L-1 during the descending limb of the 2019 freshet (late June), and a low of 3.86 mg C L-1 during low river discharge in August 2018. CDOM absorption coefficient at 412 nm (a CDOM(412)) averaged 8.23 m-1, 5.07 m-1, and 1.9 m-1, respectively. Several approaches to model DOC concentration based on its relationship with CDOM properties demonstrated cross-system seasonal and spatial robustness for these Arctic coastal systems despite spanning an order of magnitude decrease in DOC concentration from the lower Yukon River to the Northern Bering Sea as well as the North Slope systems. “Snapshot” fluxes of DOC and CDOM across the Yukon River Delta to Norton Sound were calculated from our measurements and modeled water fluxes forced with upstream USGS river gauge data. Our findings suggest that during high river flow, DOM reaches the delta largely unaltered by inputs or physical and biogeochemical processing and that the transformations of Yukon River DOM largely occur in the plume. However, during low summer discharge, multiple processes including local precipitation events, microbial decomposition, photochemistry, and likely others can alter the DOM properties within the lower Yukon River and Delta prior to flowing into Norton Sound.