Modeling the Origin of the Particulate Organic Matter Flux to the Hypoxic Zone of Chesapeake Bay in Early Summer
Modeling the Origin of the Particulate Organic Matter Flux to the Hypoxic Zone of Chesapeake Bay in Early Summer
复制标题
模拟初夏切萨皮克湾缺氧区颗粒有机物通量的起源
DOI：
10.1007/s12237-020-00806-0
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发表时间：
2020-07
影响因子：
2.7
通讯作者：
Raleigh R. Hood
中科院分区：
文献类型：
--
作者：
Jinhua Wang;Raleigh R. Hood
虽然切萨皮克湾的缺氧已经得到了很好的研究，但很少有人关注可能导致初夏缺氧的颗粒物有机物（POM）的来源。采用高分辨率斜压物理模型和拉格朗日粒子跟踪模型相结合的方法，研究了切萨皮克湾中盐层深水通道中POM的来源。环流模式较好地再现了盐度结构和环流。采用快速搜索算法对粒子跟踪模型进行了改进，并在后向跟踪模型中引入了一种预测校正方法，以保证与前向跟踪的轨迹相似。反向跟踪结果表明，POM的路径与颗粒的跟踪起始时间和位置以及下沉速度的大小有很强的相关性。总的来说，POM轨迹的行为可以用切萨皮克湾中盐流主流的三维残余环流来解释。在发生缺氧的切萨皮克湾中上层深通道积聚的颗粒主要来自下游，当颗粒返回到表层时停止追踪。下沉速度为1 m/d时，下游源约占83.5%，下沉速度为25 m/d时，下游源所占比例下降至60.5%。颗粒沉降速度小于8 m/d时，东岸源大于西海岸源。此外，来自Potomac河口的颗粒沉降速度为1 m/d，对切萨皮克湾中盐层上部底部POM积累的贡献为7.4%。当颗粒在下沉之前停留在表面一段时间时，它们会回到切萨皮克湾上游，这表明来自上海湾的更长寿的难降解有机颗粒可能有助于有机质在深水通道的积累。这些结果有助于解释为什么上中盐湾深槽缺氧发生在初级生产最大值的北部，以及为什么与其他缺氧带相比，该地区缺氧时间更早、更严重。总体而言，模型结果表明，更多具有较高下沉速率的局部POM源在驱动氧气消耗方面最为重要。本研究提高了对POM的起源和途径的理解，POM可能有助于切萨皮克湾中盐深水通道缺氧的发展。未来的研究需要进行，以更好地了解在驱动氧气减少的过程中，遥远的有机物质来源与更本地的有机物质来源的相对重要性。
Although hypoxia has been well-studied in Chesapeake Bay, little attention has been given to the origin of the particulate organic matter (POM) that potentially contributes to early summer hypoxia. A combination of a high-resolution baroclinic physical model and a Lagrangian particle tracking model was used to study the sources of POM to the deep channel of the mesohaline Chesapeake Bay. The circulation model reasonably reproduced the salinity structure and circulation compared with observations. The particle tracking model was improved with a fast search algorithm, and a predict-correct method was developed in the backward tracking model to ensure a similar trajectory with the forward tracking. Backward tracking results revealed that the pathway of the POM has a strong dependence on the tracking initiation time and location of the particles, as well as the magnitude of the sinking speed. In general, the behavior of the POM trajectories can be explained by the three-dimensional residual circulation of the mesohaline mainstem Chesapeake Bay. The particles that accumulated in the deep channel of the upper mesohaline Chesapeake Bay where the onset of hypoxia occurs mainly come from downstream when particles stop tracking when they backtracked to the surface layer. Downstream sources accounted for roughly 83.5% of particles for a sinking speed of 1 m/day, and the proportion from the downstream decreased to 60.5% as the sinking speed increased to 25 m/day. In addition, the source from the eastern shore was larger than that from the western shore for particle sinking speed less than 8 m/day. Moreover, particles from the Potomac estuary with a sinking speed of 1 m/day can contribute 7.4% of the bottom POM accumulation in the upper mesohaline Chesapeake Bay. When particles were allowed to stay on the surface for a period before they sink, they backtracked to the upper Chesapeake Bay suggesting that more long-lived refractory organic particles originating from the upper Bay can contribute to organic matter accumulation in the deep channel. These results help to explain why hypoxia in the deep channel of the upper mesohaline Bay occurs to the north of the primary production maximum and also why hypoxia is earlier and more severe in this region compared to the rest of hypoxic zone. Overall, the model results suggest that more local sources of POM with relatively high sinking rates are most important in driving oxygen depletion. This study improves understanding of the origin and pathways of the POM that can potentially contribute to the development of hypoxia in the deep channel of the mesohaline Chesapeake Bay. Future studies need to be undertaken to better understand the relative importance of remote versus more local sources of organic matter in driving oxygen drawdown.
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