局部增强的垂直扩散率对由海底峡谷引起的示踪剂跨大陆架输送的影响
The impact of locally-enhanced vertical diffusivity on the cross-shelf transport of tracers induced by a submarine canyon
摘要：
沿海和公海之间的水、营养物和氧气交换是大陆架营养收支和生物地球化学循环的关键组成部分。在区域尺度上，海底峡谷增强了陆棚-陆坡物质交换和混合等物理过程。有很好的理解周围涌升海底峡谷的流量，但是，生物相关的示踪剂的流量是了解较少。这项工作调查的影响，海底峡谷的示踪剂和水的跨大陆架交换，考虑到本地增强混合的影响，在峡谷内，并开发一个缩放估计峡谷引起的示踪剂上涌，当地浓度成正比，垂直扩散率，和以前缩放的上涌通量。为此，我们进行了数值实验模拟一个理想化的峡谷附近的上升流事件，添加一个被动示踪剂与初始线性配置文件。我们改变了垂直涡动扩散率的地理分布及其大小，初始分层，科里奥利参数，和强度的传入流。我们发现，一个峡谷，宽度的货架长度的5%，上升到货架上的示踪剂质量比沿海上升流之间的25%至89%。局部增强的垂直扩散率有一个积极的影响，是平流上升流的示踪剂，可以增加峡谷上升流示踪剂通量高达27%。
英文摘要：
The exchanges of water, nutrients and oxygen between the coastal and open ocean are key components of on-shelf nutrient budgets and biogeochemical cycles. On a regional scale, submarine canyons enhance physical processes such as shelf-slope mass exchange and mixing. There is good understanding of the flow around upwelling submarine canyons; however, the flux of biologically relevant tracers is less understood. This work investigates the impact of submarine canyons on the cross-shelf exchange of tracers and water, taking into account the impact of locally-enhanced mixing within the canyon, and develops a scaling estimate for canyon-induced upwelling of tracers, proportional to local concentration, vertical diffusivity, and previously scaled upwelling flux. For that purpose, we performed numerical experiments simulating an upwelling event near an idealized canyon, adding a passive tracer with an initially linear profile. We varied the geographic distribution of vertical eddy diffusivity and its magnitude, the initial stratification, Coriolis parameter, and the strength of the incoming flow. We find that a canyon, of width 5% of the length of the shelf, upwells between 25 to 89% more tracer mass onto the shelf than coastal upwelling. Locally-enhanced vertical diffusivity has a positive effect on the tracer that is advected by the upwelling flow and can increase canyon-upwelled tracer flux by up to 27%.
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