The role of topography in cross-shelf-break tracer exchange

地球的自转及其科里奥利力限制了沿海海洋和深海之间的水交换。这种有限的交换往往表现为搁架断裂位置附近水性质的重大变化，如颜色。各种进程可以打破这些动态约束，允许交换流动。其中之一是由水下峡谷等小尺度地形造成的。 在以前的研究中，我们已经确定了通过海底峡谷流入大陆架的水量和深度。通过峡谷的平流增强是重要的，但更重要的是，它来自更深的深处，而不是在没有峡谷的情况下。在这笔赠款中，我们建议对通过海底峡谷运输的特定、重要示踪剂的数量进行量化。这些示踪剂包括硝酸盐、溶解的无机碳和含低氧的水。硝酸盐和无机碳随着海洋深度的增加而增加，北太平洋的氧气减少到约500m的深度。从水柱深处平流到陆架，意味着更多的硝酸盐和碳，而更少的氧气。 硝酸盐是浮游植物生长的限制性营养物质，浮游植物是构成海洋食物链底部的单细胞光合作用生物。有必要对其通量进行量化，以确定将食物的可获得性改变为更高的营养水平，并通过鱼类。低氧水的平流导致缺氧，从而导致底栖生物死亡(所谓的“死区”)。尽管大部分氧气的利用是由于陆架过程，但如果流入陆架的水最初含氧量较低，最终达到的最低含氧量将会更低。溶解的无机碳平流到陆架上，可以上升，增加二氧化碳进入大气的通量。通过这一途径量化通量的数量是确定沿海海洋在碳循环中所起作用的一部分。

The rotation of the Earth, and its Coriolis force, limit the exchange of water between the coastal ocean and the deep ocean. This limited exchange is often illustrated by significant changes in water properties, such as colour, near the location of the shelf-break. Various processes can break these dynamical constraints and allow exchange flow. One of these is caused by small scale topography such as underwater canyons. In previous research, we have determined the amount and depth of water which flows onto the shelf through submarine canyons. The enhanced advection through canyons is significant but more importantly it comes from deeper depths than occurs in the absence of canyons. In this grant we propose to quantify the amount of specific, important tracers that are transported through submarine canyons. These tracers include nitrate, dissolved inorganic carbon, and water containing low oxygen. Nitrate and inorganic carbon increase with depth in the ocean and oxygen decreases in the North Pacific to depths of about 500 m. Advection onto the shelf from deeper in the water column thus implies more nitrate and carbon and less oxygen. Nitrate is a limiting nutrient for phytoplankton growth, the one-celled photosynthetic organisms that form the bottom of the ocean food chain. Quantifying its flux is necessary to determine changes food-availability to higher trophic levels and through to fish. Advection of low oxygen water contributes to anoxia which causes benthic die-offs (so called ``dead zones''). Even though much of the oxygen utilization is due to shelf processes, if the water advected onto the shelf is initially low in oxygen, the final minimum oxygen levels reached will be lower. Dissolved inorganic carbon advected onto the shelf can be upwelled and increase the flux of carbon dioxide to the atmosphere. Quantifying the amount of flux through this pathway is part of determining the coastal ocean's role in the carbon cycle.