The distribution of oceanic biogeochemical tracers is fundamentally tied to physical dynamics at and below the mesoscale. Since global climate models rarely resolve those scales, turbulent transport is parameterized in terms of the large-scale gradients in the mean tracer distribution and the physical fields. Here, we demonstrate that this form of the eddy flux is not necessarily appropriate for reactive tracers, such as nutrients and phytoplankton. In an idealized nutrient-phytoplankton system, we show that the eddy flux of one tracer should depend on the gradients of itself and the other. For certain parameter regimes, incorporating cross-diffusion can significantly improve the representation of both phytoplankton and nutrient eddy fluxes. We also show that the efficacy of eddy diffusion parameterizations requires timescale separation between the flow and reactions. This result has ramifications for parameterizing subgrid scale biogeochemistry in more complex ocean models since many biological processes have comparable timescales to submesoscale motions.

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参数化生物地球化学示踪剂的涡流传输

海洋生物地球化学示踪剂的分布从根本上与中尺度及以下的物理动力学有关。由于全球气候模型很少解析这些尺度，因此根据平均示踪剂分布和物理场中的大尺度梯度将湍流传输参数化。在这里，我们证明这种形式的涡流不一定适用于反应性示踪剂，例如营养物质和浮游植物。在理想化的养分-浮游植物系统中，我们表明一种示踪剂的涡流应取决于其自身和另一种示踪剂的梯度。对于某些参数机制，结合交叉扩散可以显着改善浮游植物和养分涡流通量的表示。我们还表明，涡流扩散参数化的有效性需要流动和反应之间的时间尺度分离。这一结果对在更复杂的海洋模型中对亚网格尺度生物地球化学进行参数化具有影响，因为许多生物过程具有与亚中尺度运动相当的时间尺度。