Numerical simulations of the competition between wind-driven mixing and surface heating in triggering spring phytoplankton blooms
Numerical simulations of the competition between wind-driven mixing and surface heating in triggering spring phytoplankton blooms
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DOI：
10.1093/icesjms/fsv071
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发表时间：
2015-08
影响因子：
3.3
通讯作者：
R. Enríquez;John R. Taylor
中科院分区：
文献类型：
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作者：
R. Enríquez;John R. Taylor
大约60年前，Sverdrup正式提出了临界深度假说，以解释春季浮游植物水华发生的时间与表面混合层的深度有关。近年来，一些改进和替代的临界深度假设已被提出，包括临界湍流假设的状态下，水华可以发生时，湍流混合是足够弱，而不管混合层的深度。在这里，我们研究风驱动的混合和净表面加热对浮游植物生长的相对影响。特别令人感兴趣的是，在冬季对流让位于地表净变暖之后，风驱动的混合是否可以推迟春季的水华。我们使用高分辨率的大涡模拟（LES）加上一个简单的浮游植物模型来解决这些问题。我们还描述了一个分析浮游植物模型与制定的湍流混合的LES结果的基础上。对于一个恒定的，规定的表面热通量，净浮游植物的增长被认为是当风应力小于一个临界值。同样，对于恒定的风应力，临界热通量将浮游植物种群增长和衰退的情况分开。使用LES的结果，我们的特征的临界风应力和临界热通量的其他物理和生物参数，并提出了一个简单的表达式为每个分析模型的分析的基础上。浮游植物生长开始时，混合深度浅滩以上的临界深度，符合临界深度假说。我们的研究结果提供了一个框架，以解释在其他条件下，湍流混合的深度和强度可能是影响浮游植物生长的关键因素的水华。
About 60 years ago, Sverdrup formalized the critical depth hypothesis to explain the timing of the spring phytoplankton bloom in terms of the depth of the surface mixed layer. In recent years, a number of refinements and alternatives to the critical depth hypothesis have been proposed, including the critical turbulence hypothesis which states that a bloom can occur when turbulent mixing is sufficiently weak, irrespective of the mixed layer depth. Here, we examine the relative influence of wind-driven mixing and net surface heating on phytoplankton growth. Of particular interest is whether wind-driven mixing can delay the spring bloom after winter convection gives way to net surface warming. We address these questions using high-resolution large-eddy simulations (LES) coupled with a simple phytoplankton model. We also describe an analytical phytoplankton model with a formulation for the turbulent mixing based on the LES results. For a constant, prescribed surface heat flux, net phytoplankton growth is seen when the windstress is smaller than a critical value. Similarly, for a constant windstress, a critical heat flux separates cases with growing and decaying phytoplankton populations. Using the LES results, we characterize the critical windstress and critical heat flux in terms of other physical and biological parameters and propose a simple expression for each based on the analysis of the analytical model. Phytoplankton growth begins when the mixing depth shoals above the critical depth, consistent with the critical depth hypothesis. Our results provide a framework to interpret blooms in other conditions where both the depth and the intensity of turbulent mixing might be crucial factors in influencing phytoplankton growth.