Has Sverdrup's critical depth hypothesis been tested? Mixed layers vs. turbulent layers
Has Sverdrup's critical depth hypothesis been tested? Mixed layers vs. turbulent layers
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DOI：
10.1093/icesjms/fsu175
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发表时间：
2015-07-01
影响因子：
3.3
通讯作者：
Franks, Peter J. S.
中科院分区：
文献类型：
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作者：
Franks, Peter J. S.
Sverdrup（1953.浮游植物春季开花的条件。Journal du Conseil International pour l 'Exploration de la Mer，18：287 - 295）在阐述他的临界深度假设时相当谨慎，具体说明了一个“完全混合的顶层”，混合“足够强，可以将浮游生物均匀地分布在整个层中”。除了少数明显的例外，大多数随后的临界深度假设的测试都忽略了这些假设，使用水文定义的混合层深度的估计作为代理的实际浮游植物的浮游生物驱动的运动。然而，对湍流层中的湍流和分层的来源进行更仔细的研究表明，活跃湍流在小时的时间尺度、米的垂直尺度和公里的水平尺度上变化很大。此外，由温度或密度梯度定义的混合层对于活跃湍流的深度或强度来说是一个很差的指标。如果没有时间序列的一致，在现场测量湍流和浮游植物的比率，这是不可能正确地测试Sverdrup的临界深度假设。
Sverdrup (1953. On conditions for the vernal blooming of phytoplankton. Journal du Conseil International pour l'Exploration de la Mer, 18: 287295) was quite careful in formulating his critical depth hypothesis, specifying a "thoroughly mixed top layer" with mixing "strong enough to distribute the plankton organisms evenly through the layer". With a few notable exceptions, most subsequent tests of the critical depth hypothesis have ignored those assumptions, using estimates of a hydrographically defined mixed-layer depth as a proxy for the actual turbulence-driven-movement of the phytoplankton. However, a closer examination of the sources of turbulence and stratification in turbulent layers shows that active turbulence is highly variable over time scales of hours, vertical scales of metres, and horizontal scales of kilometres. Furthermore, the mixed layer as defined by temperature or density gradients is a poor indicator of the depth or intensity of active turbulence. Without time series of coincident, in situ measurements of turbulence and phytoplankton rates, it is not possible to properly test Sverdrup's critical depth hypothesis.