As an essential parameter for all kinds of aquatic life, light influences life cycles and the behavior of various marine organisms. However, its primary role is that of a driver for photosynthesis and thus primary production, forming the basis of the marine food web. As a simplification when dealing with light, a common measure (e.g., used in biogeochemical models) is the photosynthetically active radiation (PAR), which integrates the spectral distribution of photon flux between 400 and 700 nm into a single value. While passing through the water column, light is attenuated by the water itself and its optically active substances (OAS) [e.g., phytoplankton, chromophoric dissolved organic matter (CDOM), and non-algal particles], summarized in the diffuse attenuation coefficient of downwelling radiation (Kd). Existing parameterizations for light attenuation in models often consider only phytoplankton as parameter, which is not sufficient for coastal areas where the contributions of CDOM and suspended mineral particles can be substantial. Furthermore, they mostly ignore the spectral variability of Kd by attenuating PAR with only a single coefficient. For this reason, this study proposes a parameterization of Kd that involves all relevant OAS and that attenuates PAR in three bands (trimodal approach). For this, the hyperspectral underwater light field was examined on three expeditions in different areas of the North Sea and along the British and Irish coasts. The derived Kd spectra were stepwise decomposed in the contributions of the different OAS and used in combination with direct OAS measurements to derive substance specific attenuation coefficients for the three bands. For comparison, also a monomodal and a spectral parameterization were developed. Evaluation showed that the trimodal approach was almost as accurate as the full spectral approach, while requiring only marginally more computational performance as the classical monomodal approach. Being therefore an excellent compromise between these factors, it can act as a valuable, yet computational affordable addition to biogeochemical models in order to improve their performance in coastal waters.

中文翻译：

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复杂沿海水域水下光的经验推导三峰参数化——北海案例研究

作为各种水生生物的基本参数，光影响生命周期和各种海洋生物的行为。然而，它的主要作用是驱动光合作用和初级生产，形成海洋食物网的基础。作为处理光时的一种简化，一种常见的度量（例如，在生物地球化学模型中使用）是光合有效辐射 (PAR)，它将 400 到 700 nm 之间的光子通量的光谱分布整合为一个值。在穿过水柱时，光会被水本身及其光学活性物质 (OAS) [例如浮游植物、发色溶解有机物 (CDOM) 和非藻类颗粒] 衰减，概括为下流扩散衰减系数辐射（Kd）。模型中现有的光衰减参数化通常只考虑浮游植物作为参数，这对于 CDOM 和悬浮矿物颗粒的贡献可能很大的沿海地区来说是不够的。此外，他们大多通过仅用单个系数衰减 PAR 来忽略 Kd 的光谱可变性。出于这个原因，本研究提出了 Kd 的参数化，它涉及所有相关的 OAS 并在三个波段中衰减 PAR（三峰方法）。为此，在北海不同地区以及英国和爱尔兰海岸的三个探险队中检查了高光谱水下光场。导出的 Kd 光谱在不同 OAS 的贡献中逐步分解，并与直接 OAS 测量结合使用，以导出三个波段的物质特定衰减系数。为了比较，还开发了单峰和光谱参数化。评估表明，三峰方法几乎与全谱方法一样准确，而只需要比经典单峰方法略高的计算性能。因此，作为这些因素之间的完美折衷，它可以作为生物地球化学模型的一种有价值但计算上负担得起的补充，以提高其在沿海水域的性能。评估表明，三峰方法几乎与全谱方法一样准确，而只需要比经典单峰方法略高的计算性能。因此，作为这些因素之间的完美折衷，它可以作为生物地球化学模型的一种有价值但计算上负担得起的补充，以提高其在沿海水域的性能。评估表明，三峰方法几乎与全谱方法一样准确，而只需要比经典单峰方法略高的计算性能。因此，作为这些因素之间的完美折衷，它可以作为生物地球化学模型的一种有价值但计算上负担得起的补充，以提高其在沿海水域的性能。