Biophysical processes that affect subsurface water clarity play a key role in ecosystem function. However, subsurface water clarity is poorly monitored in marine ecosystems because doing so requires in-situ sampling that is logistically difficult to conduct and sustain. Novel solutions are thus needed to improve monitoring of subsurface water clarity. To that end, we developed a sampling method and data processing algorithm that enable the use of bottom trawl fishing gear as a platform for conducting subsurface water clarity monitoring using trawl-mounted irradiance sensors without disruption to fishing operations. The algorithm applies quality control checks to irradiance measurements and calculates the downwelling diffuse attenuation coefficient, K_d, and optical depth, ζ– apparent optical properties (AOPs) that characterize the rate of decrease in downwelling irradiance and relative irradiance transmission to depth, respectively. We applied our algorithm to irradiance measurements, obtained using bottom-trawl-mounted archival tags equipped with a photodiode collected during NOAA’s Alaska Fisheries Science Center annual summer bottom trawl surveys of the eastern Bering Sea continental shelf from 2004 to 2018. We validated our AOPs by quantitatively comparing surface-weighted K_d from tags to the multi-sensor K_d(490) product from the Ocean Colour Climate Change Initiative project (OC-CCI) and qualitatively evaluating whether tag K_d was consistent with patterns of subsurface chlorophyll-a concentrations predicted by a coupled regional physical-biological model (Bering10K-BESTNPZ). We additionally examined patterns and trends in water clarity in the eastern Bering Sea. Key findings are: 1) water clarity decreased significantly from 2004 to 2018; 2) a recurrent, pycnocline-associated, maximum in K_d occurred over much of the northwestern shelf, putatively due to a subsurface chlorophyll maximum; and 3) a turbid bottom layer (nepheloid layer) was present over a large portion of the eastern Bering Sea shelf. Our study demonstrates that bottom trawls can provide a useful platform for monitoring water clarity, especially when trawling is conducted as part of a systematic stock assessment survey.

影响地下水净度的生物物理过程在生态系统功能中起关键作用。但是，在海洋生态系统中，对地下水的清晰度的监控很差，因为这样做需要进行后勤上难以维持的原位采样。因此，需要新的解决方案来改善对地下水的透明度的监测。为此，我们开发了一种采样方法和数据处理算法，可将底拖网渔具用作平台，使用拖网安装的辐照度传感器进行地下水的净度监控，而不会影响捕捞作业。该算法将质量控制检查应用于辐照度测量，并计算下扩散散射衰减系数K _d和光学深度ζ–表观光学特性（AOP），分别表征了向下辐射辐照度和相对辐照度向深度的透射率下降的速率。我们将算法应用于辐照度测量，该辐照度测量是使用底部拖网安装的档案标签获得的，该标签配备了光电二极管，该标签是在2004年至2018年美国国家海洋和大气管理局阿拉斯加渔业科学中心对白令海东部大陆架进行的年度夏季底部拖网调查中收集的。定量比较标签的表面加权K _d和海洋颜色气候变化倡议项目（OC-CCI）的多传感器K _d（490）产品，并定性评估标签K _d与耦合的区域物理生物学模型（Bering10K-BESTNPZ）预测的地下叶绿素a浓度模式一致。我们还检查了白令海东部水质清晰度的模式和趋势。主要发现是：1）从2004年到2018年，水的清晰度明显下降；2）周期性的，与比可可碱有关的最大K _d发生在西北大陆架的大部分地区，推测是由于地下叶绿素的最大值所致；3）在白令海东部大陆架的很大一部分上存在一个浑浊的底层（类肾上腺层）。我们的研究表明，底拖网可以提供一个有用的平台来监测水的清晰度，尤其是在作为系统库存评估调查的一部分进行拖网捕捞时。