Abstract New production of organic matter from photosynthesis based on “new” nitrate transported into the illuminated surface layer fuels temperate ecosystems during periods of stratification when surface waters are nutrient limited. Published observations from the northeastern North Sea show a large spatial heterogeneity in vertical nitrate fluxes and suggest shelf edge mixing may be the major source for new production here during the stratified summer season. In the current study, we further investigate these empirical findings with a numerical model, where physical transports and mixing are evaluated against observations of temperature, salinity, nutrients and dissipation of turbulent kinetic energy. The relatively shallow central North Sea is separated from the deep Norwegian trench by a strong shelf edge current. This shelf edge frontal zone is characterized by a vertical separation of the surface and benthic boundary layers by an intermediate layer exhibiting low turbulence. A new nitrate assimilation model, driven by light and nitrate availability, is developed and applied for quantifying the potential for, and distribution of, new production in the area. New production in the frontal zone above the shelf edge is located in a narrow high productive (~100 mg C m−2 day−1) band. This is in qualitative accordance with observations. The model results also suggest, however, that new production of similar magnitude occurs above the deep Norwegian trench, where a shallow nutricline in combination with mesoscale eddy activity leads to increased transport of nitrate to the surface layer. Increased new production along the shelf edge could potentially impact ecosystem structure and may explain the relatively high species richness and fishing activity recorded in this part of the North Sea.

中文翻译：

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北海东北部陆架边缘夏季分层新产量

摘要 在地表水养分有限的分层时期，基于“新”硝酸盐运输到受光照表层的光合作用产生的新有机物质为温带生态系统提供燃料。来自北海东北部的已发表观测表明，垂直硝酸盐通量存在很大的空间异质性，表明陆架边缘混合可能是夏季分层期间新产量的主要来源。在目前的研究中，我们使用数值模型进一步研究了这些实证结果，其中根据温度、盐度、营养物质和湍动能耗散的观察来评估物理传输和混合。相对较浅的北海中部被强大的陆架边缘流与深挪威海沟隔开。这个陆架边缘锋区的特点是表面和底栖边界层被一个表现出低湍流的中间层垂直分离。开发并应用了一种由光和硝酸盐可用性驱动的新硝酸盐同化模型，用于量化该地区新生产的潜力和分布。陆架边缘上方锋区的新产量位于狭窄的高产（~100 mg C m-2 day-1）带中。这与观察定性一致。然而，模型结果还表明，在挪威深海沟上方出现了类似规模的新产量，在那里浅层营养线与中尺度涡流活动相结合，导致硝酸盐向地表层的传输增加。