In aquatic ecosystems, allochthonous nutrient transport to the euphotic zone is an important process that fuels new production. Here, we use high‐resolution physical and biogeochemical observations from five summers to estimate the mean vertical nitrate flux, and thus new production over the Northeast U.S. Shelf (NES). We find that the summertime nitrate field is primarily controlled by biological uptake and physical advection–diffusion processes, above and below the 1% light level depth, respectively. We estimate the vertical nitrate flux to be 8.2 ± 5.3 × 10−6 mmol N m−2 s−1 for the mid‐shelf and 12.6 ± 8.6 × 10−6 mmol N m−2 s−1 for the outer shelf. Furthermore, we show that the new production to total primary production ratio (i.e., the f‐ratio), consistently ranges between 10% and 15% under summer conditions on the NES. Two independent approaches—nitrate flux‐based new production and O2/Ar‐based net community production—corroborate the robustness of the f‐ratio estimation. Since ~ 85% of the total primary production is fueled by recycled nutrients over sufficiently broad spatial and temporal scales, less than 15% of the organic matter produced in summer is available for export from the NES euphotic zone. Our direct quantification of new production not only provides more precise details about key processes for NES food webs and ecosystem function, but also demonstrates the potential of this approach to be applied to other similar datasets to understand nutrient and carbon cycling in the global ocean.

中文翻译：

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垂直硝酸盐通量为夏季美国东北部大陆架的新生产提供动力


在水生生态系统中，异质养分向真光区的运输是推动新生产的重要过程。在这里，我们使用五个夏季的高分辨率物理和生物地球化学观测来估计平均垂直硝酸盐通量，从而估计美国东北部大陆架 （NES） 的新产量。我们发现夏季硝酸盐场主要受生物吸收和物理平流-扩散过程控制，分别高于和低于 1% 的光照水平深度。我们估计中架的垂直硝酸盐通量为 8.2 ± 5.3 × 10-6 mmol N m-2 s-1，外架为 12.6 ± 8.6 × 10-6 mmol N m-2 s-1。此外，我们表明，在 NES 的夏季条件下，新生产与总初级生产比率（即 f 比率）始终在 10% 到 15% 之间。两种独立的方法——基于硝酸盐通量的新生产和基于 O2/Ar 的净群落生产——证实了 f 比估计的稳健性。由于总初级生产量的 ~ 85% 是由足够宽的空间和时间尺度上的回收营养物质提供的，因此夏季产生的有机物中只有不到 15% 可以从 NES 真光区出口。我们对新生产的直接量化不仅提供了有关 NES 食物网和生态系统功能关键过程的更精确细节，而且还证明了这种方法应用于其他类似数据集以了解全球海洋中的营养和碳循环的潜力。