Bofu Zheng, Weifeng (Gordon) Zhang, Rubao Ji, Rachel H. R. Stanley, E. Taylor Crockford, Diana N. Fontaine, Emily E. Peacock, Tatiana A. Rynearson, Heidi M. Sosik
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We estimate the vertical nitrate flux to be 8.2 ± 5.3 × 10<jats:sup>−6</jats:sup> mmol N m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> for the mid‐shelf and 12.6 ± 8.6 × 10<jats:sup>−6</jats:sup> mmol N m<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> 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 O<jats:sub>2</jats:sub>/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. 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引用次数: 0
摘要
在水生生态系统中,向透光层输送异源营养物质是促进新产量的一个重要过程。在这里,我们利用五个夏季的高分辨率物理和生物地球化学观测数据来估算硝酸盐的平均垂直通量,从而估算美国东北部大陆架(NES)的新产量。我们发现,夏季硝酸盐场主要由生物吸收和物理平流-扩散过程控制,分别位于 1%光照深度以上和以下。我们估计中大陆架的垂直硝酸盐通量为 8.2 ± 5.3 × 10-6 mmol N m-2 s-1,外大陆架为 12.6 ± 8.6 × 10-6 mmol N m-2 s-1。此外,我们还发现,在夏季条件下,NES 的新产量与总初级产量之比(即 f 比)始终介于 10% 与 15% 之间。两种独立的方法--基于硝酸盐通量的新产量和基于 O2/Ar 的群落净产量--证实了 f 比率估算的稳健性。由于初级生产总量的约 85% 是由足够宽的时空尺度上的循环营养物质提供的,因此夏季产生的有机物中只有不到 15% 可用于从 NES 的透光层输出。我们对新生成物的直接量化不仅为近海生态系统食物网和生态系统功能的关键过程提供了更精确的细节,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养分和碳循环的潜力。
Vertical nitrate flux fuels new production over summertime Northeast U.S. Shelf
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.
期刊介绍:
Limnology and Oceanography (L&O; print ISSN 0024-3590, online ISSN 1939-5590) publishes original articles, including scholarly reviews, about all aspects of limnology and oceanography. The journal''s unifying theme is the understanding of aquatic systems. Submissions are judged on the originality of their data, interpretations, and ideas, and on the degree to which they can be generalized beyond the particular aquatic system examined. Laboratory and modeling studies must demonstrate relevance to field environments; typically this means that they are bolstered by substantial "real-world" data. Few purely theoretical or purely empirical papers are accepted for review.