The amount of primary production fueled by upwelled “new” nitrate can be used to estimate the amount of organic carbon available for export to the deep ocean. Nitrate production in the euphotic zone from the microbial process of nitrification affects these estimates, yet the controls on nitrification in the upper ocean are debated. This study examines how seasonal cycles in primary production influence rates of nitrification fueled by both ammonia and urea‐derived nitrogen (N), and how these processes relate to the distribution of the greenhouse gas nitrous oxide (N₂O) using monthly rate measurements from the San Pedro Ocean Time‐series (SPOT) station. Nitrification rates were highest at the onset of upwelling and were correlated with depth‐integrated primary production in the lower euphotic zone. Similar ammonia and urea‐derived N oxidation rates suggest urea is a significant N source fueling nitrification, particularly below the euphotic zone. Nitrification supplied a large proportion of phytoplankton N demand in the lower euphotic zone, implying significant regenerated production. The Southern California Bight was always a source of N₂O to the atmosphere, which likely was advected into the system from the eastern tropical North Pacific, rather than produced locally from nitrification, and ventilated to the atmosphere during upwelling. Together, the results suggest the coupling of N remineralization and primary production in the upper ocean have important implications for the amount of organic carbon available for export out of the surface ocean, but that transport may dominate over local production in explaining local N₂O dynamics.

中文翻译：

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南加州湾的硝化作用和一氧化二氮动力学

由上升的“新”硝酸盐推动的初级生产量可用于估计可用于出口到深海的有机碳量。微生物硝化过程在富营养区产生的硝酸盐影响了这些估计，但对上层海洋硝化的控制方法存在争议。这项研究研究了初级生产中的季节性周期如何影响由氨和尿素衍生的氮（N）推动的硝化速率，以及这些过程与温室气体一氧化二氮（N _2）的分布有何关系。O）使用圣佩德罗海洋时间序列（SPOT）站的月度测量值。硝化率在上升流开始时最高，并且与较低富营养区的深度综合初级生产相关。类似的氨和尿素衍生的氮氧化速率表明，尿素是促进硝化作用的重要氮源，尤其是在富营养区以下。硝化作用在低富营养区提供了很大一部分的浮游植物氮需求，这意味着大量的再生生产。南加州湾一直是N ₂的来源大气中的O可能是从东部热带北太平洋平流到该系统中的，而不是由硝化作用局部产生的，并在上升流中通风到大气中。总之，结果表明上层海洋中氮的再矿化与初级生产的耦合对可用于表层海洋出口的有机碳数量具有重要影响，但在解释当地N ₂ O动力学方面，运输可能会超过本地生产。