Abstract. A common notion is that negative feedbacks stabilize the marine nitrogen inventory. Recent modeling studies have shown, however, some potential for localized positive feedbacks leading to substantial nitrogen losses, in regions where nitrogen fixation and denitrification occur in proximity to each other. Here we include dissolved nitrogen from river discharge in a global 3-D ocean biogeochemistry model and study the effects on near-coastal and remote open ocean biogeochemistry. We find that at steady state the biogeochemical feedbacks in the marine nitrogen cycle, nitrogen input from biological N₂ fixation, and nitrogen loss via denitrification, mostly compensate for the yearly addition of 22.8 to 45.6 Tg of riverine nitrogen and limit the impact on global marine productivity to < 2 %. Global experiments that regionally isolate river nutrient input show that sign and strength of the feedbacks depend on the location of the river discharge and the oxygen status of the receiving marine environment. Marine productivity generally increases in proximity to the nitrogen input, but we also find a decline in productivity in the Bay of Bengal and near the mouth of the Amazon River. While most of the changes are located in shelf and near coastal oceans, nitrogen supply from the rivers can impact the open ocean, due to feedbacks or knock-on effects.

中文翻译：

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向全球海洋的河流氮供应及其对全球海洋初级生产的有限影响：使用地球系统模型的反馈研究

摘要。一个普遍的观念是，负反馈可以稳定海洋中的氮库存。但是，最近的模型研究表明，在固氮和反硝化彼此接近的区域，局部正反馈可能会导致大量的氮流失。在这里，我们将全球河流3-D海洋生物地球化学模型中来自河流排放物的溶解氮纳入其中，并研究其对近岸和偏远远洋海洋生物地球化学的影响。我们发现，在稳态下，海洋氮循环中的生物地球化学反馈，即来自生物N _2的氮输入固氮和通过反硝化作用损失的氮，大部分补偿了每年增加22.8至45.6 Tg的河流氮，并将对全球海洋生产力的影响限制在<2％。局部隔离河流养分输入的全球实验表明，反馈的信号和强度取决于河流排放的位置和接收海洋环境的氧气状态。在靠近氮输入的地方，海洋生产力通常会提高，但我们在孟加拉湾和亚马逊河河口附近也发现生产力下降。尽管大多数变化位于陆架和沿海海洋附近，但是由于反馈或连锁效应，河流的氮供应会影响大洋。