The Amazon River strongly modifies the biogeochemistry of the Western Tropical Atlantic (WTA). To disentangle the different mechanisms driving these modifications, we conduct a series of modeling experiments with a high-resolution regional ocean model (ROMS) coupled to a biogeochemical/ecological model (BEC) that we augmented to include Diatom-Diazotroph-Assemblages (DDAs). In our model, the Amazon River increases net primary production (NPP) in the WTA by almost 10%, exceeding the stimulation expected from the supplied inorganic nitrogen and phosphorus by a factor of two. This amplification is fueled by new nitrogen stemming from DDA-driven N₂ fixation in the plume region, supported, in part, by the consumption of riverine dissolved organic phosphorus. The vertical export of organic carbon is enhanced by a shift of the phytoplankton community toward diatoms induced by the large amount of Si(OH)₄ delivered by the Amazon. These changes in NPP and export production induce a strong uptake of atmospheric CO₂. In contrast, the remineralization of the river-delivered terrestrial organic matter leads to a release of CO₂ over the WTA, which is partially offset by a net uptake induced by the riverine dissolved inorganic carbon and alkalinity. Overall, the Amazon reduces the strong outgassing of the WTA in our simulations by more than 50%. Our study demonstrates how rivers modify the marine biological pump and the air-sea CO₂ fluxes in the downstream ocean through a myriad of cascading effects, highlighting the need to fully consider the land-ocean aquatic continuum in the modeling of the Earth System.

中文翻译：

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亚马逊河对西热带大西洋生物泵和海气二氧化碳平衡的影响

亚马逊河极大地改变了西热带大西洋 (WTA) 的生物地球化学。为了解开驱动这些修改的不同机制，我们使用高分辨率区域海洋模型 (ROMS) 与生物地球化学/生态模型 (BEC) 耦合进行了一系列建模实验，我们将其增强为包括硅藻-固氮组合 (DDA) . 在我们的模型中，亚马逊河使 WTA 的净初级生产 (NPP) 增加了近 10%，超过了预期的无机氮和磷供应刺激作用的两倍。这种放大是由 DDA 驱动的 N ₂产生的新氮推动的固定在羽流区域，部分是由于消耗了河流溶解的有机磷。亚马逊河提供的大量 Si(OH) ₄导致浮游植物群落向硅藻转变，从而增强了有机碳的垂直输出。NPP 和出口生产的这些变化导致大气中CO _{2 的大量}吸收。相比之下，河流输送的陆地有机物的再矿化导致 CO ₂的释放在 WTA 上，这被河流溶解的无机碳和碱度引起的净吸收部分抵消。总体而言，亚马逊在我们的模拟中将 WTA 的强烈释气减少了 50% 以上。我们的研究展示了河流如何通过无数的级联效应改变下游海洋中的海洋生物泵和海气 CO ₂通量，突出了在地球系统建模中充分考虑陆海水相连续体的必要性。