04 May 2021

04 May 2021

Review status: this preprint is currently under review for the journal BG.

Riverine nitrogen supply to the global ocean and its limited impact on global marine primary production: a feedback study using an Earth System Model

Miriam Tivig, David Peter Keller, and Andreas Oschlies Miriam Tivig et al.
  • GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany

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.

Miriam Tivig et al.

Status: open (until 15 Jun 2021)

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Miriam Tivig et al.

Model code and software

Supplementary Data to "Feedbacks in the marine nitrogen cycle limit the impact of riverine nitrogen supply on global marine biology and biogeochemistry in an Earth System Model " Tivig, Miriam, Keller, David P., and Oschlies, Andreas

Miriam Tivig et al.


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Short summary
Nitrogen is one of the most important elements for life in the ocean. A major source is the riverine discharge of dissolved nitrogen. While most global models omit rivers as nutrient source, we included nitrogen from rivers in our Earth System model and found that additional nitrogen affected marine biology locally but also in regions far off the coast. Depending on regional conditions, primary production was enhanced or even decreased, due to internal feedbacks in the nitrogen cycle.