Preprints
https://doi.org/10.5194/bg-2021-293
https://doi.org/10.5194/bg-2021-293

  18 Nov 2021

18 Nov 2021

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

Riverine impact on future projections of marine primary production and carbon uptake

Shuang Gao1,2, Jörg Schwinger3, Jerry Tjiputra3, Ingo Bethke1, Jens Hartmann4, Emilio Mayorga5, and Christoph Heinze1 Shuang Gao et al.
  • 1Geophysical Institute, University of Bergen, Bjerknes Centre for Climate Research, Norway
  • 2Institute of Marine Research, Bergen, Norway
  • 3NORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, Norway
  • 4Institute of Geology, Center for Earth System Research and Sustainability (CEN), Universität Hamburg, Germany
  • 5University of Washington, USA

Abstract. Riverine transport of nutrients and carbon from inland waters to the coastal and finally the open ocean alters marine primary production (PP) and carbon (C) uptake, not only regionally but also globally. So far, this contribution is represented in the state-of-the-art Earth system models with limited effort. Here we assess changes in marine PP and C uptake projected under the Representative Concentration Pathway 4.5 climate scenario using the Norwegian Earth system model, with four riverine configurations: deactivated, fixed at a contemporary level, coupled to simulated freshwater runoff, and following four plausible future scenarios. The inclusion of riverine nutrients and carbon improves the modelled contemporary spatial distribution relative to observations, especially on the continental margins (5.4 % reduction in root mean square error [RMSE] for PP) and in the North Atlantic region (7.4 % reduction in RMSE for C uptake). Riverine nutrient inputs alleviate nutrient limitation, especially under future warmer conditions as stratification increases, and thus lessen the projected future decline in PP by up to 0.6 PgC yr−1 (27.3 %) globally depending on the riverine configuration. The projected C uptake is enhanced along continental margins where increased PP, due to riverine nutrient inputs, dominates over the CO2 outgassing owing to riverine organic matter inputs. Conversely, where the riverine organic matter inputs dominate over the nutrient inputs, the projected C uptake is reduced. The large range of the riverine input across our four riverine configurations does not transfer to a large uncertainty of the projected global PP and ocean C uptake, suggesting that transient riverine inputs are more important for high-resolution regional studies such as in the North Atlantic and along the continental margins.

Shuang Gao et al.

Status: open (until 01 Jan 2022)

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Shuang Gao et al.

Shuang Gao et al.

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Short summary
We assess the impact of riverine nutrients and carbon (C) on future projections of marine primary production (PP) and C uptake by using a fully coupled Earth system model. Riverine inputs (RI) alleviate nutrient limitation, thus lessen the projected decline in PP by up to 27.3 % globally. However, the large range of the uncertainty of the RI does not transfer to large uncertainty of the projected global PP and C uptake. Plausible transient RI may be important for high-resolution regional studies.
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