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.
Highlights
At global scale, the major sources of both dissolved and particulate materials to the oceans are river runoff, Geophysical Institute, University of Bergen, Bjerknes Centre for Climate Research, NorwayInstitute of Marine Research, Bergen, NorwayNORCE Norwegian Research Centre, Bjerknes Centre for Climate Research, NorwayInstitute of Geology, Center for Earth System Research and Sustainability (CEN), Universität Hamburg, GermanyUniversity of Washington, USA alters marine primary production (PP) and carbon (C) uptake, regionally and globally
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
The increase of PP in FIX occurs along continental margins, accounting for
Summary
University of Washington, USA alters marine primary production (PP) and carbon (C) uptake, regionally and globally. This contribution is represented in the state-of-the-art Earth system models with limited effort. 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). 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
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