Abstract
The Arctic Ocean, more than any other ocean, is influenced by riverine input of carbon and nutrients. That riverine delivery is likely to change with climate change as runoff increases, permafrost thaws, and tree lines advance. But it is unknown to what extent these changes in riverine delivery will affect Arctic Ocean primary production, air‐to‐sea CO2 fluxes, and acidification. To test their sensitivity to changing riverine delivery, we made sensitivity tests using an ocean circulation model coupled to an ocean biogeochemical model. In separate idealized simulations, riverine inputs of dissolved inorganic carbon (CT), dissolved organic carbon (DOC), and nutrients were increased by 1%/year until doubling. Doubling riverine nutrient delivery increased primary production by 11% on average across the Arctic basin and by up to 34–35% locally. Doubling riverine DOC delivery resulted in 90% of that added carbon being lost to the atmosphere, partly because it was imposed that once delivered to the ocean, the riverine DOC is instantaneously remineralized to CT. That additional outgassing, when considered alone, reduced the net ingassing of natural CO2 into the Arctic Ocean by 25% while converting the Siberian shelf seas and the Beaufort Sea from net sinks to net sources of carbon to the atmosphere. The remaining 10% of DOC remained in the Arctic Ocean, but having been converted to CT, it enhanced acidification. Conversely, doubling riverine CT increased the Arctic Ocean's average surface pH by 0.02 because riverine total alkalinity delivery increased at the same rate as riverine CT delivery.
Highlights
It is uncertain how river delivery of carbon and nutrients will change and how these changes will affect the coastal and open ocean (Regnier et al, 2013)
Riverine Forcing To evaluate the Arctic river flux estimates derived from Global NEWS 2 model (GN2) and Global Erosion Model (GEM), they were compared to data-based fluxes from the five largest Arctic rivers that drain directly into the Arctic Ocean (Table 1), that is, river fluxes from GEM's CT (RCT) is from Tank, Raymond, et al (2012), river flux of terrigenous DOC (RDOC) from Holmes et al (2012) and Manizza et al (2009), and RNUT from Holmes et al (2012)
The model's GEM-derived total RCT flux to our Arctic Ocean domain (50 Tg C/year) falls within the uncertainty range of Tank, Raymond, et al 2012's data-based estimate (41 ± 10 Tg C/year) from their extrapolation of the fluxes from the six major Arctic rivers to all rivers that discharge into the Arctic Ocean
Summary
It is uncertain how river delivery of carbon and nutrients will change and how these changes will affect the coastal and open ocean (Regnier et al, 2013). A 16–28% increase of freshwater discharge into the Arctic Ocean during the 21st century is projected by atmosphere-ocean general circulation models forced under the SRES A1, A2, and B1 scenarios (Lawrence & Slater, 2005; Nohara et al, 2006). Such increases would in turn affect Arctic Ocean circulation and biogeochemistry, for example, leading to increased stratification, decreased vertical mixing, decreased nutrient supply from deeper waters, decreased primary production, and enhanced acidification (Carmack et al, 2015)
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