Abstract
Abstract. While there is agreement that global warming over the 21st century is likely to influence the biological pump, Earth system models (ESMs) display significant divergence in their projections of future new production. This paper quantifies and interprets the sensitivity of projected changes in new production in an idealized global ocean biogeochemistry model. The model includes two tracers that explicitly represent nutrient transport, light- and nutrient-limited nutrient uptake by the ecosystem (new production), and export via sinking organic particles. Globally, new production declines with warming due to reduced surface nutrient availability, as expected. However, the magnitude, seasonality, and underlying dynamics of the nutrient uptake are sensitive to the light and nutrient dependencies of uptake, which we summarize in terms of a single biological timescale that is a linear combination of the partial derivatives of production with respect to light and nutrients. Although the relationships are nonlinear, this biological timescale is correlated with several measures of biogeochemical function: shorter timescales are associated with greater global annual new production and higher nutrient utilization. Shorter timescales are also associated with greater declines in global new production in a warmer climate and greater sensitivity to changes in nutrients than light. Future work is needed to characterize more complex ocean biogeochemical models in terms of similar timescale generalities to examine their climate change implications.
Highlights
Global warming over the 21st century is projected to alter the supply of nutrients and light to the surface ocean and drive reductions in the “biological pump”, which is the biologically mediated transfer of carbon from surface to depth and an important control on the ocean’s natural carbon inventory
We performed a set of idealized climate change experiments with the Community Earth System Model (CESM) version 2.1 in an ocean–sea-ice configuration forced by atmospheric fields derived from reanalysis
A large portion of this variability in global new production is related to the Southern Ocean, which is the basin with largest production and which our model does not represent well
Summary
Global warming over the 21st century is projected to alter the supply of nutrients and light to the surface ocean and drive reductions in the “biological pump”, which is the biologically mediated transfer of carbon from surface to depth and an important control on the ocean’s natural carbon inventory. These nutrient and light supply changes are related to physical shifts, including increased ocean surface temperatures, stronger stratification, and reduced sea-ice cover. Earth system models include a variety of differing ocean biogeochemical models that display a range of sensitivities to changes in physical climate (discussed in Oschlies, 2015)
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