Response of the Ocean Natural Carbon Storage to Projected Twenty-First-Century Climate Change

Abstract

Contact NOC NORA team at publications@noc.soton.ac.ukThe NERC and NOC trademarks and logos ('the Trademarks') are registered trademarks of NERC in the UK and other countries, and may not be used without the prior written consent of the Trademark owner. ABSTRACTThe separate impacts of wind stress, buoyancy fluxes, and CO 2 solubility on the oceanic storage of natural carbon are assessed in an ensemble of twentieth-to twenty-first-century simulations, using a coupled atmosphere-ocean-carbon cycle model. Time-varying perturbations for surface wind stress, temperature, and salinity are calculated from the difference between climate change and preindustrial control simulations, and are imposed on the ocean in separate simulations. The response of the natural carbon storage to each perturbation is assessed with novel prognostic biogeochemical tracers, which can explicitly decompose dissolved inorganic carbon into biological, preformed, equilibrium, and disequilibrium components. Strong responses of these components to changes in buoyancy and winds are seen at high latitudes, reflecting the critical role of intermediate and deep waters. Overall, circulation-driven changes in carbon storage are mainly due to changes in buoyancy fluxes, with wind-driven changes playing an opposite but smaller role. Results suggest that climate-driven perturbations to the ocean natural carbon cycle will contribute 20 Pg C to the reduction of the ocean accumulated total carbon uptake over the period 1860-2100. This reflects a strong compensation between a buildup of remineralized organic matter associated with reduced deep-water formation (196 Pg C) and a decrease of preformed carbon (2116 Pg C). The latter is due to a warming-induced decrease in CO 2 solubility (252 Pg C) and a circulation-induced decrease in disequilibrium carbon storage (264 Pg C). Climate change gives rise to a large spatial redistribution of ocean carbon, with increasing concentrations at high latitudes and stronger vertical gradients at low latitudes.

The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

“…Thus, although we could calculate O 2dis and DIC soft directly, it was necessary to use an indirect method to calculate the other three carbon tracers. Following Bernardello et al (2014), we first estimate alk pre using a regression, then calculate DIC sat using alk pre , temperature, salinity, and the known atmospheric pCO 2 of 270 ppm. DIC carb is calculated as 0.5 · (alk − alk pre ), and DIC dis is then calculated as a residual.…”

“…This theoretical framework defines four components that, together, add up to the total DIC: saturation (DIC sat ), disequilibrium (DIC dis ), carbonate (DIC carb ), and soft tissue (DIC soft ; Ito and Follows, 2013;Bernardello et al, 2014;Ödalen et al, 2018). The first two components are "preformed" quantities (DIC pre = DIC sat + DIC dis ), i.e., they are defined in the surface layer of the ocean and are carried passively by ocean circulation into the interior.…”

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

“…Following Ito and Follows (2013) and Bernardello et al (2014), we separate the total DIC into preformed and remineralized DIC (DIC pre and DIC rem ).…”

Analytically tractable climate–carbon cycle feedbacks under 21st century anthropogenic forcing

“…We do not explicitly model factors such as the thickness of ocean stratification layers, spatial variation of stratification, nutrient limitations to NPP, or changes in ocean circulation due to wind forcing, freshwater forcing, or sea-ice processes (Bernardello et al, 2014).…”