Bibliography - E. Y. Kwon

1. Galbraith, E. D., E. Y. Kwon, A. Gnanadesikan, K. B. Rodgers, Stephen M. Griffies, D. Bianchi, Jorge Sarmiento, J. P. Dunne, J. Simeon, R. D. Slater, Andrew T. Wittenberg, and I. Held, 2011: Climate Variability and Radiocarbon in the CM2Mc Earth System Model. Journal of Climate, American Meteorological Society, doi:10.1175/2011JCLI3919.1
   [ Abstract ]

   The distribution of radiocarbon (¹⁴C) in the ocean and atmosphere has fluctuated on timescales ranging from seasons to millennia. It is thought that these fluctuations partly reflect variability in the climate system, offering a rich potential source of information to help understand mechanisms of past climate change. Here, a long simulation with a new, coupled model is used to explore the mechanisms that redistribute ¹⁴C within the Earth system on inter-annual to centennial timescales. The model, CM2Mc, is a lower-resolution version of the Geophysical Fluid Dynamics Laboratory's CM2M model, uses no flux adjustments, and incorporates a simple prognostic ocean biogeochemistry model including ¹⁴C. The atmospheric ¹⁴C and radiative boundary conditions are held constant, so that the oceanic distribution of ¹⁴C is only a function of internal climate variability. The simulation displays previously-described relationships between tropical sea surface ¹⁴C and the model-equivalents of the El Niño Southern Oscillation and Indonesian Throughflow. Sea surface ¹⁴C variability also arises from fluctuations in the circulations of the subarctic Pacific and Southern Ocean, including North Pacific decadal variability, and episodic ventilation events in the Weddell Sea that are reminiscent of the Weddell Polynya of 1974-1976. Interannual variability in the air-sea balance of ¹⁴C is dominated by exchange within the belt of intense Southern Westerly winds, rather than at the convective locations where the surface ¹⁴C is most variable. Despite significant interannual variability, the simulated impact on air-sea exchange is an order of magnitude smaller than the recorded atmospheric ¹⁴C variability of the past millennium. This result partly reflects the importance of variability in the production rate of ¹⁴C in determining atmospheric ¹⁴C, but may also reflect an underestimate of natural climate variability, particularly in the Southern Westerly winds.

2. Kwon, E. Y., Jorge Sarmiento, J. R. Toggweiler, and Tim DeVries, 2011: The control of atmospheric pCO₂ by ocean ventilation change: The effect of the oceanic storage of biogenic carbon. Global Biogeochemical Cycles, American Geophysical Union, 25, doi:10.1029/2011GB004059
   [ Abstract ]

   A simple analytical framework is developed relating the atmospheric partial pressure of CO₂ to the globally-averaged concentrations of respired carbon (C_soft) and dissolved carbonate (C_carb) in the ocean. Assuming that the inventory of carbon is conserved in the ocean-atmosphere system (i.e. no seawater-sediment interactions), the resulting formula of

   ΔpCO₂ / pCO₂

   = -0.0053Δ

   C_soft + 0.0034Δ C_carb suggests that atmospheric pCO₂ would decrease by 5.3% and increase by 3.4% when C_soft and C_carb increase by 10 μmol kg^-1, respectively. Using this analytical framework along with a 3-D global ocean biogeochemistry model, we show that the response of atmospheric pCO₂ to changes in ocean circulation is rather modest because ~30% of the change in atmospheric pCO₂ caused by the accumulation of respired carbon is countered by a concomitant accumulation of dissolved carbonate in deep waters. Among the suite of circulation models examined here, the largest reduction in atmospheric pCO₂ of 44-88 ppm occurs in a model where reduced overturning rates of both southern and northern sourced deep waters result in a four-fold increase in the Southern Ocean deep water ventilation age. On the other hand, when the ventilation rate of the southern-sourced water decreases, but the overturning rate of North Atlantic Deep Water increases, the resulting decrease in atmospheric pCO₂ is only 14-34 ppm. The large uncertainty ranges in atmospheric pCO₂ arise from uncertainty in how surface productivity responds to circulation change. Although the uncertainty is large, this study suggests that a synchronously reduced rate for the deep water formation in both hemispheres could lead to the large glacial reduction in atmospheric pCO₂ of 80-100 ppm.

3. Kwon, E. Y., F. Primeau, and Jorge Sarmiento, 2009: The impact of remineralization depth on the air-sea carbon balance. Nature Geosciences, 2, doi:10.1038/ngeo612 630-635
   [ Abstract ]

   As particulate organic carbon rains down from the surface ocean it is respired back to carbon dioxide and released into the ocean's interior. The depth at which this sinking carbon is converted back to carbon dioxide—known as the remineralization depth—depends on the balance between particle sinking speeds and their rate of decay. A host of climate-sensitive factors can affect this balance, including temperature, oxygen concentration, stratification, community composition and the mineral content of the sinking particles. Here we use a three-dimensional global ocean biogeochemistry model to show that a modest change in remineralization depth can have a substantial impact on atmospheric carbon dioxide concentrations. For example, when the depth at which 63% of sinking carbon is respired increases by 24 m globally, atmospheric carbon dioxide concentrations fall by 10–27 ppm. This reduction in atmospheric carbon dioxide concentration results from the redistribution of remineralized carbon from intermediate waters to bottom waters. As a consequence of the reduced concentration of respired carbon in upper ocean waters, atmospheric carbon dioxide is preferentially stored in newly formed North Atlantic Deep Water. We suggest that atmospheric carbon dioxide concentrations are highly sensitive to the potential changes in remineralization depth that may be caused by climate change.

Direct link to page: http://cmi.princeton.edu/bibliography/results.php?author=4432