Rodgers, Keith: Princeton University (Project Lead)
Project Funding:
2014 - 2017
NRA: 2013 NASA: Carbon Cycle Science
Funded by NASA
Abstract:
Until recently, researchers interested in a state-estimate of air-sea CO2 fluxes generally could choose between using the Takahashi et al. (1993; 2002; 2009) climatology or output from free-running ocean carbon cycle models. Now, however, a number of data-based products have emerged. These range from alternative seasonal climatologies of surface pCO2 to fully time-dependent data assimilation schemes using biogeochemical models. These products differ in the overall magnitude of the ocean carbon sink that they simulate, the spatial distribution of surface flux, in regional and global trends of the ocean sink. Furthermore, they provide little insight into the ocean interior ventilation processes
that control anthropogenic carbon uptake and the implications of these products for the larger global carbon cycle. We propose to conduct a global synthesis of the new pCO2 products in order to quantify changes in ocean carbon uptake, determine ocean interior carbon subduction and obduction rates, and explore the implications of these findings on atmospheric CO2.
First, we will conduct a global synthesis of the new pCO2 products in order to quantify the extent to which the uptake of carbon is changing. We define a quantity called the Simplistic Uptake Model for Carbon (Sum-C), which is uptake expected treating anthropogenic carbon as a dye tracer that is impacted by neither changes in the physical state of the ocean, nor changes in ocean biology, nor changes in the buffering capacity of seawater. The global CO2 uptake rate implied by the various observationally-based pCO2 products will be evaluated against Sum-C as a critical diagnostic of how the ocean carbon cycle is changing relative to the behavior that would be expected in the absence of chemistry-climate feedbacks. This will lay the groundwork for analyses focused on attribution. This will include a careful evaluation of the gridded pCO2 and implied dissolved inorganic carbon (DIC) products against a number of independent observational constraints.
It is well known that the physical impedance to ocean carbon uptake posed by ocean interior ventilation processes (subduction and obduction) is significantly more important than the impedance posed by air-sea gas exchange (Bolin and Eriksson, 1958; Sarmiento et al., 1992). For this reason, in parallel to our evaluation of global air-sea fluxes, we will quantify and evaluate global subduction and obduction rates for DIC. This will be accomplished through the application of the thermodynamic framework of water mass transformation (Walin, 1982), following the application to the ocean carbon cycle presented in the modeling studies of Iudicone et al. (2011; 2013). In applying this approach to data-anchored carbon products, the following will be needed: (i) surface buoyancy forcing, consisting of net freshwater and heat fluxes; (ii) sea surface density; and (iii) sea surface DIC concentrations. Our estimate of DIC subduction and obduction will make combined use of remote sensing products, model output from the ECCO (Estimating the Circulation and Climate of the Ocean) project, the NASA MERRA reanalysis product, and the new suite of carbon data products. The goal is to quantify over the time interval 1990-2010 the net supply of DIC to the ocean interior via ventilation, and to relate this to air-sea CO2 fluxes.
Additionally, we propose to evaluate the signature of the new surface ocean carbon data products on atmospheric CO2 concentrations. We will quantify the observability of CO2 flux differences using in situ and remotely sensed atmospheric CO2 measurements using the CarbonTracker framework, through a consideration of the period 1990-2010. This will contribute directly to our final synthesis of the global implications of the new surface ocean carbon products.
Publications:
Nakano, H., Ishii, M., Rodgers, K. B., Tsujino, H., Yamanaka, G. 2015. Anthropogenic CO2uptake, transport, storage, and dynamical controls in the ocean imposed by the meridional overturning circulation: A modeling study. Global Biogeochemical Cycles. 29(10), 1706-1724. DOI: 10.1002/2015GB005128
Rodenbeck, C., Bakker, D. C. E., Gruber, N., Iida, Y., Jacobson, A. R., Jones, S., Landschutzer, P., Metzl, N., Nakaoka, S., Olsen, A., Park, G., Peylin, P., Rodgers, K. B., Sasse, T. P., Schuster, U., Shutler, J. D., Valsala, V., Wanninkhof, R., Zeng, J. 2015. Data-based estimates of the ocean carbon sink variability - first results of the Surface Ocean <i>p</i>CO<sub>2</sub> Mapping intercomparison (SOCOM). Biogeosciences. 12(23), 7251-7278. DOI: 10.5194/bg-12-7251-2015
Rodgers, K. B., Lin, J., Frolicher, T. L. 2015. Emergence of multiple ocean ecosystem drivers in a large ensemble suite with an Earth system model. Biogeosciences. 12(11), 3301-3320. DOI: 10.5194/bg-12-3301-2015
More details may be found in the following project profile(s):
