Marine Radiocarbon Reservoir Age
Some of the most widely dated fossil groups are the marine carbonates including foraminifera, mollusks, pteropods, and corals. By convention, these dates are corrected for the difference between the atmospheric 14C content and the local 14C content of ocean surface water, also known as the "radiocarbon reservoir age". However, there is only a handful of pre-anthropogenic measurements of reservoir ages uncontaminated by fossil fuel burning or thermonuclear bomb contamination for the open ocean environments, and there is little prospect for adding significantly to this data base. There are many radiocarbon reservoir age measurements from coastal environments where mollusks and other museum specimens have known collection dates. These coastal radiocarbon reservoir age data don't satisfy our need for the open ocean because of their limited geographic distribution and they are often influenced by organism diets, sediment pore waters or river mixing among other factors. The paleoceanography community in particular needs a reliable standard reference for estimating the surface ocean radiocarbon reservoir age at any point in the World's oceans. By convention, 400 years has been assumed to be the average surface ocean radiocarbon reservoir age and adjustments to this number are made on an ad hoc basis (Stuiver and Braziunas, 1993). However, the actual radiocarbon reservoir age ranges from less than 300 years in the subtropical gyres to more than 1600 years in the Southern Ocean and varies significantly between upwelling regions and the warm pools in the tropics. The surface ocean radiocarbon reservoir age varies geographically due to the combined influences of varying air-sea isotopic exchange rates and mixing with older, radiocarbon depleted, deep waters. We recognize the important contribution made by Butzin, Prange and Lohmann in their seminal paper on the radiocarbon reservoir age for the preanthropogenic and glacial world simulations (Butzin et al., 2005). Their radiocarbon reservoir age estimates are based on output from a three-dimensional global ocean circulation model described in Butzin et al., (2005). Presently, we believe that their model output is the best available estimate of the modern ocean radiocarbon reservoir ages (Cao et al., 2007). With their cooperation and collaboration, we have incorporated their interpolated model output into a searchable files and interactive maps driven by the Google Earth platform. In addition, we offer optional data overlays for a variety of relevant variables or data sets that we find useful for interpreting radiocarbon reservoir age estimates. These include, measured radiocarbon reservoir age data reported in the literature, ocean bathymetry, archived deep sea core locations, sea surface temperature, pCO2, and nutrients, among others. Corresponding metadata files are included where possible. We also provide searchable glacial radiocarbon reservoir age estimates based on several model outputs described in Butzin et al., (2005). We can assume that model outputs will become more realistic in the future but it is time to move from ad hoc estimates to one that is more firmly based on the physics and chemistry of the ocean as represented by the Hamburg ocean model. As model radiocarbon reservoir age estimates improve, particularly time-series reconstructions, we will update this site accordingly.
The marine radiocarbon reservoir correction database and software presented here was adapted for use with our radiocarbon calibration program (Fairbanks et al., 2005; http://radiocarbon.LDEO.columbia.edu/). Proper citation for the reservoir output values should include Butzin et al., (2005), Cao et al., (2007) and the site link http://radiocarbon.LDEO.columbia.edu/
Butzin, M., M. Prange and G. Lohmann, 2005. Radiocarbon simulations for the glacial ocean: the effects of wind stress, Southern Ocean sea ice and Heinrich events. Earth & Planet. Sci. Lett., 235, 45-61.
Cao, L., R.G. Fairbanks, M. Butzin and N. Naik, 2007. The marine radiocarbon reservoir age. Radiocarbon, in prep.
Fairbanks, R.G., R.A. Mortlock, T.-C. Chiu, L. Cao, A. Kaplan, T.P. Guilderson, T.W. Fairbanks, A.L. Bloom, P.M. Grootes and M.-J. Nadeau, 2005. Radiocarbon calibration curve spanning 0 to 50,000 years BP based on paired 230Th/234U/238U and 14C dates on pristine corals. Quaternary Science Reviews 24(16-17), 1781-1796.
Stuiver M. and T.F. Braziunas, 1993. 14C ages of marine samples to 10,000 BC Radiocarbon 35(1) 137-189.