Atlantic Ocean radiocarbon

The turnover time and fluxes of DOC into the ocean are obtained by comparing the reservoir size and radiocarbon age. The ocean inventory of DOC is —680 Gt, and nearly all of this carbon resides in the deep sea, where concentration profiles and radiocarbon values are constant with depth. DOC ages by —1,000 yr as deep seawater moves from the Atlantic to the Pacific Basin, but even in the Atlantic, DOC radiocarbon values are significantly depleted relative to dissolved inorganic carbon (DIC) (Druffel et al., 1992). DOC persists in seawater through several ocean... 

Broecker WS, Gerard R, Ewing M, and Heezen BC (1960) Natural radiocarbon in the Atlantic Ocean. Journal of Geophysical Research 65(a) 2903-2931. 

Figure 5 Simulated radiocarbon and carbon cycle results from a three-dimensional global ocean biogeochemical model. Depth-latitude sections are shown for (a) DIG concentration (pmoll" ) and (b) natural preindustrial) radiocarbon (A C, per mil) along the prime meridian in the Atlantic Ocean.

The radiocarbon age of surface sediments averages around 2400 yr in the basins of southern California and around 2900 yr in the Atlantic Ocean (Emery and Bray, 1962 Berger et al, 1966 Benoit et al, 1979). Obviously, the measured age of organic matter in the surface sediment of the California basins is not unique to this environment, nor does it reflect a lack of... 

Comparison of results between GEOSECS and TTO/SAVE shows that the bomb radiocarbon inventory has increased by 36% for the region north of 10° N, by 69% for the equatorial region and by 71% for the region south of 10° S. These data reflect the radiocarbon uptake for the Atlantic Ocean between 1973 (GEOSECS) and 1985 (TTO/SAVE). Along with global bomb radiocarbon distribution, this information provides crucial constraints for the carbon cycle in the ocean. Preliminary results from CGC-91, one of the WOCE cruises, show that the observed increase in bomb radiocarbon inventory from 1974 to 1991 in the northern Pacific Ocean is consistent with the first-order prediction from a box-diffusion ocean model. 

Ostlund, H.G. and C.G.H. Rooth. 1990. The North Atlantic Tritium and Radiocarbon Transients 1972-1983. Journal of Geophysical Research—Oceans 95 20,147-20,165. 

Figure 9 Measurements of " C/C ratio in a benthic coral from 1.8 km depth in the northern Atlantic reveal that the base has an apparent age 650 radiocarbon years younger than the top. Yet °Th ages on the base and crest are nearly identical (1.54XlO" yr calendar years). Adkins et al. (1998) (reproduced by permission of Jess Adkins) attribute this difference to an abrupt invasion of low " C and high cadmium content Southern Ocean water.

Figure 4 Average vertical profiles for the major ocean basins. Except for the Southern Ocean the dotted line is for the Southern Hemisphere and the solid line for the Northern Hemisphere. The Pacific and Southern Ocean profiles were compiled from WOCE data the Atlantic profiles from TTO and SAVE data and the Indian Ocean profiles from GEOSECS data. In approximately the upper 1000 m = 1000 dB) of each profile, the natural A C is contaminated with bomb-produced radiocarbon.

Figure 5 Typical meridional sections for each ocean compiled from a subset of the data used for Figure 4. The deep water contour patterns are primarily due to the large-scale thermohaline circulation. The highest deep water A C values are found in the North Atlantic and the lowest in the North Pacific. The natural A C in the upper ocean is contaminated by the influx of bomb-produced radiocarbon.

Radiocarbon has been used to study thermocline ventilation using tools ranging from simple 3-box models to full 3D ocean circulation models. Many of the ID and 2D models are based on work by W. Jenkins using tritium in the North Atlantic. In a recent example, R. Sonnerup and co-workers at the University of Washington used chlorofluorocarbon data to calibrate a ID (meridional) along-isopycnal advection-diffusion model in the North Pacific with WOCE data. [4] is the basic equation for the... 

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