Bomb radiocarbon

I. Natural Radiocarbon—For Samples Collected Prior to 1950, or Assumed to Contain No Bomb Radiocarbon. For samples not complicated by the presence of bomb 14C, the ratio of 14C/12C measured in a sample represents the rate of decomposition relative to the rate of radiodecay of 14C. This treatment is most useful for very old C found in soils. For a homogeneous carbon-containing reservoir, i, with input rate Iu first-order decomposition constant kh and carbon content C the change in stock over time (balance of inputs and outputs) is... 

Bomb Radiocarbon. One of the great uses of radiocarbon for SOM studies is the ability to estimate the turnover time of organic carbon based on the degree to which it has incorporated bomb radiocarbon since 1959. This provides one of the only tools to study C dynamics on decadal time scales. 

Geyh, M. A. (2001). Bomb radiocarbon dating of animal tissues and hair. Radiocarbon 43, 723-730. 

Goodfriend, GA., and Rollins, H.B. (1998) Recent barrier beach retreat in Georgia Dating exhumed salt marshes by aspartic acid racemization and post-bomb radiocarbon. J. Coast. Res. 14, 960-969. 

Answer 11.9 Both figures depict tritium in groundwater as a function of 14C, revealing the fact that groundwater that contains bomb tritium also has high 14C concentrations, indicating that bomb radiocarbon is present as well. 

Figure 13 shows an estimate as to how the distribution of bomb radiocarbon atoms among these active carbon reservoirs has evolved. 

In order to make use of this transient, the contributions of the natural and bomb radiocarbon had to be separated. Three sets of observations went into this separation. First, use was made of measurements on surface waters collected very early in the nuclear testing era (Broecker etal., 1960) and also with results of measurements on prenuclear growth ring-dated corals and mollusks (Drulfel and Linick, 1978 Drulfel, 1981, 1989). Second, use was made of the tritium released to the atmosphere during nuclear tests. As this bomb-test tritium swamped the natural tritium present in the ocean, the vertical distribution of tritium in the sea could be used to establish the limit of penetration of bomb radiocarbon. Finally, based on the radiocarbon analyses made on thermocline waters free of bomb tritium, it was shown that there was a close correlation between the natural ratio and the dissolved silica... 

Broecker W. S. and Peng T.-H. (1994) Stratospheric contribution to the global bomb radiocarbon inventory model versus observation. Global Biogeochem. Cycles 8, 377-384. 

Druffel E. R. M. (1989) Decade time scale variability of ventilation in the North Atlantic high-precision measurements of bomb radiocarbon in banded corals. J. Geophys. Res. 94, 3271-3285. 

The main thermocline of the ocean, from the surface down to about 1 km or so, has more rapid ventilation timescales, from a few years to a few decades. Tracers useful in this regard are chloro-fluorocarbons, tritium and its decay product He, and bomb radiocarbon, which along with tritium was released into the atmosphere in large quantities in the 1950s and 1960s by atmospheric nuclear weapons testing. 

Some anthropogenically introduced radionuclides and synthetic compounds are useful as ocean circulation tracers. These include tritium, bomb radiocarbon and CFCs. 

BerKMAN P. a. and Forman S. L. (1996) Pre-bomb radiocarbon and the reservoir correction for calcareous marine species in the Southern Ocean. Geophys. Res. Lett. 23, 363 366. 

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. 

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