Bomb-produced Radiocarbon Research Articles

Doubts raised on ocean fertilization with iron

The ability of the ocean waters off Antarctica to absorb significant amounts of atmospheric carbon dioxide after fertilization with iron has been called into question by researchers who have modeled the dynamics of the process. Using a model calibrated with data on atomic bomb-produced radiocarbon in ocean waters, Wallace S. Broecker, of Columbia University's Lamont-Doherty Geological Observatory, Palisades, N.Y., and T.-H. Peng, of Oak Ridge National Laboratory, Oak Ridge, Tenn., calculate that 100 years of completely successful iron fertilization would reduce atmospheric C0 2 by only 10% [ Nature , 349 , 227 (1991)]. That is not enough, they say, to have a positive effect on projected global warming due to the greenhouse effect. The notion that the iron content of some large expanses of ocean determines the biological productivity of those waters was first proposed by John H. Martin, director of Moss Landing Marine Laboratories, Moss Landing, Calif. (C&EN, July 2, 1990, page 21). Martin has shown that ...

Bomb-produced radiocarbon in the shell of the chambered nautilus: rate of growth and age at maturity

The temporal pattern of bomb-produced radiocarbon in the oceans provides a chronometer to estimate the rate of growth of marine organisms. Radiocarbon measurements by tandem accelerator mass spectrometry of samples from the septa and shell wall of a mature specimen of Nautilus macromphalus reveal progressively increasing values in more recently formed shell material. This pattern is similar to that recorded in a banded coral from surface waters of the Great Barrier Reef, Australia. However, the pre-bomb values of Δ 14C are lower in the nautilus than in the coral. This offset is probably due to the difference in the respective habitat depths of the two animals. Taking this difference into account, we have used the temporal pattern of Δ 14C in the coral as a point of reference to help interpret the pattern of Δ 14C in the nautilus. According to our calculations, the age of the specimen of N. macromphalus is 10–12 years and the timing of septal formation ranges from ⩾ 80 to 240 days/septum.

Radiocarbon in dissolved organic matter in the central North Pacific Ocean

The origin of dissolved organic carbon (DOC) in the ocean has been long debated. Whereas Mantoura and Woodward1 have used the conservative nature of DOC in a British estuary to conclude that ≥50% of DOC in the oceans could be river-derived, recent lignin results in the equatorial Pacific2 have indicated that ≤10% of the DOC is potentially of terrestrial origin. In addition, the δ13C signature (relative to the PDB standard) of DOC ranges from –20 to –24‰ (refs 3,4), indicating that the primary source of DOC is from marine-derived organic carbon. Here we present the first detailed profile of radiocarbon measured in DOC and dissolved inorganic carbon (DIC) in the oligotrophic gyre of the central North Pacific. δ14C (per mil deviation from the activity of 19th-century wood) of DOC ranged from –150‰ (1,310 yr BP) in surface waters to –540‰ (6,240 yr BP) at 5,710 m, 40 m off the bottom, where these 'apparent ages' or 'residence times' are mean values for the combined constituents of the DOC. The surprising similarity in the shapes of the profiles of δ14C in the DOC and DIC pools suggests that similar processes are controlling the radiocarbon distribution in each of the two reservoirs and that bomb-produced radiocarbon has penetrated the DOC + DIC pools to a depth of ˜900 m. The depletion of the δ14C DOC values by 300‰ with respect to the δ14C DIC values suggests that a certain fraction of the DOC is recycled within the ocean on longer time-scales than DIC.

Sclerosponge growth rate as determined by 210Pb and ?14C chronologies

Measurements of bomb-produced radiocarbon and 210Pb provide concordant estimates of the growth rate of the sclerosponge Ceratoporella nicholsoni collected from the reef slope of northern Jamaica. Radiocarbon measurements of older growth bands in the same specimen are similar to the time history of radiocarbon in coral bands from two sites in the northwestern Atlantic. Furthermore, 210Pb and stable Pb analyses reveal that the sclerosponge incorporates this element at much higher concentrations than corals.

A strategy for the use of bomb-produced radiocarbon as a tracer for the transport of fossil fuel CO 2 into the deep-sea source regions

Because the equilibration time for CO 2 gas between the surface ocean and atmosphere is an order of magnitude shorter than the equilibration time for the isotopes of carbon, bomb-produced radiocarbon cannot be simply used as a tracer for fossil fuel CO 2. This difference is especially important for the areas of deep water formation. In this paper we derive the relationship between the isotopic equilibration time and chemical equilibration times for carbon between sea and air. We also show that if the distribution of a second transient tracer is measured, it is possible to circumvent the ambiguity associated with this exchange time difference. Tritium, while adequate in purely diffusive models, is not ideal as the second transient in models involving advection (i.e., downwelling). For such models 85Kr or freon is a much better choice.

Modeling the Carbon System

Claims that forest cutting during the last few decades has contributed significantly to the buildup in atmospheric CO2 have cast doubt on the validity of models used to estimate CO2 uptake by the ocean. In this paper we review the existing models and conclude that the box-diffusion model of Oeschger and his co-workers provides an excellent fit to the average distributions of natural and bomb-produced radiocarbon. We also take the first steps toward a more detailed ocean model which takes into account upwelling in the equatorial zone and deep water formation in the polar zone. The model is calibrated using the distribution of bomb-produced and cosmic ray-produced radiocarbon in the ocean. Preliminary calculations indicate that the fossil fuel CO2 uptake by this model will be greater than that by the box-diffusion model of Oeschger and others (1975) but not great enough to accommodate a significant decline in the mass of the terrestrial biosphere over the past two decades.

La Jolla Measurements of Radiocarbon in the Oceans

The La Jolla Radiocarbon Laboratory has measured carbon-14 concentrations in seawater samples collected from 1957 through 1972. The dissolved inorganic carbon in seawater was extracted on board research vessels and was returned to the laboratory for processing and measurement. Both surface and sub-surface samples were collected, primarily from the Pacific Ocean, but also from the Indian Ocean. The purpose of the seawater measurements was to determine the distribution of bomb-produced radiocarbon in the surface water of the Pacific and Indian Oceans, the sub-surface penetration of bomb 14C, the change in 14C/12C ratios with depth, and thus the rate of uptake of bomb 14C by the oceans. This project was the basis of the author's doctoral dissertation (Linick, 1975).

Carbon 14 in tree rings

In order to investigate how reliably the carbon 14 content of tree rings reflects that of atmospheric carbon dioxide, two types of determinations were carried out: (1) carbon 14 determinations in annual rings from the beginning of this century until 1974 and (2) carbon 14 determinations in synchronous wood from the North American bristlecone pine and from European oak trees, dendrochronologically dated to have grown in the third and fourth century B.C. The first series of measurements showed that bomb-produced radiocarbon was incorporated in wood at a time when it was converted from sapwood to heartwood, whenever radiocarbon from bomb testing was present in the atmosphere. The second series showed that wood more than 2000 years old and grown on two different continents at different altitudes had, within the limits of experimental error, the same radiocarbon content. This work and other experimental evidence, obtained in part by other laboratories, show that tree rings reflect the average radiocarbon content of global atmospheric carbon dioxide accurately within several per mil. In rare cases, deviations of up to 10‰ may be possible. This means that a typical single radiocarbon date for wood or charcoal possesses an intrinsic uncertainty (viz., an estimated One-sigma error' in addition to all the other errors) of the order of ±50 years. This intrinsic uncertainty is independent of the absolute age of the sample. More accurate dates can, in principle, be obtained by the so-called method of ‘wiggle matching.’

Gas exchange rates between air and sea<sup>1</sup>

Gas exchange rate studies carried out in the laboratory suggest that the stagnant film model is adequate to relate the transfer coefficients of most gases between the atmosphere and sea to an accuracy of ±15%. Estimates of the average film thickness prevailing for the world ocean based on the distribution of natural radiocarbon, bomb-produced radiocarbon, and radon are in good agreement. Radon data from the BOMEX area and from station PAPA lend support to Kanwisher's suggestion that gas exchange rates should vary in proportion to the square of the wind velocity. These observations permit a number of generalizations regarding the potential of the ocean as a source and sink for trace gases to be made. They also permit the more complicated situation for carbon dioxide to be assessed. DOI: 10.1111/j.2153-3490.1974.tb01948.x

Tata Institute Radiocarbon Date List VI

This date list is comprised of archaeologic and geophysical samples. The latter are in continuation of our investigations of bomb-produced radiocarbon in atmospheric carbon dioxide reported in Tata V. We continue to count samples in the form of methane; the techniques used have been described elsewhere (Agrawalet al., 1965).

Latitudinal Effect in the Transfer of Radiocarbon from Stratosphere to Troposphere

Latitudinal variations in the descent of bomb-produced radiocarbon from the stratosphere is suggested by differences in tropospheric carbon-14 activity. The magnitude of a similar latitudinal effect in the pre-bomb steady state is estimated. This effect may be part of the explanation of the short-term oscillations in carbon-14 activity found in treerings from the last 1300 years.

Post-bomb rise in radiocarbon activity in Denmark.

During the summers of 1958 and 1959 the increase in concentration of bomb-produced radiocarbon in Denmark was several percent higher than the average increase for the hemisphere. This additional increase is probably a carbon-14 equivalent to the spring peaks in strontium-90 fallout in the North Temperate Zone in the same years, and suggests latitudinal variations in carbon-14 contamination.

Bomb Carbon-14 in Human Beings

The concentration of bomb-produced radiocarbon in human beings will lag behind the rising concentration in average atmospheric CO 2 . Measurements on human materials suggest a lag of about 1 year for both breath CO 2 and blood, with the suggestion of a somewhat higher value for lung tissue. These results are in reasonable agreement with predictions based on independent evidence.

Bomb carbon-14 in human beings.

The concentration of bomb-produced radiocarbon in human beings will lag behind the rising concentration in average atmospheric CO 2 . Measurements on human materials suggest a lag of about 1 year for both breath CO 2 and blood, with the suggestion of a somewhat higher value for lung tissue. These results are in reasonable agreement with predictions based on independent evidence.