Transient Tracers in the Ocean

Williams, R. T. (1982). "Transient Tracers in the Ocean Preliminary Hydrographic Report," Vols 1-4. Scripps Institution of Oceanography, La Jolla, CA. 

Data from GEOSECS and TTO Expeditions The GEOSECS and TTO (Transient Tracers in the Oceans) programs have provided a large source of data in the Atlantic (see Broecker 1985, and Takahashi et al., 1985). The interpretation of the chemical data from isopycnal surfaces yields a Redfield ratio of P/N/C/O2 of 1 16 103 172. The ratio of P/CaCO dissolution has been estimated to be about 1 12. This indicates that the ratio of CO2 produced by the oxidation of organic carbon to that derived from the dissolution of CaC03 is about 10 1. 

This classification has been discussed extensively within the context of a one-dimensional advection-diffusion model, along with simple solutions to the relevant equations (Craig, 1969). It should be noted, however, that specific tracers may fall into different categories depending on the nature of the specific application. For example, radiocarbon is a transient tracer in the surface waters of the ocean because its natural inventory (due to cosmic ray production) has been affected... 

Gammon, R. H., Cline, J. and Wisegarver, D. (1982). Chlorofluoromethanes in the Northeast Pacific Ocean measured vertical distributions and application as transient tracers of upper ocean mixing. /. Geophys. Res. 87, 9441-9454. 

That is, the tracer concentration age of a transient tracer whose concentration in the ocean surface water is increasing in an exactly linear fashion is equal to the first moment of the age spectrum, and thus equates to an ideal age tracer. This is precisely the conclusion reached in Section 6.08.4 (Equations (36) and (37)). 

There are also two important nonnuclear transient tracers, chlorofluorocarbons CFC-11 and CFC-12, which have also proven very useful in view of their known (changing) relative concentrations in the atmosphere. These behave essentially as conservative tracers any CFC losses would not be expected to change their ratio in the oceanic water mass. The use of new tracers (FI 13, CCI4) has extended the time-scales of CFC in both directions. 

In some instances, it is possible to use specific tracer concentrations, in particular radioactive or transient tracers to define a tracer age. The underlying premise is that the tracer age is set to zero at some starting point (usually the ocean surface) and progressively increases after contact... 

Tracers serve as a dye with which to follow the circulation of ocean waters. There are conventional ocean tracers such as temperature, salinity, oxygen, and nutrients. There are stable isotope tracers such as oxygen-18, carbon-13, and there are radioactive tracers both naturally occurring (such as the uranium/thorium series, and radium), and those produced both naturally and by the bomb tests (such as tritium and carbon-14). The bomb contributions from the latter two are called transient tracers, as are the CFCs, because they have been in the atmosphere for a short time. This implies an anthropogenic source and a nonsteady input function. 

Several further applications of the tracer technique are presently under way. Two large scale experiments in the open ocean are being actively monitored, in the Greenland Sea and the Brazil Basin. Numerous useful subsurface experiments can be imagined. However, because of the conflict between such subsurface release experiments and the use of SFg as a transient tracer, there is a need to establish a forum by which the wider oceanographic community can have input into the planning of prospective release experiments. 

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