Deep ocean circulation tracer

Joly observed elevated "Ra activities in deep-sea sediments that he attributed to water column scavenging and removal processes. This hypothesis was later challenged with the hrst seawater °Th measurements (parent of "Ra), and these new results conhrmed that radium was instead actively migrating across the marine sediment-water interface. This seabed source stimulated much activity to use radium as a tracer for ocean circulation. Unfortunately, the utility of Ra as a deep ocean circulation tracer never came to full fruition as biological cycling has been repeatedly shown to have a strong and unpredictable effect on the vertical distribution of this isotope. 

Nozaki Y, Yamada M, Nikaido H (1990) The marine geochemistry of actinium-227 evidence for its migration through sediment pore water. Geophys Res Lett 17 1933-1936 Nozaki Y (1993) Actinium-227 a steady state tracer for the deep-se basin wide circulation and mixing studes. In Deep Ocean Circulation, Physical and Chemical Aspects. Teramoto T (ed) Elsevier p 139-155... 

The primary application of early radiocarbon results was to estimate the flux of CO2 between the atmosphere and ocean and the average residence time in the ocean. Sufficient subsurface ocean measurements were made, primarily by W. Broecker (Lamont-Doherty Earth Observatory LDEO) and H. Craig (Scripps Institution of Oceanography SIO), to recognize that radiocarbon had the potential to be an important tracer of deep ocean circulation and mixing rates. 

North Atlantic Deep Water (NADW), which is formed with an initial 5 C-value between 1.0 and 1.5%c, becomes gradually depleted in C as it travels southward and mixes with Antarctic bottom water, which has an average 8 C-value of 0.3%c (Kroopnick 1985). As this deep water travels to the Pacific Ocean, its C/ C ratio is further reduced by 0.5%o by the continuous flux and oxidation of organic matter in the water column. This is the basis for using 8 C-values as a tracer of paleo-oceanographic changes in deep water circulation (e.g., Curry et al. 1988). 

The water mass tracers discussed above can be used to assess the sources of subsurface water masses and the mixture of waters from different sources. However, this information can be used only to assess the relative rates of renewal of these deep-water masses from the various source regions (e.g., LeGrand and Wunsch, 1995). There are several geochemical techniques that can be used to assess the rates of ocean circulation. 

As illustrated, the A " C distribution can be used to infer general large-scale circulation patterns. The most valuable applications for radiocarbon derive from the fact that it is radioactive and has a half-life appropriate to the study of deep ocean processes and that the bomb component is transient and is useful as a tracer for upper ocean processes. A few of the more common uses are described below. 

Arons A. B. and. Stommel H. (1967) On the abyssal circulation of the world ocean 111. An advection-lateral mixing model of the distribution of a tracer property in an ocean basin. Deep-Sea Res. 14, 441-457. 

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