Principal Investigator: Rik Wanninkhof
Collaborating scientist(s):
Peter Ortner
Gary Hitchcock
Mike Farmer
Objective: Use of deliberate tracers to study chemical and biological processes in a Lagrangian space frame.
Rationale: Chemical and biological time series studies in coastal and open ocean are hampered by advection (and dispersion) of the watermass in which the processes are studied. This problem can be circumvented by following the processes in a Lagrangian space frame. Drifters can be used for this purpose but slippage can be a serious problem. By tagging the water mass with the deliberate tracer, sulfur hexafluoride (SF6), truly Lagrangian studies can be performed of several week's duration.
Method: Deliberate tracer experiments to date on the ocean using SF6 have concentrated on gas exchange studies [Wanninkhof et al., 1993; Watson et al., 1991] , or perturbation experiments (iron fertilization) [Watson et al., 1994] . In the latter study, the primary application of SF6 was as a water mass tracer. It is well suited for oceanic tracer studies since the gas is non-reactive, non-toxic, cheap ($2 per mol), and has a minimal detectable level of 3 x 10-17 mol/L. Loss by air-sea gas exchange can be accounted for by empirical algorithms with wind speed or more accurately by injecting a second tracer 3He. The Florida Shelf Lagranian Experiment (FSLE), performed in the Spring of 1996, (Figure) showed that the tracer patch could be followed with ease over 15 days. The FSLE concentrated on following the evolution of biological processes in the tracer patch and on determining the difference in advection patterns of the tracers patch compared to drifting buoys.
Key reference:
Wanninkhof R., Hitchcock G., Wiseman W., Vargo G., Ortner P., Asher W., Ho D., Schlosser P., Dickson M.-L., Anderson M., Masserini R., Fanning K., and Zhang J.-Z. (1997) Gas Exchange, Dispersion, and Biological Productivity on the West Florida Shelf: Results from a Lagrangian Tracer Study. Geophys. Res. Let. 24, 1767-1770.

Wanninkhof, R., W. Asher, R. Weppernig, H. Chen, P. Schlosser, C. Langdon, and R. Sambrotto, Gas transfer experiment on Georges Bank using two volatile deliberate tracers, J. Geophys. Res., 98 (C11), pp. 20237-20248, 1993.

Watson, A.J., C.S. Law, K. Van Skoy, F.J. Millero, W. Yao, G.E. Friederich, M.I. Liddicoat, R.H. Wanninkhof, R.T. Barber, and K.H. Coale, Minimal effect of iron fertilization on sea-surface carbon dioxide concentrations, Nature, 371, pp. 143-145, 1994.

Watson, A.J., R.C. Upstill-Goddard, and P.S. Liss, Air-sea exchange in rough and stormy seas, measured by a dual tracer technique, Nature, 349, pp. 145-147, 1991.

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