COASTAL OCEAN LAGRANGIAN STUDIES
Use of deliberate tracers to study chemical and biological
processes in a Lagrangian space frame.
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.
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.
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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