is similar. The divergence between the two time histories after that time is probably attributable to the
fact that there were further additions of iron to the
patch water on days 3 and 7 of Ironex II, but only
the single initial iron enrichment during Ironex I,
after which the disappearance of the added Fe, presumably by sedimentation, occurred very quickly.
The simplest possible interpretation of the Ironex
results is therefore that iron supply, when increased
in the equatorial Pacific, allows diatoms to bloom
and the chemistry of the water to change, providing
that the iron concentration is elevated for several
days at least.
Conclusion
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
SF 6 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.
Small-scale releases in surface waters should not
normally compromise the transient tracer signal.
One obvious application now under way is that of
iron fertilization experiments to examine the extent
to which ‘high nutrient low chlorophyll’ regions
other than the equatorial Pacific are limited by iron
availability. The recent Southern Ocean Iron Enrichment Experiment (SOIREE) has shown unequivocal evidence that iron supply does affect the
biology of that region. This experiment was carried
out during sometimes stormy weather, confirming
that the patch-tracking technique works well in the
open ocean under storm conditions.
To summarize, experiments using SF 6 tracer in the
open ocean are now reduced to practice, if not
routine. Three experiments at the 1000-km scale
have so far been initiated, to measure ocean mixing
on these scales. There have been more than twenty
smaller scale experiments, of increasing sophistication, since they were first begun in 1986. For topics
to which they are suited, such as iron limitation,
biogeochemical budgets, gas exchange and diapycnal
mixing rates, these experiments have enabled
something of the precision of the land-based laboratory investigation to be brought to bear in at-sea
oceanography.
See also
Long-Term Tracer Changes. Tracers of Ocean
Productivity.
Further Reading
Cooper DJ, Watson AJ, and Nightingale PD (1996) Large
decrease in ocean-surface CO 2 fugacity in response to
in-situ iron fertilization. Nature 383: 511--513.
Law CS, Watson AJ, Liddicoat MI, and Stanton T (1998)
Sulphur hexaflouride as a tracer of biogeochemical and
physical processes in an open-ocean iron fertilisation
experiment. Deep-Sea Research II 45: 977--994.
Ledwell JR, Montgomery ET, Polzin KL, et al. (2000)
Evidence for enhanced mixing over rough topography
in the abyssal ocean. Nature 403: 179--182.
Ledwell JR, Watson AJ, and Law CS (1998) Mixing of a
tracer in the pycnocline. Journal of Geophysical
Research 103: 21499--21529.
Watson AJ, Law CS, Van Scoy K, et al. (1994) Minimal
effect of iron fertilization on sea-surface carbon dioxide
concentrations. Nature 371: 143--145.
Watson AJ, Messias M-J, Fogelqvist E, et al. (1999) Mixing
and convection in the Greenland sea from a tracer
release. Nature 401: 902--904.
Watson AJ, Upstill-Goddard RC, and Liss PS (1991) Air–
sea gas exchange in rough and stormy seas measured by
a dual-tracer technique. Nature 349: 145--147.
180 TRACER RELEASE EXPERIMENTS
fact that there were further additions of iron to the
patch water on days 3 and 7 of Ironex II, but only
the single initial iron enrichment during Ironex I,
after which the disappearance of the added Fe, presumably by sedimentation, occurred very quickly.
The simplest possible interpretation of the Ironex
results is therefore that iron supply, when increased
in the equatorial Pacific, allows diatoms to bloom
and the chemistry of the water to change, providing
that the iron concentration is elevated for several
days at least.
Conclusion
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
SF 6 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.
Small-scale releases in surface waters should not
normally compromise the transient tracer signal.
One obvious application now under way is that of
iron fertilization experiments to examine the extent
to which ‘high nutrient low chlorophyll’ regions
other than the equatorial Pacific are limited by iron
availability. The recent Southern Ocean Iron Enrichment Experiment (SOIREE) has shown unequivocal evidence that iron supply does affect the
biology of that region. This experiment was carried
out during sometimes stormy weather, confirming
that the patch-tracking technique works well in the
open ocean under storm conditions.
To summarize, experiments using SF 6 tracer in the
open ocean are now reduced to practice, if not
routine. Three experiments at the 1000-km scale
have so far been initiated, to measure ocean mixing
on these scales. There have been more than twenty
smaller scale experiments, of increasing sophistication, since they were first begun in 1986. For topics
to which they are suited, such as iron limitation,
biogeochemical budgets, gas exchange and diapycnal
mixing rates, these experiments have enabled
something of the precision of the land-based laboratory investigation to be brought to bear in at-sea
oceanography.
See also
Long-Term Tracer Changes. Tracers of Ocean
Productivity.
Further Reading
Cooper DJ, Watson AJ, and Nightingale PD (1996) Large
decrease in ocean-surface CO 2 fugacity in response to
in-situ iron fertilization. Nature 383: 511--513.
Law CS, Watson AJ, Liddicoat MI, and Stanton T (1998)
Sulphur hexaflouride as a tracer of biogeochemical and
physical processes in an open-ocean iron fertilisation
experiment. Deep-Sea Research II 45: 977--994.
Ledwell JR, Montgomery ET, Polzin KL, et al. (2000)
Evidence for enhanced mixing over rough topography
in the abyssal ocean. Nature 403: 179--182.
Ledwell JR, Watson AJ, and Law CS (1998) Mixing of a
tracer in the pycnocline. Journal of Geophysical
Research 103: 21499--21529.
Watson AJ, Law CS, Van Scoy K, et al. (1994) Minimal
effect of iron fertilization on sea-surface carbon dioxide
concentrations. Nature 371: 143--145.
Watson AJ, Messias M-J, Fogelqvist E, et al. (1999) Mixing
and convection in the Greenland sea from a tracer
release. Nature 401: 902--904.
Watson AJ, Upstill-Goddard RC, and Liss PS (1991) Air–
sea gas exchange in rough and stormy seas measured by
a dual-tracer technique. Nature 349: 145--147.
180 TRACER RELEASE EXPERIMENTS