I and my students are working on two problems in Chemical Oceanography:
(1) We use the distribution of major atmospheric gases, O2, N2, Ar and Ne and
their stable isotopes to study the processes of gas exchange and biological oxygen
production in the oceans. The primary goal is to determine the biologically produced
oxygen flux in the euphotic zone of the ocean. The oxygen flux is a measure of the
biological carbon export which is instrumental in controlling the CO2 content of the
atmosphere and responsible for determining the redox state of the deep sea. The net
organic carbon flux out of the upper ocean is presently poorly known and our goal is to
determine it in as many areas as possible so that generalities can be advanced about the
global rate and the factors controlling it. These studies involve measuring gases at ocean
time-series stations, developing methods to make gas measurements on autonomous
vehicles and moorings and interpretation of the results using models of atmosphere-ocean
gas exchange and upper-ocean mixing. We have on-going field programs that involve
traditional sampling on ships, oxygen and nitrogen gas determinations using sensors on
moorings, and measurement
of oxygen using an
autonomous vehicle (glider)
that travels unattended in the
upper ocean for periods of up
to 6 months.
Remote measurements of
Oxygen and Nitrogen
supersaturation (Δ) at 10
meters depth on a mooring
at the Hawaii Ocean Time
series (HOT) during the
year 2005 (from Emerson et
al., 2007)
Oxygen supersaturation
determined by a glider
survey at HOT. Colors
are in percent
supersaturation. The
dimensions are a 50 X 50
km grid X 200 m depth.
The results are
objectively mapped for
the month of August.
(from Nicholson et al.,
2007)
(2) Using the methods of mass spectrometry we have been able to show that argon
and nitrogen are undersaturated in the deep ocean and supersaturated in the thermocline
of the ocean. Processes that control the saturation state are the mechanism of deep water
formation and the rates of diapycnal mixing in the ocean thermocline. Both of these
oceanographic mechanisms are difficult to characterize in present ocean models. Our
goal is to develop the distribution of the saturation state of inert gases as tracers for
determining mixing and circulation processes in the ocean.
Argon supersaturation as a function of density at the locations indicated in the E.
Eq pacific. Densities of 24-26.5 represent depths of ~100-300 m. The
supersaturation in this region is caused by mixing across density surfaces. (From
Geherie et al., 2005)