MEASUREMENT OF THE TOTAL DISSOLVED INORGANIC CARBON
(DIC) Principal Investigator:
Tom Lantry up to 4/96
Measurement of the total dissolved inorganic carbon (DIC) to determine
oceanic carbon inventory and changes with time
DIC, which is the sum of gaseous CO2, bicarbonate and
carbonate is the major carbon reservoir in the ocean.
Invasion of anthropogenic CO2 should change the DIC
inventory. However, up until now direct observation has been problematic
because of a small signal against a large background. A 40% oceanic
uptake will correspond to average
change in DIC of 1 micromol
kg-1 year-1 in the upper ocean while the DIC
concentration ranges from 1800 to 2300 micromol kg-1.
These uptake estimates are based on observations of the fraction of
fossil fuel carbon remaining in the atmosphere and the penetration of bomb
14C into the upper ocean. However, to increase our
confidence in this value direct observations are essential. The OACES
program aims at determining
the change in oceanic DIC by occupying repeat long lines transects in
every ocean basin on five to
ten-year time scales.
Measurements are performed using a coulometer attached to a SOMMA inlet
system developed by Ken Johnson at Brookhaven National Lab.
Using state-of-the-art instrumentation and certified reference
materials calibrated independently in a land based laboratory, precisions
and accuracies of better
than 1.5 micromol kg-1 have
been obtained on cruises to date in the Atlantic, Pacific and Indian
Oceans. Robust estimates will involve detecting a small signal in a
system which sees seasonal and lateral variations of over 200 micromol
kg-1 due to consumption by
photosynthesis at the
surface and respiration below, and transport by currents (Figure 1). The biological signal can be
separated from the anthropogenic signal using other carbon system
parameters, and by use of
Lantry, T., M.F. Lamb, J.C. Hendee, R. Wanninkhof, R.A.
Feely, F.J. Millero, R. Byrne, E.T.
Peltzer, D. Wilson, and G. Berberian, Chemical and hydrographic
measurements from the Equatorial Pacific during boreal spring 1992, NOAA Data Report
ERL AOML-27, 1995.
Forde, E.B., J.C. Hendee, and R. Wanninkhof,
Hydrographic, carbon dioxide, nutrient, and productivity measurements from
the South Atlantic during July and August of 1991, NOAA Data Report
ERL AOML-24, 1994.
Castle R., Wanninkhof R.,Doney S. C., Bullister J., Johns L., Feely
R.A., Huss B. E., Millero F. J., and Lee K. (submitted, 1998) Chemical and
hydrographic profiles and underway measurements from the North Atlantic
during July and August of 1993, NOAA data report ERL AOML-XX. NOAA/ERL/AOML.
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