The carbon dioxide system in the Arabian Sea
DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY, 45 (10-11):
2225--2252 (1998)Abstract
In 1995 the WHOI (C. Goyet) and MIAMI (F.J. Miliero) groups participated
on a number of research cruises in the Arabian Sea as part of the
U.S. Joint Global Ocean Flux Study (JGOFS) sponsored by the National
Science Foundation (NSF). This paper gives the results of our total
inorganic carbon dioxide (TCO2), total alkalinity (TA) and potentiometric
pH measurements made on Arabian Sea water samples during these cruises.
Measurements made on Certified Reference Material (CRM) indicate
that the reproducibility of the measurements was +/- 0.007 in pH,
+/- 3.2 mu mol kg(-1) in TA, and +/- 1.2 mu molkg(-1) in TCO2 (N
= 180). The surface measurements (0-30 m) of pH and normalized TCO2,
and TA were quite uniform throughout the year (pH = 8.1 +/- 0.05,
NTCO2 = 1950 +/- 20 mu molkg(-1) and NTA = 2290 +/- 5 mu molkg(-1)).
The larger variations in NTCO2 in the surface waters are related
to changes in primary production and upwelling in the coastal waters.
The depth profiles of pH, pCO(2), TA, and TCO2 were similar to those
in the Equatorial Pacific Ocean. The components of the carbonate
system (CO2, HCO3-, CO32-) and the saturation state (Omega) for calcite
and aragonite were determined from the measurements of TA and TCO2.
The waters below 600 and 3400 m in the Arabian Sea were undersaturated
(Omega < 1.0) for aragonite and calcite, respectively. The CO2 measurements
have been combined with the nutrient data to examine the stoichiometric
ratios of C/N, C/P, C/O-2, and C/SiO2 of the waters. Marked differences
were found for the waters above and below the oxygen minimum zone.
The surface water results have been used to develop the following
stoichiometry for phytoplankton in the Arabian Sea (CH2O)(125)(NH3)(14)(H3PO4)(SiO2)(13).
The oxidation of this material is due to reactions with O-2 (77%)
and NO3 (23%) with the resultant formation of N-2 and N2O. The maximum
amount of organic carbon oxidized has been estimated to be 3.1 mu
molkg(-1) in the deep waters with as much as 0.9 mu molkg(-1) in
the oxygen minimum zone with NO3. The maximum amount of CaCO3 dissolved
in the deep waters is 116 mu molkg(-1). These results, together with
the organic material collected from the sediment traps, should be
useful in characterizing the formation and degradation of plant material
in the Arabian Sea. (C) 1998 Elsevier Science Ltd. All rights reserved.