4 research outputs found
A comparison of methods for the determination of dissolved oxygen in seawater
An intercalibration of dissolved oxygen methods was conducted at 2 stations
in the Sargasso Sea between April 28 and May 3, 1990. The experiment compared
three techniques using automated endpoint detection with the manual Winkler method using a starch endpoint. Institutions participating in the
intercomparison were the Bedford Institute of Oceanography (automated photometric
titration), the University of Delaware (automated amperometric titration), the
Scripps Institution of Oceanography (manual titration), and the Woods Hole
Oceanographic Institution (automated amperometric titration).
Differences in measured oxygen concentrations between institutions were
encouragingly small. However, small, systematic differences in dissolved oxygen
between institutions did exist. The range between the highest and lowest oxygen
values reported by the 4 institutions never exceeded 0.6% over the entire
concentration range studied (3.4 to 6.2 mlj1). The good agreement is probably
due to the use of the essentials of Carpenter's (1965) modification of the
Winkler method by all institutions.
The intercalibration revealed several aspects of dissolved oxygen
measurements that require further research: (1) the intercalibration should be
extended to very low oxygen concentrations; (2) procedures for measur ing and
applying corrections for the seawater blank need to be formalized; (3) a simple
procedure to measure the temperature of seawater at the time of sampling needs
to be developed; and (4) the solubility of atmospheric oxygen in the Winkler
reagents must be measured as a function of temperature.
The intercalibration also revealed that analytical techniques required for
precise and accurate volumetric measurements were often not applied, even by
experienced analysts. It was found that uncalibrated pipets were used to
dispense standards, that the volumes of oxygen flasks were not corrected for
buoyancy, and that corrections for the thermal expansion of aqueous solutions were often not applied.This research was supported by National Science Foundation Grants OCE 88-
22542 and OCE 88-21977 and OCE 89-07815. Preparation and distribution of this
report by the WHP Office, Woods Hole Oceanographic Institution, Woods Hole, MA.
02543 USA, was supported by NSF Grant OCE 89-07815
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Iodine chemistry in the water column of the Chesapeake Bay: Evidence for organic iodine forms
During the summer of 1987, we collected and analysed Chesapeake Bay water samples for the inorganic iodine species: iodide (by cathodic-stripping squarewave voltammetry) and iodate (by differential pulse polarography); and total iodine (by hypochlorite oxidation of the seawater sample to iodate). The difference between the sum of the inorganic iodine species and the total iodine was significant for about one-third of the samples collected from the Bay. Thus, in these samples, a third (or more) ‘new’ form(s) of iodine was present. These samples were primarily from oxygen-saturated surface waters of high biological activity (primary productivity and bacterial processes). This ‘new’ form can make up as much as 70% of the total iodine. Waters containing low oxygen concentrations showed less of this ‘new’ form of iodine whereas anoxic and sulphidic bottom waters contained only iodide. This ‘new’ form of iodine is organic in nature and probably non-volatile. It may reside in the peptide and humic fractions.
Only reduced iodine (iodide and organic iodine) was detected in waters from the northern section of the Bay, whereas only iodide and iodate were detected in the southern section of the Bay. In only two samples were iodide, iodate and the ‘new’ form of iodine found to coexist. Iodide and organic iodine are probably cycled in the surface waters of the northern section of the Bay via a combination of biogeochemical and photochemical processes which produce the reactive intermediates, molecular iodine and hypoiodous acid. These react quickly with reduced inorganic and organic compounds to maintain the reduced forms of iodine in the water column. Only total iodine is conservative throughout the estuary. The inorganic iodine forms can be used as geochemical tracers