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Fully automated spectrophotometric approach to determine oxygen concentrations in seawater via continuous‐flow analysis
Author(s) -
Reinthaler Thomas,
Bakker Karel,
Manuels Rinus,
van Ooijen Jan,
Herndl Gerhard J.
Publication year - 2006
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.4319/lom.2006.4.358
Subject(s) - seawater , absorbance , oxygen , ocean gyre , upwelling , chemistry , analytical chemistry (journal) , transect , distilled water , environmental chemistry , environmental science , subtropics , oceanography , chromatography , geology , ecology , organic chemistry , biology
Oxygen consumption measurements are the most common approach to estimate the remineralization of organic carbon to CO 2 . A refined protocol of the spectrophotometric Winkler approach is presented, where a continuous‐flow analyzer is coupled with a custom‐made autosampler holding up to 30 oxygen bottles. The time required for analysis is 2 min per sample, and the precision is 0.05% at ~200 mmol O 2 m −3 . Thus, analysis speed and quality are significantly improved compared to the classic Winkler titration approach to determine O 2 concentrations. The accuracy of the method is 99.7% ± 0.2% as determined by comparing the measured versus the theoretical oxygen concentration of saturated seawater at 20°C. The measured absorbance of the iodine at 460 nm wavelength was linear up to an equivalent of 320 mmol O 2 m −3 , which is within the range of open‐ocean oxygen concentrations. The instrument was tested on a cruise in the subtropical North Atlantic where community respiration (CR) and bacterial respiration (BR) were determined. Both CR and BR decreased by ~85% from the Mauritanian upwelling region and the oligotrophic gyre. Along this transect, the contribution of BR to CR increased from 36% to 76%. The instrument proved highly suitable for work at sea and should allow more rapid and precise oxygen concentration measurements under open‐ocean conditions.