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| Titel |
Spectrophotometric high-precision seawater pH determination for use in underway measuring systems |
| VerfasserIn |
S. Aßmann, C. Frank, A. Körtzinger |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1812-0784
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| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 7, no. 5 ; Nr. 7, no. 5 (2011-10-04), S.597-607 |
| Datensatznummer |
250004801
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| Publikation (Nr.) |
 copernicus.org/os-7-597-2011.pdf |
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| Zusammenfassung |
| Autonomous sensors are required for a comprehensive documentation of
the changes in the marine carbon system and thus to differentiate
between its natural variability and anthropogenic
impacts. Spectrophotometric determination of pH – a key variable of
the seawater carbon system – is particularly suited to achieve
precise and drift-free measurements. However, available
spectrophotometric instruments are not suitable for integration into
automated measurement systems (e.g. FerryBox) since they do not meet
the major requirements of reliability, stability, robustness and
moderate cost. Here we report on the development and testing of a~new
indicator-based pH sensor that meets all of these requirements. This
sensor can withstand the rough conditions during long-term deployments
on ships of opportunity and is applicable to the open ocean as well
as to coastal waters with a complex matrix and highly variable
conditions. The sensor uses a high resolution CCD spectrometer as
detector connected via optical fibers to a custom-made cuvette
designed to reduce the impact of air bubbles. The sample temperature
can be precisely adjusted (25 °C ± 0.006 °C)
using computer-controlled power supplies and Peltier
elements thus avoiding the widely used water bath. The overall setup
achieves a measurement frequency of 1 min−1 with a precision of
±0.0007 pH units, an average offset of +0.0005 pH units to
a reference system, and an offset of +0.0081 pH units to a certified
standard buffer. Application of this sensor allows monitoring of
seawater pH in autonomous underway systems, providing a key variable for
characterization and understanding of the marine carbon system. |
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