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| Titel |
Comment on: "Technical note: Consistent calculation of aquatic gross production from oxygen triple isotope measurements" by Kaiser (2011) |
| VerfasserIn |
D. P. Nicholson |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 10 ; Nr. 8, no. 10 (2011-10-27), S.2993-2997 |
| Datensatznummer |
250006168
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| Publikation (Nr.) |
 copernicus.org/bg-8-2993-2011.pdf |
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| Zusammenfassung |
| Kaiser (2011) has introduced an improved method for calculating gross
productivity from the triple isotopic composition of dissolved oxygen in
aquatic systems. His equation avoids approximations of previous
methodologies, and also accounts for additional physical processes such as
kinetic fractionation during invasion and evasion at the air-sea interface.
However, when comparing his new approach to previous methods, Kaiser
inconsistently defines the biological end-member with the result of
overestimating the degree to which the various approaches of previous
studies diverge. In particular, for his base case, Kaiser assigns a 17O
excess to the product of photosynthesis (17δP) that is too low,
resulting in his result being ~30 % too high when compared to
previous equations. When this is corrected, I find that Kaiser's equations
are consistent with all previous study methodologies within about ±20 %
for realistic conditions of metabolic balance (f) and gross
productivity (g). A methodological bias of ±20 % is of similar
magnitude to current uncertainty in the wind-speed dependence of the air-sea
gas transfer velocity, k, which directly impacts calculated gross
productivity rates as well. While previous results could and should be
revisited and corrected using the proposed improved equations, the magnitude
of such corrections may be much less than implied by Kaiser. |
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