TY - JOUR
T1 - Sampling in low oxygen aquatic environments
T2 - The deviation from anoxic conditions
AU - Garcia-Robledo, Emilio
AU - Paulmier, Aurelien
AU - Borisov, Sergey M.
AU - Revsbech, Niels Peter
N1 - Funding Information:
We would like to thank Lars B. Pedersen at Aarhus University for the construction of STOX sensors. We are grateful to the cruise leaders Bess B. Ward and Frank Stewart for the invitation to participate in OMZ cruises. We also thank the captains and crews of the R/Vs L'Atalante, New Horizon, Oceanus and Sally Ride. We additionally thank A. Franco‐Garcia, M. Giraud, J. Ledesma, F. Baurand, D. Lefèvre, B. Dewitte, C. Maes, V. Garçon and the PACOP platform (Toulouse) for operational and experimental support during the AMOP cruise. This work was funded by the Poul Due Jensen Foundation and co‐financed by the 2014–2020 ERDF Operational Programme and by the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (to EGR, project reference FEDER‐UCA18‐107225).
Publisher Copyright:
© 2021 The Authors. Limnology and Oceanography: Methods published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.
PY - 2021/11
Y1 - 2021/11
N2 - Studies of the impact of hypoxic or anoxic environments on both climate and ecosystems rely on a detailed characterization of the oxygen (O2) distribution along the water column. The former trivial separation between oxic and anoxic conditions is now often redefined as a blurry concentration range in which both aerobic and anaerobic processes might coexist, both in situ and during experimental incubations. The O2 concentrations during such incubations have often been assumed to be equal to in situ levels, but the concentration was rarely measured. In order to evaluate the actual oxygen concentration in samples collected from low-oxygen environments, a series of measurements were performed on samples collected in the Pacific oxygen minimum zones. Our results show a significant deviation from in situ anoxic conditions in samples collected by Niskin bottles where leakage from the bottle material resulted in O2 concentrations of up to 1 μM. Subsequent sampling further increased the O2 contamination. Sampling and analysis by Winkler method resulted in variable apparent concentrations of 2–4 μM. Two common procedures to avoid atmospheric contamination were also tested: allowing gentle overflow and keeping the sampling bottle submersed in a portion of the sampled water. Both procedures resulted in similar O2 contamination with values of 0.5–1.5 μM when bottles were immediately closed and measurements performed with optical sensors, and 3–4 μM apparent concentration when analyzed by the Winkler method. Winkler titration is thus not suited for analysis of low-O2 samples. It can be concluded that incubation under anoxic conditions requires deoxygenation after conventional sampling.
AB - Studies of the impact of hypoxic or anoxic environments on both climate and ecosystems rely on a detailed characterization of the oxygen (O2) distribution along the water column. The former trivial separation between oxic and anoxic conditions is now often redefined as a blurry concentration range in which both aerobic and anaerobic processes might coexist, both in situ and during experimental incubations. The O2 concentrations during such incubations have often been assumed to be equal to in situ levels, but the concentration was rarely measured. In order to evaluate the actual oxygen concentration in samples collected from low-oxygen environments, a series of measurements were performed on samples collected in the Pacific oxygen minimum zones. Our results show a significant deviation from in situ anoxic conditions in samples collected by Niskin bottles where leakage from the bottle material resulted in O2 concentrations of up to 1 μM. Subsequent sampling further increased the O2 contamination. Sampling and analysis by Winkler method resulted in variable apparent concentrations of 2–4 μM. Two common procedures to avoid atmospheric contamination were also tested: allowing gentle overflow and keeping the sampling bottle submersed in a portion of the sampled water. Both procedures resulted in similar O2 contamination with values of 0.5–1.5 μM when bottles were immediately closed and measurements performed with optical sensors, and 3–4 μM apparent concentration when analyzed by the Winkler method. Winkler titration is thus not suited for analysis of low-O2 samples. It can be concluded that incubation under anoxic conditions requires deoxygenation after conventional sampling.
UR - http://www.scopus.com/inward/record.url?scp=85113524954&partnerID=8YFLogxK
U2 - 10.1002/lom3.10457
DO - 10.1002/lom3.10457
M3 - Article
AN - SCOPUS:85113524954
SN - 1541-5856
VL - 19
SP - 733
EP - 740
JO - Limnology and Oceanography: Methods
JF - Limnology and Oceanography: Methods
IS - 11
ER -
