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In situ quantification of ultra‐low O 2 concentrations in oxygen minimum zones: Application of novel optodes
Author(s) -
Larsen Morten,
Lehner Philipp,
Borisov Sergey M.,
Klimant Ingo,
Fischer Jan P.,
Stewart Frank J.,
Canfield Donald E.,
Glud Ronnie N.
Publication year - 2016
Publication title -
limnology and oceanography: methods
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.898
H-Index - 72
ISSN - 1541-5856
DOI - 10.1002/lom3.10126
Subject(s) - oxygen sensor , detection limit , in situ , analytical chemistry (journal) , hydrostatic pressure , oxygen , chemistry , environmental science , materials science , environmental chemistry , chromatography , physics , organic chemistry , thermodynamics
Abstract Conventional sensors for the quantification of O 2 availability in aquatic environments typically have limits of detection (LOD) of > 1 μmol L −1 and do not have sufficient resolution to reliably measure concentrations in strongly O 2 depleted environments. We present a novel trace optical sensor based on the palladium(II)‐benzoporphyrin luminophore, immobilized in a perfluorinated matrix with high O 2 permeability. The trace sensor has a detection limit of ∼5 nmol L −1 with a dynamic range extending up to ∼2 μmol L −1 . The sensor demonstrates a response time < 30 s and a small, predictable, and fully reversible response to hydrostatic pressure and temperature. The sensor showed excellent stability for continuously measurements during depth profiling in Oxygen Minimum Zones (OMZ). The novel sensor was deployed in situ using a Trace Oxygen Profiler instrument (TOP) equipped with two additional O 2 optical sensors, with higher dynamic range, allowing, when combined, measurements of O 2 concentration from ∼5 nmol L −1 to 1000 μmol L −1 with a single instrument. The TOP instrument was deployed in the OMZ regions of the Eastern Tropical North Pacific (ETNP) and Bay of Bengal (BoB). The measurements demonstrated that O 2 concentrations in the ETNP generally were below the LOD of the trace sensor, but that large sub‐micromolar O 2 intrusions, spanning 60–80 m with maximum O 2 concentrations above 50 nmol L −1 , could be observed in the OMZ core. The O 2 concentrations in the BoB were high compared to the ETNP and rarely decreased below 50 nmol L −1 , but demonstrated tremendous small‐scale variability.