Construction of STOX oxygen sensors and their application for determination of O2 concentrations in oxygen minimum zones.
ABSTRACT Until recently, it has not been possible to measure O(2) concentrations in oxygen minimum zones (OMZs) with sufficient detection limits and accuracy to determine whether OMZs are anoxic or contain 1-2 μM O(2). With the introduction of the STOX (switchable trace oxygen) sensor, the level for accurate quantification has been lowered by a factor of 1000. By analysis with STOX sensors, O(2) can be prevented from reaching the sensing cathode by another cathode (front guard cathode), and it is the amplitude in signal by polarization/depolarization of this front guard that is used as a measure of the O(2) concentration. The STOX sensors can be used in situ, most conveniently connected to a conventional CTD (conductivity, temperature, and depth analyzer) along with a conventional oxygen sensor, and they can be used for monitoring O(2) dynamics during laboratory incubations of low-O(2) media such as OMZ water. The limiting factors for use of the STOX sensors are a relatively slow response, with measuring cycle of at least 30 s with the current design, and fragility. With improved procedures for construction, the time for a complete measuring cycle is expected to come down to about 10 s.
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ABSTRACT: a Joint first authorship (these authors have contributed equally to the manuscript). b present address: Abstract. In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phe-nomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and cli-mate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and con-sequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, in-cluding the Baltic Sea, the Black Sea, Scottish and Scandina-vian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxy-genation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were re-solved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophica-tion on long-term oxygen distributions. Organic and inor-ganic proxies were used to extend investigations on past oxy-gen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic com-munities that slowly recover upon a reduction in eutrophica-tion in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the mi-crobially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic min-eralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.Biogeosciences 01/2014; 11:1215-1259. · 3.75 Impact Factor
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ABSTRACT: Despite its huge ecological importance, microbial oxygen respiration in pelagic waters is little studied, primarily due to methodological difficulties. Respiration measurements are challenging because of the required high resolution of oxygen concentration measurements. Recent improvements in oxygen sensing techniques bear great potential to overcome these limitations. Here we compare 3 different methods to measure oxygen consumption rates at low oxygen concentrations, utilizing amperometric Clark type sensors (STOX), optical sensors (optodes), and mass spectrometry in combination with (18-18)O2 labeling. Oxygen concentrations and consumption rates agreed well between the different methods when applied in the same experimental setting. Oxygen consumption rates between 30 and 400 nmol L(-1) h(-1) were measured with high precision and relative standard errors of less than 3%. Rate detection limits in the range of 1 nmol L(-1) h(-1) were suitable for rate determinations in open ocean water and were lowest at the lowest applied O2 concentration.PLoS ONE 01/2014; 9(2):e89369. · 3.73 Impact Factor
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ABSTRACT: Competition for molecular oxygen (O(2)) among respiratory microorganisms is intense because O(2) is a potent electron acceptor. This competition leads to the formation of microoxic environments wherever microorganisms congregate in aquatic, terrestrial and host-associated communities. Bacteria can harvest O(2) present at low, even nanomolar, concentrations using high-affinity terminal oxidases. Here, we report the results of surveys searching for high-affinity terminal oxidase genes in sequenced bacterial genomes and shotgun metagenomes. The results indicate that bacteria with the potential to respire under microoxic conditions are phylogenetically diverse and intriguingly widespread in nature. We explore the implications of these findings by highlighting the importance of microaerobic metabolism in host-associated bacteria related to health and disease.Nature Reviews Microbiology 03/2013; 11(3):205-12. · 22.49 Impact Factor