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Characterization of a time-domain dual lifetime referencing pCO2 optode and deployment as a high-resolution underway sensor across the high latitude North Atlantic Ocean

Characterization of a time-domain dual lifetime referencing pCO2 optode and deployment as a high-resolution underway sensor across the high latitude North Atlantic Ocean
Characterization of a time-domain dual lifetime referencing pCO2 optode and deployment as a high-resolution underway sensor across the high latitude North Atlantic Ocean
The ocean is a major sink for anthropogenic carbon dioxide (CO2), with the CO2 uptake causing changes to ocean chemistry. To monitor these changes and provide a chemical background for biological and biogeochemical studies, high quality partial pressure of CO2 (pCO2) sensors are required, with suitable accuracy and precision for ocean measurements. Optodes have the potential to measure in situ pCO2 without the need for wet chemicals or bulky gas equilibration chambers that are typically used in pCO2 systems. However, optodes are still in an early developmental stage compared to more established equilibrator-based pCO2 systems. In this study, we performed a laboratory-based characterization of a time-domain dual lifetime referencing pCO2 optode system. The pCO2 optode spot was illuminated with low intensity light (0.2 mA, 0.72 mW) to minimize spot photobleaching. The spot was calibrated using an experimental gas calibration rig prior to deployment, with a determined response time (τ63) of 50 s at 25°C. The pCO2 optode was deployed as an autonomous shipboard underway system across the high latitude North Atlantic Ocean with a resolution of ca.10 measurements per hour. The optode data was validated with a secondary shipboard equilibrator-based infrared pCO2 instrument, and pCO2 calculated from discrete samples of dissolved inorganic carbon and total alkalinity. Further verification of the pCO2 optode data was achieved using complimentary variables such as nutrients and dissolved oxygen. The shipboard precision of the pCO2 sensor was 9.5 μatm determined both from repeat measurements of certified reference materials and from the standard deviation of seawater measurements while on station. Finally, the optode deployment data was used to evaluate the physical and biogeochemical controls on pCO2.
2296-7745
Clarke, Jennifer S.
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Humphreys, Matthew P.
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Tynan, Eithne
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Kitidis, Vassilis
dcefa34f-4596-4bbf-b7f8-6b3c422e2df8
Brown, Ian
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Mowlem, Matthew
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Achterberg, Eric P.
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Clarke, Jennifer S.
b52af005-821a-4b39-93b7-c0b66ce9d66c
Humphreys, Matthew P.
40cb219a-c2dd-4581-94d0-52fb1c992498
Tynan, Eithne
dfed4bbd-ea2a-4ff9-81f5-de2af563943b
Kitidis, Vassilis
dcefa34f-4596-4bbf-b7f8-6b3c422e2df8
Brown, Ian
42b64387-e5bb-4729-9b46-4bc79d749688
Mowlem, Matthew
6f633ca2-298f-48ee-a025-ce52dd62124f
Achterberg, Eric P.
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Clarke, Jennifer S., Humphreys, Matthew P., Tynan, Eithne, Kitidis, Vassilis, Brown, Ian, Mowlem, Matthew and Achterberg, Eric P. (2017) Characterization of a time-domain dual lifetime referencing pCO2 optode and deployment as a high-resolution underway sensor across the high latitude North Atlantic Ocean. Frontiers in Marine Science, 4. (doi:10.3389/fmars.2017.00396).

Record type: Article

Abstract

The ocean is a major sink for anthropogenic carbon dioxide (CO2), with the CO2 uptake causing changes to ocean chemistry. To monitor these changes and provide a chemical background for biological and biogeochemical studies, high quality partial pressure of CO2 (pCO2) sensors are required, with suitable accuracy and precision for ocean measurements. Optodes have the potential to measure in situ pCO2 without the need for wet chemicals or bulky gas equilibration chambers that are typically used in pCO2 systems. However, optodes are still in an early developmental stage compared to more established equilibrator-based pCO2 systems. In this study, we performed a laboratory-based characterization of a time-domain dual lifetime referencing pCO2 optode system. The pCO2 optode spot was illuminated with low intensity light (0.2 mA, 0.72 mW) to minimize spot photobleaching. The spot was calibrated using an experimental gas calibration rig prior to deployment, with a determined response time (τ63) of 50 s at 25°C. The pCO2 optode was deployed as an autonomous shipboard underway system across the high latitude North Atlantic Ocean with a resolution of ca.10 measurements per hour. The optode data was validated with a secondary shipboard equilibrator-based infrared pCO2 instrument, and pCO2 calculated from discrete samples of dissolved inorganic carbon and total alkalinity. Further verification of the pCO2 optode data was achieved using complimentary variables such as nutrients and dissolved oxygen. The shipboard precision of the pCO2 sensor was 9.5 μatm determined both from repeat measurements of certified reference materials and from the standard deviation of seawater measurements while on station. Finally, the optode deployment data was used to evaluate the physical and biogeochemical controls on pCO2.

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Accepted/In Press date: 24 November 2017
e-pub ahead of print date: 15 December 2017
Published date: 15 December 2017

Identifiers

Local EPrints ID: 417078
URI: https://eprints.soton.ac.uk/id/eprint/417078
ISSN: 2296-7745
PURE UUID: 4b788b71-0a5d-4db2-9b53-3439733a914d

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Date deposited: 19 Jan 2018 17:30
Last modified: 19 Jul 2019 17:38

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Contributors

Author: Jennifer S. Clarke
Author: Matthew P. Humphreys
Author: Eithne Tynan
Author: Vassilis Kitidis
Author: Ian Brown
Author: Matthew Mowlem

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