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  • 1
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    Using cavity ringdown spectroscopy for continuous monitoring of δ13C(CO2) and ƒCO2 in the surface ocean (2012)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 10 . pp. 752-766.
    Details
    Publication Date: 2019-09-23
    Description: The role of the global surface ocean as a source and sink for atmospheric carbon dioxide and the flux strengths between the ocean and the atmosphere can be quantified by measuring the fugacity of CO2 (ƒCO2) as well as the dissolved inorganic carbon (DIC) concentration and its isotopic composition in surface seawater. In this work, the potential of continuous wave cavity ringdown spectroscopy (cw-CRDS) for autonomous underway measurements of ƒCO2 and the stable carbon isotope ratio of DIC [δ13C(DIC)] is explored. For the first time, by using a conventional air-sea equilibrator setup, both quantities were continuously and simultaneously recorded during a field deployment on two research cruises following meridional transects across the Atlantic Ocean (Bremerhaven, Germany–Punta Arenas, Chile). Data are compared against reference measurements by an established underway CO2 monitoring system and isotope ratio mass spectrometric analysis of individual water samples. Agreement within ΔƒCO2 = 0.35 μatm for atmospheric and ΔƒCO2 = 2.5 μatm and Δδ13C(DIC) =0.33‰ for seawater measurements have been achieved. Whereas “calibration-free” ƒCO2 monitoring is feasible, the measurement of accurate isotope ratios relies on running reference standards on a daily basis. Overall, the installed CRDS/equilibrator system was shown to be capable of reliable online monitoring of ƒCO2, equilibrium δ13C(CO2), δ13C(DIC), and pO2 aboard moving research vessels, thus making possible corresponding measurements with high spatial and temporal resolution.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2012.10.752
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    In situ quality assessment of a novel underwater pCO2 sensor based on membrane equilibration and NDIR spectrometry (2014)
    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 31 (1). pp. 181-196.
    Details
    Publication Date: 2020-08-04
    Description: We present a detailed quality assessment of a novel underwater sensor for the measurement of CO2 partial pressure (pCO2) based on surface water field deployments carried out between 2008 and 2011. The commercially available sensor, which is based on membrane equilibration and NDIR spectrometry is small and can be integrated into mobile platforms. It is calibrated in water against a proven flow-through pCO2 instrument within a custom-built calibration setup. The aspect of highest concern with respect to achievable data quality of the sensor is the compensation for signal drift inevitably connected to absorption measurements. We use three means to correct for drift effects: (i) a filter correlation or dual-beam setup, (ii) regular zero gas measurements realized automatically within the sensor and (iii) a zero-based transformation of two sensor calibrations flanking the time of sensor deployment. Three sensors were tested against an underway pCO2 system during two major research cruises providing an in situ temperature range from 7.4 to 30.1°C and pCO2 values between 289 and 445 μatm. The average difference between sensor and reference pCO2 was found to be -0.6 ± 3 μatm with a RMSE of 3.7 μatm.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1175/JTECH-D-13-00083.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Time response of oxygen optodes on profiling platforms and its dependence on flow speed and temperature (2014)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 12 . pp. 617-636.
    Details
    Publication Date: 2019-09-23
    Description: The time response behavior of Aanderaa optodes model 3830, 4330, and 4330F, as well as a Sea-Bird SBE63 optode and a JFE Alec Co. Rinko dissolved oxygen sensor was analyzed both in the laboratory and in the field. The main factor for the time response is the dynamic regime, i.e., the water flow around the sensor that influences the boundary layer’s dynamics. Response times can be drastically reduced if the sensors are pumped. Laboratory experiments under different dynamic conditions showed a close to linear relation between response time and temperature. Application of a diffusion model including a stagnant boundary layer revealed that molecular diffusion determines the temperature behavior, and that the boundary layer thickness was temperature independent. Moreover, field experiments matched the laboratory findings, with the profiling speed and mode of attachment being of prime importance. The time response was characterized for typical deployments on shipboard CTDs, gliders, and floats, and tools are presented to predict the response time as well as to quantify the effect on the data for a given water mass profile. Finally, the problem of inverse filtering optode data to recover some of the information lost by their time response is addressed.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2014.12.617
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    In situ CO2 and O2 measurements on a profiling float (2013)
    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 30 . pp. 112-126.
    Details
    Publication Date: 2020-08-04
    Description: In recent years, profiling floats, which form the basis of the successful international Argo observatory, are also being considered as platforms for marine biogeochemical research. This study showcases the utility of floats as a novel tool for combined gas measurements of CO2 partial pressure (pCO2) and O2. These float prototypes were equipped with a small-sized and submersible pCO2 sensor and an optode O2 sensor for high resolution measurements in the surface ocean layer. Four consecutive deployments were carried out during Nov. 2010 and June 2011 near the Cape Verde Ocean Observatory (CVOO) in the eastern tropical North Atlantic. The profiling float performed upcasts every 31 h while measuring pCO2, O2, salinity, temperature and hydrostatic pressure in the upper 200 m of the water column. In order to maintain accuracy, regular pCO2 sensor zeroings at depth and surface, as well as optode measurements in air, were performed for each profile. Through the application of data processing procedures (e.g., time-lag correction) accuracies of float-borne pCO2 measurements were greatly improved (10 – 15 μatm for water column and 5 μatm for surface measurements). O2 measurements yielded an accuracy of 2 μmol kg−1. First results of this pilot study show the possibility of using profiling floats as a platform for detailed and unattended observations of the marine carbon and oxygen cycle dynamics.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/JTECH-D-12-00043.1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A novel electrochemical calibration setup for oxygen sensors and its use for the stability assessment of Aanderaa optodes (2012)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 10 . pp. 921-933.
    Details
    Publication Date: 2019-09-23
    Description: We present a laboratory calibration setup for the individual multi-point calibration of oxygen sensors. It is based on the electrochemical generation of oxygen in an electrolytic carrier solution. Under thorough control of the conditions, i.e., temperature, carrier solution flow rate, and electrolytic current, the amount of oxygen is strictly given by Faraday's laws and can be controlled to within ± 0.5 μmol L–1 (2 SD). Whereas Winkler samples can be taken for referencing with a reproducibility between triplicates of 0.8 μmol L–1 (2 SD), the calibration setup can provide a Winkler-free way of referencing with an accuracy of ± 1.2 μmol L–1 (2 SD). Thus calibrated oxygen optodes have been deployed in the Southern Ocean and the Eastern Tropical Atlantic both in profiling and underway mode and confirm the validity of the laboratory calibrations to within few μmol L–1. In two cases, the optodes drifted between deployments, which was easily identified using the calibration setup. The electrochemical calibration setup may thus facilitate accurate oxygen measurements on a large scale, and its small size makes it possible to configure as a mobile, sea-going, Winkler-free system for oxygen sensor calibrations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2012.10.921
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Oxygen sensor characterization and calibration – Providing the Argo-O2 essentials (2012)
    In:  [Poster] In: 4. Argo Science Workshop, 27.-29.09.2012, Venice, Italy .
    Details
    Publication Date: 2012-12-03
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 7
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    In Situ CO2 and O2 measurements on a profiling float at the Cape Verde Ocean Observatory | CVOO (2012)
    In:  [Poster] In: 5. SOPRAN Annual Meeting, 20.-21.03.2012, Kiel, Germany .
    Details
    Publication Date: 2012-07-12
    Description: During SOPRAN I & II, field work activities focused mainly on the Eastern Tropical North Atlantic (ETNA) near the Cape Verde Ocean Observatory (CVOO). Here we report about two major achievements during SOPRAN I & II: (i) A typical ARGO float with a small-sized and novel submersible CO2 partial pressure (pCO2) sensor and an optode O2 sensor for high resolution measurements in the upper ocean was developed and field-deployed successfully. We report on the quality of the data as well as the distribution of the air-sea fluxes of the two gases. (ii) Autonomous measurements have shown extremely low O2 concentrations below the mixed layer (〈 1 µmol/kg) in certain mesoscale features drastically contrasting the otherwise reasonably well oxygenated open North Atlantic Ocean (〉 40 µmol/kg). To our knowledge no such anoxic water parcels have ever been reported before for the open North Atlantic.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 8
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    Going Beyond Argo-O2: In Situ CO2 and O2 Measurements on Argo Floats (2012)
    In:  [Poster] In: 4. Argo Science Workshop, 27.-29.09.2012, Venice, Italy .
    Details
    Publication Date: 2012-10-12
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 9
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    Low oxygen eddies in the open North Atlantic Ocean (2012)
    In:  [Poster] In: Ocean Sciences Meeting 2012, 20.-24.02.2012, Salt Lake City, USA .
    Details
    Publication Date: 2012-11-29
    Type: Conference or Workshop Item , NonPeerReviewed , info:eu-repo/semantics/conferenceObject
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    OceanRep: Poster
  • 10
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    Spatio-Temporal Variability of the Marine Carbon Cycle at CVOO (2014)
    In:  [Poster] In: SOPRAN Annual Meeting 2014, 25.-26.03.2014, Bremen, Germany .
    Details
    Publication Date: 2014-12-05
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
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