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  • 1
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    Oxygen Optode Sensors: Principle, Characterization, Calibration, and Application in the Ocean (2018)
    Frontiers
    In:  Frontiers in Marine Science, 4 . Art.No. 429.
    Details
    Publication Date: 2021-05-19
    Description: Recently, measurements of oxygen concentration in the ocean-one of the most classical parameters in chemical oceanography-are experiencing a revival. This is not surprising, given the key role of oxygen for assessing the status of the marine carbon cycle and feeling the pulse of the biological pump. The revival, however, has to a large extent been driven by the availability of robust optical oxygen sensors and their painstakingly thorough characterization. For autonomous observations, oxygen optodes are the sensors of choice: They are used abundantly on Biogeochemical-Argo floats, gliders and other autonomous oceanographic observation platforms. Still, data quality and accuracy are often suboptimal, in some part because sensor and data treatment are not always straightforward and/or sensor characteristics are not adequately taken into account. Here, we want to summarize the current knowledge about oxygen optodes, their working principle as well as their behavior with respect to oxygen, temperature, hydrostatic pressure, and response time. The focus will lie on the most widely used and accepted optodes made by Aanderaa and Sea-Bird. We revisit the essentials and caveats of in-situ in air calibration as well as of time response correction for profiling applications, and provide requirements for a successful field deployment. In addition, all required steps to post-correct oxygen optode data will be discussed. We hope this summary will serve as a comprehensive, yet concise reference to help people get started with oxygen observations, ensure successful sensor deployments and acquisition of highest quality data, and facilitate post-treatment of oxygen data. In the end, we hope that this will lead to more and higher-quality oxygen observations and help to advance our understanding of ocean biogeochemistry in a changing ocean.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.3389/fmars.2017.00429
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Low-nutrient organic matter in the Sargasso Sea thermocline: A hypothesis for its role, identity, and carbon cycle implications (2018)
    Elsevier
    In:  Marine Chemistry, 207 . pp. 108-123.
    Details
    Publication Date: 2021-02-08
    Description: Despite slow nutrient supply to the subtropical surface ocean, its rates of annual inorganic carbon drawdown and net oxygen production are similar to those of nutrient-rich high latitude waters. This surprisingly rapid carbon drawdown, if due to the production and export of marine biomass, cannot be explained in terms of known nutrient supply mechanisms. Moreover, carbon budgets have failed to detect the export of this organic matter. One possible explanation is the export of nutrient-poor organic matter with a composition that avoids detection as sinking particles. We describe three signs of the decomposition of such organic matter in the shallow Sargasso Sea subsurface. First, summertime oxygen consumption at 80–400 m occurs without the rate of nitrate and phosphate production expected from the remineralization of marine biomass, matching the observed summertime mixed layer inorganic carbon drawdown. Second, a seasonal change in the 18O/16O of subsurface nitrate suggests summertime heterotrophic bacterial nitrate assimilation down to ~400 m, as may be required for the remineralization of nutrient-poor organic matter. Third, incubation of subsurface seawater leads to nitrate drawdown and heterotrophic bacterial growth, supporting the thermocline nitrate 18O/16O evidence for heterotrophic nitrate assimilation. These three pieces of evidence suggest the export of nutrient-poor organic matter from the surface at a rate adequate to explain net community production in the Sargasso Sea. We propose that transparent exopolymer particles or related compounds, generated by a nutrient-limited upper ocean ecosystem, comprise this nutrient-poor export, and that its properties cause its flux out of the euphotic zone to be underestimated by sediment traps. Such nutrient-poor organic matter would contribute little to fisheries, deep ocean carbon dioxide storage, or organic carbon burial, so that it may change our view of the significance of net community production in the subtropical ocean
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.marchem.2018.10.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    On the Future of Argo: A Global, Full-Depth, Multi-Disciplinary Array (2019)
    Frontiers
    In:  Frontiers in Marine Science, 6 . Art.Nr. 439.
    Details
    Publication Date: 2022-01-31
    Description: The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opportunistically from the combination of great scientific need and technological innovation. Through the data system, Argo provides fundamental physical observations with broad societally-valuable applications, built on the cost-efficient and robust technologies of autonomous profiling floats. Following recent advances in platform and sensor technologies, even greater opportunity exists now than 20 years ago to (i) improve Argo's global coverage and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems, and (iv) consider experimental sensors that might be included in the future, for example to document the spatial and temporal patterns of ocean mixing. For Core Argo and each of these enhancements, the past, present, and future progression along a path from experimental deployments to regional pilot arrays to global implementation is described. The objective is to create a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System (Legler et al., 2015). The integrated system will deliver operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.3389/fmars.2019.00439
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Coulometric total carbon dioxide analysis for marine studies: measurement and internal consistency of underway TCO2 concentrations (1999)
    Elsevier
    In:  Marine Chemistry, 67 . pp. 123-144.
    Details
    Publication Date: 2017-08-21
    Description: A coulometrically-based SOMMA system for the determination of total dissolved carbon dioxide (TCO2) in a continuous mode was designed and tested at sea. The new continuous technique approached the same high accuracy and reliability associated with prior discrete TCO2 measurements. During three cruises encompassing more than 19 weeks and 6000 continuous TCO2 measurements none of the three different systems tested exhibited any hardware-related failures. We found that coulometer cell lifetimes can greatly exceed prior expectations with many of the titration cells in the continuous mode remaining accurate for up to 72 h at carbon ages exceeding 50 mg C. We suggest a practical definition based on the CRM analyses for changing coulometer cells in the continuous mode. Systematic deviations of the SOMMA pipette volume from a theoretical temperature dependence were identified both from field data comparisons and pipette calibrations. Hence pipettes should be kept at constant temperature or they must be gravimetrically calibrated over the expected temperature range. Comparison of the continuous TCO2 data together with simultaneously measured additional CO2 system parameters showed that the refitted “Mehrbach” dissociation constants for carbonic acid best-represent fCO2 when calculated from TCO2 and alkalinity over a wide range of sea-surface temperatures and salinities. Some remaining systematic differences of calculated–measured fCO2 of up to 9 μatm likely reflect uncertainty in the temperature-dependence of the “Mehrbach” constants as well as possible uncertainty in the alkalinity–salinity relationship used to estimate alkalinity in the consistency checks.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0304-4203(99)00055-9
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    A rapid, batch equilibration method for the measurement of CO2 on discrete water samples (1998)
    ASLO (Association for the Sciences of Limnology and Oceanography)
    In:  Limnology and Oceanography, 42 . pp. 1774-1783.
    Details
    Publication Date: 2014-01-29
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    The international at-sea intercomparison of fCO2 systems during the R/V Meteor Cruise 36/1 in the North Atlantic Ocean (2000)
    Elsevier
    In:  Marine Chemistry, 72 . pp. 171-192.
    Details
    Publication Date: 2017-08-22
    Description: The ‘International Intercomparison Exercise of fCO2 Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO2) systems, one discrete fCO2 system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO2 measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final fCO2 were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO2 in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO2 measurements can be made in good agreement (±3 μatm) with underway fCO2 data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO2 system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO2 results. Calculation of fCO2 from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO2 measurements.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0304-4203(00)00080-3
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Global Oceans (2020)
    AMS (American Meteorological Society)
    Details
    Publication Date: 2024-04-08
    Description: State of the climate in 2019
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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