Preprints
https://doi.org/10.5194/os-2019-101
https://doi.org/10.5194/os-2019-101

  11 Oct 2019

11 Oct 2019

Review status: this preprint is currently under review for the journal OS.

Medusa-Aqua system: simultaneous measurement and evaluation of novel potential halogenated transient tracers HCFCs, HFCs and PFCs in the ocean

Pingyang Li and Toste Tanhua Pingyang Li and Toste Tanhua
  • Marine Biogeochemistry, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel 24105, Germany

Abstract. This study evaluates the potential usefulness of the halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116 as the time-dependent oceanographic transient tracers in order to better constrain ocean ventilation processes. We collected seawater samples and improved on an established analytical technique, the Medusa-Aqua system, to simultaneous measure them, and estimate their stability in seawater following previous work on the atmospheric history and solubility. HCFC-22, HCFC-141b, HCFC-142b, HFC-134a and HFC-125 have been measured in profiles in the Mediterranean Sea for the first time. We estimated the historic surface saturation anomalies of transient tracers in the Mediterranean Sea by evaluating the historic record. Their stability in seawater was estimated by analysis of their ocean partial lifetimes, seawater surface saturations and concentrations compared to CFC-12 measurements by a well-established technique. Of the investigated compounds, HCFC-141b was found to be the most promising transient tracer in the ocean; it fulfills several essential requirements by virtue of well-documented atmospheric history, established seawater solubility, inertness in seawater and feasible measurements and indication of conservative behavior in seawater by having mean ages in agreement to be expected from both CFC-12 and SF6 observations. However, more information on degradation is needed to further identify its stability in seawater, and HCFC-141b has restrictions on production and consumption imposed by the Montreal Protocol leading to its decreasing atmospheric mole fractions since 2017. The most potential oceanic transient tracers were PFC-14 and PFC-116 due to their stability in seawater, the long and well-documented atmospheric concentrations histories and constructed seawater solubility functions, although the low solubility in seawater creates challenging measurement conditions (i.e. low concentration). Measurements of PFCs can be potentially improved by modifying the Medusa-Aqua analytical system. With the exception of providing the information on the novel potential alternative oceanic transient tracers, this study also provides a method on how to evaluate the feasibility for a compound to be a transient tracer in the ocean.

Pingyang Li and Toste Tanhua

 
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Status: final response (author comments only)
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Pingyang Li and Toste Tanhua

Pingyang Li and Toste Tanhua

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Short summary
Observations of transient tracer distribution provide essential information on ocean ventilation. The use of several commonly used transient traces is impeded as their atmospheric mole fractions are decreasing with time. Here we explore new potential oceanic transient tracers with a novel analytical system that simultaneous measures a large range of compounds. Combined with the known atmospheric history and seawater solubility we discuss the utility of selected HCFC, HFC and PFC as tracers.