| 17 Nov 2025
Glass plate sampling efficiency for trace gases in the sea surface microlayer
Abstract. Many climate-active trace gases in the atmosphere are closely linked to production and consumption in the ocean, which are, in turn, influenced by the sea surface microlayer (SML). The SML is the upper most layer of the ocean with up to 1 mm thickness, often enriched in organics. Studies of trace gases in the SML aim to identify and quantify potential processes unique to the SML and to understand the SML's influence on the transfer between air and sea. Established sampling techniques of the SML (e.g., glass plate, mesh screen) are associated with high losses for the volatile trace gases. Despite the high losses, in this study we find that meaningful analysis of glass plate samples for trace gases is possible. We experimentally determined the sampling efficiency for the short-lived trace gases dimethyl sulphide (DMS), isoprene, and carbon disulphide (CS2). Water temperature and trace gas concentration were the main drivers for sampling efficiency variability, while salinity and the number of dips of the glass plate were not significant. The effect of surfactants could not finally be untangled. Although our results are consistent, we do not quantify a sampling efficiency to correct individual measurements, as our experiments did not encompass the full suite of environmental parameters normally encountered in the field. Instead, we suggest to use 0.13 ± 0.01 (± standard error) for DMS and isoprene, and 0.12 ± 0.01 for CS2 as thresholds to identify cases of net production in the SML. Future studies should extend to long-lived species (e.g., nitrous oxide, methane), include the effect of wind, and be repeated for the mesh screen. We hypothesize that a correction of individual measurements requires to determine sampling efficiency as a function of environmental parameters, for which the underlying physicochemical relationships need to be unraveled by increasing the parameter space studied here.
Competing interests: Hermann W. Bange is a member of the editorial board of Biogeosciences.
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Comments on “Glass plate sampling efficiency for trace gases in the sea surface microlayer”
EGUsphere-2025-5361
General Comments
This manuscript addresses an important methodological gap in sea surface microlayer (SML) research by quantifying the sampling efficiency of the glass plate technique for short-lived trace gases (DMS, isoprene, CS₂). The topic is highly relevant for SML biogeochemistry and air–sea exchange studies. The manuscript is generally well structured, and the authors make a commendable effort to analyse their data comprehensively.
However, there are several limitations that prevent the study from supporting some of its conclusions in the current form. The experimental configuration is constrained by practical conditions (homogeneous tank, no natural organic enrichment, oversaturated conditions) and does not fully represent the complexity of natural SMLs. The key assumption that SML and ULW have identical concentrations (CSML = CULW) requires further clarification, especially under oversaturation and in surfactant treatments. Moreover, differences between experiments are confounded by changes in tank material, location, and artificial sea salt formulation. In addition to the major points above, several specific issues in the manuscript should also be addressed.
Specific Comments
Minor Comments
Page 1, line 18 – “in the field. . Instead,” → remove extra period.
Page 4, Line 121: Two types of artificial seawater (Tropic Marin® Pro-Reef Sea Salt vs. ordinary aquarium salt) are used. It would help to explain the rationale for these choices and how their compositions differ (e.g. trace metals, alkalinity, additives). Since sampling efficiency differs between experiments B and C, the role of salt composition should be discussed more concretely.
Page 6, Line 140: The text notes that a single glass plate dip yields 1.8–6.3 mL of medium, leading to substantial variability in sample volume per dip. Could you clarify what factors drive this large range in collected volume per dip? Understanding these drivers is important for assessing whether volume variability introduces bias to sampling efficiency.
Page 7, Line 190: The decision to use peak area ratios without GC-MS calibration is stated, but the assumption of a linear relationship between peak area and concentration is not validated. Including a brief note on how this assumption was tested or acknowledging its limitations would enhance transparency.
Page 13 Line 337: Correct figure reference formatting. Several places refer to “Fig. Figure X” (e.g. Figure 1, Figure 2, Figure 3, Figure 5, Figure 6, Figure 7), which is clearly a typesetting artefact.
Page 21, Lines 490–495: The total water temperature range is modest (ΔT ≈ 5.9 °C). You might add that this limited range likely contributes to the relatively weak apparent temperature effect in the raw data, despite statistical significance in the MLR.