Technical Note: Comparison of storage strategies of sea surface microlayer samples

Abstract

The sea surface microlayer (SML) is an important biogeochemical system whose physico-chemical analysis often necessitates some degree of sample storage. However, many SML components degrade with time so the development of optimal storage protocols is paramount. We here briefly review some commonly used treatment and storage protocols. Using freshwater and saline SML samples from a river estuary, we investigated temporal changes in surfactant activity (SA) and the absorbance and fluorescence of chromophoric dissolved organic matter (CDOM) over four weeks, following selected sample treatment and storage protocols. Some variability in the effectiveness of individual protocols most likely reflects sample provenance. None of the various protocols examined performed any better than dark storage at 4 °C without pre-treatment. We therefore recommend storing samples refrigerated in the dark

Surfactant control of gas transfer velocity along an offshore coastal transect: results from a laboratory gas exchange tank

“…At each station we made three Garrett screen dips, with a typical total yield for all three dips of 400 to 500 mL, corresponding to an estimated sampling depth of 65 to 80 µm. The samples were transferred to three 50 mL high-density polyethylene (HDPE) bottles and stored in an on-board refrigerator at 4 • C (Cunliffe et al, 2013;Schneider-Zapp et al, 2013). SSW (∼ 100 L) was sampled from a non-toxic supply pump located ∼ 1 m below the water surface and collected in 5 × 20 L HDPE carboys that were pre-cleaned with 20 % HCl to remove leachable organics.…”

“…During our study period U 10 ranged from 4.7 to 11.4 m s −1 with the highest values between October and February and lowest values in June and July. On return to the laboratory, typically within 6 h of sampling, all samples were stored in a 4 • C dark cold room according to the procedure of Schneider-Zapp et al (2013). The SML and SSW were analysed for surfactant activity (SA) and chromophoric dissolved organic matter (CDOM) absorbance and the SSW was additionally analysed for Chlorophyll a (Chl a).…”

“…The SSW samples (volume ∼ 93 L) were used to estimate the spatial variability in k w using a fully automated, closed air-water gas exchange tank. Tank design, operation and routine procedures for its rigorous cleaning are all described in detail in Schneider-Zapp et al (2014). In brief, the system generates water-side turbulence with an electronic baffle operated at three increasingly turbulent boundary conditions of 0.6, 0.7, and 0.75 Hz.…”

“…In brief, the system generates water-side turbulence with an electronic baffle operated at three increasingly turbulent boundary conditions of 0.6, 0.7, and 0.75 Hz. Although turbulence created in a laboratory tank inevitably differs from turbulence in situ, which is primarily wind-driven, our experimental system avoids the practical complications of simulating wind-induced turbulence in a laboratory while maintaining well-defined and reproducible conditions (Schneider-Zapp et al, 2014). The purpose of the tank is to facilitate an improved understanding of k w suppression by natural surfactants that will subsequently enable more complex experiments involving winddriven turbulence.…”

“…The tank is coupled to two gas chromatographs (GCs) and an integral equilibrator in a continuous gas-tight loop (Schneider-Zapp et al, 2014). This enables temporal changes in the partial pressures of gaseous tracers artificially enriched in the tank water (SF 6 , CH 4 , and N 2 O) to be measured si-multaneously in tank water and headspace, thereby deriving three independent estimates of k w for each turbulence setting.…”