Abstract
Gas exchange across the air-water interface is strongly influenced by the uppermost water layer (<1 mm), the sea-surface microlayer (SML). However, a clear understanding about how the distinct physicochemical and biological properties of the SML affect gas exchange is lacking. We used an automatic microprofiler with Clark-type microsensors to measure small-scale profiles of dissolved oxygen in the upper 5 cm of the water column in a laboratory tank filled with natural seawater. We aimed to link changing oxygen concentrations and profiles with the metabolic activity of plankton and neuston, i.e. SML-dwelling organisms, in our artificial, low-turbulence set-up during diel cycles. We observed that temporal changes of the oxygen concentration in near surface water (5 cm depth) could not be explained by diffusive loss of oxygen, but by planktonic activity. Interestingly, no influence of strong neuston activity on oxygen gradients at the air-water interface was detectable. This could be confirmed by a modeling approach, which revealed that neuston metabolic activity was insufficient to create distinct curvatures into these oxygen gradients. Moreover, the high neuston activity in our study contributed only less than 7% to changes in oxygen concentration in the tank. Overall, this work shows that temporal and vertical variation of oxygen profiles across the air-water interface in controlled laboratory set-ups is driven by biological processes in the underlying bulk water, with negligible effects of neuston activity.
Highlights
The sea-surface microlayer (SML) forms a boundary layer at the air-water interface, which has distinct physicochemical and biological properties compared to the underlying water (ULW) (Hardy, 1982; Wurl et al, 2017)
Our study presents highly-resolved vertical (50–500 μm-steps) O2 and temperature profiles across the SML into the ULW to a depth of 5 cm in a tank filled with natural seawater
I.e., diel and light-dependent changes in O2 concentration at this depth are related to net community production (NCP) in SML and ULW
Summary
The sea-surface microlayer (SML) forms a boundary layer at the air-water interface, which has distinct physicochemical and biological properties compared to the underlying water (ULW) (Hardy, 1982; Wurl et al, 2017). Organic surface-active substances, i.e., surfactants, accumulate in the SML. Within the SML, microbial heterotrophic metabolism is often enhanced compared to the ULW (Obernosterer et al, 2005; Reinthaler et al, 2008). This is most likely driven by the strong accumulation of organic matter within a gelatinous matrix (Cunliffe et al, 2013). Even though it has been observed that photosynthetic activity in the SML may be inhibited by high light intensities (Albright, 1980; Hardy and Apts, 1984), strong enrichments of phytoneuston may occur, for instance in sheltered bays and lagoons (Hardy, 1973), in foams (Maynard, 1968), and in association with surface slicks (Sieburth and Conover, 1965; Carlson, 1982b; Wurl et al, 2016)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
