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A new bubble-generating glass chamber design with an extensive set of aerosol production experiments is presented. Compared to the experiments described in the literature, current setup is among the medium-sized installations allowing precise control over the air discharge, water temperature and salinity. The size and material of the chamber offer variety of applications due to its portability, measurement setup adjustability and sterilization option. The experiments have been conducted in a cylindrical bubbling tank of 10 L volume filled by ~30-40 % with water of controlled salt content and temperature and covered with a hermetic lid. The chamber was used to study the characteristics of the aerosols produced by bursting bubbles under different conditions. In line with previous findings, the sea spray aerosol production was shown to depend linearly on the surface area covered by the bubbles, which in turn is a near-linear function of the air discharge through the water. Observed dependencies of the aerosol size spectra and particle fluxes on water salinity and temperature, being qualitatively comparable with the previous experiments, substantially refined the existing parameterizations. In particular, the bubble size was practically independent from the air discharge through the water body, except for very small flows. Also, the dependence of aerosol spectrum and amount on salinity was much weaker than suggested in some previous experiments. The temperature dependence, to the contrary, was significant and consistent, with a transition in the spectrum shape at ~10 °C. Theoretical analysis based on the basic conservation laws supported the main results of the experiments but also highlighted the need of better understanding of the aerosol production from a cold water surface. [ABSTRACT FROM AUTHOR]

Nearly all molecular oxygen (O2) on Earth is produced via oxygenic photosynthesis by plants or photosynthetically active microorganisms. Light-independent O2 production, which occurs both abiotically, e.g., through water radiolysis, or biotically, e.g., through the dismutation of nitric oxide or chlorite, has been thought to be negligible to the Earth system. However, recent work indicates that O2 is produced and consumed in dark and apparently anoxic environments at a much larger scale than assumed. Studies have shown that isotopically light O2 can accumulate in old groundwaters; that strictly aerobic microorganisms are present in many apparently anoxic habitats; and that microbes and metabolisms that can produce O2 without light are widespread and abundant in diverse ecosystems. Analysis of published metagenomic data reveals that the enzyme putatively capable of nitric oxide dismutation (NOD) forms four major phylogenetic clusters and occurs in at least 16 bacterial phyla most notably the Bacteroidota. Similarly, a re-analysis of published isotopic signatures of dissolved O2 in groundwater suggests in-situ production in up to half of the studied ecosystems. Geochemical and microbiological data supports the conclusion that "dark oxygen" production is an important and widespread yet overlooked process in apparently anoxic environments with far-reaching implications for subsurface biogeochemistry and ecology., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)