Abstract
The sea-surface microlayer (SML) forms the uppermost boundary layer between atmosphere and ocean, and has distinctive physico-chemical and biological features compared to the underlying water. First findings on metabolic contributions of microorganisms to gas exchange processes across the SML raised the need for new in situ technologies to explore plankton-oxygen turnover in this special habitat. Here, we describe an inexpensive research tool, the Surface In Situ Incubator (SISI), which allows simultaneous incubations of the SML, and water samples from 1 m and 5 m, at the respective depths of origin. The SISI is deployed from a small boat, seaworthy up to 5 bft (Beaufort scale), and due to global positioning system (GPS) tracking, capable of drifting freely for hours or days. We tested the SISI by applying light/dark bottle incubations in the Baltic Sea and the tropical Pacific Ocean under various conditions to present first data on planktonic oxygen turnover rates within the SML, and two subsurface depths. The SISI offers the potential to study plankton-oxygen turnover within the SML under the natural influence of abiotic parameters, and hence, is a valuable tool to routinely monitor their physiological role in biogeochemical cycling and gas exchange processes at, and near, the sea surface.
Highlights
The sea-surface microlayer (SML) at the air–sea interface spans two-thirds of the global surface area
For demonstrating that incubations with the Surface In Situ Incubator (SISI) lead to reasonable results of O2 turnover rates at different incubation depths, we applied the device at three stations of two different marine systems; in the enclosed Baltic Sea and in the open Pacific Ocean
net community production (NCP) rates were generally positive in 1 m and 5 m water depth incubations in the Baltic Sea assuming the presence of photosynthesizing organisms in coastal proximity
Summary
The sea-surface microlayer (SML) at the air–sea interface spans two-thirds of the global surface area. The direct metabolic control of gas exchange by the SML microorganisms has been previously suggested [26,27] Such findings demonstrate that biology-driven gas turnover within the SML requires further attention, and stresses the need for new methodologies to improve our knowledge on the SML’s biogeochemical nature and climate-related implications. The aim of this technical note is to describe the SISI as a new and inexpensive research tool for oceanographers to carry out routine incubation studies in the SML and the near surface layer. We present a range of other possible applications in the field of environmental science
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