The Sea-Surface Microlayer - Exploratory study of a biofilm-like interface between the ocean and atmosphere
Final Report Abstract
The sea-surface microlayer is the boundary interface between the atmosphere and ocean, covering about 70% of the Earth’s surface. With a typical thickness of 40-100 μm, the microlayer has physicochemical and biological properties that are measurably distinct from underlying waters. Because of its unique position at the air-sea interface, characterization and understanding the processes at the sea surface are essential in determining how the ocean and atmosphere interact and respond to environmental changes. The enrichment of naturally occurring organic compounds, such as carbohydrates, proteins and lipids, modifies the chemical and physical properties of the sea surface to form the microlayer as a laminar film. In a seminal paper, Sieburth (1983) postulated that the microlayer is a gelatinous microbial-rich habitat, and our earlier studies made an incremental contribution towards his hypothesis by reporting the accumulation of transport exopolymer particles (TEP) within the microlayer. TEPs are the most abundant gel particles in the ocean. Occasionally I found extreme enrichments of TEP with the appearance of slicks, wave-damped areas through the excessive accumulation of organic material. In this study, I compared slick and non-slick sea surfaces on chemical and microbiological parameter relevant to biofilm formation. I found up to 40 times more gel substances, the foundation of any biofilm, in slicks at multiple stations in the North Pacific, Yellow Sea and Baltic Sea. Gel substances were still enriched in non-slick surfaces, but only up to an enrichment of 3 and probably too low to form a biofilm matrix. The gel matrix found in slicks was inhabited by a unique microbial community with a larger biomass (up to 10 times more), another shared feature with conventional biofilms on solid surfaces. With a bioassay, I found that the physiological profiles and carbon utilization patterns are distinct between microbial communities inhabiting slicks, non-slick microlayer and bulkwater. Bubbling experiments showed that bubbling bulkwater, through breaking waves, can provide fresh organic material and cells to the sea surface, and, therefore, with surface convergence an important process in the formation of slicks. I, therefore, conclude that slicks can feature biofilm-like properties with the accumulation of particles and microbes embedded in a gel matrix. I also assess the potential distribution and frequency of slick formation in coastal and oceanic regions, and conclude that slicks play an important local and regional role in the regulation of air-sea interaction, i.e. exchange of gas and heat, and aerosol composition exchange.
Publications
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2014. Guide to best practices to study the ocean’s surface. Report from the SCOR working Group, 141. 2014.
O. Wurl, M. Cunliffe
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2015. A marine biogenic source of atmospheric ice nucleating particles. Nature, Vol. 525. 2015, pp. 234–238.
Wilson, T. W., et al.
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2016. Biofilm-like properties of the sea surface and predicted effects on air-sea CO2 exchange. Prog. Oceanogr., Volume 144, May 2016, Pages 15-24
Wurl, O., Stolle, C., Thuo; C. V, Thu, P. C., Mari, X.
