Abstract
Exchanges of matter and energy between ocean and atmosphere occur through the sea surface microlayer (SML). The SML is the thin surface layer of the ocean at the ocean-atmosphere interface that has distinctive physical, chemical and biological properties compared with the underlying water. We measured the concentration of two types of exopolymer particles in the SML and underlying water in the Pacific Ocean off the coast of Oregon (United States) during July 2011. Transparent exopolymer particles (TEP) are defined by their acidic polysaccharide content, whereas Coomassie staining particles (CSP) are composed of protein. TEP and CSP were ubiquitous in the SML. TEP were not significantly enriched in the SML compared with the underlying water. CSP were significantly enriched in the SML, with an enrichment factor (EF) of 1.4 to 2.4. The distribution of exopolymer particles in the water and microscopic imaging indicated that TEP and CSP are distinct populations of particles rather than different chemical components of the same particles. Dissolved polysaccharides were not enriched in the SML, whereas monosaccharides had an EF of 1.2 to 1.8. Sampling occurred during the collapse of a diatom bloom, and diatoms were found both in the water column and SML. While there were living diatoms in the samples, most of the diatoms were dead and there were abundant empty frustules covered in layer of TEP. The collapsing diatom bloom was probably the source of exopolymer particles to both the SML and underlying water. Exopolymer particles are a component of the SML that may play a significant role in the marine carbon and nitrogen cycles, and the exchange of material between ocean and atmosphere.
Highlights
The sea surface microlayer (SML) is the thin skin that covers the ocean, and the majority (71%) of the Earth’s surface. Hunter (1997) defined the SML as “that microscopic portion of the surface ocean which is in contact with the atmosphere and which may have physical, chemical or biological properties that are measurably different from those of adjacent sub-surface waters.” It is operationally defined as being 1–1000 μm thick (Liss and Duce, 1997)
As we were interested in the SML, the depth profiles presented in this paper are to a relatively shallow depth of 25 m (Figures 2, 3)
Detailed depth profiles are presented for stations A and D, as these were the stations at which samples for exopolymer particles were taken at several depths (Table 1)
Summary
The sea surface microlayer (SML) is the thin skin that covers the ocean, and the majority (71%) of the Earth’s surface. Hunter (1997) defined the SML as “that microscopic portion of the surface ocean which is in contact with the atmosphere and which may have physical, chemical or biological properties that are measurably different from those of adjacent sub-surface waters.” It is operationally defined as being 1–1000 μm thick (Liss and Duce, 1997). Hunter (1997) defined the SML as “that microscopic portion of the surface ocean which is in contact with the atmosphere and which may have physical, chemical or biological properties that are measurably different from those of adjacent sub-surface waters.”. It is operationally defined as being 1–1000 μm thick (Liss and Duce, 1997). Exopolymer Particles in the Sea Surface Microlayer relative to the underlying water and are the quotient of the concentration in the SML and bulk water. The SML is dynamic, and its composition and the enrichment in particular chemicals or organisms varies considerably in time and space (Karavoltsos et al, 2015)
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