Protein and Carbohydrate Exopolymer Particles in the Sea Surface Microlayer (SML)

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 1.4-2.4. 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 1.2-1.8. 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.

Exopolymer production as a function of cell permeability and death in a diatom (Thalassiosira weissflogii) and a cyanobacterium (Synechococcus elongatus)

“…The surface of live diatom cells recovered from Pacific Ocean waters stained with Coomassie Brilliant Blue, indicating that they were covered in proteins (Thornton et al. ).…”

“…, Engel , Thornton et al. ), in mesocosm experiments with natural waters (Engel et al. , ), and batch cultures (Corzo et al.…”

“…While both TEP and CSP can be quantified by microscopy, these methods tend to be time consuming and labor intensive (Alldredge et al 1993, Engel 2009). However, both TEP and CSP cooccur in cultures of diatoms (Galgani and Engel 2013), mesocosm experiments with natural blooms of phytoplankton , and the ocean (Long and Azam 1996, Engel and Galgani 2016, Thornton et al 2016).…”

“…Alternatively, the polymeric material that forms CSP may be sloughed or dissolved from the proteins coating the surface of the cells. The surface of live diatom cells recovered from Pacific Ocean waters stained with Coomassie Brilliant Blue, indicating that they were covered in proteins (Thornton et al 2016).…”

Ice Nucleation by Marine Aerosols Over the North Atlantic Ocean in Late Spring

“…The sea surface microlayer (SML) is the thin layer of ocean at the air-sea interface, which is operationally defined as 1 to 1000 μm thick (Engel et al, 2017;Liss & Duce, 1997). Since the SML is selectively enriched in some classes of organic matter relative to the underlying water, it plays an important role in the introduction of INPs into the atmosphere (Aller et al, 2005(Aller et al, , 2017Chance et al, 2018;Cunliffe et al, 2013;Hunter, 1997;Irish et al, 2017Irish et al, , 2019Thornton et al, 2016;Zeppenfeld et al, 2019). Enhancement in the concentrations of INPs active between −14 and −27°C in the SML relative to bulk seawater have been observed in some cases, including Arctic melt ponds and marginal ice zones, (Irish et al, 2019;Zeppenfeld et al, 2019).…”