Marine microgels as a source of cloud condensation nuclei in the high Arctic

Abstract

Marine microgels play an important role in regulating ocean basinscale biogeochemical dynamics. In this paper, we demonstrate that, in the high Arctic, marine gels with unique physicochemical characteristics originate in the organic material produced by ice algae and/or phytoplankton in the surface water. The polymers in this dissolved organic pool assembled faster and with higher microgel yields than at other latitudes. The reversible phase transitions shown by these Arctic marine gels, as a function of pH, dimethylsulfide, and dimethylsulfoniopropionate concentrations, stimulate the gels to attain sizes below 1 μm in diameter. These marine gels were identified with an antibody probe specific toward material from the surface waters, sized, and quantified in airborne aerosol, fog, and cloud water, strongly suggesting that they dominate the available cloud condensation nuclei number population in the high Arctic (north of 80°N) during the summer season. Knowledge about emergent properties of marine gels provides important new insights into the processes controlling cloud formation and radiative forcing, and links the biology at the ocean surface with cloud properties and climate over the central Arctic Ocean and, probably, all oceans.air-sea exchange | immunological probes | Melosira arctica O ur limited knowledge about cloud radiative processes remains a major weakness in our understanding of the climate system and consequently in developing accurate climate projections (1). This is especially true for low-level Arctic clouds, which play a key role in regulating surface energy fluxes, affecting the freezing and melting of sea ice, when the climate is changing faster in the Arctic than at any other place on earth. The radiative or reflective (albedo) properties of clouds strongly depend on the number concentration of aerosol particles available for uptake or condensation of water vapor at a given water supersaturation. Such particles are known as cloud condensation nuclei (CCN), and their activation and growth (2) depend on the equilibrium thermodynamics by which water vapor condenses on CCN and forms a liquid cloud drop. In the high Arctic, the aerosol-cloud-radiation relationship is more complex than elsewhere, and for most of the year, the low-level clouds constitute a warming factor for climate rather than cooling (3). In summer, this is due to the semipermanent ice cover, which raises the albedo of the surface, and to the clean Arctic air (4), which decreases the albedo of the low-level clouds. Small changes in either factor are very important to the heat transfer to the ice and the subsequent summertime ice-melt. The high Arctic CCN originate in the open leads in the pack ice and from sources along the marginal ice edge; they are formed mostly by aggregates of organic material, presumably of marine origin (5-7).Marine polymer microgels are 3D polymer hydrogel networks that result from the spontaneous assembly/dispersion equilibrium of free biopolymers in the dissolved organic matter (DOM) pool. Microgels fo...

Effect of wind speed on the size distribution of gel particles in the sea surface microlayer: insights from a wind–wave channel experiment

“…In addition, it has been suggested that gels play an important role in air-sea exchange processes. Gel particles with a polysaccharide composition ejected by bubble bursting events may act as cloud condensation nuclei (CCN) in low-level cloud regions (Leck and Bigg, 2005;Russell et al, 2010;Orellana et al, 2011). Also, proteinaceous gels and amino acids can be enriched in the SML and in sea spray aerosols (SSAs) (Kuznetsova et al, 2005).…”

“…Two kinds of gel particles have been widely studied in aquatic environments: transparent exopolymer particles (TEP), which include acidic polysaccharides, and Coomassie stainable particles (CSP), which are protein-containing particles and can serve as a N source for bacteria and other organisms (Alldredge et al, 1993;Long and Azam, 1996;Passow, 2002;Engel et al, 2004). A major source of TEP and CSP in the ocean are phyto-and bacterioplankton (Alldredge et al, 1993;Long and Azam, 1996;Stoderegger and Herndl, 1999).…”

“…It has been demonstrated that marine heterotrophs feed on gel particles within specific size ranges (Mari and Kiorboe, 1996). Bacterial colonization of TEP varies as a function of size (Mari and Kiorboe, 1996;Passow, 2002). Thus, changes in size distribution of gel particles will likely alter food-web structure and dynamics in the ocean and SML.…”

“…In addition, the abundance and size of gels in the SML and in subsurface waters may determine their potential fate as CCN in the atmosphere (Orellana et al, 2011).…”

Seasonal microbial community dynamics correlate with phytoplankton-derived polysaccharides in surface coastal waters

“…Marine gel particles are released from the sea into the atmosphere by fragmentation of the sea surface microlayer during bubble bursting (Russell et al, 2010), and are subsequently a source of aerosols and cloud condensation nuclei (Orellana et al, 2011). The realisation of the importance of marine gels in climate regulation has forced a fundamental paradigm shift away from an exclusively dimethylsulfide-controlled marine boundary layer, to a complex system where marine gels are integral (Quinn and Bates, 2011).…”