Prospects for simulating macromolecular surfactant chemistry at the ocean–atmosphere boundary

Abstract

Biogenic lipids and polymers are surveyed for their ability to adsorb at the water-air interfaces associated with bubbles, marine microlayers and particles in the overlying boundary layer. Representative ocean biogeochemical regimes are defined in order to estimate local concentrations for the major macromolecular classes. Surfactant equilibria and maximum excess are then derived based on a network of model compounds. Relative local coverage and upward mass transport follow directly, and specific chemical structures can be placed into regional rank order. Lipids and denatured protein-like polymers dominate at the selected locations. The assigned monolayer phase states are variable, whether assessed along bubbles or at the atmospheric spray droplet perimeter. Since oceanic film compositions prove to be irregular, effects on gas and organic transfer are expected to exhibit geographic dependence as well. Moreover, the core arguments extend across the sea-air interface into aerosol-cloud systems. Fundamental nascent chemical properties including mass to carbon ratio and density depend strongly on the geochemical state of source waters. High surface pressures may suppress the Kelvin effect, and marine organic hygroscopicities are almost entirely unconstrained. While bubble adsorption provides a well-known means for transporting lipidic or proteinaceous material into sea spray, the same cannot be said of polysaccharides. Carbohydrates tend to be strongly hydrophilic so that their excess carbon mass is low despite stacked polymeric geometries. Since sugars are abundant in the marine aerosol, gel-based mechanisms may be required to achieve uplift. Uncertainties distill to a global scale dearth of information regarding

Impact of anions on the surface organisation of lipid monolayers at the air–water interface

“…[8,9] Film drops (,1 mm in diameter) produced by bursting of the bubble film efficiently transfer surface-active species that reside at the air-water interface into the atmosphere; this explains the presence of surfactants in fine SSA particles (,2.5 mm in diameter). [10] Given that the relative concentration of organic matter to inorganic salts in the ocean is extremely low (60-90 mM organic matter compared with approximately 460 000 mM Na þ ), [3] the high relative fraction of organic matter in SSA shows that the transfer of organic species from the ocean to SSA proceeds through selective processes. To better understand the biogeochemical connections between the ocean and atmosphere, it is critical to improve our understanding of the processes that control SSA composition in order to determine their effects on atmospheric chemistry and climate.…”

Strategies for the Simulation of Sea Ice Organic Chemistry: Arctic Tests and Development

“…Background humic acid mixes or freezes-in at a constant level reflective of the seawater source, and it is then modulated in bulk by the local porosity. Since this carbon pool is considered refractory [27][28][29]77], inputs and channel tightening are the only factors involved. By contrast, proteins and polysaccharides are injected even at a minimum by grazing or mortality processes, as determined by the network of routings (Appendices A and B).…”

“…A rich oceanic dissolved organic chemistry may in fact be driven independently by under-ice blooms [78][79]. The effects are parameterized here through variable mixed layer concentrations in springtime, set highest for the longer lived polysaccharides [28].…”

“…Grazing and mortality are routed into a complex network of spillage, assimilation and remineralization pathways [14, appendices]. Dissolved carbon of biological origin is present initially as a refractory humic background which predates and underpins the time dependent superposition of fresh macromolecules [28][29]. As will be shown, disruptive releases do not suffice to explain the available analytical chemical observations, and therefore exudation is introduced in several modes to provide additional sourcing.…”

“…Macromolecules in dissolved form or else present as colloids and gels are now added to the scheme. We begin with compound types which have proven useful in studies of global surfactant behavior at the water-air interface [9,[27][28]. To this list one could, and perhaps should, add specific intentional releases including polysaccharides [117], aminosugars [118], siderophores [99] and more.…”