On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer

[摘要] The surface microlayer (SML) represents a unique system of which thephysicochemical characteristics may differ from those of the underlyingsubsurface seawater (SSW). Within the Arctic pack ice area, the SML has beencharacterized as enriched in small colloids of biological origin, resultingfrom extracellular polymeric secretions (EPS). During the Arctic SummerCloud Ocean Study (ASCOS) in August 2008, particulate organic matter (POM,with size range > 0.22 μm) and dissolved organic matter (DOM, < 0.22 μm,obtained after filtration) samples were collected andchemically characterized from the SML and the corresponding SSW at an openlead centered at 87.5° N and 5° E. Total organic carbon waspersistently enriched in the SML with a mean enrichment factor (EF) of 1.45 ± 0.41,whereas sporadic depletions of dissolved carbohydrates andamino acids were observed. Monosaccharide compositional analysis revealsthat EPS in the Arctic lead was formed mainly of distinctiveheteropolysaccharides, enriched in xylose, fucose and glucose. The meanconcentrations of total hydrolysable neutral sugars in SSW were 94.9 ± 37.5 nM in high molecular weight (HMW) DOM (> 5 kDa) and 64.4 ± 14.5 nMin POM. The enrichment of polysaccharides in the SML appeared to be acommon feature, with EFs ranging from 1.7 to 7.0 for particulatepolysaccharides and 3.5 to 12.1 for polysaccharides in the HMW DOM fraction.A calculated monosaccharide yield suggests that polymers in the HMW DOMfraction were scavenged, without substantial degradation, into the SML.Bubble scavenging experiments showed that newly aggregated particles couldbe formed abiotically by coagulation of low molecular weight nanometer-sizedgels. Aerosol particles, artificially generated by bubbling experiments,were enriched in polysaccharides by factors of 22–70, relative to the sourceseawater. We propose that bubble scavenging of surface-activepolysaccharides could be one of the possible mechanisms for the enrichmentof polysaccharides in the high Arctic open lead SML.

[学科分类] 海洋学与技术