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

Abstract

Abstract. Gel particles, such as transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP), are important organic components in the sea surface microlayer (SML). Here, we present results on the effect of different wind speeds on the accumulation and size distribution of TEP and CSP during a wind wave channel experiment in the Aeolotron. Total areas of TEP (TEP SML ) and CSP (CSP SML ) in the surface microlayer were exponentially related to wind speed. At wind speeds < 6 m s −1 , accumulation of TEP SML and CSP SML occurred, decreasing at wind speeds of > 8 m s −1 . Wind speeds > 8 m s −1 also significantly altered the size distribution of TEP SML in the 2-16 µm size range towards smaller sizes. The response of the CSP SML size distribution to wind speed varied through time depending on the biogenic source of gels. Wind speeds > 8 m s −1 decreased the slope of CSP SML size distribution significantly in the absence of autotrophic growth. For the slopes of TEP and CSP size distribution in the bulk water, no significant difference was observed between high and low wind speeds. Changes in spectral slopes between high and low wind speed were higher for TEP SML than for CSP SML , indicating that the impact of wind speed on size distribution of gel particles in the SML may be more pronounced for TEP than for CSP, and that CSP SML are less prone to aggregation during the low wind speeds. Addition of an E. huxleyi culture resulted in a higher contribution of submicron gels (0.4-1 µm) in the SML at higher wind speed (> 6 m s −1 ), indicating that phytoplankton growth may potentially support the emission of submicron gels with sea spray aerosol.

Eukaryotic community composition in the sea surface microlayer across an east-west transect in the Mediterranean Sea

“…Fogg, 1995;Wikner and Hagstrom, 1988) where low phytoplankton abundances, but high TEP enrichments of 1.1-17.3 were found. Wind speed correlated negatively with TEP abundance and area in the SML, showing that wind can negatively affect TEP concentrations at the air-sea interface as has been previously suggested (Sun et al, 2018).…”

Depth is relative: the importance of depth for transparent exopolymer particles in the near-surface environment

“…Thus, bubbling and turbulence at moderate wind speeds can induce more complex enrichment processes and subdue any direct correlation with wind speed. We never observed wind speeds greater than 8 m s −1 , which has been found to be the threshold speed for the breakup of TEPs during experiments in a wind-wave tunnel by Sun et al (2018). Thus, the moderate wind speeds we observed likely had an indirect positive effect on enrichment.…”

“…The filters were stored frozen (−18 • C) until processed. Chl a was then analysed according to the method described by Wasmund et al (2006) using a fluorometer (Jenway 6285, precision of 0.01± < 1 ng mL −1 ). During the Norwegian cruise (HE491), in vivo Chl a was measured with a hand fluorometer (Turner Designs, AquaFlu-orTM, precision of 0.001 absorption) and related to µg of Chl a using a calibration factor between filtered Chl a (Chl a standard in EtOH as reference) and in vivo absorbance.…”

A link between the ice nucleation activity and the biogeochemistry of seawater

“…Further studies have also determined a link between wind speed and the composition of the sea surface microlayer. Sun et al (2018) determined that the abundance and size of macromolecular gels in a wave tank's microlayer decreased with winds above 8 m s −1 . Other studies have found an organic enrichment in the microlayer with wind speeds ranging from 10 to 13 m s −1 (Sabbaghzadeh et al, 2017;Wurl et al, 2011), indicating that conditions were at times conducive to microlayer formation during our sampling.…”

“…This suggests individual components of seawater are more important than bulk composition in driving ice nucleation. Candidates may be carbohydrates, individual proteins, and polysaccharides, as these compounds are effective depositional INPs and are enriched in the microlayer (Engel et al, 2018;Russell et al, 2010;Thornton et al, 2016;Zäncker et al, 2017;Zeppenfeld et al, 2019).…”