The distribution and fate of surface-active substances in the sea-surface microlayer and water column

Results from a study of surface-active substances (SAS) in the sea-surface microlayer (SML) of the Santa Barbara Channel suggest that the SML is stable enough to exist at typical oceanic wind conditions and that stratification plays an important role in SML formation through accumulation of surface-active organic matter above the pycnocline. We measured surface-active substances, total dissolved carbohydrates (TDC), chromophoric dissolved organic matter (CDOM) and transparent exoploymer particles (TEPs) in the SML and the underlying bulk water. While the enrichment factors of those compounds, defined as the ratio of the concentration in the SML to that in the corresponding underlying water, were generally less than 3, significant enrichment in the microlayer persisted at wind speeds greater than 6 m s− 1 (up to 9.6 m s− 1, the highest winds observed), which is close to the average global wind speed over the ocean. Additional measurements from three water column profiles indicated that stratification of the water column led to an accumulation of surface-active organic matter above the pycnocline. Carbohydrate-rich TEP correlated significantly with the density of the water column indicating an upward flux of these gel-like particles towards the SML.