Surfactants during upwelling events in the sea-surface microlayer and 1 m depth during METEOR cruise M117, Baltic Sea

Results from a study of surfactants (SAS) in the sea surface microlayer (SML) and underlying water (ULW) at different locations in the Baltic Sea. The total SAS concentrations were measured using phase-sensitive alternative current voltammetry with hanging mercury drop electrode (HMDE) in unfiltered samples. The concentrations of SAS were expressed as the equivalent concentration of nonanionic surfactants Triton-X-100. The enrichment factors (EF) of SAS were calculated as the ratio of concentration in SML to the corresponding ULW samples.

Upwelling and associated heat flux in the equatorial Atlantic inferred from helium isotope disequilibrium

Sea-to-air and diapycnal fluxes of nitrous oxide (N2O) into the mixed layer were determined during three cruises to the upwelling region off Mauritania. Sea-to-air fluxes as well as diapycnal fluxes were elevated close to the shelf break, but elevated sea-to-air fluxes reached further offshore as a result of the offshore transport of upwelled water masses. To calculate a mixed layer budget for N2O we compared the regionally averaged sea-to-air and diapycnal fluxes and estimated the potential contribution of other processes, such as vertical advection and biological N2O production in the mixed layer. Using common parameterizations for the gas transfer velocity, the comparison of the average sea-toair and diapycnal N2O fluxes indicated that the mean sea-toair flux is about three to four times larger than the diapycnal flux. Neither vertical and horizontal advection nor biological production were found sufficient to close the mixed layer budget. Instead, the sea-to-air flux, calculated using a parameterization that takes into account the attenuating effect of surfactants on gas exchange, is in the same range as the diapycnal flux. From our observations we conclude that common parameterizations for the gas transfer velocity likely overestimate the air-sea gas exchange within highly productive upwelling zones.