Total surfactant activity (SA) from the sea surface microlayer (SML) and depth profiles collected from CTD bottles and surface underway water on the cruise AMT25 (JR15001) along the Atlantic Meridional Transect (AMT) from September 2015 to November 2015.

Total surfactant activity (SA: equivalent to Triton-X-100, mg/L) was determined daily between the UK and the Falkland Islands, during the Atlantic Meridional Transect cruise AMT25 (JR15001). Samples were simultaneously obtained from the surface microlayer (SML) by a Garrett screen microlayer sampler, the ship’s underway system (inlet at 7m) and from CTD depth profiles to 500m from a 24 x 20 L water-bottle rosette. SA measurements were carried out using a Metrohm 797 VA Computerace voltametric measuring stand with a hanging mercury drop electrode. SA measurements were calibrated using a 10-point linear regression of electrode potential response against increasing Triton-X-100 concentration in a 0.55 mol/L NaCl solution. The SA of the samples was measured from the reduction of the capacity current over a range of potentials after 0, 15 and 60s accumulation of surfactants on the hanging mercury drop. The data were generated under the Plymouth Marine Laboratory National Capability (PML NC) project funded by the Natural Environmental Research Council (NERC) and contribute to the aims of NERC's 'Radiatively active gases from the North Atlantic Region and Climate Change' (RAGNARoCC) programme.