During the expedition HE491, our main objectives were to increase our understanding of (i) the abundance and biodiversity of phytoplankton near the sea surface (< 5m), (ii) the link between hyperspectral light availability and phytoplankton biogeography and (iii) effects by plankton communities on air-sea CO2 fluxes. We deployed state-of-the-art technology to make observations close to the sea surface including a hyperspectral radiometric profiler, a remote-controlled research catamaran and an
autonomous gas flux buoy. In addition, a High-volume Sampler for the Verticals (HSV) has been developed for the expedition and successfully deployed to collect discrete water samples in the upper 2 meter from six different depths. With samples from the catamaran (from the sea-surface microlayer and 1 meter), near-surface gradients of eight depths for pigments, nutrients, surface-active substances, particulate matter, cell abundances and taxonomy has been obtained from 14 stations. The catamaran was deployed at each station for up to 7 hours retrieving up to 2500 in situ data points from the microlayer and 1 meter depth for pH, salinity, temperature and chromophoric dissolved organic matter (CDOM).