The sea surface microlayer (SML) is the seawater layer (about 100 µm thick) located at the air-ocean interface, usually enriched in organic and inorganic matter compared to the underlying water (UW) sampled between 5 cm and 50 cm depth. This article is aimed at providing novel data for a better quantification of the SML enrichment and knowledge of associated processes. First, the mean 1 to 100 cm depth profile for dissolved total carbohydrates (DTCHO) established from a set of 10 stations in coastal northwestern Mediterranean waters (off Barcelona and Banyuls-sur-mer) indicates that (1) this layer is not necessarily homogeneous as generally admitted and (2) an exploratory survey is needed before undertaking an extensive sampling, to determine the most appropriate depth for sampling UW. Second, two samplers, glass plate (GP) and metal screen (MS), are compared for their ability to collect several classes of biomolecules at the first 50 µm and 440 µm layers below the interface, respectively. GP is shown to collect more efficiently (1) hydrophobic amino acids and phytoplanktonderived detrital matter, as shown by statistical results on a set of eight stations, and (2) fatty acids originating from bacteria and continental higher plants (inferred from a lower number of stations). Thus, it is well adapted for studying interactions between ocean, atmosphere, and continent. On the contrary, MS is better adapted for recovering phytoplankton organisms, as shown by data for chlorophyll a, pheophytin a, and unsaturated fatty acids. DTCHO are equally sampled by GP and MS.

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