Gel particles in the sea-surface microlayer during an experimental study

Since the early 80's, the sea-surface microlayer (SML) has been hypothesized as being a gelatinous film. Recent studies have confirmed this characteristic, which confers properties that mediate mass and energy fluxes between ocean and atmosphere, including the emission of primary organic aerosols from marine systems. We investigated SML thickness and composition in five replicate indoor experiments between September and December 2010. During each experiment, the SML and underlying seawater were sampled from four seawater tanks: one served as control, and three were inoculated with Thalassiosira weissflogii grown in chemostats at 180, 380 and 780 ppm pCO2. We examined organic material enrichment factors in each tank, paying particular attention to gel particles accumulation such as polysaccharidic Transparent Exopolymer Particles (TEP) and the proteinaceous Coomassie Stainable Particles (CSP). While previous studies have observed carbohydrates and TEP enrichment in the microlayer, little is yet known about proteinaceous gel particles in the SML. Our experiments show that CSP dominate the gelatinous composition of the SML. We believe that the enrichment in CSP points to the importance of bacterial activity in the microlayer. Bacteria may play a pivotal role in mediating processes at the air-sea interface thanks to their exudates and protein content that can be released through cell disruption.

Time series of ZOOSCAN images and results of zooplankton samples at Villefranche from 1966 to 2003

ZooScan with ZooProcess and Plankton Identifier (PkID) software is an integrated analysis system for acquisition and classification of digital zooplankton images from preserved zooplankton samples. Zooplankton samples are digitized by the ZooScan and processed by ZooProcess and PkID in order to detect, enumerate, measure and classify the digitized objects. Here we present a semi-automatic approach that entails automated classification of images followed by manual validation, which allows rapid and accurate classification of zooplankton and abiotic objects. We demonstrate this approach with a biweekly zooplankton time series from the Bay of Villefranche-sur-mer, France. The classification approach proposed here provides a practical compromise between a fully automatic method with varying degrees of bias and a manual but accurate classification of zooplankton. We also evaluate the appropriate number of images to include in digital learning sets and compare the accuracy of six classification algorithms. We evaluate the accuracy of the ZooScan for automated measurements of body size and present relationships between machine measures of size and C and N content of selected zooplankton taxa. We demonstrate that the ZooScan system can produce useful measures of zooplankton abundance, biomass and size spectra, for a variety of ecological studies.

Vertical distribution of suspended aggregates in the equatorial Pacific

Marine snow (MS) distribution from the surface to 1000 m depth was determined in the equatorial Pacific using the underwater video profiler during the Etude du Broutage en Zone Equatoriale cruise in fall 1996. The latitudinal transect was carried out at 17 stations along the 180° meridian from 8°S to 8°N during a cold phase of El Niño-Southern Oscillation. Higher MS concentrations were found below the equatorial zone than poleward. At the equator the estimated integrated MS carbon/m**2 in the upper kilometer was 5.7 g/m**2, while both southward and northward (between 1° and 8°) the mean integrated MS carbon was about 2.7 g/m**2. In the upper 50 m the MS carbon was twofold lower than the combined carbon of autotrophic and heterotrophic protists and four times lower than the mesozooplankton carbon biomass, both measured concurrently during the cruise. Different water bodies had different MS content. The highest concentrations were found in the South Equatorial Current, the South Equatorial Counter Current, and the North Equatorial Countercurrent. Tropical waters at the south in the South Subsurface Countercurrents and the warm northern superficial waters had the lowest MS biomass. Mechanistically, a latitudinal "conveyor belt", a poleward divergence of upwelled waters that return to the equator after being downwelled at north and south convergent zones, may partially explain the vertical distribution of particulate matter observed during the studied period.