We report here on a survey of phenolic contents in all seaweeds forming belts on a sheltered rocky shore in Brittany (France). Eight species of brown algae (7 Fucales and 1 Laminariales) were investigated over a 14-month period. Levels of phenolic compounds in members of the Fucales were generally above 2% DW and exceeded those found in the Laminariales by a factor of ten. The highest contents were found in species growing at mid-tide level, with a decrease above and below this shore level. There was a seasonal pattern, with a summer maximum for the Fucales and winter maximum for a member of the Laminariales.

Bursting bubbles at the ocean-surface produce airborne salt-water spray-droplets, in turn, forming climate-cooling marine haze and cloud layers. The reflectance and ultimate cooling effect of these layers is determined by the spray’s water-uptake properties that are modified through entrainment of ocean-surface organic matter (OM) into the airborne droplets. We present new results illustrating a clear dependence of OM mass-fraction enrichment in sea spray (OM_ss) on both phytoplankton-biomass, determined from Chlorophyll-a (Chl-a) and Net Primary Productivity (NPP). The correlation coefficient for OM_ss as a function of Chl-a increased form 0.67 on a daily timescale to 0.85 on a monthly timescale. An even stronger correlation was found as a function of NPP, increasing to 0.93 on a monthly timescale. We suggest the observed dependence is through the demise of the bloom, driven by nanoscale biological processes (such as viral infections), releasing large quantities of transferable OM comprising cell debris, exudates and other colloidal materials. This OM, through aggregation processes, leads to enrichment in sea-spray, thus demonstrating an important coupling between biologically-driven plankton bloom termination, marine productivity and sea-spray modification with potentially significant climate impacts.

International audienceThis study focuses on the intra-thallus variation in phlorotannin content and antioxidant activity in temperate brown seaweeds. Two species of Fucales (Ascophyllum nodosum and Sargassum muticum) and two species of Laminariales (Laminaria digitata and L. hyperborea) were collected from the shoreline of Brittany (France). Both Fucales contained high phenolic levels along their thallus (ca. 5% DW in A. nodosum and 6% DW in S. muticum). No significant differences were found between vegetative and reproductive parts of A. nodosum. In contrast, intra-thallus and inter-specific variations were observed in phenolic contents of the two species of Laminariales studied. In L. digitata, phenolic content was about 0.2% DW, with a maximum in the holdfast, whereas in L. hyperborea, it averaged about 2.6% DW, with the highest value measured in the basal part of the old blade. In both species, phlorotannin contents were lower in the meristematic region. Intra-thallus variations of the antioxidant activity measured by the DPPH (2,2-diphenyl-1-picrylhydrazyl) method were also detected. Antioxidant activity was correlated to the phenol contents of the different parts of thalli in three species. In L. digitata, no activity was found because of low phenol levels. The observed variations in both the antioxidant activity and the phenol content could result from qualitative features of the phenolic pool

The present study reports on observations carried out in the Tropical North Atlantic in summer and autumn 2017, documenting Sargassum aggregations using both ship-deck observations and satellite sensor observations at three resolutions (MSI-10 m, OLCI-300 m, VIIRS-750 m and MODIS-1 km). Both datasets reported that in summer, Sargassum aggregations were mainly observed off Brazil and near the Caribbean Islands, while they accumulated near the African coast in autumn. Based on in situ observations, we propose a five-class typology allowing standardisation of the description of in situ Sargassum raft shapes and sizes. The most commonly observed Sargassum raft type was windrows, but large rafts composed of a quasi-circular patch hundreds of meters wide were also observed. Satellite imagery showed that these rafts formed larger Sargassum aggregations over a wide range of scales, with smaller aggregations (of tens of m² area) nested within larger ones (of hundreds of km²). Match-ups between different satellite sensors and in situ observations were limited for this dataset, mainly because of high cloud cover during the periods of observation. Nevertheless, comparisons between the two datasets showed that satellite sensors successfully detected Sargassum abundance and aggregation patterns consistent with in situ observations. MODIS and VIIRS sensors were better suited to describing the Sargassum aggregation distribution and dynamics at Atlantic scale, while the new sensors, OLCI and MSI, proved their ability to detect Sargassum aggregations and to describe their (sub-) mesoscale nested structure. The high variability in raft shape, size, thickness, depth and biomass density observed in situ means that caution is called for when using satellite maps of Sargassum distribution and biomass estimation. Improvements would require additional in situ and airborne observations or very high-resolution satellite imagery.