Biogenic composition of the sea-surface microlayer from a mesocosm study (Bergen 2011)

The sea-surface microlayer (SML) is the ocean's uppermost boundary to the atmosphere and in control of climate relevant processes like gas exchange and emission of marine primary organic aerosols (POA). The SML represents a complex surface film including organic components like polysaccharides, pro- teins, and marine gel particles, and harbors diverse microbial communities. Despite the potential relevance of the SML in ocean-atmosphere interactions, still little is known about its structural characteristics and sen- sitivity to a changing environment such as increased oceanic uptake of anthropogenic CO2. Here we report results of a large-scale mesocosm study, indicating that ocean acidification can affect the abundance and activity of microorganisms during phytoplankton blooms, resulting in changes in composition and dynam- ics of organic matter in the SML. Our results reveal a potential coupling between anthropogenic CO2 emis- sions and the biogenic properties of the SML, pointing to a hitherto disregarded feedback process between ocean and atmosphere under climate change.

Mercury concentrations in waters of the Atlantic Ocean and Mediterranean Sea

Total mercury concentration in waters of the Atlantic Ocean and Mediterranean Sea measured in January-April 1982 varied from 0.007 to 0.192 µg/l. Particulate form was 1.6-16% of dissolved form. Inorganic mercury accounted for 16-67% of dissolved mercury. Total mercury concentration in the surface film was 0.74-1.85 µg/l, 10-40 times higher than in seawater. Concentration of particulate form in the film was from 100 to 400 times higher than in seawater.

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.

Seasonal variations in surface metabolite composition of Fucus vesiculosus and Fucus serratus sampled at outer Kiel Fjord (August 2012 - July 2013)

The chemical composition of surface associated metabolites of two Fucus species (Fucus vesiculosus and Fucus serratus) was analysed by means of gas chromatography-mass spectrometry (GC-MS) to describe temporal patterns in chemical surface composition. Method: The two perennial brown macroalgae F. vesiculosus and F. serratus were sampled monthly at Bülk, outer Kiel Fjord, Germany (54°27'21 N / 10°11'57 E) over an entire year (August 2012 - July 2013). Per month and species six non-fertile Fucus individuals were collected from mixed stands at a depth of 0.5 m under mid water level. For surface extraction approx. 50 g of the upper 5-10 cm apical thalli tips were cut off per species. The surface extraction of Fucus was performed according to the protocol of de Nys and co-workers (1998) with minor modifications (see Rickert et al. 2015). GC/EI-MS measurements were performed with a Waters GCT premier (Waters, Manchester, UK) coupled to an Agilent 6890N GC equipped with a DB-5 ms 30 m column (0.25 mm internal diameter, 0.25 mM film thickness, Agilent, USA). The inlet temperature was maintained at 250°C and samples were injected in split 10 mode. He carrier gas flow was adjusted to 1 ml min-1. Alkanes were used for referencing of retention times. For further details (GC-MS sample preparation and analysis) see the related publication (Rickert et al. submitted to PLOS ONE).