Enhanced warming and bacterial biomass production as key factors for coastal hypoxia in the southwestern Baltic Sea.

Coastal ecosystems are affected by a multitude of anthropogenic stressors. As the Baltic Sea ecosystems rank among the most altered marine ecosystems worldwide, they represent ideal model regions to study ecosystem responses to anthropogenic pressures. Our statistical analysis of data including dissolved organic carbon and nitrogen, as well as bacterial abundance and -biomass production from the time-series station Boknis Eck in the southwestern Baltic Sea reveals that bacterial biomass production intensifies towards summer following the phytoplankton spring bloom.

Environmental control and metabolic strategies of organic-matter-responsive bacterioplankton in the Weddell Sea (Antarctica).

Heterotrophic microbial communities play a significant role in driving carbon fluxes in marine ecosystems. Despite their importance, these communities remain understudied in remote polar oceans, which are known for their substantial contribution to the biological drawdown of atmospheric carbon dioxide. Our research focused on understanding the environmental factors and genetic makeup of key bacterial players involved in carbon remineralization in the Weddell Sea, including its coastal polynyas.

Organic matter availability drives the spatial variation in the community composition and activity of Antarctic marine bacterioplankton.

Carbon cycling by Antarctic microbial plankton is poorly understood but it plays a major role in CO sequestration in the Southern Ocean. We investigated the summer bacterioplankton community in the largely understudied Weddell Sea, applying Illumina amplicon sequencing, measurements of bacterial production and chemical analyses of organic matter. The results revealed that the patchy distribution of productive coastal polynyas and less productive, mostly ice-covered sites was the major driver of the spatial changes in the taxonomic composition and activity of bacterioplankton.

On the effect of low oxygen concentrations on bacterial degradation of sinking particles.

In marine oxygen (O) minimum zones (OMZs), the transfer of particulate organic carbon (POC) to depth via the biological carbon pump might be enhanced as a result of slower remineralisation under lower dissolved O concentrations (DO). In parallel, nitrogen (N) loss to the atmosphere through microbial processes, such as denitrification and anammox, is directly linked to particulate nitrogen (PN) export. However it is unclear (1) whether DO is the only factor that potentially enhances POC transfer in OMZs, and (2) if particle fluxes are sufficient to support observed N loss rates.

Inter-annual variability of transparent exopolymer particles in the Arctic Ocean reveals high sensitivity to ecosystem changes.

Transparent exopolymer particles (TEP) are a class of marine gel particles and important links between surface ocean biology and atmospheric processes. Derived from marine microorganisms, these particles can facilitate the biological pumping of carbon dioxide to the deep sea, or act as cloud condensation and ice nucleation particles in the atmosphere. Yet, environmental controls on TEP abundance in the ocean are poorly known.

Combined Carbohydrates Support Rich Communities of Particle-Associated Marine Bacterioplankton.

Carbohydrates represent an important fraction of labile and semi-labile marine organic matter that is mainly comprised of exopolymeric substances derived from phytoplankton exudation and decay. This study investigates the composition of total combined carbohydrates (tCCHO; >1 kDa) and the community development of free-living (0.2-3 μm) and particle-associated (PA) (3-10 μm) bacterioplankton during a spring phytoplankton bloom in the southern North Sea.

Biopolymers form a gelatinous microlayer at the air-sea interface when Arctic sea ice melts.

The interface layer between ocean and atmosphere is only a couple of micrometers thick but plays a critical role in climate relevant processes, including the air-sea exchange of gas and heat and the emission of primary organic aerosols (POA). Recent findings suggest that low-level cloud formation above the Arctic Ocean may be linked to organic polymers produced by marine microorganisms. Sea ice harbors high amounts of polymeric substances that are produced by cells growing within the sea-ice brine.