(Table 3) Stable isotope composition of sof t tissues of specimens from the Sea of Okhotsk

We discovered and investigated several cold-seep sites in four depth zones of the Sea of Okhotsk off Northeast Sakhalin: outer shelf (160-250 m), upper slope (250-450 m), intermediate slope (450-800 m), and Derugin Basin (1450-1600 m). Active seepage of free methane or methane-rich fluids was detected in each zone. However, seabed photography and sampling revealed that the number of chemoautotrophic species decreases dramatically with decreasing water depth. At greatest depths in the Derugin Basin, the seeps were inhabited by bacterial mats and bivalves of the families Vesicomyidae (Calyptogena aff. pacifica, C. rectimargo, Archivesica sp.), Solemyidae (Acharax sp.) and Thyasiridae (Conchocele bisecta). In addition, pogonophoran tubeworms of the family Sclerolinidae were found in barite edifices. At the shallowest sites, on the shelf at 160 m, the seeps lack chemoautotrophic macrofauna; their locations were indicated only by the patchy occurrence of bacterial mats. Typical seep-endemic metazoans with chemosynthetic symbionts were confined to seep sites at depths below 370 m. A comparative analysis of the structure of seep and background communities suggests that differences in predation pressure may be an important determinant of this pattern. The abundance of predators such as carnivorous brachyurans and asteroids, which can invade seeps from adjacent habitats and efficiently prey on sessile seep bivalves, decreased very pronouncedly with depth. We conclude from the obvious correlation with the conspicuous pattern in the distribution of seep assemblages that, on the shelf and at the upper slope, predator pressure may be high enough to effectively impede any successful settlement of viable populations of seep-endemic metazoans. However, there was also evidence that other depth-related factors, such as bottom-water current, sedimentary regimes, oxygen concentrations and the supply of suitable settling substrates, may additionally regulate the distribution of seep fauna in the area. As a consequence of the pronounced pattern in the distribution of seep communities, their ecological significance as food sources of surrounding background fauna increased with water depth. Isotopic analyses suggest that in the Derugin Basin seep colonists feed on chemoautotrophic seep organisms, either directly or by preying on metazoans with chemosynthetic symbionts. In contrast, seep organisms apparently do not contribute to the nutrition of the adjacent background fauna on the shelf and at the slope. In this area, elevated epifaunal abundances at seep sites were caused primarily by the availability of suitable settling substrates rather than by an enrichment of food supply.

(Table 1) Stable isotope data of chemoherm carbonates at Hydrate Ridge on the Cascadia continental margin

Two active chemoherm build-ups growing freely up into the oceanic water column, the Pinnacle and the South East-Knoll Chemoherms, have been discovered at Hydrate Ridge on the Cascadia continental margin. These microbially-mediated carbonate formations rise above the seafloor by several tens of meters and display a pinnacle-shaped morphology with steep flanks. The recovered rocks are pure carbonates dominated by aragonite. Based on fabric and mineralogic composition different varieties of authigenic aragonite can be distinguished. Detailed visual and petrographic investigations unambiguously reveal the involvement of microbes during the formation of the carbonates. The fabric of the cryptocrystalline and fibrous aragonite can be described as thrombolitic. Fossilized microbial filaments in the microcrystalline aragonite indicate the intimate relationship between microbes and carbonates. The strongly 13C-depleted carbon isotope values of the samples (as low as -48.1 per mill PDB) are characteristic of methane as the major carbon source for the carbonate formation. The methane-rich fluids from which the carbonates are precipitated originate most probably from a gas reservoir below the bottom-simulating reflector (BSR) and rise through fault systems. The d18O values of the aragonitic chemoherm carbonates are substantially higher (as high as 5.0 per mill PDB) than the expected equilibrium value for an aragonite forming from ambient seawater (3.5 per mill PDB). As a first approximation this indicates formation from glacial ocean water but other factors are considered as well. A conceptual model is presented for the precipitation of these chemoherm carbonates based on in situ observations and the detailed petrographic investigation of the carbonates. This model explains the function of the consortium of archaea and sulfate-reducing bacteria that grows on the carbonates performing anaerobic oxidation of methane (AOM) and enabling the precipitation of the chemoherms above the seafloor surrounded by oxic seawater. Beggiatoa mats growing on the surface of the chemoherms oxidize the sulfide provided by sulfate-dependent anaerobic oxidation of methane within an oxic environment. The contact between Beggiatoa and the underlying microbial consortium represents the interface between the overlying oxic water column and an anoxic micro-environment where carbonate formation takes place.

Horizontal profiles of longwave and shortwave radiation components over sea ice near Barrow, Alaska during the 2011 melt

An integrated instrument package for measuring and understanding the surface radiation budget of sea ice is presented, along with results from its first deployment. The setup simultaneously measures broadband fluxes of upwelling and downwelling terrestrial and solar radiation (four components separately), spectral fluxes of incident and reflected solar radiation, and supporting data such as air temperature and humidity, surface temperature, and location (GPS), in addition to photographing the sky and observed surface during each measurement. The instruments are mounted on a small sled, allowing measurements of the radiation budget to be made at many locations in the study area to see the effect of small-scale surface processes on the large-scale radiation budget. Such observations have many applications, from calibration and validation of remote sensing products to improving our understanding of surface processes that affect atmosphere-snow-ice interactions and drive feedbacks, ultimately leading to the potential to improve climate modelling of ice-covered regions of the ocean. The photographs, spectral data, and other observations allow for improved analysis of the broadband data. An example of this is shown by using the observations made during a partly cloudy day, which show erratic variations due to passing clouds, and creating a careful estimate of what the radiation budget along the observed line would have been under uniform sky conditions, clear or overcast. Other data from the setup's first deployment, in June 2011 on fast ice near Point Barrow, Alaska, are also shown; these illustrate the rapid changes of the radiation budget during a cold period that led to refreezing and new snow well into the melt season.

Meiobenthos investigations in the Black Sea during Poseidon cruise POS317/3

Meiobenthos densities and higher taxon composition were studied in an active gas seepage area at depths from 182 to 252 m in the submarine Dnieper Canyon located in the northwestern part of the Black Sea. The meiobenthos was represented by Ciliata, Foraminifera, Nematoda, Polychaeta, Bivalvia, Gastropoda, Amphipoda, and Acarina. Also present in the sediment samples were juvenile stages of Copepoda and Cladocera which may be of planktonic origin. Nematoda and Foraminifera were the dominant groups. The abundance of the meiobenthos varied between 2397 and 52593 Ind./m**2. Maximum densities of Nematoda and Foraminifera were recorded in the upper sediment layer of a permanent H2S zone at depths from 220 to 250 m. This dense concentration of meiobenthos was found in an area where intense methane seeps were covered by methane-oxidizing microbial mats. Results suggest that methane and its microbial oxidation products are the factors responsible for the presence of a highly sulfidic and biologically productive zone characterized by specially adapted benthic groups. At the same time, an inverse correlation was found between meiofauna densities and methane concentrations in the uppermost sediment layers. The hypothesis is that the concentration of Nematoda and Foraminifera within the areas enriched with methane is an ecological compromise between the food requirements of these organisms and their adaptations to the toxic H2S.