Meiobenthos at the Arctic Håkon Mosby Mud Volcano

Håkon Mosby Mud Volcano (HMMV, SW Barents Sea slope, 1280 m) is one of the numerous cold methane-venting seeps existing along the continental margins. Analyses of video-guided core samples revealed extreme differences in the diversity and density of the metazoan meiobenthic communities associated with the different sub-habitats (centre, microbial mats, Pogonophora field, outer rim) of this mud volcano. Diversity was lowest in the sulphidic, microbial mat sediments that supported the highest standing stock, with unusually high densities (11000 ind./10 cm**2) of 1 nematode species related to Geomonhystera disjuncta. Stable carbon isotope analyses revealed that this nematode species was thriving on chemosynthetically derived food sources in these sediments. Ovoviviparous reproduction has been identified as an important adaptation of parents securing the survival and development of their brood in this toxic environment. The proliferation of this single species in exclusive association with free-living, sulphide-oxidising bacteria (Beggiatoa) indicates that its dominance is strongly related to trophic specialisation, evidently uncommon among the meiofauna. This chemoautotrophic association was replaced by copepods in the bare, sulphide-free sediments of the volcano's centre, dominated by aerobic methane oxidation as the chemosynthetic process. Copepods and nauplii reached maximum densities and dominance in the volcano's centre (500 ind./10 cm**2). Their strongly depleted carbon isotope signatures indicated a trophic link with methane-derived carbon. This proliferation of only selected meiobenthic species supported by chemosynthetically derived carbon suggests that, in addition to the sediment geochemistry, the associated reduced meiobenthic diversity may equally be related to the trophic resource specificity in HMMV sub-habitats.

Chemical and isotopic compositions of samples from the Haakon Mosby mud volcano and nearby

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active methane-bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanotrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (aver. d13C = -28.9 per mil) of CO2 produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (aver. d18O = 5 per mil) in carbonates is inherited from seawater sulfate. Rapid sulfate reduction (up to 12 mg S/dm**3/day) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this carbonates can only be formed in surface sediments near the water-bottom interface. Salinity as well as CO3/Ca and Mg/Ca ratios correspond to the field of non-magnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. Radiocarbon age of carbonates is about 10 Ka.

Estimation of cooling of lavas from Serocki volcano

A dynamic crystallization study was undertaken to provide a framework for linking the textural variations observed in the Hole 648B lavas with the size and morphology of cooling units inferred from drilling and submersible observation. The textures produced in cooling rate experiments carried out using a Serocki lava (ALV-1690-20) are comparable to the groundmass textural characteristics of lavas from Serocki volcano. The results of the dynamic crystallization study provide a quantitative link between texture, cooling rate, and eruption temperature. The maximum half-width of cooling units estimated from textural characteristics is on the order of 3 m, a value consistent with constraints from drilling and submersible observation. Textural characteristics indicate that the temperature from which cooling began was slightly above the liquidus. The relation between cooling rate and texture are also tested on a drill core sample of basalt of similar composition from a 9-m-thick flow in DSDP Hole 396B.

Pore water geochemistry of Håkon Mosby mud volcano sediments measured at station PS74/169-1_PUC-15 (Z1-S1, new flow surface)

Pore water and turnover rates were determined for surface sediment cores obtained in 2009 and 2010. The pore water was extracted with Rhizons (Rhizon CSS: length 5 cm, pore diameter 0.15 µm; Rhizosphere Research Products, Wageningen, Netherlands) in 1 cm-resolution and immediately fixed in 5% zinc acetate (ZnAc) solution for sulfate, and sulfide analyses. The samples were diluted, filtered and the concentrations measured with non-suppressed anion exchange chromatography (Waters IC-Pak anion exchange column, waters 430 conductivity detector). The total sulfide concentrations (H2S + HS- + S**2-) were determined using the diamine complexation method (doi:10.4319/lo.1969.14.3.0454). Samples for dissolved inorganic carbon (DIC) and alkalinity measurements were preserved by adding 2 µl saturated mercury chloride (HgCl2) solution and stored headspace-free in gas-tight glass vials. DIC and alkalinity were measured using the flow injection method (detector VWR scientific model 1054) (doi:10.4319/lo.1992.37.5.1113). Dissolved sulfide was eliminated prior to the DIC measurement by adding 0.5 M molybdate solution (doi:10.4319/lo.1995.40.5.1011). Nutrient subsamples (10 - 15 ml) were stored at - 20 °C prior to concentration measurements with a Skalar Continuous-Flow Analyzer (doi:10.1002/9783527613984).