Seasonal dynamics of microbial sulfate reduction in temperate intertidal surface sediments: controls by temperature and organic matter

The role of microbial sulfate reduction on organic matter oxidation was studied quantitatively in temperate intertidal surface sediments of the German Wadden Sea (southern North Sea) on a seasonal base in the years 1998–2007. The sampling sites represent the range of sediments found in the back-barrier tidal area of Spiekeroog Island: sands, mixed and muddy flats. The correspondingly different contents in organic matter, metals, and porosities lead to significant differences in the activity of sulfate-reducing bacteria with volumetric sulfate reduction rates (SRR) in the top 15 cm of up to 1.4 μmol cm^?3 day^?1. Depth-integrated areal SRR ranged between 0.9 and 106 mmol m^?2 day^?1, with the highest values found in the mudflat sediments and lower rates measured in sands at the same time, demonstrating the impact of both temperature and organic matter load. According to a modeling approach for a 154-km² large tidal area, about 39, 122, and 285 tons of sulfate are reduced per day, during winter, spring/autumn, and summer, respectively. Hence, the importance of areal benthic organic matter mineralization by microbial sulfate reduction increases during spring/autumn and summer by factors of about 2 and 7, respectively, when compared to winter time. The combined results correspond to an estimated benthic organic carbon mineralization rate via sulfate reduction of 78 g C m^?2 year^?1.     

Thermal simulation experiments of saturated hydrocarbons with calcium sulfate and element sulfur: Implications on origin of H<Subscript>2</Subscript>S

Temperature-programmed simulation experiments of saturated hydrocarbons with calcium sulfate and element sulfur were compared in this study. Based on the variation analysis of the yields and evolvement features of gaseous hydrocarbon (C1-C5) and inorganic gaseous CO2, H2 and H2S, the reaction mechanisms were analyzed and discussed. In the calcium sulfate-saturated hydrocarbon system, H2S was produced by a small quantity, which indicates this reaction belongs to the low-degreed thermal sulfate reduction (TSR...     

Cluster analysis of soil CO<Subscript>2</Subscript> data from Mt. Etna (Italy) reveals volcanic influences on temporal and spatial patterns of degassing

Soil CO₂ concentration data were collected periodically from July 2001 to June 2005 from sampling site grids in two areas located on the lower flanks of Mt. Etna volcano (Paternò and Zafferana Etnea–Santa Venerina). Cluster analysis was performed on the acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources. In both areas three clusters were recognised, whose average CO₂ concentration values throughout the whole study period remained significantly different from one another. The clusters with the lowest CO₂ concentrations showed time-averaged values ranging from 980 to 1,170 ppm vol, whereas those with intermediate CO₂ concentrations showed time-averaged values ranging from 1,400 to 2,320 ppm vol, and those with the highest concentrations showed time-averaged values between 1,960 and 55,430 ppm vol. We attribute the lowest CO₂ concentrations largely to a biogenic source of CO₂. Conversely, the highest CO₂ concentrations are attributed to a magmatic source, whereas the intermediate values are due to a variable mixing of the two sources described above. The spatial distribution of the CO₂ values related to the magmatic source define a clear direction of anomalous degassing in the Zafferana Etnea–Santa Venerina area, which we attribute to the presence of a hidden fault, whereas in the Paternò area no such oriented anomalies were observed, probably because of the lower permeability of local soil. Time-series analysis shows that most of the variations observed in the soil CO₂ data from both areas were related to changes in the volcanic activity of Mt. Etna. Seasonal influences were only observed in the time patterns of the clusters characterised by low CO₂ concentrations, and no significant interdependence was found between soil CO₂ concentrations and meteorological parameters. The largest observed temporal anomalies are interpreted as release of CO₂ from magma batches that migrated from deeper to shallower portions of Etna’s feeder system. The pattern of occurrence of such episodes of anomalous gas release during the observation period was quite different between the two studied areas. This pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano’s feeder system after June 2003, interpreted as magma accumulation into a shallow (<8 km depth) reservoir.     

Characteristics of <Emphasis Type="Italic">p</Emphasis>CO<Subscript>2</Subscript> in surface water of the Bering Abyssal Plain and their effects on carbon cycle in the

Characteristics of the pCO₂ distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO₂ in surface water of the Bering Abyssal Plain and the Chukchi Sea. Data in this study are from a field investigation during the First Chinese National Arctic Research Expedition in 1999. Compared to the high productivity in the Bering Continental Shelf, much lower levels of chlorophyll a were observed in the Bering Abyssal Plain. The effect of hydrological factors on the pCO₂ distribution in surface seawater of the Plain in summer has become a major driving force and dominated over biological factors. The Plain also presents a High Nutrient Low Chlorophyll (HNLC). In addition, the pCO₂ distribution in the Bering Abyssal Plain has also been found to be influenced from the Bering Slope Current which would transform to the Anadyr Current when it inflows northwestward over the Plain. The Anadyr Current would bring a high nutrient water to the western Arctic Ocean where local nutrients are almost depleted in the surface water during the summer time. Resupplying nutrients would stimulate the growth of phytoplankton and enhance capacity of absorbing atmospheric CO₂ in the surface water. Otherwise, in the Bering Sea the dissolved inorganic carbon brought from freshwater are not deposited down to the deep sea water but most of them would be transported into the western Arctic Ocean by the Alaska Coastal Current to form a carbon sink there. Therefore, the two carbon sinks in the western Arctic Ocean, one carried by the Anadyr Current and another by the Alaska Costal Current, will implicate the western Arctic Ocean in global change.