Microbial ecology of the stratified water column of the Black Sea as revealed by a comprehensive biomarker study

The stratified water column of the Black Sea is partitioned into oxic, suboxic, and euxinic zones, each characterized by different biogeochemical processes and by distinct microbial communities. In 2003, we collected particulate matter by large volume in situ filtration at the highest resolution to date for lipid biomarker analysis and bacterioplankton for enumeration of major prokaryotic groups. Abundances of several prokaryotic groups were estimated using CARD-FISH probes specific for Bacteria, Archaea (Crenarchaeota and Euryarchaeota), epsilonproteobacteria (mainly sulfide oxidizers) and sulfate reducing bacteria. We also measured a wide range of bacterial and archaeal lipid biomarkers. Depth distributions of diagnostic biomarkers are matched with zonation of microbial processes, including aerobic bacterial oxidation of methane, oxidation of ammonium by bacteria and archaea, metal reduction, and sulfide oxidation at the chemocline, and bacterial sulfate reduction and anaerobic oxidation of methane by archaea in the anoxic zone. Cell densities for archaea and sulfate reducing bacteria are estimated based on water column biomarker concentrations and compared with CARD-FISH results.     

Influence of freeze-thaw events on carbon dioxide emission from soils at different moisture and land use

Background  

The repeated freeze-thaw events during cold season, freezing of soils in autumn and thawing in spring are typical for the tundra, boreal, and temperate soils. The thawing of soils during winter-summer transitions induces the release of decomposable organic carbon and acceleration of soil respiration. The winter-spring fluxes of CO₂ from permanently and seasonally frozen soils are essential part of annual carbon budget varying from 5 to 50%. The mechanisms of the freeze-thaw activation are not absolutely clear and need clarifying. We investigated the effect of repeated freezing-thawing events on CO₂ emission from intact arable and forest soils (Luvisols, loamy silt; Central Germany) at different moisture (65% and 100% of WHC).     

Using Strong Solar Coronal Emission Lines as Coronal Flux Proxies

We investigate the possibility that strong EUV lines observed with the Goddard Solar EUV Rocket Telescope and Spectrograph (SERTS) provide good proxies for estimating the total coronal flux over shorter wavelength ranges. We use coordinated SERTS and Yohkoh observations to obtain both polynomial and power-law fits relating the broad-band soft X-ray fluxes to the intensities of Fexvi 335 Ú and 361 Ú, Fexv 284 Ú and 417 Ú, and Mgix 368 Ú measured with SERTS. We found that the power-law fits best cover the full range of solar conditions from quiet Sun through active region, though not surprisingly the cooler Mgix 368 Ú line proves to be a poor proxy. The quadratic polynomial fits yield fair agreement over a large range for all but the Mgix line. However, the linear fits fail conspicuously when extrapolated into the quiet-Sun regime. The implications of this work for the Heii 304 Ú line formation problem are also briefly considered.     

Petrology and geochronology of basalt breccia from the 1996 earthquake swarm of Loihi seamount, Hawaii: magmatic history of its 1996 eruption

 Samples of basalt were collected during the Rapid Response cruise to Loihi seamount from a breccia that was probably created by the July to August 1996 Loihi earthquake swarm, the largest swarm ever recorded from a Hawaiian volcano. ²¹⁰Po–²¹⁰Pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996, making this the first documented historical eruption of Loihi. Sonobuoys deployed during the August 1996 cruise recorded popping noises north of the breccia site, indicating that the eruption may have been continuing during the swarm. All of the breccia lava fragments are tholeiitic, like the vast majority of Loihi's most recent lavas. Reverse zoning at the rim of clinopyroxene phenocrysts, and the presence of two chemically distinct olivine phenocryst populations, indicate that the magma for the lavas was mixed just prior to eruption. The trace element geochemistry of these lavas indicates there has been a reversal in Loihi's temporal geochemical trend. Although the new Loihi lavas are similar isotopically and geochemically to recent Kilauea lavas and the mantle conduits for these two volcanoes appear to converge at depth, distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes. The mineralogy of Loihi's recent tholeiitic lavas signify that they crystallized at moderate depths (∼8–9 km) within the volcano, which is approximately 1 km below the hypocenters for earthquakes from the 1996 swarm. Taken together, the petrological and seismic evidence indicates that Loihi's current magma chamber is considerably deeper than the shallow magma chamber (∼3–4 km) in the adjoining active shield volcanoes. Received: 21 August 1997 / Accepted: 15 February 1998     

On the properties of strange modes

Properties of the so-called strange modes occurring in linear stability calculations of stellar models are discussed. The behaviour of these modes is compared for two different sets of stellar models, for very massive zero-age main-sequence stars and for luminous hydrogen-deficient stars, both with high luminosity-to-mass ratios. We have found that the peculiar behaviour of the frequencies of the strange modes with the change of a control parameter is caused by the pulsation amplitude of a particular eigenmode being strongly confined to the outer part of the envelope, around the density inversion zone. The frequency of a strange mode changes because the depth of the confinement zone changes with the control parameter. Weakly non-adiabatic strange modes tend to be overstable because the amplitude confinement quenches the effect of radiative damping. On the other hand, extremely non-adiabatic strange modes become overstable because the perturbation of radiation force (gradient of radiation pressure) provides a restoring force that can be out of phase with the density perturbation. We discuss this mechanism by using a plane-parallel two-zone model.     

Detection of subsidence conditions by photogeology

A variety of air-photo interpretation criteria need to be used for detecting areas of potential subsidence. An initial step is to search for past failures showing on air photographs, to establish the cause and to interpret the boundaries of the environment that might be affected. Causes detectable include karstic terrain, areas liable to piping, or containing concealed peat, old shafts, and stratiform or vein workings. Airborne imaging conditions can be selected to improve the possibility of detection in some situations.

The technique can indicate situations where risks are high, but cannot be used to map with certainty voids liable to collapse.     

Numerical study of the nocturnal urban boundary layer

A two-dimensional time-dependent Earth-atmosphere model is developed which can be applied to the study of a class of atmospheric boundary-layer flows which owe their origin to horizontal inhomogeneities with respect to surface roughness and temperature. Our main application of the model is to explore the governing physical mechanisms of nocturnal urban atmospheric boundarylayer flow.A case study is presented in which a stable temperature stratification is assumed to exist in the rural upwind area. It is shown through integration of the numerical model that as this air passes over a city, the heat is redistributed due to increased surface friction (and hence increased turbulent mixing). This redistribution of heat results in the formation of an urban heat island.Additional numerical integrations of the model are conducted to examine the dependence of induced perturbations on: (1) the upwind temperature inversion; (2) the geostrophic wind speed; and (3) urbanization. The results show a linear relationship between heat-island intensity and the rural temperature inversion with the heat island increasing in intensity as the upwind inversion becomes stronger; that the heat-island intensity close to the surface is inversely proportional to the geostrophic wind; and that the effects of anthropogenic heat cause an increase in the perturbation temperature with the perturbation extending to higher altitudes. From this study, we conclude that with an upwind temperature inversion, a city of any size should generate a heat island as a result of increased surface roughness. The heat-island intensity should increase with city size because of two factors: larger cities are usually aerodynamically rougher; and larger cities have a larger anthropogenic heat output.Research supported in part by NSF Grant GA-16822.