The Orientational Relaxation of Bipolar Active Regions

In the mean, bipolar active regions are oriented nearly toroidally, according to Hale's polarity law, with a latitude-dependent tilt known as Joy's Law. The tilt angles of individual active regions deviate from this mean behavior and change over time. It has been found that on average the change is toward the mean angle at a rate characteristic of 4.37 days (Howard, 1996). We show that this orientational relaxation is consistent with the standard model of flux tube emergence from a deep dynamo layer. Under this scenario Joy's law results from the Coriolis effect on the rising flux tube (D'Silva and Choudhuri, 1993), and departures from it result from turbulent buffeting of the tubes (Longcope and Fisher, 1996). We show that relaxation toward Joy's angle occurs because the turbulent perturbations relax on shorter time scales than the perturbations from the Coriolis force. The turbulent perturbations relax more rapidly because they are localized to the topmost portion of the convection zone while the Coriolis perturbations are more widely distributed. If a fully-developed active region remains connected to the strong toroidal magnetic field at the base of the convection zone, its tilt will eventually disappear, leaving it aligned perfectly toroidally. On the other hand, if the flux becomes disconnected from the toroidal field the bipole will assume a tilt indicative of the location of disconnection. We compare models which are connected and disconnected from the toroidal field. Only those disconnected at points very deep in the convection zone are consistent with observed time scale of orientational relaxation.     

Climate change perception in Romania

Theoretical and Applied Climatology - In the last decades, anthropogenic drivers have significantly influenced the natural climate variability of Earth’s atmosphere. Climate change has become...     

Accumulation and distribution of petroleum hydrocarbons found in mussels (Mytilus galloprovincialis) in the canals of Venice, Italy

Petroleum contamination was assessed in indigenous and transplanted mussels for three types of environments within the Venice Lagoon and its associated interior canals. Indigenous and transplanted mussels were least impacted by petroleum contamination at open-water stations, but more affected in partially-enclosed areas indicating that physical processes of tidal or wind activities can remove organic contaminants such as petroleum from these areas more effectively. Limited tidal flushing of the interior canals resulted in contaminated locations unable to support indigenous mussels. Clean mussels transplanted to these highly impacted sites accumulated the highest levels of petroleum hydrocarbons. The distribution of polycyclic aromatic hydrocarbons (PAHs) indicated mainly combustion-related activities from sources such as the nearby industrial zones and boat traffic, with some evidence of fresher petroleum inputs. Total hydrocarbons found in all mussels could be related to concentrations found in the surrounding sediments as reported in an earlier study.     

Inventory and Ventilation Efficiency of Nonnative and Native Phragmites australis (Common Reed) in Tidal Wetlands of the Chesapeake Bay

Nonnative Phragmites is among the most invasive plants in the U.S. Atlantic coast tidal wetlands, whereas the native Phragmites has declined. Native and nonnative patches growing side by side provided an ideal setting for studying mechanisms that enable nonnative Phragmites to be a successful invader. We conducted an inventory followed by genetic analysis and compared differences in growth patterns and ventilation efficiency between adjacent native and nonnative Phragmites stands. Genetic analysis of 212 patches revealed that only 14 were native suggesting that very few native Phragmites populations existed in the study area. Shoot density decreased towards the periphery of native patches, but not in nonnative patches. Ventilation efficiency was 300?% higher per unit area for nonnative than native Phragmites, likely resulting in increased oxidation of the rhizosphere and invasive behavior of nonnative Phragmites. Management of nonnative Phragmites stands should include mechanisms that inhibit pressurized ventilation of shoots.     

Experimental insights into the formation of high-Mg basaltic andesites in the trans-Mexican volcanic belt

High-Mg basaltic andesites and andesites occur in the central trans-Mexican volcanic belt, and their primitive geochemical characteristics suggest equilibration with mantle peridotite. These lavas may represent slab melts that reequilibrated with overlying peridotite or hydrous partial melts of a peridotite source. Here, we experimentally map the liquidus mineralogy for a high-Mg basaltic andesite (9.6 wt% MgO, 54.4 wt% SiO₂, Mg# = 75.3) as a function of temperature and H₂O content over a range of mantle wedge pressures. Our results permit equilibration of this composition with a harzburgite residue at relatively high water contents (>7 wt%) and low temperatures (1,080–1,150°C) at 11–14 kbar. However, in contrast to the high Ni contents characteristic of olivine phenocrysts in many such samples from central Mexico, those of olivine phenocrysts in our sample are more typical of mantle melts that have fractionated a small amount of olivine. To account for this and the possibility that the refractory mantle source may have had olivine more Fo-rich than Fo₉₀, we numerically evaluated alternative equilibration conditions, using our starting bulk composition adjusted to be in equilibrium with Fo₉₂ olivine. This shifts equilibration conditions to higher temperatures (1,180–1,250°C) at mantle wedge pressures (11–15 kbar) for H₂O contents (>3 wt%) comparable to those analyzed in olivine-hosted melt inclusions from this region. Comparison with geodynamic models shows that final equilibration occurred shallower than the peak temperature of the mantle wedge, suggesting that basaltic melts from the hottest part of the wedge reequilibrated with shallower mantle as they approached the Moho.     

Origin of a complex and spatially diverse dune-field pattern, Algodones, southeastern California

The Algodones Dune Field of southeastern California shows a complex and spatially diverse dune-field pattern that is superimposed upon a series of topographic lineations. Analysis of dune-field pattern parameters (dune crest length, crest orientation, dune spacing and defect density) derived from aerial images indicates that the dune-field pattern represents two constructional generations. Prominent compound crescentic dunes formed during the first constructional generation. A younger generation consists of a variety of simple crescentic dunes, linear dunes and zibars. Statistical differences in the pattern parameters between the dune groups within the second generation are resolved through consideration of the boundary conditions under which the dune pattern evolved, and provide explanations for: (1) diversity of dune types, (2) range in implied constructional times, (3) range in crest orientations, and (4) the anomalous nature of the population of linear dunes. The boundary conditions that have modified pattern development include orographic effects, grain size, vegetation, areal extent and antecedent conditions. Topographic lineations in the Algodones range from the Western Ramp, which defines the field margin, to subtle features masked by the pattern of dunes. Imaging of the Western Ramp using Ground Penetrating Radar shows high-angle cross-strata migrating perpendicular to the lineation trend. The most plausible hypothesis for the origin of the lineations is as dune ridges sequentially shed from adjacent Lake Cahuilla, which is the source of Algodones sands. The overall geomorphic complexity of the Algodones originates from the emplacement of the dune ridges during stages of Lake Cahuilla, the two generations of dune-field construction, and the controls exerted by boundary conditions.     

Three‐dimensional architecture and hydrostratigraphy of cross‐cutting buried valleys using airborne electromagnetics,glaciated Central Lowlands,Nebraska, USA

Buried valleys are characteristic features of glaciated landscapes, and their deposits host important aquifers worldwide. Understanding the stratigraphic architecture of these deposits is essential for protecting groundwater and interpreting sedimentary processes in subglacial and ice‐marginal environments. The relationships between depositional architecture, topography and hydrostratigraphy in dissected, pre‐Illinoian till sheets is poorly understood. Boreholes alone are inadequate to characterize the complex geology of buried valleys, but airborne electromagnetic surveys have proven useful for this purpose. A key question is whether the sedimentary architecture of buried valleys can be interpreted from airborne electromagnetic profiles. This study employs airborne electromagnetic resistivity profiles to interpret the three‐dimensional sedimentary architecture of cross‐cutting buried valleys in a ca 400 km² area along the western margin of Laurentide glaciation in North America. A progenitor bedrock valley is succeeded by at least five generations of tunnel valleys that become progressively younger northward. Tunnel‐valley infills are highly variable, reflecting under‐filled and over‐filled conditions. Under‐filled tunnel valleys are expressed on the modern landscape and contain fine sediments that act as hydraulic barriers. Over‐filled tunnel valleys are not recognized in the modern landscape, but where they are present they form hydraulic windows between deep aquifer units and the land surface. The interpretation of tunnel‐valley genesis herein provides evidence of the relationships between depositional processes and glacial landforms in a dissected, pre‐Illinoian till sheet, and contributes to the understanding of the complex physical hydrology of glacial aquifers in general.     

Production of oxalates In Vitro by Microbes Isolated from Rock Surfaces with prehistoric paints in the Lower Pecos Region,Texas

Calcium oxalate‐rich rock coatings are ubiquitous on limestone inside dry rock shelters and under bluff overhangs along canyon walls in southwestern Texas. Prehistoric pictographs occur in more than 250 such sites, and the ancient paints are encapsulated within the natural rock coating. Previous studies suggest lichens were the source of the oxalate; however, we report here that microbes cultured and isolated from samples of the coating produce oxalate in vitro. Twenty different bacteria species have been identified in samples from eight different sites, with Bacillus the most common genus, represented by five species. HPLC analyses of inoculated R2B medium after eight months of bacterial growth revealed the presence of oxalate ions in the solid phase of the growth medium. © 2008 Wiley Periodicals, Inc.     

137Cs and 210Po in Pacific walrus and bearded seal from St. Lawrence Island, Alaska

The activity concentration of Cesium-137 ((137)Cs) and naturally-occurring Polonium-210 ((210)Po) were measured in the muscle tissue, kidney and liver of Pacific walrus (Odobenus rosmarus divergens) and bearded seal (Erignathus barbatus) collected by native hunters from the Bering Sea during May 1996. The mean (137)Cs concentrations in muscle, liver and kidney of Pacific walrus were 0.07, 0.09 and 0.07 Bq kg(-1) (n=5, wet weight), respectively, and 0.17, 0.10, and 0.17 Bq kg(-1) (n=2, wet weight), respectively, in bearded seal. In general, (137)Cs tissue concentrations are significantly lower than those previously reported for mammals from other regions. By comparison, (210)Po activity concentrations are more variable and appear to be higher level compared with mammal data from other regions. The mean (210)Po concentration in the muscle tissue, liver and kidney of Pacific walrus (n=5, wet weight) were 28.7, 189, and 174 Bq kg(-1), respectively. This compares with (210)Po concentration values (n=2, wet weight) of 27, 207 and 68 Bq kg(-1) measured in the muscle tissue, liver and kidney, of bearded seal, respectively. Estimated concentration factors--as defined by the radionuclide concentration ratio between the target tissue to that in sea water--were two to three orders of magnitude higher for (210)Po that those of (137)Cs. We conclude from radiological dose estimates that ingestion of (137)Cs in foods derived from walrus and seal will pose no threat to human health. This work has important implications for assessment of risks of Alaskan coastal communities concerned about the dumping of nuclear waste in the Russia Arctic.