Recovery of surface albedo and plant cover after wildfire in a Picea mariana forest in interior Alaska

Albedo influences vegetation structure, permafrost thawing, etc., in particular, after wildfires in Picea mariana forests in Alaska, USA, while albedo changes with plant succession. To understand interactions between albedo and ecosystem recovery after wildfire, surface albedo was measured in the spring and summer of 2005 at Poker Flat, interior Alaska, where P. mariana forest was dominant. The ground surface was mostly covered with Sphagnum moss before the 2004 wildfire, and was variously burned by the fire. The measured wavelengths ranged from 0.3 to 3.0 μm. We measured four independent variables, incidence, plant cover on the forest floor, cover of burned ground surface, canopy openness and incidence, to examine the determinants on surface albedo. Multiple regression analysis showed that total plant cover positively and mostly determines albedo, indicating that plant recovery is prerequisite to return high albedo. When the ground surface was damaged by fire, changes in albedo were mostly derived from decrease in reflectance wavelengths between 0.7 and 1.4 μm. The fluctuations of reflectance wavelengths did not differ greatly between damaged-moss and burned surfaces. We must mention the dynamics of Sphagnum to understand various environmental changes including surface albedo.     

Effect of grain growth on cation exchange between dunite and fluid: implications for chemical homogenization in the upper mantle

The effect of grain growth on the cation exchange between synthesized forsterite aggregates (i.e., dunite) and nickel-rich aqueous fluid was evaluated experimentally at 1.2 GPa and 1,200°C. The grain boundary (GB) migration caused nickel enrichment in the area swept by the GBs in a fashion similar to that reported for stable isotope exchange in the quartz aggregates. The progress of the grain growth resulted in an increase in the average nickel concentration in the dunites of up to ~80 times that was calculated for a system having stationary GBs. The overall diffusivity of the nickel along the wet GBs and interconnected fluid networks was found to be 6.5 × 10⁻¹⁹–6.7 × 10⁻¹⁸ m³/s, which is 4–5 orders of magnitude higher than the grain boundary diffusivity in the dry dunite. These results show that the grain growth rate is a fundamental factor in the evaluation of the time scale of chemical homogenization in the upper mantle.     

The paleolimnology of a small waterbody in the Pocono Mountains of Pennsylvania,USA: reconstructing 19th–20th century specific conductivity trends in relation to changing land use

Remains of scaled chrysophytes, magnetic minerals and pollen were used to analyze the recent paleolimnological history of a small lake, Lake Waynewood, in the Pocono Mountains of Pennsylvania. Important shifts in all three variables were observed over the 133 years represented by the core. The most significant changes occurred near the turn of the century when the watershed was heavily logged. Before the logging event, species such asSynura sphagnicola, S. spinosa, Mallomonas galeiformis andM. duerrschmidtiae were co-dominant members of the flora. Subsequent to the deforestation of the watershed other taxa, includingM. crassisquama, M. caudata andS. petersenii, increased in relative importance. Concurrent with changes in the scaled chrysophytes was a six-fold increase in the concentrations of magnetic material, presumably the result of increased erosion caused by the logging. Changes in pollen grains also correlate well with the onset of the deforestation event. The scaled chrysophyte inferred specific conductivity of the lake has more than tripled, with the primary increase occurring concurrent with the commencement of logging and the increase in magnetic mineral material. The effects of other human-related disturbances are also discussed.     

Environmental magnetic and magnetic fabric studies in LakeWaynewood, northeastern Pennsylvania, USA: Evidence for changes inwatershed dynamics

An environmental magnetic and magnetic fabric study of sedimentscollected from Lake Waynewood, a post-glacial lake in the PoconoMountains of Pennsylvania, USA, provided a history of the lake's watersheddynamics over the past 3500 years. Two 5 m long, Mackereth coresof lake sediments and three watershed soil profiles were analyzed magnetically.Paleosecular variation and ¹⁴C measurements allowed timing ofchanges in the lake's watershed which are documented by changes in ARM,SIRM,, S-ratio, SIRM/, ARM/ and ARM/SIRMdowncore. Prior to 2900 years BP, there is little evidence for allogenicinflux. Dramatic changes in mineral magnetic properties and a strong AARmagnetic fabric appear approximately 2900 years BP, suggesting major changes inwatershed conditions, either in the hydrologic regime or in vegetative cover.Between 2900 and 1800 yrs BP, large variations in magnetic mineralogy areapparent, whereas about 1800 years BP, a single sediment source began todominate the magnetic mineralogy. About 100–200 years ago, conditionsagain changed, probably due to clearcutting and settlement of the watershed.Topsoil erosion appears to have dominated the magnetic signal. S and Mnconcentration downcore indicate that there is little evidence for reductiondiagenesis having caused the changes observed in magnetic mineral type andconcentration, except in the top 10 centimeters of the sediment column.     

Magnetic interaction in biotites and oxidised biotites

Mössbauer spectra of biotites (1) and (2) with relative iron concentrations ～1:1·6 and of their oxidation products are recorded at 4 K in zero field and in applied fields up to 5 T. Magnetic susceptibility data are also reported. The results show that Fe III spins are in a ferromagnetic configuration in the c-plane in both biotites. Partial oxidation of biotite (1) leads to a canted ferromagnetic structure, while complete oxidation of biotite (2) yields an antiferromagnetic spin configuration. Nearest-neighbour antiferromagnetic Fe III-O-Fe III, and ferromagnetic Fe III-O-Fe II and Fe II-O-Fe II superexchange can account for the results. For biotites with higher concentrations of iron, Fe II and Fe III seem to be distributed randomly in the triangular lattice. From susceptibility results in biotites dilute in iron, an estimate of the ratio of nearest-neighbour and next-nearest neighbour magnetic interaction in the triangular lattice is derived.     

Groundmass pargasite in the 1991–1995 dacite of Unzen volcano: phase stability experiments and volcanological implications

Pargasite commonly occurs in the dacitic groundmass of the 1991–1995 eruption products of Unzen volcano. We described the occurrence and chemical compositions of amphibole in the dacite, and also carried out melting experiments to determine the low-pressure stability limit of amphibole in the dacite. The 1991–1995 ejecta of the Unzen volcano show petrographic evidence of magma mixing, such as reverse compositional zoning of plagioclase and amphibole phenocrysts, and we used a groundmass separate as a starting material for the experiments. Reversed experiments show that the maximum temperature for the crystallization of amphibole is 930°C at 196 MPa, 900°C at 98 MPa, and 820°C at 49 MPa. Compared with the experimental results on the Mount St. Helens dacite, present experiments on the Unzen dacitic groundmass show that amphibole is stable to pressures ca. 50 MPa lower at 850°C. Available Fe–Ti oxide thermometry indicates the crystallization temperature of the groundmass of the Unzen dacite to be 880±30°C, suggesting that the groundmass pargasite crystallized at >70 MPa, corresponding to a depth of more than 3 km in the conduit. The chlorine content of the groundmass pargasite is much lower than that of phenocrystic magnesiohornblende in the 1991–1995 dacite of Unzen volcano, indicating that vesiculation/degassing of magma took place before the crystallization of the groundmass pargasite. The present study shows that the magma was water oversaturated and that the degassing of magma along with magma mixing caused crystallization of the groundmass amphibole at depths of more than 3 km in the conduit.