Using GRASS GIS to Model Solar Irradiation on North Carolina Aquatic Habitats with Canopy Data

Sunlight can have a significant impact on freshwater aquatic communities. Using 64‐ bit GRASS, a previously generated 18.2 m resolution forest canopy height grid for the State of North Carolina was used as a base elevation layer for calculation of 18.2 m resolution total irradiance (Watt‐hours/square meter/day) grids for 365 days of the year. Daily calculations were aggregated annually and overlaid on rasterized 1:24,000‐scale USGS hydrology with canopy type and seasonal filters to quantify annual solar irradiation input to streams and rivers in North Carolina. Bare earth calculations of solar irradiation for the aquatic habitats were compared to the canopy filtered calculations. There was substantially less solar irradiation in aquatic habitats under the canopy filtered model. Total solar irradiation for subbasins created from point locations of occurrences of Dwarf wedgemussel (Alasmidonta heterodon) were compared with total solar irradiation for watersheds created from locations with no mussels for the full subbasin, 1 km, and 500 m upstream from the sampling point. There was no significant difference in the amount of total solar irradiation modeled for the subbasins with Dwarf wedgemussel and watersheds with no mussels.     

Microseismic Full Waveform Modeling in Anisotropic Media with Moment Tensor Implementation

Seismic anisotropy which is common in shale and fractured rocks will cause travel-time and amplitude discrepancy in different propagation directions. For microseismic monitoring which is often implemented in shale or fractured rocks, seismic anisotropy needs to be carefully accounted for in source location and mechanism determination. We have developed an efficient finite-difference full waveform modeling tool with an arbitrary moment tensor source. The modeling tool is suitable for simulating wave propagation in anisotropic media for microseismic monitoring. As both dislocation and non-double-couple source are often observed in microseismic monitoring, an arbitrary moment tensor source is implemented in our forward modeling tool. The increments of shear stress are equally distributed on the staggered grid to implement an accurate and symmetric moment tensor source. Our modeling tool provides an efficient way to obtain the Green’s function in anisotropic media, which is the key of anisotropic moment tensor inversion and source mechanism characterization in microseismic monitoring. In our research, wavefields in anisotropic media have been carefully simulated and analyzed in both surface array and downhole array. The variation characteristics of travel-time and amplitude of direct P- and S-wave in vertical transverse isotropic media and horizontal transverse isotropic media are distinct, thus providing a feasible way to distinguish and identify the anisotropic type of the subsurface. Analyzing the travel-times and amplitudes of the microseismic data is a feasible way to estimate the orientation and density of the induced cracks in hydraulic fracturing. Our anisotropic modeling tool can be used to generate and analyze microseismic full wavefield with full moment tensor source in anisotropic media, which can help promote the anisotropic interpretation and inversion of field data.     

Impact of an 0.2 km3 Rock Avalanche on Lake Eibsee (Bavarian Alps,Germany) – Part II: Catchment Response to Consecutive Debris Avalanche and Debris Flow

The ~0.2 km³ Eibsee rock avalanche impacted Paleolake Eibsee and completely displaced its waters. This study analyses the lake impact and the consequences, and the catchment response to the landslide. A quasi-3D seismic reflection survey, four sediment cores from modern Lake Eibsee, reaching far down into the rock avalanche mass, nine radiocarbon ages, and geomorphic analysis allow us to distinguish the main rock avalanche event from a secondary debris avalanche and debris flow. The highly fluidized debris avalanche formed a megaturbidite and multiple swashes that are recorded in the lake sediments. The new calibrated age for the Eibsee rock avalanche of ~4080–3970 cal yr BP indicates a coincidence with rockslides in the Fernpass cluster and subaquatic landslides in Lake Piburg and Lake Plansee, and raises the possibility that a large regional earthquake triggered these events. We document a complex history of erosion and sedimentation in Lake Eibsee, and demonstrate how the catchment response and rebirth of the lake are revealed through the complementary application of geophysics, sedimentology, radiocarbon dating, and geomorphology. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Carbon Stores, Sinks, and Sources in Forests of Northwestern Russia: Can We Reconcile Forest Inventories with Remote Sensing Results?

Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha^–1 yr^–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha^–1 yr^–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates.     

Long-term spatial and temporal trends in frost indices in Kansas, USA

Frost indices such as number of frost days (nFDs), number of frost-free days (nFFDs), last spring freeze (LSF), first fall freeze (FFF), and growing-season length (GSL) were calculated using daily minimum air temperature (T_min) from 23 centennial weather stations across Kansas during four time periods (through 1919, 1920–1949, 1950–1979, and 1980–2009). A frost day is defined as a day with T_min?<?0 °C. The long- and short-term trends in frost indices were analyzed at monthly, seasonal, and annual timescales. Probability of occurrence of the indices was analyzed at 5 %, 25 %, 50 %, 75 %, and 95 %. Results indicated a general increase in T_min from 1900 through 2009 causing a decrease in nFDs. LSF and FFF occurred earlier and later than normal in the year, respectively, thereby resulting in an increase in GSL. In general, northwest Kansas recorded the greatest nFD and lowest T_min, whereas southeast Kansas had the lowest nFD and highest T_min; however, the magnitude of the trends in these indices varied with location, time period, and time scales. Based on the long-term records in most stations, LSF occurred earlier by 0.1–1.9 days/decade, FFF occurred later by 0.2–0.9 day/decade, and GSL was longer by 0.1–2.5 day/decade. At the 50 % probability level, Independence in the south-eastern part of Kansas had the earliest LSF (6 April), latest FFF (29 October) and longest GSL (207 days). Oberlin (north-western Kansas) recorded the shortest GSL (156 days) and earliest FFF (7 October) had the latest LSF (2 May) at the 50 % probability level. A positive correlation was observed for combinations of indices (LSF and GSL) and elevation, whereas a negative correlation was found between FFF and elevation.     

Atmospheric equilibrium,instability and energy transport at the last glacial maximum

A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM) is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the LGM, while they only account for half the seasonal range at the present-day.     

Crustal constraints on the origin of mantle seismicity in the Vrancea Zone, Romania: The case for active continental lithospheric delamination

The Vrancea zone of Romania constitutes one of the most active seismic zones in Europe, where intermediate-depth (70–200 km) earthquakes of magnitude in excess of M_w = 7.0 occur with relative frequency in a geographically restricted area within the 110° bend region of the southeastern Carpathian orogen. Geologically, the Vrancea zone is characterized by (a) a laterally restricted, steeply NW-dipping seismogenic volume (30 × 70 × 200 km), situated beneath (b) thickened continental crust within the highly arcuate bend region of the Carpathian orocline, and (c) miscorrelation of hypocenters with the position of known or inferred suture zones in the Carpathian orogenic system. Geologic data from petroleum exploration in the Eastern Carpathians, published palinspastic reconstructions, and reprocessing of industry seismic data from the Carpathian foreland indicate that (1) crust of continental affinity extends significantly westward beneath the external thrust nappes (Sub-Carpathian, Marginal Folds, and Tarcau) of the Eastern Carpathians, (2) Cretaceous to Miocene strata of continental affinity can be reconstructed westward to a position now occupied by the Transylvanian basin, and (3) geologic structure in the Carpathian foreland (including the Moho) is sub-horizontal directly to the east and above the Vrancea seismogenic zone. Taken together, these geologic relationships imply that the Vrancea zone occupies a region overlain by continental crust and upper mantle, and does not appear to originate from a subducted oceanic slab along the length of the Carpathian orogen. Accordingly, the Vrancea zone appears to potentially be an important place to establish evidence for active lithospheric delamination.     

Ca-Eskola incorporation in clinopyroxene: limitations and petrological implications for eclogites and related rocks

Clinopyroxene is an essential mineral in eclogitic rocks. It commonly contains minor amounts of the defect-bearing Ca-Eskola (CaEs, Ca_0.5□_0.5AlSi₂O₆) component, with higher concentrations generally considered to indicate a high-pressure origin at least within the coesite stability field. Changes in pressure and temperature conditions can lead to exsolution of this component as a free SiO₂ phase, which may have a number of petrological implications. This makes it important to understand the factors that maximize CaEs incorporation in clinopyroxene. We have undertaken a series of experiments at high pressures and temperatures (4–10 GPa and 1000–1350 °C) to further investigate the systematics of CaEs incorporation in eclogite-like clinopyroxene and the factors responsible for maximizing CaEs contents. Two simple chemical systems were chosen that allow unambiguous interpretation of the results: (1) CMAS + H₂O and (2) two compositions in the NCMAS system. All experimental products contained clinopyroxene and garnet along with either a free SiO₂ phase or a silicate melt. Coexisting garnet is grossular-rich, generally with X _gr ≥ 0.67. Compositional variations are attributable to the presence or absence of melt and changes in modal amounts of garnet at different pressure–temperature conditions. Even small amounts of H₂O lower the solidus temperature and the presence of a melt reduces the SiO₂ activity, which destabilizes the CaEs component in clinopyroxene. The CaEs and the Ca-Tschermaks (CaTs, CaAl₂SiO₆) components in clinopyroxene decrease with increasing jadeite mole fraction, which is also a function of pressure and bulk Al content. Modeling X-ray powder diffraction data yields a molar volume for the CaEs endmember of V _CaEs = 60.87(63) cm³, which reasonably agrees with a literature value that was estimated from natural samples. In the presence of coexisting coesite, the CaEs and CaTs do not vary independently of each other, being controlled by the internal equilibrium 2CaEs = CaTs + 3SiO₂ (coesite). This relation, observed in simple systems (i.e., CMAS ± Na), is also obeyed by clinopyroxene in more complex, natural analog bulk compositions. An assessment of available experimental data reveals a maximum of 15–18 mol% CaEs in eclogitic clinopyroxene at conditions corresponding to 130–180 km depth. CaEs contents are maximized at high temperatures; i.e., at or near the solidus in the presence of coesite. Thus, this study supports the role of CaEs exsolution in contributing to melt generation during upwelling of eclogite bodies in the mantle, albeit with some caveats. Somewhat higher maximum CaEs contents (~20 mol%) are found in Ca and Al-rich bulk compositions, such as grospydite xenoliths. Such bulk compositions also seem to require the coexistence of kyanite. Other Ca and Al-rich rock types, like rodingites, should have the potential of containing CaEs-rich clinopyroxenes, except that they are SiO₂-undersaturated. This emphasizes the further role of bulk composition, in addition to high temperatures, in achieving maximum CaEs contents in high-pressure clinopyroxene.