TWO ELECTRIC POTENTIAL SIGNATURES OF SERIAL DIURNAL FROST

During a 96-hour period in mid-March 1987, a series of four serial frost-thaw events occurred in a research field at the University of Michigan Matthaei Botanical Gardens. Soil temperature and electric potential were recorded at two near surface probe arrays (0, 3, 6 & 9 cm) and (0, 5, 10 & 15 cm) with a horizontal separation of approximately 1 m beneath the organic-mineral soil interface at hourly intervals. These time series revealed strong repetitive serial patterns. When the electric potential measurements were converted to a surrogate measure of electrolyte concentration, the C-index, strong coupled flow effects appeared to be present in the time series owing to the effects of surface freeze-thaw, evaporation-distillation and soil water advection.

The data set shows the low frequency effects of upward soil water advection increasing the soil temperature and modulating the electrolyte concentration. These observations also demonstrate that soil freezing processes have two distinct regimes dominated by (1) early soil water advection toward the frost front from below and (2) downward expulsion of electrolyte-rich water as ice fills the pore space. These two processes of soil water advection and expulsion augmented by local evaporation produce two distinct near surface C-index signatures of serial diurnal frost. The signature depends on the direction of the vertical electrolyte gradient near the surface. [Key words: soil, frost-thaw, soil water, soil temperature.]     

Organic micropollutants in marine plastics debris from the open ocean and remote and urban beaches

To understand the spatial variation in concentrations and compositions of organic micropollutants in marine plastic debris and their sources, we analyzed plastic fragments (∼10 mm) from the open ocean and from remote and urban beaches. Polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), dichloro-diphenyl-trichloroethane and its metabolites (DDTs), polybrominated diphenyl ethers (PBDEs), alkylphenols and bisphenol A were detected in the fragments at concentrations from 1 to 10,000 ng/g. Concentrations showed large piece-to-piece variability. Hydrophobic organic compounds such as PCBs and PAHs were sorbed from seawater to the plastic fragments. PCBs are most probably derived from legacy pollution. PAHs showed a petrogenic signature, suggesting the sorption of PAHs from oil slicks. Nonylphenol, bisphenol A, and PBDEs came mainly from additives and were detected at high concentrations in some fragments both from remote and urban beaches and the open ocean.     

Crust restoration for the western Lachlan Orogen using the strain-reversal,area-balancing technique: implications for crustal components and original thicknesses

Strain reversal of structural/stratigraphic profiles at different scales in the western Lachlan Orogen provides a perspective on original crustal thickness estimates, the former depositional basin width of the proto-western Lachlan Orogen, the original sedimentary-fan thickness, and the possible length extent of lower crust lost by subduction. Retrodeformation using strain-reversal techniques allows basin reconstruction giving an original width of the western Lachlan Orogen basin receptor of between 800 km (minimum) and ～1150 km (maximum), depending on the amount of stratal duplication allowed in the turbidites. Crude area balancing of the regional cross-section, adding in sectional volume lost by erosion and assuming strain compatibility between the upper and lower crust, suggests that the predeformation crustal thickness ranges between 15 km and ～21 km, with a lower crustal thickness (oceanic lithosphere) of ～9 km and a turbidite fan thickness of ～6 km (minimum) and ～12 km (maximum allowable), respectively. Disparity between the calculated fan thickness and that derived from measured stratigraphic sections adjusted for strain (～6 km) indicates that some form of crustal stacking must be important in structural thickening of the turbidite crustal component. By varying shortening due to fault stacking, mass balance dictates the mismatch of the upper crustal (uc) and lower crustal (lc) retrodeformed lengths, and therefore provides an estimate of lower crustal loss by subduction. End members range from: (i) a 12 km-thick fan without fault duplication, a basin width of ～800 km where uc = lc giving no lower crustal loss by subduction; to (ii) a ～6 km fan, requiring duplication by faulting, a basin of ～1150 km where uc > lc, and ～360 km of lower crust length (～30%) lost by subduction. This suggests that the total thickness of underplated igneous material in the western Lachlan Orogen is low, probably < ～2 km.     

Chronology of landscape evolution and soil development in the upper Flinders River area,Queensland, based on isotopic dating of Cainozoic basalts

Victorian granites containing more than 750 ppm Ba are almost entirely confined to the region between a line from Geelong to Swan Hill and the Wonnangatta Fault Zone. Granite Ba contents normalised to 70% SiO₂ range from 620 to 733 ppm in western Victoria, 719 to 1560 ppm in central Victoria and 493 to 689 ppm in eastern Victoria. Melting of Ba-rich (meta)sedimentary rocks in the lower – middle crust is implicated in the petrogenesis of central Victorian S types, at least. Thus, granite geochemistry supports the concept of some sort of (largely concealed) Ba-rich Selwyn Block beneath central Victoria, although the boundaries that have been proposed for the block are modified here. There is a strong possibility that the Selwyn Block is an exotic terrane emplaced by northwest-directed strike-slip movement during the Bindian Orogeny. Such movement appears to have been controlled by the previously postulated Baragwanath Transform and another fundamental fault here called the Ulrich Transform. Asthenospheric upwelling related to movement on the Ulrich and Baragwanath Transforms may be the explanation for the twin belts of 400 Ma plutonism occurring to the west of the former and to the east of the latter. The southern extension of the Ulrich Transform may be the Tamar – Tiers structure in Tasmania. Plate-tectonic models suggesting Ordovician – Silurian subduction in Victoria need to be carefully revisited given the possibility of Siluro-Devonian exotic terrane emplacement.     

The parnell quartz monzonite: A proterozoic zoned pluton in the archaean pilbara block,Western Australia

The Parnell Quartz Monzonite in the Pilbara Block of Western Australia is a Proterozoic (1731 ± 14 Ma) pluton characterized by high modal K‐feldspar and a greater abundance of hornblende relative to biotite, as is typical of Phanerozoic monzonitic rocks in eastern Australia. The only geochemical features reflecting its setting in an Archaean terrain are high Na2O, Ni and Cr. The pluton is zoned, with an increase in K‐feldspar, quartz and biotite and a decrease in plagioclase and hornblende from margin to core. Chemically, this zoning is reflected by systematic variation of CaO, K₂O, Na₂O, Sr and Rb, but ferromagnesian elements have irregular trends, implying preferential extraction of feldspars relative to mafic minerals during differentiation of the magma. The unusual geochemical trends are explained by a model involving ‘in situ’ feldspar fractionation of a K‐rich residual liquid from a mafic crystalline mush.

A parent magma similar to the average rock composition of the pluton is deduced because high ferromagnesian trace element abundances preclude extensive fractionation of mafic minerals. Geochemical and isotopic constraints suggest that the ultimate source was chemically similar to a shoshonitic basaltic andesite, that must have been emplaced beneath the eastern margin of the Pilbara Block in the Early Proterozoic. Subsequent partial melting of this postulated underplated source at ～ 1700 Ma to produce the Parnell Quartz Monzonite was probably associated with tectonism in the Gregory Range Complex.     

Thermodynamically constrained averaging theory approach for modeling flow and transport phenomena in porous medium systems: 4. Species transport fundamentals

This work is the fourth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. The general TCAT framework and the mathematical foundation presented in previous works are built upon by formulating macroscale models for conservation of mass, momentum, and energy, and the balance of entropy for a species in a phase volume, interface, and common curve. In addition, classical irreversible thermodynamic relations for species in entities are averaged from the microscale to the macroscale. Finally, we comment on alternative approaches that can be used to connect species and entity conservation equations to a constrained system entropy inequality, which is a key component of the TCAT approach. The formulations detailed in this work can be built upon to develop models for species transport and reactions in a variety of multiphase systems.     

Thermodynamically constrained averaging theory approach for modeling flow and transport phenomena in porous medium systems: 6. Two-fluid-phase flow

This work is the sixth in a series of papers on the thermodynamically constrained averaging theory (TCAT) approach for modeling flow and transport phenomena in multiscale porous medium systems. Building upon the general TCAT framework and the mathematical foundation presented in previous works, the limiting case of connected two-fluid-phase flow is considered. A constrained entropy inequality is developed based upon a set of primary restrictions. Formal approximations are introduced to deduce a general simplified entropy inequality (SEI). The SEI is used along with secondary restrictions and closure approximations consistent with the SEI to produce a general functional form of a two-phase-flow model. The general model is in turn simplified to yield a hierarchy of models by neglecting common curves and by neglecting both common curves and interfaces. The simplest case considered corresponds to a traditional two-phase-flow model. The more sophisticated models including interfaces and common curves are more physically realistic than traditional models. All models in the hierarchy are posed in terms of precisely defined variables that allow for a rigorous connection with the microscale. The explicit nature of the restrictions and approximations used in developing this hierarchy of models provides a clear means to both understand the limitations of traditional models and to build upon this work to produce more realistic models.     

The formation of tropical cyclones

Summary This paper attempts a synthesis of new observations and new concepts on how tropical cyclone formation occurs. Despite many worthy observational and numerical modeling studies in recent decades, our understanding of the detailed physical processes associated with the early stages of tropical cyclone formation is still inadequate; operational forecast skill is not very high. Although theoretical ideas cover a wide range of possibilities, results of new observations are helping us to narrow our search into more specific and relevant topic areas.With 33 FiguresPrologueThis paper is dedicated to Professor Herbert Riehl under whom I studied tropical meteorology at the University of Chicago from 1957–1961 and was later associated with at Colorado State University (CSU). Professor Riehl arranged my first aircraft flights into hurricanes in the late 1950s and gave great encouragment to me to explore the secrets of what causes a tropical disturbance to be transformed into a tropical storm.Herbert would persist in asking me nearly every week or so what causes a hurricane to form? I and my graduate students and research colleagues at CSU have been working to uncover the secrets of tropical cyclone formation ever since. The following article gives my current best estimate of the primary physical processes involved with this topic.     

Impact of stratospheric variability on tropospheric climate change

An improved stratospheric representation has been included in simulations with the Hadley Centre HadGEM1 coupled ocean atmosphere model with natural and anthropogenic forcings for the period 1979–2003. An improved stratospheric ozone dataset is employed that includes natural variations in ozone as well as the usual anthropogenic trends. In addition, in a second set of simulations the quasi biennial oscillation (QBO) of stratospheric equatorial zonal wind is also imposed using a relaxation towards ERA-40 zonal wind values. The resulting impact on tropospheric variability and trends is described. We show that the modelled cooling rate at the tropopause is enhanced by the improved ozone dataset and this improvement is even more marked when the QBO is also included. The same applies to warming trends in the upper tropical troposphere which are slightly reduced. Our stratospheric improvements produce a significant increase of internal variability but no change in the positive trend of annual mean global mean near-surface temperature. Warming rates are increased significantly over a large portion of the Arctic Ocean. The improved stratospheric representation, especially the QBO relaxation, causes a substantial reduction in near-surface temperature and precipitation response to the El Chichón eruption, especially in the tropical region. The winter increase in the phase of the northern annular mode observed in the aftermath of the two major recent volcanic eruptions is partly captured, especially after the El Chichón eruption. The positive trend in the southern annular mode (SAM) is increased and becomes statistically significant which demonstrates that the observed increase in the SAM is largely subject to internal variability in the stratosphere. The possible inclusion in simulations for future assessments of full ozone chemistry and a gravity wave scheme to internally generate a QBO is discussed.