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The use of thermally modified timber (TMT) in outdoor applications is well established, but its performance against the stresses of outdoor conditions is not comprehensively understood. This study investigates the changes in density, surface chemical composition, color, equilibrium moisture content (EMC), checking, hardness, and cupping of thermally modified boards of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst.), and European ash (Fraxinus excelsior L.) during a two-year weather exposure test in Eastern Finland. Unmodified pine, spruce, and ash and copper salt impregnated pine boards were used as controls. The results show that a two-year weather exposure period causes degradation of hydrophobic lignin, and the leaching of the degraded compounds changed the color, increased the EMC, and decreased the hardness of specimens. Although the EMC of TMT specimens was lower compared with unmodified and impregnated ones during weathering, the changes were more obvious in TMT than in the controls. More checks occurred in the TMT specimens than in unmodified ones after the exposure. On the other hand, the TMT specimens had a lower degree of cupping. These findings also indicate that an increase in modification temperature induces more checks but improves the durability of all studied species by reducing the chemical degradation, color change, cupping, and hygroscopicity during weather exposure. Key words: thermally modified wood, weathering, FTIR, checking, cupping. L'utilisation du bois modifie thermiquement (BMT) pour des usages exterieurs est bien etablie mais sa performance face aux stress dus aux conditions exterieures n'est pas completement connue. Cette etude examine les changements dans la densite, la composition chimique en surface, la couleur, le degre d'humidite d'equilibre (EMC), le fendillement, l'indice de durete et le voilement de planches de pin sylvestre (Pinus sylvestris L.), d'epicea commun (Picea abies (L.) H. Karst.) et de frene commun (Fraxinus excelsior L.) modifiees thermiquement durant un test d'exposition aux intemperies d'une duree de deux ans dans l'est de la Finlande. Des planches non modifiees de pin, d'epicea et de frene ainsi que des planches de pin impregnees de sel de cuivre ont ete utilisees comme temoins. Les resultats montrent qu'une periode d'exposition aux intemperies de deux ans a cause une degradation de la lignine hydrophobe et que le lessivage des composes engendres par la degradation a change la couleur, augmente l'EMC et diminue l'indice de durete des specimens. Bien que l'EMC des specimens de BMT ait ete plus faible comparativement a ceux qui ont ete impregnes ou qui n'ont pas ete modifies lors du vieillissement aux intemperies, les changements etaient plus evidents chez le BMT que chez les temoins. Davantage de fendillement est survenu chez les specimens de BMT que chez les specimens non modifies suivant l'exposition aux intemperies. Par contre, les specimens de BMT avaient un plus faible degre de voilement. Ces resultats indiquent aussi qu'une augmentation de la temperature du traitement thermique entraine davantage de fendillement mais ameliore la durabilite de toutes les especes etudiees en reduisant la degradation chimique, le changement de couleur, le voilement et l'hygroscopicite durant l'exposition aux intemperies. [Traduit par la Redaction] Mots-cles: bois modifie thermiquement, vieillissement aux intemperies, FTIR, fendillement, voilement., Introduction Thermal modification (TM) reduces the hygroscopicity and equilibrium moisture content (EMC) of wood without using chemicals and, consequently, increases its dimensional stability and biological durability (Hill 2006). Due to [...]

For the first four billion years of Earth's history, climate was marked by apparent stability and warmth despite the Sun having lower luminosity.sup.1. Proposed mechanisms for maintaining an elevated partial pressure of carbon dioxide in the atmosphere ([Formula omitted]) centre on a reduction in the weatherability of Earth's crust and therefore in the efficiency of carbon dioxide removal from the atmosphere.sup.2. However, the effectiveness of these mechanisms remains debated.sup.2,3. Here we use a global carbon cycle model to explore the evolution of processes that govern marine pH, a factor that regulates the partitioning of carbon between the ocean and the atmosphere. We find that elevated rates of 'reverse weathering'--that is, the consumption of alkalinity and generation of acidity during marine authigenic clay formation.sup.4-7--enhanced the retention of carbon within the ocean-atmosphere system, leading to an elevated [Formula omitted] baseline. Although this process is dampened by sluggish kinetics today, we propose that more prolific rates of reverse weathering would have persisted under the pervasively silica-rich conditions.sup.8,9 that dominated Earth's early oceans. This distinct ocean and coupled carbon-silicon cycle state would have successfully maintained the equable and ice-free environment that characterized most of the Precambrian period. Further, we propose that during this time, the establishment of a strong negative feedback between marine pH and authigenic clay formation would have also enhanced climate stability by mitigating large swings in [Formula omitted]--a critical component of Earth's natural thermostat that would have been dominant for most of Earth's history. We speculate that the late ecological rise of siliceous organisms.sup.8 and a resulting decline in silica-rich conditions dampened the reverse weathering buffer, destabilizing Earth's climate system and lowering baseline [Formula omitted].Elevated rates of reverse weathering within silica-rich oceans led to enhanced carbon retention within the ocean-atmosphere system, promoting a stable, equable ice-free climate throughout Earth's early to middle ages., Author(s): Terry T. Isson [sup.1] , Noah J. Planavsky [sup.1] Author Affiliations:(1) Department of Geology and Geophysics, Yale University, New Haven, USAMain Stability was a hallmark feature of Earth's early [...]

This article reports the results of studies on the degradation of the blend of low-density polyethylene (LDPE) with a starch based prodegradant additive, named commercially as Polystarch plus H and abbreviated as PSH, under natural weather, underground soil aging, and sea water aging in Dhahran, Saudi Arabia. The work includes measurements of tensile properties, thermal behavior, and scanning electron microscopic (SEM) studies on the unaged and aged LOPE and the LDPE/PSH blend having 25% (w/w) of PSH. Results of the preliminary experiments showed that changes in properties are not prominent at lower loadings of PSH. In the case of the blend, incorporation of the additive PSH caused a reduction in elongation at break, which is accentuated under aging. The effectiveness of the prodegradant additive in the degradation behavior follows the order, natural aging > underground soil aging > sea water aging. It is believed that the prodegradant additive is effective in chain scission in sunlight under natural weathering conditions, in contrast to underground soil aging and sea water. POLYM. ENG. SCI., 53:2389-2397, 2013. © 2013 Society of Plastics Engineers, INTRODUCTION Plastics have become an indispensable item in our daily life. Their specific properties such as light weight, easy processability, low cost, good resistance to chemicals and microorganisms, nonbiodegradable nature, [...]

Acrylonitrile-butadiene-styrene copolymers (ABS) are known to be sensitive towards ageing which can lead to color changes, primary interest in this study. The color changes were expressed in terms of the CIELAB color system. ABS plaques were subjected to heat ageing and artificial weathering. Uncolored ABS and dark gray colored specimens were employed. The pigmented ABS plaques were also imposed with different surface textures. In general, the uncolored material suffered from the most severe discoloration and the artificial weathering produced the strongest effect. For both types of specimens, a clear yellowing took place. Both the pigment system and the surface texture affected the color development during the ageing test. The latter can be of significant importance in certain applications when components with different surface textures are placed adjacent to each other. The surface micro-hardness increased with increasing ageing time and its change followed that of the discoloration. Chemical changes of the surface layers were characterized by FTIR and were in accordance with results reported in the literature; i.e., an increase of the bands associated with carbonyl groups with increasing ageing time and a decrease of the bands associated with the polybutadiene phase clearly indicated chemical degradation due to ageing treatments. POLYM. ENG. SCI., 53: 1687-1695, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION Many polymeric materials are subjected to changes in mechanical properties, appearance and surface finish due to prolonged exposure to atmospheric conditions. These include effects of UV-light, temperature, humidity, oxygen [...]

The genesis of fermginous nodules and pisoliths in soils and weathering profiles of coastal southern and eastern Australia has long been debated. It is not clear whether iron (Fe) nodules are redox accumulations, residues of Miocene laterite duricrust, or the products of contemporary weathering of Fe-rich sedimentary rocks. This study combines a catchment-wide survey of Fe nodule distribution in Poona Creek catchment (Fraser Coast, Queensland) with detailed investigations of a representative ferric soil profile to show that Fe nodules are derived from Fe-rich sandstones. Where these crop out, they are broken down, transported downslope by colluvial processes, and redeposited. Chemical and physical weathering transforms these eroded rock fragments into non-magnetic Fe nodules. Major features of this transformation include lower hematite/goethite and kaolinite/gibbsite ratios, increased porosity, etching of quartz grains, and development of rounded morphology and a smooth outer cortex. Iron nodules are commonly concentrated in ferric horizons. We show that these horizons form as the result of differential biological mixing of the soil. Bioturbation gradually buries nodules and rock fragments deposited at the surface of the soil, resulting in a largely nodule-free 'biomantle' over a ferric 'stone line'. Maghemite-rich magnetic nodules are a prominent feature of the upper half of the profile. These are most likely formed by the thermal alteration of non- magnetic nodules located at the top of the profile during severe bushfires. They are subsequently redistributed through the soil profile by bioturbation. Iron nodules occurring in the study area are products of contemporary weathering of Fe-rich rock units. They are not laterite duricrust residues nor are they redox accumulations, although rcdox-controlled dissolution/reprecipitation is an important component of post-depositional modification of these Fe nodules. Additional keywords: bioturbation, ferric horizoniron nodule, iron oxide, iron pisolith, laterite, maghemite, weathering., Introduction Iron (Fe) nodules and pisoliths are a common feature of many soils and weathering profiles in the tropics, subtropics, regions of Mediterranean climate and even temperate regions (Amouric et [...]

Iron speciation data for the late Archean Mount McRae Shale provide evidence for a euxinic (anoxic and sulfidic) water column 2.5 billion years ago. Sulfur isotope data compiled from the same stratigraphic section suggest that euxinic conditions were stimulated by an increase in oceanic sulfate concentrations resulting from weathering of continental sulfide minerals exposed to an atmosphere with trace amounts of photosynthetically produced oxygen. Variability in local organic matter flux likely confined euxinic conditions to midportions of the water column on the basin margin. These findings indicate that euxinic conditions may have been common on a variety of spatial and temporal scales both before and immediately after the Paleoproterozoic rise in atmospheric oxygen, hinting at previously unexplored texture and variability in deep ocean chemistry during Earth's early history. 10.1126/science.1176711

The effects of the sediment regime on the flood level in the middle reach of the Yangtze River before and after the construction of the Three Gorges Dam (TGD) are investigated. Before the dam construction, the sediment regime has driven the flood level higher and higher over recent decades in the middle reach of the Yangtze River, which has reflected changes in the location and amount of sediment deposition. After dam completion, the magnitude and rate of channel degradation determines the process of flood stage lowering but they are difficult to estimate owing to insufficient understanding of the sediment discharge recovery process. To make a rational prediction of channel degradation of the Yangtze River downstream from the TGD, the sediment transport rate during channel degradation downstream from other dams is examined. It is found that, for any grain size, postdam sediment transport rates cannot exceed the predam level at any location along the downstream channel. Erosion amounts predicted for the reach downstream from the TGD before its closure are too high. In light of this, a numerical simulation of the channel degradation process is carried out. The results indicate that, although degradation takes place immediately after the TGD closure, the flood level in the middle reach of the Yangtze River will still remain at its predam condition in the following 20 years. This is determined not only by the regional characteristics of the middle reach of the Yangtze River but also by the common law of sediment transportation downstream from dams. CE Database subject headings: Degradation; China; Reservoirs; Dam construction; Floods; Sediment.

Soil micromorphology, using light microscopy and scanning electron microscopy (SEM), was used to describe detailed soil morphological and compositional changes and determine mineral weathering pathways in acid sulfate soils (ASS) from the following 2 contrasting coastal environments in Barker Inlet, South Australia: (i) a tidal mangrove forest with sulfidic material at St Kilda, and (ii) a former supratidal samphire area at Gillman that was drained in 1954 causing sulfuric material to form from sulfidic material. Pyrite framboids and cubes were identified in sulfidic material from both sites and are associated with sapric and hemic materials. Gypsum crystals, interpreted as a product of sulfide oxidation, were observed to have formed in lenticular voids within organic matter in the tidal mangrove soils at St Kilda. Sulfide oxidation was extensive in the drained soil at Gillman, evidenced by the formation of iron oxyhydroxide pseudomorphs (goethite crystallites and framboids) after pyrite and jarosite, and of gypsum crystals. Gypsum crystals occur where a local source of calcium such as shells or calcareous sand is present. Sporadic oxidation episodes are indicated by the formation of iron oxide and jarosite coatings around coarse biogenic voids. These observations indicate that mineral transformation pathways are strongly influenced by soil physico-chemical characteristics (i.e. oxidation rate, Eh, pH, soil solution chemistry, mineralogy, and spatial distribution of sulfides). This information has been used to illustrate the interrelationships of pyrite, carbonate, gypsum, jarosite, and organic matter and help predict soil evolution under changing hydro-geochemical, redoximorphic, and thermal conditions in soils from coastal environments. Additional keywords: mineralogy, micromorphology, organic materials, soil classification, pyrite., Introduction Acid sulfate soils (ASS) are soils in which sulfuric acid may be produced, is being produced, or has been produced in amounts that have a lasting effect on main [...]

To understand the response of Alloy 617 to long-time exposure conditions and to determine the supplementary data needs for structural components in Gen IV nuclear reactors, literature of aging and aging effects in the alloy was reviewed. Most of the reviewed data were produced in connection with the international research effort supporting high temperature gas-cooled reactor projects in the 1970s and 1980s. Topics considered included microstructural changes, hardness, tensile properties, toughness, creep-rupture, fatigue, and crack growth. It became clear that, for the long-time very high-temperature conditions of the Gen IV reactors, a significant effort would be needed to fully understand and characterize property changes. Several topics for further research were recommended. [DOI: 10.1115/1.2967885]

The mineralogy of bulk and rhizosphere soils was compared to assess the effect of roots on mineral weathering in a Typic Dystrochrept supporting Norway spruce (Picea abies [L.] Karst) and oak (Quercus sessiliflora Smith). In an experimental forest site (Breuil-Chenue, France), systematic soil sampling was performed in forty pits. The soil adhering to the roots was considered as rhizosphere soil. The remaining material was regarded as bulk soil. The mineralogy of the clay-sized particles of both fractions was determined by x-ray diffraction (XRD). Amorphous solid phases were estimated by extracting Fe and Al with hot Na-citrate and dithionite-citrate-bicarbonate. Total chemical analyzes were performed on the clay-sized particles via Ba[Cl.sub.2]-saturation and an iso-zirconium weathering balance was calculated. The XRD demonstrated an increase of illite-like minerals in the rhizosphere of both species and the selective extractions revealed a decrease in the amorphous phases. The total chemical analyzes showed that the rhizosphere clay-sized fraction contained significantly more Si and K (for oak only) and less Fe and Al than the bulk soil. By way of the iso-zirconium weathering balance, these losses of Fe and AI in the rhizosphere were estimated at several tens of kilograms by hectare for the surface horizon (0-3 cm). This study demonstrates that, despite the short duration of the contact between the active part of a root and the solid mineral phase, the intensity of the processes occurring in the rhizosphere significantly increases mineral weathering. Abbreviations: B, bulk soil; BS, base saturation; subscript c, hot Na-citate treatment; CEC, cation exchange capacity; subscript d, dithionite-citrate-bicarbonate treatment; EA, exchangeable acidity; EG, ethylene glycol treatment; HIS, hydroxy-interlayered smectite; HIV, hydroxy-interlayered vermiculite; ICP-AES, inductively coupled plasma spectrometry-atomic emission spectrometry; ICP-MS, inductively coupled plasma spectrometry- mass spectrometry; R, rhizosphere; subscript [tot], total; XRD, x-ray diffraction.

Soil surface sealing is one of the main causes for low infiltration rate (IR) and high runoff and soil loss under raindrop impact conditions in arid and semiarid regions. Many studies have focused on the effects of soil properties on seal formation under fast wetting conditions. However, in the field, soils can be exposed to different wetting conditions, before an intense rainfall event, which can affect the role of the soil properties on seal formation. The present paper reviews the effects of different initial wetting conditions and their interactions with soil properties on seal formation, IR, runoff, and soil loss in smectitic soils. Fast wetting of soil causes aggregate slaking, which enhances seal formation, runoff, and soil loss under rainfall, mainly in soils with > 40% clay content. An increase in clay content of the soil increases aggregate strength, but at the same time increases the slaking forces. Hence, in soils with low clay content (40% clay content and high aggregate stability, slaking plays an important role in aggregate breakdown and seal formation. An increase of raindrop kinetic energy, from 8 to 15.9 kJ/[m.sup.3], decreased the effect of the slaking forces on seal formation and runoff. It was suggested that the effects of raindrop kinetic energy and of the slaking forces on aggregate disintegration and seal formation are complementary. An increase in soil exchangeable sodium percentage (ESP), from 0.9 to 20.4%, decreased the effect of slaking forces on seal formation and runoff production under rainfall with 15.9kJ/[m.sup.3] kinetic energy. Probably, increasing the ESP increased the soil dispersivity, and therefore diminished the effect of the slaking forces on aggregate disintegration and seal formation. Aging (the time since wetting) of soil increased the stability of soil structure, decreased the seal formation, maintained high IR, and diminished soil loss amounts. These effects of soil aging depend on both the prewetting rate of the soil and soil texture., Introduction Arid and semiarid regions are characterised by water scarcity and highly variable precipitation. In addition, the water resources in some parts of these regions are expected to decrease as [...]

The chemical weathering of ultramafic rocks has resulted in eluvial concentration of Pt-group minerals (PGM) in lateritic weathering profiles of southern New Caledonia. The Pt mineralization interpreted as being primary consists of Pt-group minerals included within chromite crystals. The occurrence of PGM as free particles in the weathering profile results from the supergene dissolution of Pt-bearing chromite (Traore et al. 2008). Following their release in the profile, supergene dissolution processes variably affect the PGM particles. The behavior of Pt-group elements in the weathering profile is characterized by significant loss of Pd and relative enrichment of Pt indicating that Pd is more mobile than Pt in the exogenous cycle. Unstable Pt-Fe-Cu-Pd alloys and PGE oxides undergo chemical and mineralogical changes to acquire the chemical configuration ofisoferroplatinum ([Pt.sub.3]Fe), which is the most stable Pt phase in a lateritic environment. The isoferroplatinum phase may also be dispersed throughout the weathering mantle and/or accumulated in the lower parts of profiles according to a translocation mechanism of residual Pt-rich fine particles driven by percolation of water through the connected pore spaces. Keywords: Platinum group minerals, platinum group elements, lateritic weathering, ultramafic rocks, New Caledonia

Chemical weathering and supergene dissolution processes of Pt-bearing chromite have been studied in a lateritic weathering profile developed on ultramafic rocks in New Caledonia (southwest Pacific). The chemical distributions of alkaline earth, transition metals, and precious metals (including Pt and Pd) were determined in a weathering profile varying from bedrock at the base upward through coarse and fine saprolites, and capped by a mottled zone and a lateritic colluvial nodular horizon. Chemical analyses and mass-balance calculations suggest that progressive weathering of the parent rock is characterized by an enrichment of Fe, Co, and Mn, a segregation of Ni at the boundary between the bedrock and the coarse sapolite and in the lower part of the fine saprolite, and a depletion of Mg, Ca, Si, Al, and Cr. The higher concentration of transition metals at the interface between the coarse and fine saprolite is due to vertical transfer and precipitation at the base of the weathering profile. In such a lateritic environment, the Pt-bearing chromite grains are progressively dissolved and the Pt-group minerals (PGM) are released in the weathering mantle with a preferential depletion of Pd with regard to Pt. Keywords: Lateritic weathering, ultramafic rocks, mass-balance calculation, Pt-chromite, New Caledonia

Conventional wisdom once held that weathering in cold climates was overwhelmingly due to physical processes. However, that convention was challenged when chemical weathering was identified, but unexplained, as the dominant landscape denudation process in Karkevagge, an alpine valley in Swedish Lapland. The research reported here involved scanning electron microscopy and energy dispersive X-ray fluorescence of rock coatings to investigate chemical weathering in Karkevagge. Analyses revealed that white coatings associated with streams emerging on the valley cliff face are commonly an amorphous aluminum oxyhydroxide sulfate such as basaluminite [[Al.sub.4](S[O.sub.4])[(OH).sub.10]x[H.sub.2]O]. Efflorescence on seasonal vegetation in stream channels demonstrates that this is an active process. The white coating chemistry exhibited no systematic spatial patterns along the valley axis or with position on the cliff face. Although the white coatings were not crystalline and did not contain appreciable amounts of Fe or Ca, in sheltered overhangs among boulders on the valley floor there were other well-crystallized secondary sulfate minerals commonly associated with pyrite oxidation, including gypsum, jarosite, and amorphous Fe compounds. This difference is due presumably to the pH of the associated waters, because Fe compounds tend to precipitate only at pH 5, which is the pH of the stream water. Pyrite oxidation may be an important early weathering process in this and in many other environments. However, it largely goes unrecognized because it occurs relatively rapidly in a geological sense and typically is only identified in recently disturbed landscapes associated with mining or other large-scale earth-moving activities. Karkevagge demonstrates that subarctic conditions do not preclude intense chemical weathering where conditions are favorable, but it does not establish that strong chemical weathering is a widespread attribute of subarctic conditions. Keywords: weathering, pyrite, Sweden, Arctic, efflorescence, rock coating, scanning electron microscopy. doi: 10.1130/B26228.1

A large-scale field-monitoring program for studying residual forces in long-driven piles is described. Eleven steel H-piles, 34.2-59.8 m in embedded length, were instrumented with vibrating-wire strain gauges, installed and subjected to static loading tests in a building site in Hong Kong. The residual forces in these piles during and after pile installation were recorded. The development of residual forces as it relates to the pile penetration depth during construction, and in time after the piles were installed, is presented. The measured load transfers in the piles from static loading tests are reported and the effect of the residual forces on the interpretation of load- transfer behavior is studied. The field measurements show that residual forces increase approximately exponentially with penetration depth. The residual forces continue to increase with time after pile driving due to secondary compression of disturbed soils around the pile shaft and other factors. The large residual forces in the long piles significantly affect the interpretation of the pile load distributions. The effect of residual forces on the shaft resistance is significant at shallow depths. Bearing-capacity theory tends to overpredict the true toe resistance of the long piles founded in weathered soils. DOI: 10.1061/(ASCE)1090-0241(2007)133:10(1216) CE Database subject headings: Driven piles; Full-scale tests; Load tests; Load transfer; Pile foundations; Residual stress; Time factors; Hong Kong; Weathering.

Abstract. -- The Blanco River is a karst stream that traverses the Texas Hill Country and Balcones Fault Zone regions associated with the eastern Edwards Plateau. It is closely connected [...]

Sediment erosion laws form the basis for most landscape evolution models and guide geomorphologists in the pursuit of understanding how landscapes evolve. This focus on the alluvial surface, however, ignores the role of intrinsic feedbacks between sediment transport and bedrock weathering in shaping Earth's landforms. Here, we present a new, parsimonious explanation for the origin and maintenance of pediments, piedmont junctions, and tors, which emerge spontaneously in a numerical model coupling bedrock weathering and sediment transport. The spatial uniformity of the thin regolith mantle that often characterizes pediments is a manifestation of a negative feedback between bedrock weathering and regolith thickness: if regolith thins (thickens) by sediment transport, the regolith production rate will increase (decrease), maintaining an equilibrium regolith thickness on the piedmont. We propose that high infiltration capacities and the instability of ephemeral channel banks in arid and semiarid environments suppress fluvial incision and promote the smoothness of pediments. A positive feedback between bedrock weathering and regolith thickness causes tor growth: if regolith thins locally below a critical value, regolith production slows while surrounding areas continue to weather and erode more rapidly. We suggest that many pedimented and tor-studded landscapes may therefore be a consequence of intrinsic sediment transport-weathering feedbacks mediated by climatic and tectonic conditions, not by lithologic templates. Keywords: pediments, tors, regolith, weathering, deserts.

The evolution of Tethyan phosphogenesis during the Cretaceous--Eocene is examined to try to explain fluctuations of phosphogenesis through time, and whether or not they reflect long-term changes in ocean circulation or in continental weathering. Twenty-seven time-stratigraphic phosphate levels in various Tethyan sites, covering a time span of about 90 Myr from the Hauterivian to the Eocene, were analyzed for [sup.44]Ca/[sup.42]Ca and [sup.143]Nd/[sup.144]Nd in their carbonate fluorapatite (CFA) fraction. P and Ca accumulation rates and bulk sedimentation rates were quantified throughout the Cretaceous-Eocene Negev sequence to examine how changes in [sup.44]Ca/[sup.42]Ca and [sup.143]Nd/[sup.144]Nd are reflected in the intensity of phosphogenesis. A clear-cut change occurs in [[epsilon].sub.Nd(T)] and [delta][sup.44]Ca and in the rates of P and Ca accumulation and bulk sedimentation through the time analyzed, [[epsilon].sub.ND(T)] is much lower in the Hauterivian--Lower Cenomanian (-12.8 to 10.9) than in the Upper Cenomanian--Eocene (-7.8 to -5.9). Much lower [[delta].sup.44]Ca values occur in the Hauterivian--Yuronian (-0.22 to +0.02) than in the Coniacian--Eocene (+0.23 to +0.40). P accumulation rates in the Negev steeply increase from The culmination of P accumulation rates in the Negev during the Campanian, occurring with a high in [[epsilon].sub.Nd(T)] and [[delta].sup.44]Ca and a low in sedimentation rates, indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area. The abrupt [[epsilon].sub.Nd(T)] rise after the Cenomanian is attributed to increased incursion of Pacific (radiogenic) water masses into the Tethys, driven by the Late Cretaceous global sea-level rise, the connection between North and South Atlantic, the global post-Santonian cooling, and the progressive widening of the Caribbean threshold, all acting in combination to significantly intensify the Tethyan circumglobal current (TCC). It also reflects a weakening of the continental Nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves. High [[delta].sup.44]Ca values at those times also point to a decrease in weathering [Ca.sup.+2] fluxes and expansion of carbonate sedimentation in shelves, both enriching seawater with isotopically heavy [Ca.sup.+2]. Deep ocean circulation intensified by the post-Santonian cooling of high latitudes increased P inventory in the Tethys basin, whereas the strengthened TCC and the folded shelf likely resulted in coastal and topographically-induced upwelling, supplying P-rich intermediate waters to southeastern Tethys shelves. Only in the Paleocene--Eocene, following major changes in global circulation produced by narrowing of Tethys and widening of the Atlantic, did phosphogenesis shifts its locus of high intensity to the western (Atlantic) Tethys and West African Atlantic coasts. This change in paleocirculation is expressed by distinctly differing [[epsilon]sub.Nd(T)] in the Middle East and the North and West African phosphorites, suggesting different oceanic P sources and current systems for these two major groups of phosphorites. Our Nd isotope results further suggest a weaker TCC during the Mid-Cretaceous, becoming more intense in Late Cretaceous times. They also point to the North Pacific Ocean as major source of deep water formation for the intermediate--deep waters in the Tethys Basin during the Late Cretaceous. Keywords: phosphogenesis; south Tethys margins; Cretaceous--Eocene; [[epsilon].sub.Nd(T)]; [[delta].sup.44/42]Ca; P accumulation rates; paleoceanography; TCC; deep water formation

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.01.020 Byline: Christoph Kolb (a)(b), Josep A. Martin-Fernandez (c), Rainer Abart (d), Helmut Lammer (a) Keywords: Mars; surface; Geochemistry; Geological processes; Volcanism; Atmospheres; evolution Abstract: Compositional data analysis was performed on chemical compositions of martian surface materials in order to unravel scenarios of past and present weathering and to evaluate the role of meteoritic accumulation. The observed chemical variability is analyzed by means of principal component analysis. Potential reservoirs that may have contributed primary material to soil formation are assessed. Chemical alteration in the course of in situ weathering is described in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts. The interplay of localized chemical alteration and global scale re-distribution and mixing of fines material is documented through the identification of different soil forming branches. These branches emanate from distinct compositional domains, which comprise basaltic and basalt-andesitic primary materials, and they converge to a global dust composition, which represents the product of chemical and physical disintegration and subsequent global mixing. Mass balance considerations applied to localized weathering phenomena are in line with findings from experimental acid-sulfate weathering on olivine-bearing basalts and the persistence of secondary silica in evaporitic rocks. In addition the composition and oxidation state of involved volcanic gases is deduced. Our findings corroborate the past activity of volcanic exhalation products in combination with liquid water. We conclude that average martian crust is dominated by basaltic materials at its topmost level and that the amount of meteoritic accumulation may contribute about 6 wt% to the martian fines. From the meteoritic contribution minimum soil formation rates of 60[+ or -]20 cm/Gyr are derived. Sequestration of atmospheric oxygen during weathering of primary materials may account for the oxygen deficiency of the martian atmosphere. A 4-14-m-thick layer of oxidized martian fines may account for the estimated deficit of 1.7x10.sup.18 mol O.sub.2 in the martian atmosphere depending on the primary oxidation state of volatile volcanic emanations. Author Affiliation: (a) Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria (b) Institute for Earth Sciences, University of Graz, Universitatsplatz 2, A-8010 Graz, Austria (c) Department for Computer Science and Applied Mathematics, University of Girona, Edifici P-IV, Campus Montilivi, E-17071 Girona, Spain (d) Institute for Geological Sciences, Free University-Berlin, Malteserstrasse 74-100, D-12249 Berlin, Germany Article History: Received 19 March 2004; Revised 16 January 2006

Abstract: In situ, seasonal changes expose soils to frequent wetting-drying-freezing-thawing cycles. Such processes can favour and trigger shallow instabilities controlled by the weathering process. This paper presents an experimental study [...]

Byline: R. D. Schuiling (1), P. Krijgsman (2) Abstract: Weathering and subsequent precipitation of Ca- and Mg-carbonates are the main processes that control the CO.sub.2-concentration in the atmosphere. It seems logical, therefore, to use enhanced weathering as a tool to reduce rising CO.sub.2-levels. This can be applied as a technology, by reacting captured CO.sub.2 with olivine or calcium-silicates in autoclaves. It can also be applied extensively, by spreading fine-powdered olivine on farmland or forestland. Measures to control the CO.sub.2-levels of the atmosphere will be adopted more readily if they also serve some broader economic goals. An effective strategy for CO.sub.2 control will require many parallel approaches simultaneously. Author Affiliation: (1) Institute of Earth Sciences, 3508 TA, Utrecht, The Netherlands (2) Groteweg 10, 8191 JW, Wapenveld, The Netherlands Article History: Registration Date: 01/01/2005 Received Date: 19/02/2004 Online Date: 05/01/2006

In situ quantification of localized weathering processes on basalt flows in New Mexico and Hawaii demonstrates that small-area factors can be more important than other more readily observable factors. Further, it demonstrates that the factorial concept of the Pope Boundary-Layer weathering model is partially solvable, that organic weathering can accentuate glass weathering (with implications for climate models and storage of nuclear waste), and that silica coatings are not a simple solution for the preservation of stone monuments. Enhancement of glass weathering by lichens on the McCartys flow, El Malpais National Monument, New Mexico, remains restricted to a half-millimeter directly underneath the lichen-covered surface. In contrast, although the inorganic rock coating of silica glaze reduces weathering directly underneath the coating by up to nine times rates found in uncoated locales, silica glaze can almost double variability in weathering along its margins. Key Words: geomorphology, Hawaii, lichen, rate, weathering.

The large variation in the ratio of uranium-234 to uranium-238 ([sup.234]U/[sup.238]U) in rivers is not well understood, but may provide information about past weathering and rainfall and is important because it controls seawater ([sup.234]U/[sup.238]U). Here, we demonstrate the importance of physical weathering and rainfall for ([sup.234]U/[sup.238]U), using rivers from South Island, New Zealand, These data allow interpretation of an existing speleothem ([sup.234]U/[sup.238]U) record and suggest that New Zealand glacier advance 13,000 years ago was influenced by increased rainfall rather than by Younger Dryas-like cooling. A model of seawater ([sup.234]U/[sup.238]U) during glacial cycles indicates that rejection of corals based on modern ([sup.234]U/[sup.238]U) ±, The energetic alpha decay of [sup.238]U makes its great-granddaughter, [sup.234]U, relatively mobile and causes variability in the ratio of activities of [sup.234]U and [sup.238]U ([sup.234]U/[sup.238]U) in the surface-Earth environment (1). [...]

An interesting prediction problem involving degradation of materials exposed to outdoor environments (weathering) is estimating the distribution of future cumulative degradation using small- to moderate-sized degradation datasets. This distribution, which [...]

The importance of moisture in determining which rock weathering processes may operate, as well as the rate at which rock weathering occurs, has long been recognised. However, little is known about how often or when moisture is available to the rock surface, or for how long the surface may be wetted. This paper gives some initial results from current research on granite rocks in Antarctica. Recordings of surface moisture, for two aspects and three locations in Victoria Land, show that moisture reaches the rock surface more frequently than might initially have been expected in this dry climate. The number of occasions the surface is wetted, and the quantity of moisture the surface received, varied with aspect and time of year. Rock surfaces could be wet for up to 40% of the time during the summer months. This has important implications for rock weathering where some processes are deemed not to operate, or to operate in very restricted locations, due to the apparent absence of moisture.

The long-term stability of Earth's climate throughout the Phanerozoic stands in marked contrast to the dramatic fluctuations that have taken place on time scales as short as a few years, reflecting the high efficiency of longer-term climate regulation through negative feedbacks. A fundamental mechanism is thought to involve control of C[O.sub.2] in the ocean-atmosphere system through continental weathering, although unambiguous, high-resolution data supporting this hypothesis have hitherto not been available. Organic-rich mudrocks from Yorkshire, England, which were deposited during the Toarcian oceanic anoxic event (ca. 181 Ma, Early Jurassic), contain evidence of an exceptionally large excursion in the [sup.187][Os/.sup.l88]Os ratio of contemporaneous seawater, from ~0.4 to ~1.0. The most likely explanation for this excursion is that it resulted from a transient increase in global continental weathering rates of ~400%-800%. The Os isotope excursion coincided with a well-documented global [[delta].sup.13]C excursion of -6% that affected all the major biospheric reservoirs of the time. Higher mean global temperatures caused global chemical weathering rates to increase substantially, while, in turn, chemical weathering was very effective in reducing the elevated levels of atmospheric C[O.sub.2] and the high temperatures to preexcursion levels. Keywords: osmium, weathering, Toarcian, oceanic anoxic event, strontium, methane hydrate.

A review of some recent studies on rock weathering in Antarctica has revealed that Antarctic weathering research has a significant contribution to make to the ongoing debate about rock weathering in cold climates. Largely conducted in the field rather than the laboratory as in the Northern Hemisphere, it demonstrates that whilst all weathering processes can occur in Antarctica this is highly localised and dependent on the particular micro-environment. Freeze-thaw, for example, is not the most dominant process in many parts of Antarctica. The right combination of rock temperature and moisture can mean that salt, insolation, hydration or even chemical weathering can predominate.

We investigated rock outcrops spanning the middle Miocene, global climate-cooling step on the Maltese Islands in order to reconstruct continental weathering rates and terrigenous fluxes, as well as to explore the coupling between these later, regional climate and carbonate accumulations. Sedimentation at this location was dominated during the Oligocene and early Miocene by a transitional platform to slope carbonates but progressively switched to a clay-rich carbonate slope system in the middle Miocene. Around 13 Ma, an abrupt change toward clay-dominated marls occurred, and marl deposition persisted until the Tortonian (ca. 12 Ma), when a shallow-water carbonate ramp was reestablished. Clay mineralogy and bulk-rock oxygen isotope analyses suggest that the deposition of the Blue Clay formation was mainly caused by global climate change and related change in the rate of continental weathering. A significant negative correlation ([R.sup.2] = 0.65) exists between the carbonate content and the [delta][sup.18]O record. This, combined with the variation of mass accumulation rate of terrigenous material, suggests that shorter-term periods of globally cooler climate (Mi events) were associated with higher rates of accumulation in continental-derived material. Since during the Miocene Malta was attached to the North African Margin, we propose that the observed trends were due to a regional increase in rainfall during cooler periods, which consequently increased continental weathering and runoff. We further suggest that this pattern was linked to the perturbation of atmospheric fronts due to an increased thermal gradient during the Miocene. Thus, regional increase in rainfall might have been linked to the northward migration of the Intertropical Convergence Zone (ITCZ). Keywords: Miocene, climate, weathering, clay mineralogy, continental margin, Malta.

Ilmenite grains from weathering profiles developed on granite and ultramafic chlorite schist in the Georgia Piedmont were studied for evidence of morphological and chemical alteration. Ilmeniterich concentrates from the fine sand (90-150 [micro]m) component were studied to test the assumption that there is no difference between ilmenite in the parent rock and that in colluvium delivered to primary drainage systems. Ilmenite grains in the granite profile are rounded to subhedral, and commonly contain hematite exsolution blebs. Dissolution pits are observed along the boundaries of the exsolution blebs, with goethite occurring as an alteration product. Ilmenite grains in the schist profile occur as fractured anhedral grains with uncommon lamellae of rutile. Grain fractures are filled with goethite and hematite, particularly in the B-horizon. Ilmenite from the granite profile is Mn rich (7-15 mol% MnTi[O.sub.3]), whereas ilmenite from the schist profile contains only 1-2 mol% MnTi[O.sub.3] and up to 8 mol% MgTip[O.sub.3]. Two populations of grains develop in both profiles. Grains with abundant exsolution blebs and fractures alter through a proposed two-step reaction mechanism. It is proposed that ilmenite first undergoes a solid-state transformation to pseudorutile via an anodic oxidation mechanism. Oxidized Fe and Mn diffuse from the structure and precipitate as goethite and Mn[O.sub.2]. Pseudorutile is ephemeral and undergoes incongruent dissolution to form anatase, hematite, and goethite. The second population of grains experienced only slight oxidation and dissolution on grain surfaces, and they persist through the weathering profile. The [Fe.sup.2+] content of competent ilmenite grains is somewhat lower in the C-horizon, compared with grains in the host rock. In horizons above the C-horizon, the [Fe.sup.2+] contents of the ilmenite are similar to those in the host rock. This study shows that using ilmenite minor-element chemistry as a tracer for sediment provenance is a valid technique, however, textural features of ilmenite in colluvium may be distinct from those in the parent rock. Also, the production of secondary phases, such as anatase, goethite, and hematite, in soil profiles results in part from the alteration of ilmenite.

In a headwater catchment in the Oregon Coast Range, we find that solid-phase mass losses due to chemical weathering are equivalent in the bedrock and the soil. However, the long-term rate of mass loss per unit volume of parent rock is greater in the soil than in the rock. We attribute this finding to the effects of biotic processes in the soil and to hydrologic conditions that maximize contact time and water flux through the mineral matrix in the soil. This result stems both from earlier work in which we demonstrated that rock and soil contribute equally to the solute flux and from arguments presented here that the basin is in dynamic equilibrium with respect to erosion and uplift. The silica flux of 10.7 [+ or -] 7.1 t.[km.sup.-2]x[yr.sup.-1] from the basin is several times larger than the flux from older soils elsewhere, but comparable to the flux from sites with similar physical erosion rates. This result argues that physical denudation or uplift rates play an important role in setting the chemical denudation rate. Physical processes appear to influence chemical-weathering rates in several ways. First, they limit chemical evolution by removing material, thus setting the residence time within the weathered rock and the soil. Second, bioturbation mixes rock fragments into the more reactive soil and maintains high soil porosity, allowing free circulation of water. Because the weathering in the soil is more intense than in the rock, we argue that the chemical denudation rate will diminish where uplift rates--and, hence, physical-denudation rates--are great enough to lead to a bedrock-dominated landscape. Chemical denudation rates will increase with physical-denudation rates, but only as long as the landscape remains mantled by soil. Keywords: chemical erosion, denudation, physical weathering, soil dynamics, uplift, weathering.

Weathering fluxes from four small catchments in the Himalayas, one forested, one agricultural, and two glacial, have been calculated by quantifying stream discharge, deposition, and biomass uptake of major ions. These fluxes were partitioned between silicate and carbonate sources by using a mineral mass-balance model. This approach provides the first well-defined estimates of Himalayan weathering fluxes from small catchments. Silicate weathering rates are highest in the favorable weathering environment of the Middle Hills catchments, despite higher dissolved fluxes in the High Himalayas attributed to high carbonate weathering. The silicate weathering fluxes for High Himalayan small catchments are similar to estimates from the chemistry of large rivers draining the same regions. Much higher silicate weathering intensity for the Ganges basin indicates that the silicate material eroded from the High Himalayas undergoes up to six times as much weathering in the Ganges Plain as in the High Himalayan mountains. Himalayan silicate weathering rates are higher than in equivalent continental settings and, on an area-normalized basis, are comparable to fluxes from weathering of basalts on ocean islands and tropical volcanic provinces. Keywords: catchment, erosion, flux, Himalayas, weathering.

Deterioration models are essential components of infrastructure management systems (IMSs) because they predict the future condition of infrastructure facilities and consequently assist in optimizing maintenance decisions. Case-based reasoning (CBR) is proposed to generate deterioration models that benefit from the large amount of facility data stored in IMS databases and updated on a regular basis. CBRMID (CBR for modeling infrastructure deterioration) is a new CBR system developed to satisfy the special requirements of modeling infrastructure deterioration and to provide government agencies with practical, accurate, and versatile deterioration models. CBRMID is required to support (1) hierarchial decomposition of infrastructure facilities; (2) representation of facility component interactions; (3) versatility and extensibility of case and knowledge representation; (4) data musing and sharing; (5) representation of time-dependent data; and (6) fuzziness of retrieval knowledge. In this paper, the architecture of CBRMID is described in terms of case representation, case retrieval, case adaptation, and case accumulation. An application example generated using CBRMID is also presented. DOI: 10.1061/(ASCE)0887-3801(2002)16:2(104) CE Database keywords: Infrastructure; Deterioration; Bridges, highway; Decomposition; Databases.

Coarse rock debris exposed in the subaerial environment of northern Sweden displays the development of a wide variety of surface coatings. These include weathering rinds as well as a great diversity of geochemical coatings, including those dominated by Ca, Fe, Si, and Al. Each of these types of rock coatings displays a high degree of geochemical complexity. The weathering rinds exhibit both geochemical and morphologic changes to the parent rock cores, including extensive dissolution, oxidation, and hydration as well as disaggregation, fracturing, and cementation by secondary geochemical coatings. Chemical breakdown of the rock to form weathering rinds includes loss of K, Si, Mg, and Ca and build-up of Fe. Weathering rinds are fundamentally the result of dissolution, as no clay minerals were identified in the rinds. Rock coatings are distinguished from rinds by their clear accretionary nature. Despite the distinction made between weathering rinds and rock coatings, it is important to note that often the two are intimately related. The presence of rock coatings as well as weathering rinds on rock surfaces amplifies the important role played by geochemical processes in the Arctic alpine climate of northern Sweden in particular, as well as its significance in landscape evolution in such environments in general. Keywords: alpine environments, Arctic environments, chemical weathering, rock coatings, weathering rinds.

Two-stage development of landforms has been appreciated for more than two centuries with respect to minor features, and major forms and landscapes have been viewed in similar terms for almost a hundred years. Early workers understood the significance of fractures as passages for water and, hence, as avenues of weathering, the tendency for weathering to produce rounded forms, the progression of weathering from the surface downwards, weathering contrasts between wet and dry sites, contrasted erosive susceptibility of weathered and unweathered rock, and reinforcement effects. Forms of deep and shallow derivation can be differentiated. By whatever name it is known--etch, double planation, subcutaneous, or two-stage--the concept is one of the most fruitful developed in the last century, for it bears not only on the origin of a wide range of landforms, but also on the crucial role of water and weathering, the age of landforms and landscapes, palaeogeographic reconstructions, climatic geomorphology and theories of landscape development. Keywords: etching; two-stage development; double planation; regolith; weathering front; azonality

Critical consideration of varied Phanerozoic climatic models, and comparison of them against Phanerozoic global climatic gradients revealed by a compilation of Cambrian through Miocene climatically sensitive sediments (evaporites, coals, tillites, lateritic soils, bauxites, calcretes, etc.) suggests that the previously postulated climatic models do not satisfactorily account for the geological information. Nor do many climatic conclusions based on botanical data stand up very well when examined critically. Although this account does not deal directly with global biogeographic information, another powerful source of climatic information, we have tried to incorporate such data into our thinking wherever possible, particularly in the earlier Paleozoic. In view of the excellent correlation between C[O.sub.2] present in Antarctic ice cores, going back some hundreds of thousands of years, and global climatic gradient, one wonders whether or not the commonly postulated Phanerozoic connection between atmospheric C[O.sub.2] and global climatic gradient is more coincidence than cause and effect. Many models have been proposed that attempt to determine atmospheric composition and global temperature through geological time, particularly for the Phanerozoic or significant portions of it. Many models assume a positive correlation between atmospheric C[O.sub.2] and surface temperature, thus viewing changes in atmospheric C[O.sub.2] as playing the critical role in regulating climate/temperature, but none agree on the levels of atmospheric C[O.sub.2] through time. Prior to the relatively recent interval of time in which atmospheric C[O.sub.2] is directly measurable, a variety of biological and geological proxies have been proposed to correlate with atmospheric C[O.sub.2] level or with pC[O.sub.2]/temperature. Atmospheric models may be constructed for the Pre-Cenozoic but the difficulties of assessing variables in their construction are many and complex. None of the modelers have gathered enough biological and geological data to impart reliability to the model constructs. Most modelers focus almost exclusively on one or a few variables as proxy to measure atmospheric C[O.sub.2], nor consider the many other variables involved, nor agree on what these variables are or how to measure them. In this paper, it is the reliability of the present data bases used in these atmospheric models that we wish to consider. We focus most attention on the Berner models, such as GEOCARB I, II and BLAG, because of the basic role they attribute to tracheophytes in regulating atmospheric C[O.sub.2] and our own interest in pre-tracheophytic land plants and the atmospheric composition of the pre-tracheophytic Paleozoic. We survey the presence of symbiotic mycorrhizae and question the assumption that all tracheophytes are obligately associated with them. Although pre-tracheophytic embryophytes, cyanobacteria, and possibly other organisms preceded tracheophytes on land by millions of years. Berner's models do not consider a significant role for them in affecting pre-Devonian climate/temperature and atmospheric composition. In effect, Berner assumes the pre-tracheophytic life inhabited a world governed largely by abiotic physical and chemical reactions. We consider uncertainties raised by minimizing possible roles for pre-tracheophytic oxygenic and heterotrophic microorganisms analogous to those speculated to be unique to tracheophytes both with regard to an active role in biodeterioration of rock and soil mineral substrates and in the sequestration of organic carbon. Additionally, Berner does not consider marine productivity, which might have been high in the Precambrian and Early Paleozoic and possibly consequent organic carbon sequestration, even in the possible absence of terrestrial organisms, or even in the absence of a significant preserved biomass of terrestrial and marine organisms. The important roles played by cyanobacteria, for example, are briefly reviewed by Giller and Malmqvist in lakes and rivers as regards both planktonic and benthic taxa, and it is not safe to assume that these organisms were absent or of no potential significance in the pre-embryophytic, i.e. earlier Ordovician and well back into the Precambrian. Berner's models have met with a large measure of consensus about C[O.sub.2] balance during the Phanerozoic, about the role played by tracheophytes, and have been used to test or evaluate other data. After reviewing the biological and geological assumptions and estimates on which these Models are based, we conclude that they do not provide reliable information about atmospheric C[O.sub.2] composition through Phanerozoic time, particularly in the Early Phanerozoic. We compare many atmospheric C[O.sub.2] models, while considering the numerous proxies on which they are based and conclude that the competing models are inadequate for atmospheric C[O.sub.2] estimation. Many possibilities not considered in present models must either be included or eliminated based on reliable evidence. We suggest that assessing Phanerozoic climate/temperature based on the available geological/climatic proxies would appear to provide a more reliable method of estimating variations in C[O.sub.2], and hence atmospheric C[O.sub.2]:[O.sub.2] balance, than most proxy constructs on which atmospheric models are presently based, because of the critical role postulated for atmospheric C[O.sub.2] in regulating Earth's surface temperature. We present our own Phanerozoic climate estimate, based on readily available geological/climatic data, for comparison with postulated coeval atmospheric C[O.sub.2] levels as a test of the postulated correlation. Keywords: global climatic gradient; atmospheric C[O.sub.2]; Phanerozoic; stomates; mycorrhizae; paleogeography; weathering

Activation energy and apatite surface area are important when controlling the phosphorus flux from marine net ecosystem production in geologic time. This conclusion was derived through a kinetic treatment of existing data used in a weathering model.

Honeycomb weathering is a common surface phenomenon affecting a variety of rocks in a range of environments. It develops on building stones and it shapes ocean cliffs, rocks in hot deserts, and Arctic landscapes. Honeycomb weathering may also help alter rocks on other planets, such as Mars. Although first noted in the nineteenth century, its origins are still not well understood, and a dearth of laboratory experiments testing the many theories proposed for its development has added to the ambiguity. Incipient honeycomb weathering in a homogeneous limestone has been experimentally reproduced by wind exposure and salt crystallization. Our experiments show that heterogeneous wind flow over a stone surface is important in the development of this weathering pattern. Wind promotes evaporative salt growth between grains on a stone surface, resulting in the development of small, randomly distributed cavities. A reduction in air pressure within the cavities results in increased wind speed and rapid evaporation. A high evaporation rate and evaporative cooling of the saline solution in the cavity leads to more rapid and greater granular disintegration than in the surrounding areas. It seems that this local supersaturation and subsequent buildup of salt crystallization pressure ultimately result in the formation of honeycomb features. For the first time, these experimental results demonstrate the close relationship between salts, wind, and honeycomb weathering. They also offer new ways to understand the genesis of this striking and sometimes harmful weathering pattern.

Microorganisms modify rates and mechanisms of chemical and physical weathering and clay growth, thus playing fundamental roles in soil and sediment formation. Because processes in soils are inherently complex and difficult to study, we employ a model based on the lichen-mineral system to identify the fundamental interactions. Fixed carbon released by the photosynthetic symbiont stimulates growth of fungi and other microorganisms. These microorganisms directly or indirectly induce mineral disaggregation, hydration, dissolution, and secondary mineral formation. Model polysaccharides were used to investigate direct mediation of mineral surface reactions by extracellular polymers. Polysaccharides can suppress or enhance rates of chemical weathering by up to three orders of magnitude, depending on the pH, mineral surface structure and composition, and organic functional groups. Mg, Mn, Fe, Al, and Si are redistributed into clays that strongly adsorb ions. Microbes contribute to dissolution of insoluble secondary phosphates, possibly via release of organic acids. These reactions significantly impact soil fertility. Below fungi-mineral interfaces, mineral surfaces are exposed to dissolved metabolic byproducts. Through this indirect process, microorganisms can accelerate mineral dissolution, leading to enhanced porosity and permeability and colonization by microbial communities.

The weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric C[O.sub.2] over geologic time, and vascular plants may have played an important role in this process. In western Iceland, we have examined the role of plants in weathering by measuring the chemistry of waters draining adjacent areas of basaltic rocks that are either barren (having a partial cover of mosses and lichens) or populated by trees. The study area was chosen to maximize vegetational differences and to minimize differences in microclimate, slope, and lithology, while avoiding hydrothermal waters and anthropogenic acid rain. Results, including data on cation uptake by growing trees, indicate that the rate of weathering release of Ca and Mg to streams and vegetation is two to five times higher in vegetated areas than the release of Ca and Mg to streams in barren areas. This finding suggests a major role for vascular plants in accelerating weathering and thereby lowering atmospheric C[O.sub.2] as they invaded upland areas of the continents between 380 and 350 Ma.

Periglacial weathering limits on two mountains in northwest Scotland separate zones of contrasting exposure history. Exposure dating of bedrock below the weathering limits gives ages consistent with late Devensian deglaciation, but six out of seven samples from above the weathering limits give minimum exposure ages older than late Devensian ice expansion. These results suggest that mountain summits stood as nunataks above the last ice-sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation, trimming of frost debris during an ice-sheet readvance, or enhanced weathering prior to climatic warming during ice-sheet downwastage. The dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold-based ice on mountain summits and erosive, warm-based ice at lower elevations, although 26Al/10Be ratios for high-level bedrock surfaces provide no evidence of prolonged static ice cover.

Feldspar surfaces respond to chemical, biological, and mechanical weathering. The simplest termination is hydroxyl (OH), which interacts with any adsorption layer. Acid leaching of alkalis and aluminum generated a silica-rich, nanometers-thick skin on certain feldspars. Natural K, Na-feldspars develop fragile surfaces as etch pits expand into micrometer honeycombs, possibly colonized by lichens. Most crystals have various irregular coats. based on surface-catalytic processes in molecular sieve zeolites, I proposed that some natural feldspars lose weakly bonded Al-OH (aluminol) to yield surfaces terminated by strongly bonded Si-OH (silanol). This might explain why some old feldspar-bearing rocks weather slower than predicted from brief laboratory dissolution. Lack of an Al-OH infrared frequency from a feldspar surface is consistent with such a silanol-dominated surface. Raman spectra of altered patches on acid-leached albite correspond with amorphous silica rather than hydroxylated silica-feldspar, but natural feldspar may respond differently. The crystal structure of H-exchanged feldspar provides atomic positions for computer modeling of complex ideas for silica-terminated feldspar surfaces. Natural weathering also depends on swings of temperature and hydration, plus transport of particles, molecules, and ionic complexes by rain and wind. Soil formation might be enhanced by crushing granitic outcrops to generate new Al-rich surfaces favorable for chemical and biological weathering. Ornamental slabs used by architects and monumental masons might last longer by minimizing mechanical abrasion during sawing and polishing and by silicifying the surface. Silica-terminated feldspar might be a promising ceramic surface.