Magnetic polarity stratigraphy of the Upper Siwalik deposits,Pabbi Hills,Pakistan

Over 1000 m of fluvial molasse, exhibiting a stable detrital remanent magnetization, is exposed in a mammal-bearing sequence in the Upper Siwalik Group of the Pabbi Hills, Pakistan. The magnetic polarity chronology reveals that the sequence records a time period of 2.6 m.y., extending from the early Gauss Normal Epoch into the Brunhes Normal Epoch. During this period, sedimentation rates increased upward in time from 0.25 m/1000 yr to 0.45 m/1000 yr. The sudden disappearance of red beds and a change in the lithoclastic composition of basal channel sands suggests that about 800,000 years ago the primary source area began shifting from the metamorphic terrane of the Himalayan Orogen to a more local sedimentary terrane on the folded margins of the Himalayan foredeep. About 500,000 years ago the anticlinal Pabbi Hills attained surface expression. Uplift continued at a minimum rate of 1 m/1000 yr.A local Pliocene/Pleistocene boundary based on the Olduvai Normal Event is clearly recognized. Local fossil finds reveal thatEquus, diagnostic element of the Pinjor faunal zone, appeared locally about 1.8 m.y. ago and thatHipparion, a faunal element of the Tatrot and earlier faunal zones, persisted locally until at least 3.0 m.y. ago.     

Changes in atmospheric circulation and the Arctic Oscillation preserved within a millennial length reconstruction of summer cloud cover from northern Fennoscandia

Cloud cover currently represents the single greatest source of uncertainty in General Circulation Models. Stable carbon isotope ratios (δ¹³C) from tree-rings, in areas of low moisture stress, are likely to be primarily controlled by photosynthetically active radiation (PAR), and therefore should provide a proxy record for cloud cover or sunshine; indeed this association has previously been demonstrated experimentally for Scots pine in Fennoscandia, with sunlight explaining ca 90% of the variance in photosynthesis and temperature only ca 4%. We present a statistically verifiable 1011-year reconstruction of cloud cover from a well replicated, annually-resolved δ¹³C record from Forfjord in coastal northwestern Norway. This reconstruction exhibits considerable variability in cloud cover over the past millennium, including extended sunny periods during the cool seventeenth and eighteenth centuries and warm cloudy periods during the eleventh, early fifteenth and twentieth centuries. We find that while a generally positive relationship persists between sunshine and temperature at high-frequency, at lower (multi-decadal) frequencies the relationship is more often a negative one, with cool periods being sunny (most notably the Little Ice Age period from 1600 to 1750 CE) and warm periods more cloudy (e.g. the mediaeval and the twentieth century). We conclude that these long-term changes may be caused by changes in the dominant circulation mode, likely to be associated with the Arctic Oscillation. There is also strong circumstantial evidence that prolonged periods of high summer cloud cover, with low PAR and probably high precipitation, may be in part responsible for major European famines caused by crop failures.     

Recent summer precipitation trends in the Greater Horn of Africa and the emerging role of Indian Ocean sea surface temperature

We utilize a variety of climate datasets to examine impacts of two mechanisms on precipitation in the Greater Horn of Africa (GHA) during northern-hemisphere summer. First, surface-pressure gradients draw moist air toward the GHA from the tropical Atlantic Ocean and Congo Basin. Variability of the strength of these gradients strongly influences GHA precipitation totals and accounts for important phenomena such as the 1960s–1980s rainfall decline and devastating 1984 drought. Following the 1980s, precipitation variability became increasingly influenced by the southern tropical Indian Ocean (STIO) region. Within this region, increases in sea-surface temperature, evaporation, and precipitation are linked with increased exports of dry mid-tropospheric air from the STIO region toward the GHA. Convergence of dry air above the GHA reduces local convection and precipitation. It also produces a clockwise circulation response near the ground that reduces moisture transports from the Congo Basin. Because precipitation originating in the Congo Basin has a unique isotopic signature, records of moisture transports from the Congo Basin may be preserved in the isotopic composition of annual tree rings in the Ethiopian Highlands. A negative trend in tree-ring oxygen-18 during the past half century suggests a decline in the proportion of precipitation originating from the Congo Basin. This trend may not be part of a natural cycle that will soon rebound because climate models characterize Indian Ocean warming as a principal signature of greenhouse-gas induced climate change. We therefore expect surface warming in the STIO region to continue to negatively impact GHA precipitation during northern-hemisphere summer.     

Short‐term rock surface expansion and contraction in the intertidal zone

Transverse micro‐erosion meter (TMEM) stations were installed in rock slabs from shore platforms in eastern Canada. The slabs were put into artificial sea water for 1, 6 or 11 hours, representing high, mid‐ and low tidal areas, respectively. The TMEMs were used to record changes in surface elevation as the rocks dried during the remainder of the 12 h of a semi‐diurnal tidal cycle. A similar technique was used on the same rock types at intertidal TMEM stations in the field, as the rocks dried during low tide. Argillite and basalt surface contraction was from 0 to 0·04 mm: there was little surface expansion. Sandstones contracted by up to 0·03 mm in the field, but there was almost no contraction in the laboratory. Argillite and basalt contraction tended to be greatest in the upper intertidal zone, and to increase with rates of longer‐term surface downwearing, but there was little relationship with rock hardness or air temperature and humidity. Changes in elevation at the same points at TMEM stations in the laboratory and field were quite consistent from one tidal cycle to the next, but there were considerable variations within single tidal cycles between different points within each station. The data suggest that contraction within the elevational zone that is normally submerged twice a day by the tides is by alternate wetting and drying. Short‐term changes in elevation are generally low compared with annual rates of downwearing owing to erosion, but they may generate stresses that contribute to rock breakdown. Copyright © 2007 John Wiley & Sons, Ltd.     

Fluoride-Selective Electrode as a Tool to Evaluate the Degradation of PFAS in Groundwater: A Bench-Scale Investigation

Fluoride (F⁻) concentration in groundwater can be used as an independent measure of the degradation of per- and polyfluoroalkyl substances (PFAS) at contaminated sites. This study assessed the impact of the groundwater matrix, oxidizing reagents, quenching agent, and sample handling procedures (filtration) on determinations of F⁻. F⁻ was quantified using a fluoride-selective electrode (FSE) using matrix spike recovery (acceptable range 75 to 125%) and electrode slope performance (ideal range −54 to −60 mV). For the unaltered aqueous matrices considered (ultrapure water, ultrapure water with sodium chloride, and simulated groundwater), matrix spike recoveries were greater than 93% and acceptable electrode slopes (−59.5 ± 0.2 mV) were obtained. Matrix spike recoveries and electrode slopes when persulfate or permanganate was added were 87 and 93%, and −58.4 ± 1.3 and −47.3 ± 2.2 mV, respectively. Therefore, quantifying F⁻ in matrices containing permanganate should involve use of either a matrix-matched calibration curve or the method of standard additions due to the low electrode slope. The addition of ascorbic acid as a quenching agent resulted in a decrease in matrix spike recoveries to <74% and suggests alternate quenching procedures should be used if an FSE is employed to measure F⁻. Removal of sediments by filtration prior to the addition of the fluoride spike led to improved matrix spike recoveries (>96%), which were otherwise underestimated using the FSE in the presence of sediments. While the FSE may be a quick and portable tool, its significant limitations need to be fully understood before it can be used to quantify the production of F⁻ resulting from the potential degradation of PFAS at field sites.     

Scenario Evaluator for Electrical Resistivity Survey Pre‐modeling Tool

Geophysical tools have much to offer users in environmental, water resource, and geotechnical fields; however, techniques such as electrical resistivity imaging (ERI) are often oversold and/or overinterpreted due to a lack of understanding of the limitations of the techniques, such as the appropriate depth intervals or resolution of the methods. The relationship between ERI data and resistivity is nonlinear; therefore, these limitations depend on site conditions and survey design and are best assessed through forward and inverse modeling exercises prior to field investigations. In this approach, proposed field surveys are first numerically simulated given the expected electrical properties of the site, and the resulting hypothetical data are then analyzed using inverse models. Performing ERI forward/inverse modeling, however, requires substantial expertise and can take many hours to implement. We present a new spreadsheet‐based tool, the Scenario Evaluator for Electrical Resistivity (SEER), which features a graphical user interface that allows users to manipulate a resistivity model and instantly view how that model would likely be interpreted by an ERI survey. The SEER tool is intended for use by those who wish to determine the value of including ERI to achieve project goals, and is designed to have broad utility in industry, teaching, and research.     

Rare-gas-rich separates from carbonaceous chondrites

Samples studied were residual, carbonaceous /Alates—a coined word to designate colloids prepared sometimes before and sometimes after acid demineralization—from Murray, Murchison, Cold Bokkeveld (type C2s) and Allende (type CV3) meteorites. Characterization: C2 /Alates, comprising 0.5% of the bulk meteorite are fine-grained (< 100 Å), amorphous, sulfide-free, oxidizable, 95% carbonaceous materials which pyrolyze bimodally at 200–700 and 800–1200°C. Allende /Alates are similar but with traces of inferred spinel and chromite and of sulfur, Rare gas results: Elemental: Release from stepwise heated Murray is bimodal with maximum release and upper temperature peak at 1000°C, probably accompanying chemical reaction. All /Alates studied had very nearly the same elemental concentrations, distinctly planetary in pattern. Isotopic: Trapped neon compositions are unprecedentedly close to Pepin's neon-A corner but nevertheless show signs of complexity, as if accompanied by neon-E. The trapped ³He/⁴He ratio is essentially constant at (1.42 ± 0.2 × 10^?4. The isotopically anomalous heavy noble gases, easily detected in the residues of oxidized /Alates, were not conspicuous in this particular study. Comparison and Chicago results: Concentrations of heavy rare gases in our /Alates agree with concentrations measured directly (as opposed to inferred by difference) in acid resistant residues at Chicago. Alone, our results support the idea of a carbonaceous gas-carrier uniformly present in meteorites of various types, but Chicago characterizations of the samples can apply to both their samples and ours provided that the right amount of gas was lost in the Berkeley procedures to make the uniform gas contents in various samples a coincidence.