The composition and crystallinity of the near-surface regions of weathered alkali feldspars

Our ability to identify thin non-stoichiometric and amorphous layers beneath mineral surfaces has been tested by undertaking X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) work on alkali feldspars from pH 1 dissolution experiments. The outcomes of this work were used to help interpret XPS and TEM results from alkali feldspars weathered for <10,000 years in soils overlying the Shap Granite (north-west England). The chemistry of effluent solutions indicates that silica-rich layers a few nanometers in thickness formed during the pH 1 experiments. These layers can be successfully identified by XPS and have lower Al/Si, Na/Si, K/Si and Ca/Si values than the outermost ∼9 nm of unweathered controls. Development of Al-Si non-stoichiometry is coupled with loss of crystal structure to produce amorphous layers that are identifiable by TEM where >∼2.5 nm thick, whereas the crystallinity of albite is retained despite leaching of Na to depths of tens to hundreds on nanometers. Integration of XPS data over the outermost 6-9 nm of naturally weathered Shap feldspars shows that they have stoichiometric Al/Si and K/Si ratios, which is consistent with findings of previous TEM work on the same material that they lack amorphous layers. There is some XPS evidence for loss of K from the outermost couple of nanometers of Shap orthoclase, and the possibility of leaching of Na from albite to greater depths cannot be excluded using the XPS or TEM results. This study demonstrates that the leached layer model, as formulated from laboratory experiments, is inapplicable to the weathering of alkali feldspars within acidic soils, which is an essentially stoichiometric reaction.     

Survey of Nitrate Contamination in Shallow Domestic Drinking Water Wells of the Inner Coastal Plain of Georgia

Beginning in 1990, 2,588 wells were sampled within the Inner Coastal Plain of Georgia in an effort to assess the quality of ground water in this major farm belt. The project was one aspect of an EPA-sponsored program to assess ground-water quality statewide. Several variables were measured, including pH, specific conductivity, dissolved oxygen, temperature, nitrate, nitrite, total hardness, calcium, magnesium, and bicarbonate. In some wells sulfate, chloride, potassium, iron, and manganese contents were also determined. Particular emphasis was placed, however, on pH, specific conductivity, temperature, and nitrite/nitrate content. Generally, pH was between 6 and 8, and temperatures were within a range of 18° and 24°Celsius. Measurements of specific conductivity varied, but averaged 250–275 microsiemens/cm. Nitrite contamination was negligible, and nitrate contamination of the ground water within the shallow aquifers did not appear to be significant. In fact, 56% of the wells sampled showed no detectable signs of nitrate or nitrite contamination. There were, however, a few isolated wells where nitrate as nitrogen measurements exceeded the EPA's Safe Drinking Water Standard of 10 ppm. The general lack of contamination may be the result of the nature of the agricultural practices used in this region and/or the effect of natural denitrification.     

Magnetization of Jurassic red deep-sea sediments in the Atlantic (DSDP site 105)

Measurement of the remanent magnetization of samples of Jurassic oceanic red sediments recovered in the western Atlantic on Leg 11, site 105 of the Deep Sea Drilling Project yields quite different results, depending on the demagnetization processes used. Both the Jurassic section and the Berriasian-Valanginian part of the Lower Cretaceous were measured, but with less satisfactory results for the Lower Cretaceous. The natural remanent magnetization of the Jurassic section is almost entirely normal, with 44.6° inclinations (standard deviation = 13.9°) and is not changed by 1000 Oe alternating field (AF) demagnetization. Thermal demagnetization to temperatures of 630°C brings the inclination and polarity sequence in line with that expected for Oxfordian through Tithonian time at this site. The average inclination after thermal demagnetization is 22.1°, standard deviation = 12.1°, and the polarity pattern is one of frequently alternating polarity, much more similar to published reversal patterns for this time than the all normal results of AF demagnetization. The polarity pattern is not identical to the published ones as a result of insufficiently detailed sampling. Thermomagnetic and X-ray analyses were ambiguous, but suggest the presence of titanomagnetite, hematite, and possibly titanomaghemite and pyrrhotite. The primary remanence is carried by hematite.     

Glacial forest refugium in Howard Valley,South Island,New Zealand

Fossils of forest habitat beetles and leaves of Nothofagus menziesii provide evidence of a forest refugium at times between ca. 34 000 and ca. 18 500 cal. a BP at an upland site in Howard Valley, located adjacent to glaciated valleys in South Island, New Zealand. The stratigraphy of the glacial‐aged terrace sequence of organic‐rich silts and fluvial sand/gravels indicates that soil development occurred episodically for around 15 000 a. Fifty‐four beetle taxa represent seven habitat types: forest, forest or scrub, riparian and aquatic, litter, grass/tussock, marshland and moss habitats. Leaf and beetle fossils indicate that forest dominated by N. menziesii persisted at the site for most of the time period represented, and tree line taxa such as Taenarthrus sp. 1 (Carabidae) and Podocarpus sp. (Podocarpaceae) indicate that the site may represent the upper tree limit for full‐glacial time. The finding of forest at this elevated site adds to the growing fossil evidence for multiple forest refugia in New Zealand during the last glaciation and is consistent with the pollen records, which have consistently indicated the presence of forest species during the last glaciations. Copyright © 2009 John Wiley & Sons, Ltd.     

Cross-basin differences in particulate organic carbon export and flux attenuation in the subtropical North Atlantic gyre

We compared in-situ and satellite-derived measures of the biological carbon pump efficiency at the two seemingly similar subtropical North Atlantic gyre time series sites, the Bermuda time series (BATS, Bermuda Atlantic time-series study and OFP, ocean flux program) in the western gyre and the ESTOC time series (European station for time-series in the ocean, Canary Islands) in the eastern gyre. Satellite-derived surface chlorophyll a was slightly lower at Bermuda compared to ESTOC (annual average of 0.10±0.04 vs. 0.14±0.05-mg-m^?3), as was satellite-derived primary production (annual average of 380±77 vs. 440±80-mg C-m^?2 d^?1). However, export production normalized to primary production (export ratio) was higher at Bermuda by a factor of 2–3 when estimated using mesopelagic traps moored at 500-m depth and by a factor of 3–4 when estimated using surface-tethered drifting traps. When averaged seasonally, flux at BATS was highest in spring (March, April, May) at all depths followed by summer (June, July, August) and decreasing towards fall, but this seasonality was less visible at ESTOC. Seasonal comparison showed the fastest flux attenuation at Bermuda in winter and spring, coinciding with the highest POC flux. POC/PIC ratios derived from the moored traps were significantly higher at BATS than at ESTOC in fall and winter, but this difference was not significant in spring (p>0.05). This study shows that while the western and eastern Atlantic subtropical gyres have similar rates of primary production, the biological carbon pump differs between the two provinces. Higher new nutrient input observed at Bermuda compared to ESTOC might explain part of the difference in export ratio but alone is insufficient. Greater winter mixed-layer depths and higher mesoscale eddy activity at Bermuda resulting in pulsed production events of labile organic matter might explain both the higher export flux and export ratios found at Bermuda.     

SCUBA-2 CCD-STYLE IMAGING FOR THE JCMT

SCUBA-2 will replace SCUBA (Submillimetre Common User Bolometer Array) on the James Clerk Maxwell Telescope in 2006 and will be the first CCD-style camera for submillimetre astronomy. The instrument will simultaneously image at 850 and 450 microns using two focal plane arrays of 5120 pixels each. SCUBA-2 will map the submillimetre sky 1000 times faster than SCUBA to the same signal-to-noise ratio. This paper introduces the detector technology and the challenges faced in reading out a detector array cooled to ～120 mK.     

Asteroid 21 Lutetia at 3 μm: Observations with IRTF SpeX

We present observations of Asteroid 21 Lutetia collected 2003–2008 using the SpeX instrument on the NASA Infrared Telescope Facility (IRTF) covering 2–4 μm. We also reevaluate NSFCam observations obtained in 1996 (Rivkin, A.S., Lebofsky, L.A., Clark, B.E., Howell, E.S., Britt, D.T. [2000]. Icarus 145, 351–368). Taken together, these show deeper 3-μm band depths (of order 3–5%) in the southern hemisphere of Lutetia, and shallower band depths (of order 2% or less) in the north. Such variation is consistent with observations at shorter wavelength by previous workers (Nedelcu, D.A. et al. [2007]. Astron. Astrophys. 470, 1157–1164; Lazzarin, M. et al. [2010]. Mon. Not. R. Astron. Soc. 408, 1433–1437), who observed hemispheric-level variations from C-like spectra to X-like spectra.While the shallowness of absorption bands on Lutetia hinders identification of its surface composition, goethite appears plausible as a constituent in its southern hemisphere (Beck, P., Quirico, E., Sevestre, D., Montes-Hernandez, G., Pommerol, A., Schmitt, B. [2011]. Astron. Astrophys. 526, A85–A89). Mathematical models of space weathered goethite are most consistent with Lutetia’s southern hemisphere spectrum, but more work and further observations are necessary to confirm this suggestion.