The role of forcing and internal dynamics in explaining the “Medieval Climate Anomaly”

Proxy reconstructions suggest that peak global temperature during the past warm interval known as the Medieval Climate Anomaly (MCA, roughly 950–1250 AD) has been exceeded only during the most recent decades. To better understand the origin of this warm period, we use model simulations constrained by data assimilation establishing the spatial pattern of temperature changes that is most consistent with forcing estimates, model physics and the empirical information contained in paleoclimate proxy records. These numerical experiments demonstrate that the reconstructed spatial temperature pattern of the MCA can be explained by a simple thermodynamical response of the climate system to relatively weak changes in radiative forcing combined with a modification of the atmospheric circulation, displaying some similarities with the positive phase of the so-called Arctic Oscillation, and with northward shifts in the position of the Gulf Stream and Kuroshio currents. The mechanisms underlying the MCA are thus quite different from anthropogenic mechanisms responsible for modern global warming.     

Enthalpies of proton adsorption onto Bacillus licheniformis at 25, 37, 50, and 75 °C

Understanding bacterial surface reactivity requires many different lines of investigation. Toward this end, we used isothermal titration calorimetry to measure heats of proton adsorption onto a Gram positive thermophile Bacillus licheniformis at 25, 37, 50, and 75 °C. Proton adsorption under all conditions exhibited exothermic heat production. Below pH 4.5, exothermic heats decreased as temperature increased above 37 °C; above pH 4.5, there was no significant difference in heats evolved at the temperatures investigated. Total proton uptake did not vary significantly with temperature. Site-specific enthalpies and entropies were calculated by applying a 4-site, non-electrostatic surface complexation model to the calorimetric data. Interpretation of site-specific enthalpies and entropies of proton adsorption for site L₁, L₂, and L₄ are consistent with previous interpretations of phosphoryl, carboxyl, and hydroxyl/amine site-identities, respectively, and with previous calorimetric measurements of proton adsorption onto mesophilic species. Enthalpies and entropies for surface site L₃ are not consistent with the commonly inferred phosphoryl site-identity and are more consistent with sulfhydryl functional groups. These results reveal intricacies of surface reactivity that are not detectable by other methods.     

Magma accumulation rates and thermal histories of plutons of the Sierra Nevada batholith,CA

Zircon U–Pb geochronology results indicate that the John Muir Intrusive Suite of the central Sierra Nevada batholith, California, was assembled over a period of at least 12 Ma between 96 and 84 Ma. Bulk mineral thermochronology (U–Pb zircon and titanite, ⁴⁰Ar/³⁹Ar hornblende and biotite) of rocks from multiple plutons comprising the Muir suite indicates rapid cooling through titanite and hornblende closure following intrusion and subsequent slow cooling through biotite closure. Assembly of intrusive suites in the Sierra Nevada and elsewhere over millions of years favors growth by incremental intrusion. Estimated long-term pluton assembly rates for the John Muir Intrusive Suite are on the order of 0.001 km³ a⁻¹ which is inconsistent with the rapid magma fluxes that are necessary to form large-volume magma chambers capable of producing caldera-forming eruptions. If large shallow crustal magma chambers do not typically develop during assembly of large zoned intrusive suites, it is doubtful that the intrusive suites represent cumulates left behind following caldera-forming eruptions.     

Agriculturally induced environmental changes in the Burren Karst,Western Ireland

 The Burren plateau of County Clare is a classic example of a plateau karst characterised by patchy, thin soils, a lack of defined surface drainage, and in the instance of the Burren, a rich floristic, archaeological and landscape heritage. Since accession to the European Union and, in particular, as a result of Common Agricultural Policy initiatives, attempts have been made to raise farm incomes and to modernise agriculture in areas such as the Burren. Due to the encouragement of land reclamation and silage production has largely replaced hay farming for winter fodder. These changes pose a threat to groundwater quality by enhancing the leaching of artificial fertilizers or of organic pollutants. The Burren is highly vulnerable to water pollution from silage effluent because of its thin or absent soils and its highly karstified aquifers. A full survey of silage clamps was made in the summers of 1991 and 1992. For each site data were collected to derive the following: mass of silage, effluent produced, hazard rating of site to groundwater, likely discharge of effluent to groundwater and groundwater dilution index. About 60% of clamps were considered to be high risk and 23% medium risk. About 92% of all sites probably allow some effluent to infiltrate groundwater. Received: 1 June 1995 · Accepted: 4 December 1995     

The properties of cataclysmic variables in photometric Hα surveys

We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission-line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern galactic plane (IPHAS) will soon provide r ',  i ' and narrow-band Hα measurements down to   r '≃ 20  for all northern objects between  − 5° < b < +5°  . IPHAS thus provides a unique resource, both for studying the emission-line properties of known CVs and for constructing a new CV sample selected solely on the basis of Hα excess. Our goal here is to carry out the first task and prepare the way for the second. In order to achieve this, we analyse data on 19 CVs already contained in the IPHAS data base and supplement this with identical observations of 52 CVs outside the galactic plane.
Our key results are as follows: (i) the recovery rate of known CVs as Hα emitters in a survey like IPHAS is ≃70 per cent; (ii) of the ≃30 per cent of CVs which were not recovered ≃75 per cent were clearly detected but did not exhibit a significant Hα excess at the time of our observations; (iii) the recovery rate depends only weakly on CV type; (iv) the recovery rate depends only weakly on orbital period; (v) short-period dwarf novae tend to have the strongest Hα lines. These results imply that photometric emission-line searches provide an efficient way of constructing CV samples that are not biased against detection of intrinsically faint, short-period systems.