Comparative analysis of relationships between NLDAS‐2 forcings and model outputs

This study reports results from an analysis of the relationship between atmospheric forcing and model‐simulated water and energy fluxes for the North American Land Data Assimilation System Project Phase 2 (NLDAS‐2). The relationships between mean monthly precipitation and total runoff are stronger in the Sacramento (SAC) and variable infiltration capacity (VIC) models, which grew out of the hydrological community, than in the Noah and Mosaic models, which grew out of the soil‐vegetation‐atmosphere transfer (SVAT) community. The reverse is true for the relationship between mean monthly precipitation and evapotranspiration. In addition, surface energy fluxes in VIC are less sensitive to model forcing (except for air temperature) than those in the Noah and Mosaic model. Notwithstanding these general conclusions, the relationships between forcings and model‐simulated water and energy fluxes for all models vary for different seasons, variables, and regions. These findings will ultimately inspire a combination of SVAT‐type model energy components with hydrological model water components to develop a SVAT‐hydrology model to improve both evapotranspiration and total runoff simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

Application of Laser Ablation ICP-MS to U-Th-Pb Dating of Monazite

Recent advances in laser ablation ICP-MS techniques allow accurate U-Th-Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real-time mass bias correction via nebulisation of a solution containing enriched ²³³U and natural Tl isotopes. The Tl-U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured ²⁰⁵Tl/²³³U ratios in the tracer solution allow direct measurement of ²³⁵U in monazite. Combined with high-sensitivity laser ablation ICP-MS measurements, direct measurement of ²³⁵U particularly improves the precision of U-Pb dating of young monazites. Correction for laser-induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count-rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP-MS technique more flexible for in situ U-Th-Pb analysis.     

Changes in phytoplankton following nitrate and phosphate additions to large enclosures in Marion Lake,British Columbia

The addition of nitrate, phosphate and a nitrate phosphate combination to replicated wooden enclosures in Marion Lake resulted in significant increases in primary productivity and algal standing crop in each of the three types of treated enclosures. This indicated that no single nutrient is likely to simultaneously limit the growth of all phytoplankton species present at any one time in the lake epilimnion. The relevance of this to the detergent controversy is discussed. Canadian Contribution to the International Biological Programme No. CCIBP 208.     

The relationships between the velocities,attenuations and petrophysical properties of reservoir sedimentary rocks1

We have measured the velocities and attenuations of compressional and shear waves in 29 water-saturated samples of sandstones and shales at a confining pressure of 60 MPa and at frequencies of about 0.85 MHz. The measurements were made using a pulse echo method in which the samples (diameter 5 cm, length 1.5 cm to 2.5 cm) were placed between perspex buffer rods inside a high-pressure cell. The velocity of each seismic wave was determined from the traveltime difference of equivalent phase points (corrected for diffraction effects) of the signals reflected from the top and from the base of each sample. Attenuation was determined in a similar way by comparison of the diffraction corrected amplitudes of the signals. The attenuation data are presented as ‘quality factors’: Q_p and Q_s for compressional and shear waves respectively. The results show that Q_s is strongly correlated with V_s, that Q_p is weakly correlated with V_p, and that Q_p is strongly correlated with Q_s. Q_p is strongly dependent on the volume percentage of the assemblage of intra-pore minerals, whether they are clays or carbonates. It is concluded that the attenuation mechanism is due to the local fluid flow arising from the differential dilation of the solid rock frame and the intra-pore mineral assemblage, which is a result of their very different elastic moduli.     

Kaersutite-peridotite inclusions and kindred megacrysts in basanitic lavas,Grand Canyon,Arizona

Essentially two types of ultramafic inclusions occur in the basanitic lavas and ejecta deposits of the northwestern Grand Canyon, Arizona. Abundant, olivine-rich nodules contain an emerald green, chrome-rich diopside and chrome-rich spinels. A much less common group of inclusions generally containing poikilitic kaersutite have more variable modal compositions, more variable but iron-rich and chrome-poor mineral compositions, and are characterized by the presence of a titaniferous clinopyroxene which appears black in hand specimen. The nature and petrologic significance of these black clinopyroxene-bearing inclusions, together with megacrysts of kaersutite and black clinopyroxene, are discussed in this paper.Petrographic aspects indicate an origin as cumulates of fractionating basaltic magma. Compositions of pyroxenes suggest high pressures of crystallization. The co-precipitation of orthopyroxene, clinopyroxene, olivine and Mg-spinel from what in all probability was under-saturated magma, together with the total absence of feldspar as a cumulate or intercumulate phase, is compatible with crystallization near 10 kb, on the basis of quite limited experimental data on anhydrous basaltic compositions. Pressures of this sort are attained at depths close to the mantle-crust boundary in the western Grand Canyon. By way of comparison, cumulate-textured inclusions from central Nevada containing rare orthopyroxene, widespread plagioclase, and more Fe-enriched clinopyroxenes, kaersutites, olivines and spinels are postulated to have crystallized at lower temperatures (or at a more advanced stage of fractionation) and possibly at lower pressures.Numerous occurrences, worldwide, of kaersutite-bearing inclusions, always in undersaturated host rocks, have recently been reported. Compositionally, the kaersutites are quite uniform, whether coexistent with pyropic garnet-clinopyroxene (Kakanui, New Zealand), with ortho-pyroxene-clinopyroxene-olivine-Mg spinel (Grand Canyon), or with plagioclase-clinopyroxene-olivine-magnetite. The last assemblage is found in shallow-seated igneous bodies of alkalic, mafic composition, as well as in inclusions within basaltic rocks. These occurrences imply the precipitation of kaersutite amphibole over a broad range of pressures, and as high as those prevailing in the upper mantle.