Stable isotopes in the ostracod shell: a preliminary study

Oxygen and carbon isotope ratios of Recent ostracods from six localities are presented. The δO¹⁸ data are consistent with precipitation of the shells in isotopic equilibrium with seawater. although additional data are necessary to confirm equilibrium precipitation. No strong correlation between carbon isotope ratios and temperature or salinity were observed for ostracods.     

Characteristics of 3-dimensional earthquake ground motions

An orthogonal set of principal axes is defined for earthquake ground motions along which the component variances have maximum, minimum and intermediate values and the covariances equal zero. Corresponding axes are defined which yield maximum values for the covariances. The orthogonal transformations involved are identical in form to those used in the transformation of stress. Examination of real accelerograms reveals that the major principal axis points in the general direction of the epicentre and the minor principal axis is nearly vertical. It is concluded that artificially generated components of ground motion need not be correlated statistically provided they are directed along a set of principal axes.     

Residual currents in juan de Fuca strait

Abstract

We examine the residual (non‐tidal) flow in Juan de Fuca Strait on the west coast of Canada using current and bottom pressure data collected on cross‐channel sections in the summers of 1975 and 1984. A positive estuarine circulation was evident in both sections but was better defined at the mid‐strait section than at the outer section near the mouth of the strait. Magnitudes of the volume transports in both the upper and lower layers of the channel ranged from ～ 0.25 X 10 m s at the mid‐strait section to ～ 0.15 X 10 m s～ at the outer section. The method of geostrophic levelling (Garrett and Pétrie, 1981; Pétrie et al, 1988) is used to determine the relationship between the daily averaged long‐strait velocity component and the cross‐strait pressure difference. A statistically significant relationship, consistent with a cross‐strait geostrophic balance, is obtained between the time series of shallow currents and shallow bottom pressures at the mid‐strait section. The deep currents and cross‐strait pressure differences were correlated at both sections but, because of the placement of the pressure gauges and/or ageostrophic effects such as bottom friction, were not related through a simple geostrophic balance. Cross‐spectral analysis and the calculation of the current amplitude ratios (square root of the energy ratio between the deep and shallow currents) are used to examine the baroclinicity of the flow as a function of frequency. Results suggest that flow variability in Juan de Fuca Strait is strongly baroclinic and has marked cross‐channel structure throughout the low‐frequency band.     

A mathematical model of permeability alteration around wells

This paper presents an analytical solution of the permeability alteration problem around the wellbore. This alteration may be a permeability reduction due to drilling fluid invasion or mudcake formation around the wellbore. On the other hand, the alteration may be a permeability increase resulting from stimulation by acidizing the formation matrix around the well. This permeability discontinuity in a reservoir forms a composite reservoir system. With the composite model, both the degree and the radial extent of permeability alteration can be adequately predicted. The conventional skin concept is inadequate and physically unrealistic in most of these cases. This paper describes the application of an automatic weighted constrained least-squares parameter estimation technique and the analytical model for pressure transient analysis. The parameters of the composite reservoir system are determined from a match of the pressure transient data. The behaviour of the pressure transient in such composite systems is presented using the analytical solution.     

Jet Deflection by a Quasi-Steady-State Side Wind in the Laboratory

We present experimental data on the steady state deflection of a highly supersonic jet by a side-wind in the laboratory. The use of a long interaction region enables internal shocks to fully cross the jet, leading to the development of significantly more structure in the jet than in previous work with a similar setup (Lebedev et al., 2004). The ability to control the length of the interaction region in the laboratory allows the switch between a regime representing a clumpy jet or wind and a regime similar to a slowly varying mass loss rate. The results indicate that multiple internal oblique shocks develop in the jet and the possible formation of a second working surface as the jet attempts to tunnel through the ambient medium.     

Do paleoclimate proxies agree? A test comparing 19 late Holocene climate and sea‐ice reconstructions from Icelandic marine and lake sediments

Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP₂₅, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.     

Nonlinear bacterial load‐streamflow response on a marine beach

Bacterial concentration (Escherichia coli) is used as the key indicator for marine beach water quality in Hong Kong. For beaches receiving streamflow from unsewered catchments, water quality is mainly affected by local nonpoint source pollution and is highly dependent on the bacterial load contributed from the catchment. As most of these catchments are ungauged, the bacterial load is generally unknown. In this study, streamflow and the associated bacterial load contributed from an unsewered catchment to a marine beach, Big Wave Bay, are simulated using a modelling approach. The physically based distributed hydrological model, MIKE‐SHE, and the empirical watershed water quality model (Hydrological Simulation Program – Fortran) are used to simulate streamflow and daily‐averaged E. coli concentration/load, respectively. The total daily derived loads predicted by the model during calibration (June–July 2007) and validation (July–October 2008) periods agree well with empirical validation data, with a percentage difference of 3 and 2%, respectively. The simulation results show a nonlinear relationship between E. coli load and rainfall/streamflow and reveal a source limiting nature of nonpoint source pollution. The derived load is further used as an independent variable in a multiple linear regression (MLR) model to predict daily beach water quality. When compared with the MLR models based solely on hydrometeorological input variables (e.g. rainfall and salinity), the new model based on bacterial load predicts much more realistic E. coli concentrations during rainstorms. Copyright © 2014 John Wiley & Sons, Ltd.     

Stellar chromospheres,coronae, and winds (invited review)

Within the last few years there have been important advances in our understanding of the chromospheres, coronae, and winds of late-type stars. This progress has been the result of ultraviolet and X-ray observations obtained from space with theInternational Ultraviolet Explorer andEinstein satellites. In addition, ground-based astronomy has contributed much to synoptic studies of stellar activity. In this review I summarize some of the major recent developments in this field.Presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Geodetic constraints on active tectonics of the Western Mediterranean: Implications for the kinematics and dynamics of the Nubia-Eurasia plate boundary zone

We present GPS observations in Morocco and adjacent areas of Spain from 15 continuous (CGPS) and 31 survey-mode (SGPS) sites extending from the stable part of the Nubian plate to central Spain. We determine a robust velocity field for the W Mediterranean that we use to constrain models for the Iberia-Nubia plate boundary. South of the High Atlas Mountain system, GPS motions are consistent with Nubia plate motions from prior geodetic studies. We constrain shortening in the Atlas system to <1.5 mm/yr, 95% confidence level. North of the Atlas Mountains, the GPS velocities indicate Nubia motion with respect to Eurasia, but also a component of motion normal to the direction of Nubia-Eurasia motion, consisting of southward translation of the Rif Mountains in N Morocco at rates exceeding 5 mm/yr. This southward motion appears to be directly related to Miocene opening of the Alboran Sea. The Betic Mountain system north of the Alboran Sea is characterized by WNW motion with respect to Eurasia at ～1–2 mm/yr, paralleling Nubia-Eurasia relative motion. In addition, sites located in the Betics north of the southerly moving Rif Mountains also indicate a component of southerly motion with respect to Eurasia. We interpret this as indicating that deformation associated with Nubia-Eurasia plate motion extends into the southern Betics, but also that the Betic system may be affected by the same processes that are causing southward motion of the Rif Mountains south of the Alboran Sea. Kinematic modeling indicates that plate boundary geometries that include a boundary through the Straits of Gibraltar are most compatible with the component of motion in the direction of relative plate motion, but that two additional blocks (Alboran-Rif block, Betic Mountain block), independent of both Nubia and Eurasia are needed to account for the motions of the Rif and Betic Mountains normal to the direction of relative plate motion. We speculate that the southward motions of the Alboran-Rif and Betic blocks may be related to mantle flow, possibly induced by southward rollback of the subducted Nubian plate beneath the Alboran Sea and Rif Mountains.