Antarctic circumpolar modes in a coupled ocean–atmosphere model

Eastward-propagating patterns in anomalous potential temperature and salinity of the Southern Ocean are analyzed in the output of a 1000-year simulation of the global coupled atmosphere–ocean GCM ECHO-G. Such features can be associated with the so-called Antarctic Circumpolar Wave (ACW). It is found that time–longitude diagrams that have traditionally been used to aid the visualization of the ACW are strongly influenced by the width of the bandpass time filtering. This is due to the masking of considerable low-frequency variability that occurs over a broad range of time scales. Frequency–wavenumber analysis of the ACW shows that the eastward-propagating waves do have preferred spectral peaks, but that both the period and wavenumber change erratically when comparing different centuries throughout the simulation. The variability of the ACW on a variety of time scales from interannual to centennial suggests that the waiting time for a sufficient observational record to determine the time scale of variability of the real world ACW (and the associated decadal time scale predictability of climate for southern landmasses) will be a very long one.Responsible Editor: Dirk Olbers     

Can the nitrogen and carbon stable isotopes of the pygmy mussel,Xenostrobus securis, indicate catchment disturbance for estuaries in northern New South Wales, Australia?

The nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of the pygmy mussel,Xenostrobus securis, were determined for three estuaries with varying levels of catchment disturbance in northern New South Wales, Australia. The lower Manning River catchment supported the highest human population densities with 3% residential development and some livestock agriculture (41%); the Wallamba River catchment was mostly livestock agriculture (56%) while the Wallingat River catchment was mostly vegetated (79%). Mussels, estuarine particulate organic matter (POM), and livestock and human-derived waste were collected in two stages during the austral summers of 2001–2002 and 2002–2003 for dual carbon-nitrogen stable isotope analysis. The disturbed Manning and Wallamba River catchment mussels were enriched in¹⁵N by an average of 3.2‰ and 1.5‰, respectively, compared to the vegetated Wallingat River mussels. Mussel δ¹³C values ranged from −24.8‰ to −30.3‰ and showed an estuarine gradient becoming enriched with distance downstream within estuaries, but were unable to distinguish patterns in catchment disturbance between estuaries. The δ¹⁵N and δ¹³C values of POM showed a similar pattern to mussels, indicating a direct link between them within each estuary. A multiple regression model of mussel δ¹⁵N using the fractions of land used for livestock agriculture and residential development within 5 km zones from river networks to a distance equivalent to a tidal ellipse from sites explained 67% of the variation in mussel δ¹⁵N with 95% of the differences lying within 1.6‰ of observed values. Increasing fractions of land used for livestock agriculture depleted mussel δ¹⁵N values estimated by the regression equation, indicating the use of cow manure as a nutrient source with a value of 2.0‰. Increasing fractions of land used for residential development enriched estimated mussel δ¹⁵N, indicating the use of human-derived waste with a value of 20.8‰. Pygmy mussels are a useful long-term bio-indicator for the effects of anthropogenic catchment disturbance and nutrient enrichment in estuaries.     

Identifying characteristics of charge transfer transitions in minerals

Criteria used to identify Fe²⁺-Fe³⁺ and Fe²⁺-Ti⁴⁺ intervalence charge transfer absorption bands in electronic spectra are reviewed and compared to the characteristics of unperturbed Fe²⁺ crystal field bands and those that are intensified by interaction with Fe³⁺. Band energy is the least definitive diagnostic criterion. Changes in band intensity with temperature are also of limited value. Large widths are the most reliable characteristic of charge transfer bands. New optical absorption spectra are presented for euclase, as well as 80 K spectra of rockbridgeite, babingtonite and lazulite. Comparison of optical spectra to magnetic susceptibility measurements for rockbridgeite and babingtonite provides support for recent theories regarding the effect of magnetic coupling on the variation of charge transfer intensity with temperature.     

Magnitudes of detectable and localizable shocks in nw bohemia

Summary The effectiveness of recording seismic phenomena in the Kruné hory (Mts.) region in NW Bohemia by selected stations in the CSR, GDR and Poland has been estimated. Magnitude isolines of the weakest earthquakes, which can be localized and detected with an 0.9 probability, were calculated on the basis of the level of seismic disturbances at the individual stations and of the empirical dependence of the attenuation of seismic waves with distance.

---

a a mum umauu uu u amu ¶rt; ana¶rt; uu uau mauu a mumuu , u a a uu n a m¶rt; mau u nuu auumu amau uu m amu u auma uuuu aum¶rt; a a mu, m mm 0.9 auuam u aum.

     

Turbulence Structure in the Wake Region of a Meteorological Tower

A meteorological tower significantly modifies the air flow, the mean windspeed and wind direction as well as the turbulencestructure of the air. Suchchanges can be noticed in particular in the wake region of the tower.Measurementson the 200 m tower ofForschungszentrum Karlsruhewere carried outusing Solent sonic anemometers in the lee of the towerand cup anemometers on both sides.In the wake region, spectral energydensity is increased in the high-frequency range. Superposition of this disturbance spectrum on the undisturbedspectrum yields a `knee' in the resulting spectrum. In the case of low turbulence intensity with stable stratification,a plateau with a constant energy content is observed in front of the knee.This effect is caused by the new production of turbulence energy from the mean flow as well as by an energy transfer fromlarger to smaller vortices. Power spectra in strongly stable conditionsshow a more rapid decrease of intensity in the region where the inertialsubrange is expected.The relevant scales of wake turbulence are derived from the maximum of the disturbance spectrum.Locations of the high-frequency peak do not depend on atmospheric stability,but are controlled mainly by mean wind speed.Apart from the reduction of the mean wind speed, the spectra and cospectra exhibit a strong anisotropy for such cases.The results demonstrate the significant influence of a tower on turbulence spectra in the wake region.     

Isotopic evidence for the magmatic and tectonic histories of the Carolina terrane: implications for stratigraphy and terrane affiliation

Establishing the age and crustal nature of exotic terranes and their underlying basements helps to determine their paleogeographic origin and tectonic histories. We present U–Pb ages of zircons and Sm–Nd whole rock isotopic data for volcanic and plutonic rocks of the Carolina terrane, one of several peri-Gondwanan terranes that were accreted to the margins of the circum-Atlantic continents during the Paleozoic. Volcanism in this subduction-related arc culminated in the eruption of the Morrow Mountain rhyolite, at ca. 540 Ma; thus, magmatism in the Carolina terrane ceased at the beginning of the Cambrian. The presence of inherited zircons and non-juvenile depleted mantle model ages of Carolina slate belt rocks favor a basement that is, at least in part, composed of evolved continental crust. Ages of inherited xenocrystic zircons cluster at ca. 1000, 2100 and 2500 Ma. These ages, in addition to volcanism at ca. 618–540 Ma, correlate best with well-known tectonic events in present-day northern South America. Specifically, the Orinoquian-Sunsas, the Trans-Amazonian and the Central Amazonian orogenic zones are likely candidates for potential basement correlatives to the Carolina terrane. Sm–Nd isotopic signatures vary significantly, but permit assimilation of Orinoquian age (1000 Ma) crust by magmas derived from the depleted mantle in a subduction (arc-related) setting. Our findings are also consistent with proposed correlations between the Carolina terrane and Avalonia which is likewise believed to have formed along the northern margin of present-day South America.     

The shape of Fraught – urban – rural – the nation-state: tensions and dynamics

I argue that the tension between cities and nation states go through the countryside, or rural areas, at least in the U.S. Further, cities are decidedly constrained in their abilities to effectuate many of the changes associated with them: addressing climate change, economic inequality and more. What is missing is the way in which rural alienation from economic prosperity plays out politically.     

The planet formation imager

The Planet Formation Imager (PFI, www.planetformationimager.org) is a next-generation infrared interferometer array with the primary goal of imaging the active phases of planet formation in nearby star forming regions. PFI will be sensitive to warm dust emission using mid-infrared capabilities made possible by precise fringe tracking in the near-infrared. An L/M band combiner will be especially sensitive to thermal emission from young exoplanets (and their disks) with a high spectral resolution mode to probe the kinematics of CO and H₂O gas. In this paper, we give an overview of the main science goals of PFI, define a baseline PFI architecture that can achieve those goals, point at remaining technical challenges, and suggest activities today that will help make the Planet Formation Imager facility a reality.