Large phreatomagmatic vent complex at Coombs Hills, Antarctica: Wet, explosive initiation of flood basalt volcanism in the Ferrar-Karoo LIP

The Mawson Formation and correlatives in the Transantarctic Mountains and South Africa record an early eruption episode related to the onset of Ferrar-Karoo flood basalt volcanism. Mawson Formation rocks at Coombs Hills comprise mainly (≥80% vol) structureless tuff breccia and coarse lapilli tuff cut by irregular dikes and sills, within a large vent complex (>30 km²). Quenched juvenile fragments of generally low but variable vesicularity, accretionary lapilli and country rock clasts within vent-fill, and pyroclastic density current deposits point to explosive interaction of basalt with groundwater in porous country rock and wet vent filling debris. Metre-scale dikes and pods of coherent basalt in places merge imperceptibly into peperite and then into surrounding breccia. Steeply dipping to sub-vertical depositional contacts juxtapose volcaniclastic rocks of contrasting componentry and grainsize. These sub-vertical tuff breccia zones are inferred to have formed when jets of debris + steam + water passed through unconsolidated vent-filling deposits. These jets of debris may have sometimes breached the surface to form subaerial tephra jets which fed subaerial pyroclastic density currents and fall deposits. Others, however, probably died out within vent fill before reaching the surface, allowing mixing and recycling of clasts which never reached the atmosphere. Most of the ejecta that did escape the debris-filled vents was rapidly recycled as vents broadened via lateral quarrying of country rock and bedded pyroclastic vent-rim deposits, which collapsed along the margins into individual vents. The unstratified, poorly sorted deposits comprising most of the complex are capped by tuff, lapilli tuff and tuff breccia beds inferred to have been deposited on the floor of the vent complex by pyroclastic density currents. Development of the extensive Coombs Hills vent-complex involved interaction of large volumes of magma and water. We infer that recycling of water, as well as recycling of pyroclasts, was important in maintaining water supply for phreatomagmatic interactions even when aquifer rock in the vent walls lay far from eruption sites as a consequence of vent-complex widening. The proportion of recycled water increased with vent-complex size in the same way that the proportion of recycled tephra did. Though water recycling leaves no direct rock record, the volcaniclastic deposits within the vent complex show through their lithofacies/structural architecture, lithofacies characteristics, and particle properties clear evidence for extensive and varied recycling of material as the complex evolved. Editorial responsibility: J. Donnelly-Nolan     

Decadal- to interannual-scale source water variations in the Caribbean Sea recorded by Puerto Rican coral radiocarbon

Water that forms the Florida Current, and eventually the Gulf Stream, coalesces in the Caribbean from both subtropical and equatorial sources. The equatorial sources are made up of, in part, South Atlantic water moving northward and compensating for southward flow at depth related to meridional overturning circulation. Subtropical surface water contains relatively high amounts of radiocarbon (¹⁴C), whereas equatorial waters are influenced by the upwelling of low ¹⁴C water and have relatively low concentrations of ¹⁴C. We use a 250 year record of Δ¹⁴C in a coral from southwestern Puerto Rico along with previously published coral Δ¹⁴C records as tracers of subtropical and equatorial water mixing in the northern Caribbean. Data generated in this study and from other studies indicate that the influence of either of the two water masses can change considerably on interannual to interdecadal time scales. Variability due to ocean dynamics in this region is large relative to variability caused by atmospheric ¹⁴C changes, thus masking the Suess effect at this site. A mixing model produced using coral Δ¹⁴C illustrates the time varying proportion of equatorial versus subtropical waters in the northern Caribbean between 1963 and 1983. The results of the model are consistent with linkages between multidecadal thermal variability in the North Atlantic and meridional overturning circulation. Ekman transport changes related to tradewind variability are proposed as a possible mechanism to explain the observed switches between relatively low and high Δ¹⁴C values in the coral radiocarbon records.     

Luminescence dating of old (>70 ka) Chinese loess: A comparison of single-aliquot OSL and IRSL techniques

The applicability of two different approaches in the luminescence dating of old (>70 ka) Chinese loess is investigated. Both SAR-OSL ages obtained on 63–90 μm quartz grains and SAR-IRSL ages obtained on 4–11 μm polymineral grains, for samples collected from two sites in the Chinese Loess Plateau (Luochuan and Dongchuan) are presented. The characteristics of the luminescence signals stimulated by blue and infrared light are investigated in terms of dose response and dose recovery, and as a function of age. Additionally, anomalous fading measurements from the 410 nm IRSL emission in polymineral fine-grains are reported. An average value of g_2days amounting to 3% per decade was measured and seems to be independent of site location and age. For the samples from Luochuan, independent age control (pedostratigraphy and palaeomagnetism) is available. At both sites, the SAR-OSL ages are always lower than the SAR-IRSL ages after they have been corrected for anomalous fading. It seems that the quartz-based SAR-OSL ages are accurate for the younger ages, but that they underestimate the true age of deposition for loess that was deposited about 60–70 ka ago. The fading-corrected SAR-IRSL ages are in better agreement with the pedostratigraphic age control (75 and 130 ka) and allow dating beyond the quartz OSL range. Based on our results, we suggest that conventional SAR-OSL and SAR-IRSL protocols at these sites should be restricted to samples of ages not exceeding 40–50  and 100–120 ka, respectively.     

Outgoing long wave radiation variability from IR satellite data prior to major earthquakes

Our analysis of the continuous outgoing long wave earth radiation (OLR) indicates anomalous variations prior to a number of medium to large earthquakes. The most recent analysis of OLR is from the M9.0 Sumatra Andaman Islands mega trust event. We compared the reference fields for December 2001 to 2004 and found OLR anomalous values, > 80 W/m², (2σ) within the epicentral area on Dec 21, 2004, 5 days before the event. We used the NOAA/IR daily (one degree) and monthly (two and half degree) gridded data to differentiate between the global and seasonal variability and the transient local anomalies. The cause of such anomalies is not fully understood; one possible explanation is the existence of thermal outgoing radiation as a result of near ground air ionization and latent heat change due to change of air humidity and temperature. This phenomenon is hypothesized to be part of a relationship between tectonic stresses, electrochemical and thermodynamic processes in the atmosphere and increasing mid IR flux, all part of a family of electromagnetic (EM) phenomena related to earthquake activity. The time scale of the observed variations is a few weeks before the onset of the seismic event. In comparison with several years of data, the observed time-series preceding the earthquake had unusually high OLR. The OLR anomaly corresponds to a large area of ground coverage and coincides with the main epicentral zone. The significance of these observations is explored using data from most recent East Asian earthquake swarm of December 2004 and three other earthquakes.     

Economic consequences of consideration of permanence, leakage and additionality for soil carbon sequestration projects

This paper introduces, explains, and describes methods for addressing the issues of permanence, leakage, and additionality (PLA) of agricultural soil carbon sequestration (ASCS) activities at the project level. It is important to cast these as project-level issues, because they relate to the integrity and consistency of using location-specific ASCS projects as an offset against GHG emissions generated in other sectors (e.g., energy). The underlying objective is to understand and quantify what the net carbon benefits of an ASCS project are once we account for the fact that (1) the sequestered carbon may be stored impermanently, (2) the project may displace emissions outside the project boundaries (leakage), and (3) the project’s carbon sequestration may not be entirely additional to what would have occurred anyway under business-as-usual (no project) conditions. This article evaluates methods for identifying and estimating PLA and gauges the potential magnitude of these effects on the economic returns to a project. This work reflects ongoing collaborative efforts of the authors and Bruce McCarl (Texas A&M University), Allan Sommer, Jui-Chen Yang, and Laurel Clayton (RTI International), Sandra Brown (Winrock International), Ken Andrasko and Ben DeAngelo (US EPA), and various participants in the World Resources Institute/World Business Council workgroup to develop GHG project reporting protocols. All opinions, errors and omissions are those of the authors only.     

Post-Palaeozoic evolution of weathered landsurfaces in Uganda by tectonically controlled deep weathering and stripping

A model for the evolution of weathered landsurfaces in Uganda is developed using available geotectonic, climatic, sedimentological and chronological data. The model demonstrates the pivotal role of tectonic uplift in inducing cycles of stripping, and tectonic quiescence for cycles of deep weathering. It is able to account for the development of key landforms, such as inselbergs and duricrust-capped plateaux, which previous hypotheses of landscape evolution that are based on climatic or eustatic controls are unable to explain. Development of the Ugandan landscape is traced back to the Permian. Following late Palaeozoic glaciation, a trend towards warmer and more humid climates through the Mesozoic enabled deep weathering of the Jurassic/mid-Cretaceous surface in Uganda during a period of prolonged tectonic quiescence. Uplift associated with the opening South Atlantic Ocean terminated this cycle and instigated a cycle of stripping between the mid-Cretaceous and early Miocene. Deep weathering on the succeeding Miocene to recent (African) surface has occurred from Miocene to present but has been interrupted in the areas adjacent to the western rift where development of a new drainage base level has prompted cycles of stripping in the Miocene and Pleistocene.     

The Mars oxidant experiment (MOx) for Mars '96

The MOx instrument was developed to characterize the reactive nature of the martian soil. The objectives of MOx were: (1) to measure the rate of degradation of organics in the martian environment; (2) to determine if the reactions seen by the Viking biology experiments were caused by a soil oxidant and measure the reactivity of the soil and atmosphere: (3) to monitor the degradation, when exposed to the martian environment, of materials of potential use in future missions; and, finally, (4) to develop technologies and approaches that can be part of future soil analysis instrumentation. The basic approach taken in the MOx instrument was to place a variety of materials composed as thin films in contact with the soil and monitor the physical and chemical changes that result. The optical reflectance of the thin films was the primary sensing-mode. Thin films of organic materials, metals, and semiconductors were prepared. Laboratory simulations demonstrated the response of thin films to active oxidants.     

The kinematics of the ionized gas in the Circinus galaxy

The TAURUS-2 Fabry–Perot interferometer, mounted on the 3.9-m Anglo-Australian Telescope, has been used to observe the Circinus galaxy. We have mapped the intensity and velocity distribution of the ionized hydrogen in the galaxy using the Balmer series Hα spectral line.
The semiresolved core (observed with a seeing disc of 30 pc) appears amorphous in shape, which is commonly observed in Seyfert 2 galaxies. Its peak coincides with the core position measured in the radio continuum, suggesting that ionized gas surrounds a non-thermal source.
A circumnuclear ring or spiral of radius 220 pc and a rotational velocity of 350 km s⁻¹ (assuming circular motions) surrounds the core. The inclination angle of this feature, i =40°±10°, is less than that of the previously observed radio continuum disc. The velocity channel maps obtained for the Hα ring show that the kinematics resemble those of a rotating ring and the intensity displays a complex structure indicative of several, unresolved, H II regions. We believe the ring to represent a circumnuclear starburst.
Our Hα data also show the presence of the previously detected [O III ] ionization cone to the north-west of the core, measuring more than 400 pc in length. We suggest that the ionization cone lies in a different plane from that of the starburst ring and is directed away from us. Several kinematic components of the core are derived and we calculate an outflow velocity in excess of 150–200 km s⁻¹ for gas above the core of Circinus. We also present evidence for inflowing ionized gas at the centre of Circinus.
The correlation of the Hα and radio continuum features is discussed, as well as the possible presence of a starburst-driven superwind in the Circinus galaxy.     

Isotope geology of the bakircay porphyry copper prospect,northern turkey

Isotopic data for the Bakircay granodiorite porphyry, give a Late Eocene age for the development of the porphyry copper system. They suggest a close temporal and genetic relationship between igneous and hydrothermal activity, and indicate that magmatic-hydrothermal fluids produced potassic alteration and that meteoric fluids enriched in radiogenic⁸⁷Sr were responsible for propylitic alteration. The granodiorite porphyry is petrologically similar to porphyry copper-related intrusions from island arc and continental margin settings, which form a group with initial⁸⁷Sr/⁸⁶Sr ratios of less than 0. 7043, representing magmas produced in tectonic environments lacking any important component of old (i. e. Precambrian) continental material.