Occurrence of Almandine, and Its Implications for Ancient High Temperature Activity of the Orakeikorako Geothermal Field, Taupo Volcanic Zone, New Zealand

Abstract: Exploration drilling at Orakeikorako provides information on the hydrologic and thermal regime of the geothermal system, which is presently as high as 265C. The presence of almandine in Drillhole OK–1, at 1312. 5m drilled depth, is the only known occurrence of hydrothermal garnet in an active geothermal system from New Zealand. The formation temperature of the almandine, is not consistent with measured (bore) temperatures, but does coincide with fluid inclusion data and temperatures inferred from other secondary minerals, which suggest it formed at >240C, and possibly as much as 310C. Almandine is an important mineral geothermometer in active hydrothermal systems, and implications for its occurrence should not be discounted in fossil (mineralised) epithermal-type hydrothermal systems.     

Transient sea-ice polynya forced by oceanic flow variability

In the Weddell Sea during the winters of 1974–1976 a significant opening in the sea-ice cover occurred in the vicinity of a large bathymetric feature — the Maud Rise seamount. The event is commonly referred to as the Weddell Polynya. Aside from such a large-scale, relatively persistent polynya in the Weddell Sea, transient, small-scale polynya can also appear in the sea-ice cover at various times throughout the winter and at various locations with respect to the Maud Rise. The underlying causes for the occurrence of such transient polynya have not been unambiguously identified. We hypothesize that variations in the mean ocean currents are one major contributor to such variability in the sea-ice cover. Analysis of the sea-ice equations with certain idealized patterns of ocean currents serving as forcing is shown to lead to Ekman transports of sea ice favorable to the initiation of transient polynya. Aside from the actual spatial pattern of the idealized ocean currents, many other factors need also be taken into account when looking at such transient polynya. Two other such factors discussed are variations in the sea-ice thickness field and the treatment of the sea-ice rheology. Simulations of a sea-ice model coupled to a dynamical ocean model show that the interaction of (dynamical) oceanic currents with large-scale topographic features, such as the Maud Rise, does lead to the formation of transient polynya, again through Ekman transport effects. This occurs because the seamount has a dynamic impact on the three-dimensional oceanic flow field all the way up through the water column, and hence on the near surface ocean currents that are in physical contact with the sea ice. Further simulations of a sea-ice model coupled to a dynamic ocean model and forced with atmospheric buoyancy fluxes show that transient polynya can be enhanced when atmospheric cooling provides a positive feedback mechanism allowing preferential open-ocean convection to occur. The convection, which takes hold at sites where transient polynya have been initiated by sea-ice–ocean stress interaction, has an enhancing effect arising from the convective access to warmer, deeper waters. To investigate all of these effects in a hierarchical manner we use a primitive equation coupled sea-ice–ocean numerical model configured in a periodic channel domain with specified atmospheric conditions. We show that oceanic flow variability can account for temporal variability in small-scale, transient polynya and thus point to a plausible mechanism for the initiation of large-scale, sustained polynya such as the Weddell Polynya event of the mid 1970s.     

El Niño–Southern Oscillation diversity and Southern Africa teleconnections during Austral Summer

Climate Dynamics - A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–Southern Oscillation events of 1950–2010, which have occurred...     

Impacts of Coastal Development on the Ecology of Tidal Creek Ecosystems of the US Southeast Including Consequences to Humans

Upland areas of southeastern United States tidal creek watersheds are popular locations for development, and they form part of the estuarine ecosystem characterized by high economic and ecological value. The primary objective of this work was to define the relationships between coastal development, with its concomitant land use changes and associated increases in nonpoint source pollution loading, and the ecological condition of tidal creek ecosystems including related consequences to human populations and coastal communities. Nineteen tidal creek systems, located along the southeastern US coast from southern North Carolina to southern Georgia, were sampled in the summer, 2005 and 2006. Within each system, creeks were divided into two primary segments based upon tidal zoning—intertidal (i.e., shallow, narrow headwater sections) and subtidal (i.e., deeper and wider sections)—and then watersheds were delineated for each segment. Relationships between coastal development, concomitant land use changes, nonpoint source pollution loading, the ecological condition of tidal creek ecosystems, and the potential impacts to human populations and coastal communities were evaluated. In particular, relationships were identified between the amount of impervious cover (indicator of coastal development) and a range of exposure and response measures including increased chemical contamination of the sediments, increased pathogens in the water, increased nitrate/nitrite levels, increased salinity range, decreased biological productivity of the macrobenthos, alterations to the food web, increased flooding potential, and increased human risk of exposure to pathogens and harmful chemicals. The integrity of tidal creeks, particularly the headwaters or intertidally dominated sections, was impaired by increases in nonpoint source pollution associated with sprawling urbanization (i.e., increases in impervious cover). This finding suggests that these habitats are valuable early warning sentinels of ensuing ecological impacts and potential public health and flooding risk from sprawling coastal development. The results also validate the use of a conceptual model with impervious cover thresholds for tidal creek systems in the southeast region.     

Controls on slope‐to‐channel fine sediment connectivity in a largely ice‐free valley,Hoophorn Stream,Southern Alps,New Zealand

There has been little work to date into the controls on slope‐to‐channel fine sediment connectivity in alpine environments largely ice‐free for most of the Holocene. Characterization of these controls can be expected to result in better understanding of how landscapes “relax” from such perturbations as climate shock. We monitored fine sediment mobilization on a slope segment hydrologically connected to a stream in the largely ice‐free 8·3 km² Hoophorn Valley, New Zealand. Gerlach traps were installed in ephemeral slope channels to trap surficial material mobilized during rainfall events. Channel sediment flux was measured using turbidimeters above and below the connected slope, and hysteresis patterns in discharge‐suspended sediment concentrations were used to determine sediment sources. Over the 96 day measurement period, sediment mobilization from the slope segment was limited to rainfall events, with increasingly larger particles trapped as event magnitude increased. Less than 1% of the mass of particles collected during these events was fine sediment. During this period, 714 t of suspended sediment was transported through the lower gauging station, 60% of it during rainfall events. Channel sediment transfer patterns during these events were dominated by clockwise hysteresis, interpreted as remobilization of nearby in‐channel sources, further suggesting limited input of fine sediment from slopes in the lower valley. Strong counterclockwise hysteresis, representing input of fine sediment from slope segments, was restricted to the largest storm event (JD2 2009) when surfaces in the upper basin were activated. The results indicate that the slopes of the lower Hoophorn catchment are no longer functioning as sources of fine sediment, but rather as sources of coarse material, with flux rates controlled by the intensity and duration of rainfall events. Although speculative, these findings suggest a shift to a coarse sediment dominated slope‐to‐channel transfer system as the influence of pre‐Holocene glacial erosion declines. Copyright © 2011 John Wiley & Sons, Ltd.     

Core lithologies and their constraints on gas-hydrate occurrence in the East Sea, offshore Korea: Results from the site UBGH1-9

Drilling at the site UBGH1-9, offshore Korea in 2007, revealed varied gas-hydrate saturation with depth and a wide variety of core litholgies, demonstrating how the variations in the lithology are linked with those in gas-hydrate saturation and morphology. Discrete excursions to low chlorinity values from in situ background chlorinity level occur between 63 and 151 mbsf. In this occurrence zone, gas-hydrate saturations estimated from the low chlorinity anomalies range up to 63.5% of pore volume with an average of 9.9% and do not show a clear depth-dependent trend. Sedimentary facies analysis based on grain-size distribution and sedimentary structures revealed nine sediment facies which mainly represent hemipelagic muds and fine- to medium-grained turbidites. According to the sedimentary facies distribution, the core sediments are divided into three facies associations (FA): FA I (0–98 mbsf) consisting mainly of alternating thin- to medium-bedded hemipelagic mud and turbidite sand or mud beds, FA II (98–126 mbsf) dominated by medium- to very thick-bedded turbidite sand or sandy debris flow beds, and FA III (126–178 mbsf) characterized by thick hemipelagic mud without intervening discrete turbidite sand layers. Thermal anomalies from IR scan, mousse-like and soupy structures on split-core surfaces, non-destructive measurements of pressure cores, and comparison of gas-hydrate saturations with sand contents of corresponding pore-water squeeze cakes, collectively suggest that the gas hydrate at the site UBGH1-9 generally occurs in two different types: “pore-filling” type preferentially associated with thin- to medium-turbidite sand beds in the FA I and “fracture-filling” type which occurs as hydrate veins or nodules in hemipelagic mud of the FA III. Gas-hydrate saturation in the FA II is generally anomalously low despite the dominance of turbidite sand or sandy debris flow beds, suggesting insufficient methane supply.     

SOUSA: the Swift Optical/Ultraviolet Supernova Archive

This paper studies the motion of an infinitesimal mass in the framework of Robe’s circular restricted three-body problem in two cases; the first case is when the hydrostatic equilibrium figure of the first primary is an oblate spheroid, the shape of the second primary is considered as an oblate spheroid with oblateness coefficients up to the second zonal harmonic, while the first primary is a Roche ellipsoid in the second case and the full buoyancy of the fluid is taken into account. In case one; it is observed that there are two axial libration points on the line joining the centres of the primaries, points on the circle within the first primary are also libration points under certain conditions. It is further found that the first axial point is stable, while the second one is conditionally stable, and the circular points are unstable. It is found in case two that there is exist only one libration point (0,0,0) this point is stable.