Finite volume discretization with imposed flux continuity for the general tensor pressure equation

We present a new family of flux continuous, locally conservative, finite volume schemes applicable to the diagonal and full tensor pressure equations with generally discontinuous coefficients. For a uniformly constant symmetric elliptic tensor field, the full tensor discretization is second order accurate with a symmetric positive definite matrix. For a full tensor, an _M-matrix with diagonal dominance can be obtained subject to a sufficient condition for ellipticity. Positive definiteness of the discrete system is illustrated. Convergence rates for discontinuous coefficients are presented and the importance of modeling the full permeability tensor pressure equation is demonstrated.     

Variability of C02 distributions and sea-air fluxes in the central and eastern equatorial Pacific during the 199–1994 El Nin˜o

As part of the U.S. JGOFS Program and the NOAA Ocean-Atmosphere Carbon Exchange Study (DACES), measurements of C02 partial pressure were made in the atmosphere and in the surface waters of the central and eastern equatorial Pacific during the boreal spring and autumn of 1992, the spring of 1993, and the spring and autumn of 1994. Surface-water pC0₂ data indicate significant diurnal, seasonal, and interannual variations. The largest variations were associated with the 1991–1994 ENSO event, which reached maximum intensity in the spring of 1992. The lower values of surface-water ΔpC0₂ observed during the 1991–1994 ENSO period were the result of the combined effects of both remotely and locally forced physical processes. The warm pool, which reached a maximum eastward extent in January-February of 1992, began in September of 1991 as a series of westerly wind events lasting about 30 days. Each wind event initiated an eastward propagating Kelvin wave which caused a deepening of the thermocline. By the end of January 1992 the thermocline was at its maximum depth, so that the upwelled water was warm and C0₂-depleted. In April of the same year, the local winds were weaker than normal, and the upwelling was from shallow depths. These changes resulted in a lower-than-normal C02 flux to the atmosphere. The results show that for the one-year period from the fall of 1991 until the fall of 1992, approximately 0.3 GtC were released to the atmosphere; 0.6 GtC were released in 1993, and 0.7 GtC in 1994, in good agreement with the model results of Ciais et al. [Science,269,1098–1102;J. Geophys. Res.,100, 5051–5070]. The net reduction of the ocean-atmosphere C02 flux during the 1991–1994 El Nifio was on the order of 0.8 – 1.2 GtC. Thus, the total amount of C02 sequestered in the equatorial oceans during the prolonged 1991–1994 El Nin˜o period was about 25% higher than the severe El Nin˜o of 1982–1983.     

A direct recording ocean bottom seismometer

We have designed a simple, cheap and reliable ocean-bottom seismometer. Signals from three-component geophones are recorded directly on magnetic tape running continuously at a speed of 1 mm s¹. Time reference is derived from a temperature-compensated quartz crystal oscillator and encoded on a fourth channel as an amplitude modulation of a 20 Hz carrier. A bipolar square-root signal-compression scheme doubles the tape dynamic range to 80 db, and the available bandwidth is 2 to 100 Hz. Tape and batteries are capable of 500-hr operation, and the unique magnetic release comes close to being a fail-safe system. A heavy, high-drag concrete anchor shaped like a flower-pot provides easy launching, fast stable descent and good coupling to the ocean floor. We have had numerous successful field emplacements which have yielded good earthquake and shot-refraction data.     

Dispersal patterns of the eggs and larvae of spring-spawning fish in the Irish Sea, UK

Many marine species produce pelagic propagules which, because of their life-history characteristics and the local hydrodynamics, can disperse considerable distances from the point of release. Distances travelled are affected by factors such as: release time and location, egg and larval stage duration, local environmental conditions and active swimming and settlement behaviours. Understanding such dispersal patterns is important for the design of effective ecosystem-conservation strategies. We used a regional scale, coupled physical-biological model for the Irish Sea to simulate the possible dispersal of eggs and larvae of five species of fish with contrasting early life histories (cod Gadus morhua, plaice Pleuronectes platessa, witch Glyptocephalus cynoglossus, sprat Sprattus sprattus and pogge Agonus cataphractus). The hydrodynamic model was forced with meteorological data for 1995, a year when extensive plankton surveys were conducted in the Irish Sea. A particle tracking method featuring particle release (spawning) and species-dependent particle development and behaviour was then run based on flow and temperature fields from the hydrodynamical model. Modelled larval distributions and settlement areas corresponded favourably with observations from field sampling. The settlement destinations (or onset of shoaling for sprat) were affected both by their initial spawning location and by the species-specific development rates and behaviours coded into the model. Eggs and larvae typically remained within 160 km of their spawning origin, although a minority travelled up to 300 km. Even in a relatively enclosed sea such as the Irish Sea, fish eggs and larvae can be dispersed over 100s of km. This provides a major challenge for the design of effective spatial management strategies if it is necessary to protect a species across its life-history stages. Further progress in the design of effective conservation measures for species or communities will need an integrated approach taking account of key aspects of early life history and behaviour.     

The petroleum geology of the Unst Basin, North Sea

The Unst Basin is situated in the northern North Sea between the East Shetland Basin and the Shetland Isles. The basin is essentially a three-armed, Permo-Triassic fault-controlled basin containing up to 3600 m of red-beds. This is overlain by a westerly thickening Jurassic and early Cretaceous sequence, the stratigraphy of which is very similar to that of the East Shetland Basin. In particular, the Brent Group (140 m), Humber Group (685 m) and Cromer Knoll Group (300 m) are well represented.As a result of Laramide uplift of the area, the thick Upper Cretaceous and Palaeocene strata of the East Shetland Basin are absent from the Unst Basin. This uplift resulted in substantial erosion within the Unst Basin providing the major source for Palaeocene sands in the Viking Graben and the Faeroes Basin. Late Palaeocene and younger Tertiary strata transgress westwards across this erosion surface.Petroleum exploration within the basin culminated in the drilling of two exploration wells. These wells encountered potential reservoir and source rocks in the Jurassic section. However, geochemical analyses indicate these source rocks are immature for hydrocarbon generation within the Unst Basin. It is concluded that the Unst Basin has a low petroleum potential.     

Radio AGN in the local universe: unification,triggering and evolution

Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN (\(L_{1.4\,\mathrm{GHz}} > 10^{24}\) W \(\hbox {Hz}^{-1}\)) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts (\(z < 0.7\)), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff–Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.     

Assessing Possible Impacts of Climate Change on Species Important for Forestry in Vietnam

The likely effects on two tree species of a range of scenarios of climatic and atmospheric change expected by the year 2050 are investigated using a climatic mapping program, a simple simulation model and a process-based simulation model. Styrax tonkinensis is a native species for which relatively little information is available. Acacia mangium is an introduced species, which is important for pulp production in several other countries, and for which there is considerable information for growth and utilization. A climatic mapping program is used to show areas which may be suitable for these species under present and predicted conditions. Two simulation models are used to investigate likely effects on productivity of the two species for a range of climatic change scenarios for Hanoi and Ho Chi Minh City. The estimated changes in production are predicted to be relatively small, though uncertainities associated with the simulations are quite high. However, the models highlight areas where more data are needed and also suggest some key regions in Vietnam which would be worth monitoring to detect early signs of the effects of climatic and atmospheric change.     

Surge in sulphur and halogen degassing from Ambrym volcano,Vanuatu

Volcanoes provide important contributions to atmospheric budgets of SO₂ and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18–270 kg s^-1 of SO₂, and 62–110 g s^-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8–14 and ~27–50 kg s^-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO₂ output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.     

The state of water resources in major Mediterranean islands

This work analyses the state of water resources in six Mediterranean islands: Corsica, Crete, Cyprus, Mallorca, Malta and Sicily. The analysis is focused on the prevailing social, economic and hydroclimatological characteristics of these islands in order to identify the main common features affecting water availability, demand and use. A detailed analysis of the state of water resources in all the considered islands has been carried out. A background of current conditions relating to freshwater availability, quality and use has been established. Different strategies to face water scarcity and enhance water quality in theislands have been assessed in a context of climate change which is a common threat. The identification of similar problems for all the islands highlights the importance of strengthening inter-islands co-operation in the field of sustainable water resources management.