Sensitivity of the last glacial inception to initial and surface conditions

We investigate the sensitivity of simulations of the last glacial inception (LGI) with respect to initial (size of the Greenland ice sheet) and surface (state of ocean/vegetation) conditions and two different CO₂ reconstructions. Utilizing the CLIMBER-2 Earth system model, we obtain the following results: (a) ice-sheet expansion in North America at the end of the Eemian can be reduced or even completely suppressed when pre-industrial or Eemian ocean/vegetation is prescribed. (b) A warmer surrounding ocean and, in particular, a large Laurentide ice sheet reduce the size of the Greenland ice sheet before and during the LGI. (c) A changing ocean contributes much stronger to the expansion of the Laurentide ice sheet when we apply the CO₂ reconstruction according to Barnola et al. (Nature 329:408–414, 1987) instead of Petit et al. (Nature 399:429–436, 1999). (d) In the fully coupled model, the CO₂ reconstruction used has only a small impact on the simulated ice sheets but it does impact the course of the climatic variables. (e) For the Greenland ice sheet, two equilibrium states exist under the insolation and CO₂ forcing at 128,000 years before present (128 kyear BP); the one with an ice sheet reduced by about one quarter as compared to its simulated pre-industrial size and the other with nearly no inland ice in Greenland. (f) Even the extreme assumption of no ice sheet in Greenland at the beginning of our transient simulations does not alter the simulated expansion of northern hemispheric ice sheets at the LGI.     

A conceptual template for integrative human–environment research

Knowledge integration, the blending of concepts from two or more disciplines to create innovative new worldviews, is a key process in attempts to increase the sustainability of human activities on Earth. In this paper, we describe a ‘conceptual template’ that can be used to catalyse this process. The template comprises (a) a list of high-level concepts that capture the essential aspects of any significant human–environment problem, plus (b) broad lists of low-level basic concepts drawn from a range of disciplines. Our high-level concepts, which we call ‘conceptual clusters’, are labelled Dynamics & System, Organisation & Scale, Controlling Models, Management & Policy, Adaptation & Learning, and History. Many of the clustered, lower-level concepts are synonyms and thus provide possible connections between disciplines—for this reason we call them ‘nexus concepts’. We suggest that a conceptual template like that presented here can provide strong support to the initial phases of integrative research programs.     

3D seismic analysis of slope-confined canyons from the Plio–Pleistocene of the Ebro Continental Margin (Western Mediterranean)

This paper documents the importance of three‐dimensional (3D) seismic data for integrated stratigraphic–morphological analysis of slope systems. Furthermore, it contributes to the general understanding of the evolutionary mechanisms of slope‐confined submarine canyons on continental margins and their significance in a sequence stratigraphic framework. Recently acquired 3D seismic data from the Ebro Continental Margin (Western Mediterranean) have been used to study a series of remarkably well‐imaged submarine canyons in the Plio‐Pleistocene succession. Detailed mapping shows that these canyons are restricted to the slope, and thus can be compared with slope‐confined canyons observed on the present day seabed of many continental margins. The slope‐confined canyons are typically 0.5–2 km wide, 10–15 km long, and incise more than 50 m into the slope units. Their most striking characteristic is an upslope branching geometry in the head region involving up to three orders of bifurcation, with downslope development of a single incisional axis. The submarine canyons are characterized by a nested stacking pattern, undergoing alternating phases of cutting and filling. Limited parts of the upper and middle slope remain outside the canyon system, confined in sharp depositional ridges. The canyons are observed on closely spaced surfaces and exhibit a geometry that allowed the construction and discussion of a local sequence stratigraphic model for their evolution. In general, active incision of the canyons is observed at times throughout almost the entire cycle of base‐level change. However, erosional activity is more significant during the later stages of the relative sea level rise and the entire falling stage, with the timing of maximum erosion observed at the end of the cycle. The minimum erosional activity of the canyons is linked instead to the earliest part of the relative sea level rise.     

Effects of the herbicide diuron on the early life history stages of coral

The effects of the herbicide diuron on the early life history stages of broadcast spawning and brooding corals were examined in laboratory experiments. Fertilisation of Acropora millepora and Montipora aequituberculata oocytes were not inhibited at diuron concentrations of up to 1000 microg l(-1). Metamorphosis of symbiont-free A. millepora larvae was only significantly inhibited at 300 microg l(-1) diuron. Pocillopora damicornis larvae, which contain symbiotic dinoflagellates, were able to undergo metamorphosis after 24 h exposure to diuron at 1000 microg l(-1). Two-week old P. damicornis recruits on the other hand were as susceptible to diuron as adult colonies, with expulsion of symbiotic dinoflagellates (bleaching) evident at 10 microg l(-1) diuron after 96 h exposure. Reversible metamorphosis was observed at high diuron concentrations, with fully bleached polyps escaping from their skeletons. Pulse amplitude modulation (PAM) chlorophyll fluorescence techniques demonstrated a reduction in photosynthetic efficiency (Delta F/F(m)') in illuminated P. damicornis recruits after a 2 h exposure to 1 microg l(-1) diuron. The dark-adapted quantum yields (F(v)/F(m)) also declined, indicating chronic photoinhibition and damage to photosystem II.     

Application of biomarkers for assessing the biological impact of dredged materials in the Mediterranean: the relationship between antioxidant responses and susceptibility to oxidative stress in the red mullet (Mullus barbatus)

In the period 1997-2000, approximately 1,800,000 m3 of material dredged from the Port of Leghorn was discharged into a sea dumping site located 14 miles from the coast. The red mullet (Mullus barbatus) was used as a bioindicator species for monitoring the biological impact of these discharges on a geographical and temporal scale. Organisms were sampled over three years (1998-2000) at different stations and several biomarkers, both of exposure and effect, were analyzed. Bioavailability of specific classes of pollutants was evaluated by analyzing levels of metallothioneins, the activity of cytochrome P450 1A (CYPIA) and of glutathione S-transferases. Among biomarkers of effect, special attention was paid to the balance between prooxidant challenge and antioxidant defenses, and to the appearance of damage caused by oxidative stress. The analyses of the main components of the antioxidant system included superoxide dismutase, catalase, glutathione peroxidases, glutathione reductase, glyoxalase I and II, and total glutathione. These data were integrated with the measurement of total oxyradical scavenging capacity (TOSC) as an indication of the overall biological resistance to toxicity of different forms of oxyradicals (peroxyl radicals, hydroxyl radicals and peroxynitrite). Results indicated a biological impact in organisms sampled near the disposal site; the impact was particularly evident during 1999 and mainly related to organic chemicals such as PAH. Exposure to these pollutants also caused variations in the levels and activity of several antioxidants. The analysis of TOSC, however, revealed that the overall capacity of specific tissues of organisms to absorb various oxidants was not seriously compromised when challenged with increased prooxidant pressures. Variations of single antioxidants were useful in revealing early warning "biological responses", while integration with TOSC analyses indicated if such changes also reflect a more integrated and functional "biological effect" with possible consequences at the organisms level. The red mullet appears to be a useful sentinel species for a biomarker approach to monitoring impact caused by dredged materials.     

Ages of Detrital Zircon from Siliciclastic Successions South of the São Francisco Craton, Brazil: Implications for the Evolution of Proterozoic Basins

In this work we report ²⁰⁷Pb/²⁰⁶Pb LA-ICPMS ages of 152 detrital zircons from lower greenschist facies quartzites from Proterozoic basin successions of the southern border of the São Francisco Craton, southern Minas Gerais State, Brazil. These are the intracratonic São João del Rei basin, the intraplate continental margin Andrelândia basin, and the Serra do Ouro Grosso sequence, developed on a crystalline basement older than 1.8 Ga, and deformed and metamorphosed during the Brasiliano Orogeny, ca. 0.59–0.50 Ga. The data constrain both the ages of the sources and the interval of sedimentation. The detrital zircons of the Serra do Ouro Grosso sequence were derived predominantly from the erosion of a Neoarchean crust, 2.5–2.8 Ga old, with only one grain showing a Paleoproterozoic age (2, 245±83 Ma) older than the Transamazonian event. Zircons extracted from a shelf quartzite of the lowermost sequence of the São João del Rei basin indicate derivation from the 1.8–2.2 Ga Transamazonian crust, with subordinate contribution from the 2.5–2.9 Ga Archean crust. The 1, 809±41 Ma age is interpreted as the maximum limit for sedimentation in this basin. The results confirm the regional correlation with the Espinhaço Rift successions. The zircons extracted from an autochthonous quartzite of the Andrelândia sequence yielded ages in the 1.0–2.2 Ga range, with a modal class at 1.2–1.3 Ga. Only two of the forty analyzed zircons yield Archean ages. The youngest zircon yields 1, 086±85 Ma. The zircons from the allochthonous quartzite yield ages between 1.0–2.7 Ga, with a modal class at 2.1–2.2 Ga. Only five of 45 analyzed grains yield Archean ages. The youngest zircon has an age of 1, 047±77 Ma. The results indicate that the detrital sediments deposited during the second marine flooding event of the Andrelândia sedimentation were mainly derived from the erosion of Mesoproterozoic and Paleoproterozic rocks. The 1, 047±77 Ma age is interpreted as the maximum depositional age for the described association.     

A mechanical fluid-dynamical model for ground movements at Campi Flegrei caldera

We present here a consistent model, which explains the mechanisms of unrest phenomena at Campi Flegrei (Italy), both at short-term (years) and at secular scales. The model consists basically of two effects: the first one is related to the elastic response of the shallow crust to increasing pressure within a shallow magma chamber; the second involves the fluid-dynamics of shallow aquifers in response to increasing pressure and/or temperature at depth. The most important roles in the proposed model are played by the effect of lateral stress–strain discontinuities marking the inner caldera borders and by the response of the geothermal system to the increase of pressure and/or temperature coming from the magma chamber. The model takes into account most results of recent research, and it is able to explain in a unitary way most of geophysical observations recently collected at Campi Flegrei. Some new results, presented in this paper, explain the mechanism of generation of seismicity in terms of Coulomb stress changes, and the difference between secular and short-term deformations, in terms of the non linear effect of the bordering discontinuities. The coupled effects of magma chamber stresses with the dynamics of shallow fluids provide results for a semi-quantitative interpretation of observed ground deformation, seismicity and of their time evolution. The model has very important implications for the hazard assessment during unrest phenomena. It represents, for the part involving the fluid-dynamical response, the ideal continuation of the basic, fundamental models and intuitions of Oliveri del Castillo and coworkers (Oliveri del Castillo, A., Quagliariello, M.T., 1969. Sulla genesi del bradisimo flegro. Atti Associazione Geofisica Italiana, 18th Congress, Napoli, pp. 557–594; Casterano, L., Oliveri del Castillo, A., Quagliariello, M.T., 1976. Hydromdynamics and geodynamics in the Phlegraean Fields area of Italy. Nature, 264, 161–154).     

Geotechnical engineering practice for collapsible soils

Conditions in arid and semi-arid climates favor the formation of the most problematic collapsible soils. The mechanisms that account for almost all naturally occurring collapsible soil deposits are debris flows, rapid alluvial depositions, and wind-blown deposits (loess). Collapsible soils are moisture sensitive in that increase in moisture content is the primary triggering mechanism for the volume reduction of these soils. One result of urbanization in arid regions is an increase in soil moisture content. Therefore, the impact of development-induced changes in surface and groundwater regimes on the engineering performance of moisture sensitive arid soils, including collapsible soils, becomes a critical issue for continued sustainable population expansion into arid regions.In practicing collapsible soils engineering, geotechnical engineers are faced with (1) identification and characterization of collapsible soil sites, (2) estimation of the extent and degree of wetting, (3) estimation of collapse strains and collapse settlements, and (4) selection of design/mitigation alternatives. Estimation of the extent and degree of wetting is the most difficult of these tasks, followed by selection of the best mitigation alternative.