Evaluation of the relative roles of global versus local sedimentary controls on Middle to Late Pleistocene formation of continental margin strata,Canterbury Basin,New Zealand

Determining the relative influence of eustasy versus local sedimentary processes on strata formation is a fundamental challenge in the study of continental margin stratigraphy. In this paper, the relative contribution of these factors on continental margin evolution during the Middle to Late Pleistocene is evaluated using samples from Integrated Ocean Drilling Program Expedition 317. Core‐logging, biostratigraphy and quantitative X‐ray diffraction mineralogy are used to delineate continental shelf sedimentary systems. Major lithological unconformities bound stratigraphic sequences that contain recurring compositional patterns and that resemble other examples of Middle to Upper Pleistocene sequences. However, a preliminary chronology suggests that sequence boundary formation cannot be linked ‘one to one’ with eustatic cycles and therefore these sequences can contain multiple ca 100 ka eustatic cycles. Smaller amplitude, higher frequency transitions in sediment composition are interpreted as stratigraphic sequences driven by more rapid perturbations in the interplay of accommodation and sediment supply; their stratigraphy is variable in time and across the shelf, suggesting a strong influence of local sedimentary forcing in their formation. Changes in sediment composition after the Middle Pleistocene Transition indicate that sediment transfer from onshore sources in the glaciated Southern Alps to the middle‐shelf occurred over a single 100 ka glacio‐eustatic cycle, with an additional 100 ka lag before the mineralogical signal was preserved on the outer‐shelf. This phenomenon is coincident with rapid shelf progradation in this basin, suggesting a causal relation between across‐shelf sediment transport and margin progradation. This is one of very few studies that provide insights at the core scale into the processes driving continental margin evolution during the Middle to Late Pleistocene. This work shows that compositional changes in mud‐dominated successions can lead to a sequence stratigraphic interpretation and the identification of high‐frequency sequences, which may not be possible using a conventional stratigraphic approach.     

Vorticity and astrophysical magnetism

Viscous resistance to differential rotation causes a current whose magnetic field is proportional to the vorticity of the medium. The magnetic fields of stars and galaxies could arise in this manner, provided that the time scale for development of the field is reasonable. The latter condition (assuming Ohmic rather than synchroton dissipation) requires that the scale length for a galactic field be less than 3×10¹³ cm. It is suggested that there may be continual generation of field within the core of a vortex of this dimension in the galactic nucleus, the field lines then being carried outwards by expanding plasma. The main observational evidence in connection with solar, stellar and galactic magnetic fields is appraised in the context of the above theory.     

The ECOMAN project: A novel approach to defining sustainable ecosystem function

The ECOMAN was initiated in 2001 by the University of Plymouth, UK, Plymouth Marine Laboratory and the Department of the Environment, Fisheries and Rural Affairs (DEFRA) to address the need for more pragmatic assessment techniques linking environmental degradation with its causes. The primary aim of the project was to develop an evidence-based approach in which suites of easy-to-use, cost-effective and environmentally valid biological responses (biomarkers) could be used together to assess the health of coastal systems through the general condition of individuals. A range of sub-lethal endpoints, chosen to reflect successive levels of biological organisation (molecular, cellular, physiological), was evaluated in common coastal organisms showing different feeding types (filter feeding, grazing, predation) and habitat requirements (estuary, rocky shore). Initially, the suite of biomarkers was used in laboratory studies to determine the relative sensitivities of key species within different functional groups to common contaminants. These results were then validated in field studies performed in a range of ecosystems exhibiting different degrees/signatures of contamination. Here, an example is provided of a field study in the Humber Estuary, UK, which illustrates how multivariate statistical analysis can be used to identify patterns of response to discriminate between contaminated and clean sites. The use of a holistic, integrated approach of this kind is advocated as a practical means of assessing the impact of chemical contamination on organismal health and of ranking the status of marine ecosystems.     

Origin and evolution of the Steamboat Springs siliceous sinter deposit, Nevada, U.S.A.

Siliceous hot spring deposits from Steamboat Springs, Nevada, U.S.A., record a complex interplay of multiple, changing, primary environmental conditions, fluid overprinting and diagenesis. Consequently these deposits reflect dynamic geologic and geothermal processes. Two surface sinters were examined—the high terrace, and the distal apron-slope, as well as 13.11 m (43 ft) of core material from drill hole SNLG 87-29. The high terrace sinter consists of vitreous and massive-mottled silica horizons, while the distal deposit and core comprise dominantly porous, indurated fragmental sinters. Collectively, the three sinter deposits archive a complete sequence of silica phase diagenetic minerals from opal-A to quartz. X-ray powder diffraction analyses and infrared spectroscopy of the sinters indicate that the distal apron-slope consists of opal-A and opal-A/CT mineralogy; the core yielded opal-A/CT and opal-CT with minor opal-A; and the high terrace constitutes opal-C, moganite, and quartz. Mineralogical maturation of the deposit produced alternating nano–micro–nano-sized silica particle changes. Based on filament diameters of microbial fossils preserved within the sinter, discharging thermal outflows fluctuated between low-temperatures (< 35 °C, coarse filaments) and mid-temperatures ( 35–60 °C, fine filaments). Despite transformation to quartz, primary coarse and fine filaments were preserved in the high terrace sinter. AMS ¹⁴C dating of pollen from three horizons within core SNLG 87-29, from depths of 8.13 to 8.21 m (26′8″ to 26′11″), 10.13 to 10.21 m (33′3″ to 33′6″), and 14.81 to 14.88 m (48′7″ to 48′10″), yielded dates of 8684 ± 64 years, 11,493 ± 70 years and 6283 ±60 years, respectively. In the upper section of the core, the stratigraphically out-of-sequence age likely reflects physical mixing of younger sinter with quartzose sinter fragments derived from the high terrace. Within single horizons, mineralogical and morphological components of the sinter matrix were spatially patchy. Overall, the deposit was modified by sub-surface flow of alkali-chloride thermal fluids depositing a second generation of silica, and periodically, by acidic steam condensate formed during periods when the water table was low. Local faulting produced considerable fracturing of the sinter. Hence, the Steamboat Springs sinter experienced a complex history of primary and secondary hydrothermal, geologic and diagenetic events, and their inter-relationships and effects are locked within the physical, chemical and biological signatures of the deposit.     

Projected increased risk of water deficit over major West African river basins under future climates

Despite decades of research, large multi-model uncertainty remains about the Earth’s equilibrium climate sensitivity to carbon dioxide forcing as inferred from state-of-the-art Earth system models (ESMs). Statistical treatments of multi-model uncertainties are often limited to simple ESM averaging approaches. Sometimes models are weighted by how well they reproduce historical climate observations. Here, we propose a novel approach to multi-model combination and uncertainty quantification. Rather than averaging a discrete set of models, our approach samples from a continuous distribution over a reduced space of simple model parameters. We fit the free parameters of a reduced-order climate model to the output of each member of the multi-model ensemble. The reduced-order parameter estimates are then combined using a hierarchical Bayesian statistical model. The result is a multi-model distribution of reduced-model parameters, including climate sensitivity. In effect, the multi-model uncertainty problem within an ensemble of ESMs is converted to a parametric uncertainty problem within a reduced model. The multi-model distribution can then be updated with observational data, combining two independent lines of evidence. We apply this approach to 24 model simulations of global surface temperature and net top-of-atmosphere radiation response to abrupt quadrupling of carbon dioxide, and four historical temperature data sets. Our reduced order model is a 2-layer energy balance model. We present probability distributions of climate sensitivity based on (1) the multi-model ensemble alone and (2) the multi-model ensemble and observations.