New evidence for drowned shelf edge reefs in the Great Barrier Reef,Australia

We present four new high-resolution multibeam bathymetry datasets from the shelf edge of the northern Great Barrier Reef (GBR). Analysis of these data, combined with Chirp sub-bottom profiles and existing submersible observation data provides a fresh insight into the detailed morphology and spatial distribution of submerged reefs and terraces at the shelf edge. An extensive and persistent line of drowned shelf edge reefs exist on the GBR margin in about 40 to 70 m. They appear as barrier reefs up to 200 m wide and comprising twin parallel ridges of rounded pinnacles. Subtle yet consistent terrace and step features lie between 78 and 114 m seaward of the shelf edge reefs in the southern study area. Submersible observations confirm that the drowned reefs now provide a favorable hard substrate for live soft corals and algae. They form a consistent and extensive seabed habitat that extends for possibly 900 km along the GBR shelf edge. The submerged reef and terraces features may reflect a complex history of growth and erosion during lower sea-levels, and are now capped by last deglaciation reef material.     

Governing fisheries as complex adaptive systems

Fisheries are complex human-in-nature systems. The conventional approach to fisheries systems has been to treat them as predictable and controllable. As complex systems they are neither of the two and have to be approached differently. Complex systems often exhibit the capacity to self-organize or adapt, even without outside influence. If this is true of fisheries, it should lead to a radically different approach to management of fisheries systems that places much emphasis on enabling self-organization, learning and adaptation. Conceptual and practical frameworks for enabling activities are needed.     

Optical long baseline intensity interferometry: prospects for stellar physics

More than sixty years after the first intensity correlation experiments by Hanbury Brown and Twiss, there is renewed interest for intensity interferometry techniques for high angular resolution studies of celestial sources. We report on a successful attempt to measure the bunching peak in the intensity correlation function for bright stellar sources with 1 meter telescopes (I2C project). We propose further improvements of our preliminary experiments of spatial interferometry between two 1 m telescopes, and discuss the possibility to export our method to existing large arrays of telescopes.     

Evaluating sampling efficiency when estimating sediment source contributions to suspended sediment in rivers by fingerprinting

A general method is proposed which measures the increase in uncertainty when sampling effort is reduced in sediment fingerprinting. The method gives quantitative measures of how reduced sampling of material in one of the source areas, and/or of suspended sediment in streams, increases the uncertainties in the proportions of sediment contributed from the sources. Because the proportions of sediment contributed by the source areas must add to one, standard errors of the estimated proportions cannot be used as the usual measures of uncertainty: the paper uses instead the volume of the joint 95% confidence region for the estimated proportions. The paper shows how the uncertainty in this volume changes as numbers of suspended sediment samples, and the numbers of samples collected from cropped fields, are reduced by successive steps from 24 (20, in the case of cropped fields) to 16, 12, 8, 4 and 2 samples. As expected, uncertainty increases rapidly as the number of samples – whether of suspended sediment or from cropped fields – is reduced drastically. The pattern of increasing uncertainty is similar both for reductions in suspended sediment sampling, and for reduced sampling from cropped areas. When the number of suspended sediment samples, and the number of samples from cropped fields, are reduced to the same values, the increase in uncertainty from fewer suspended sediment samples was always slightly greater than the increased uncertainty from the reduced sampling of cropped areas, although this finding took no account of differences in the costs of field sampling and laboratory analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

A remarkable pulse of large-scale volcanism on New Britain Island,Papua New Guinea

New studies of the deposits from the latest caldera-forming eruption (the “Dk” event) at Dakataua Volcano, New Britain Island, Papua New Guinea, help identify an intense space-time concentration of large-scale volcanism during the 7th century AD on New Britain. Radiocarbon dating of charcoal from the Dk deposits yields an age of 1,383 ± 28 BP. Calibration of this result gives an age in the range AD 635–670 (at 1 s. d.). At about the same time, two other volcanoes on New Britain, Rabaul and Witori, also produced very large eruptions. Very high acidity levels in ice cores from Antarctica and Greenland at AD 639 and AD 640 respectively may be linked to either or both of the Dakataua and Rabaul eruptions. Another ice core high acidity level, at AD 692, may be associated with the Witori eruption. Significant volcanic risk within the New Britain region is indicated by its Late Cenozoic history of relatively frequent large-scale eruptions from as many as 8 caldera systems within an arc-parallel zone about 380 km long. Over the last 20 ka the return period for major (VEI 5+) eruptions in this region was about 1.0 ka and individually high frequencies of major eruptive activity were experienced at Witori and Rabaul. The relatively short return period for major eruptions in the region would tend to increase the chance that such events could cluster in time.     

Evidence for pre-orogenic,Early Devonian rifting in the Variscan belt: stratigraphy and structure of the Palaeozoic cover of the Mauges Unit (Upper Allochthon,Armorican massif,France)

The Palaeozoic sediments from the Mauges Unit (Armorican Massif, France) are the best-preserved pre-orogenic sequences belonging to the Upper Allochthon. Two coherent sequences are identified. The southern unit (Chateaupanne Unit) represents the cover of the Proterozoic basement and consists of Ordovician sediments unconformably overlain by Emsian carbonates followed by Emsian to earliest Eifelian immature sandstones. The northern unit (Tombeau Leclerc Unit) consists of an Hirnantian to Emsian condensed sequence, in reverse position, that has been thrust over the southern unit. The Devonian unconformity is interpreted as evidence for an Early Devonian extension, recorded by normal faults affecting both the Early Devonian limestones and the underlying Ordovician series. This crustal extension, recorded here for the first time, is possibly related to the opening of a back-arc basin (Saint-Georges-sur-Loire) associated with the subduction of an ocean located further south (Galicia-Brittany-Massif Central Ocean).     

Intrinsic bioremediation of a petroleum-impacted wetland

Following the 1994 San Jacinto River flood and oil spill in southeast Texas, a petroleum-contaminated wetland was reserved for a long-term research program to evaluate bioremediation as a viable spill response tool. The first phase of this program, presented in this paper, evaluated the intrinsic biodegradation of petroleum in the contaminated wetland. Sediment samples from six test plots were collected 11 times over an 11-month period to assess the temporal and spatial petroleum concentrations. Petroleum concentrations were evaluated using gas chromatography-mass spectrometer analyses of specific target compounds normalized to the conservative biological marker, C(30)17alpha,21beta(H)-hopane. The analyses of specific target compounds were able to characterize that significant petroleum biodegradation had occurred at the site over the one-year period. Total resolved saturate and total resolved aromatic hydrocarbon data indicated the petroleum was degraded more than 95%. In addition, first-order biodegradation rate constants were calculated for the hopane-normalized target compounds and supported expected biodegradation patterns. The rapid degradation rates of the petroleum hydrocarbons are attributed to conditions favorable to biodegradation. Elevated nutrient levels from the flood deposition and the unconsolidated nature of the freshly deposited sediment possibly provided a nutrient rich, oxic environment. Additionally, it is suggested that an active and capable microbial community was present due to prior exposure to petroleum. These factors provided an environment conducive for the rapid bioremediation of the petroleum in the contaminated wetland.     

Potential collapse of the upper slope and tsunami generation on the Great Barrier Reef margin, north-eastern Australia

Analysis of high-resolution multibeam bathymetry and seismic profiles in the Noggin Passage region, north-eastern Australia, has identified a small area (Noggin block) in the upper-slope offshore Cairns that may potentially collapse and generate a tsunami wave. The Noggin block extends from 340 to 470 m depth covering a roughly circular (2.4 km long and 3.7 km wide) area of about 5.3 km². The well-defined margins of the block correspond to different bounding seabed features. These features include steep headscarps, small landslides and a group of aligned circular pockforms up to 500 m wide and 20 m deep. Slope stability simulations indicate that the Noggin block is stable under normal present-day gravitational conditions on the upper slope. However, block failure may result under external loads, such as those produced by earthquakes. Failure modelling shows that critical peak horizontal accelerations of 0.2–0.4 g could lead to the collapse of the Noggin block. In north-eastern Australia, these acceleration values would involve earthquakes generated at short hypocentral distances and short periods. The collapse of the potential sediment slide mass of about 0.86 km³ (162 m average thickness) may lead to the formation of a landslide-generated tsunami wave. Semi-empirical equations indicate the collapse of this mass would yield a 7–11-m high three-dimensional tsunami wave. These waves could reach an estimated run-up height at the coast of 5–7 m. Our first-order approach highlights the potential consequences for nearby coastal communities, the need for better sediment characterisation in the study area, and the systematic identification of other areas prone to slope failures along the Great Barrier Reef margin.     

The geology and geochemistry of the Lumwana Cu (± Co ± U) deposits, NW Zambia

The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz–feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz–feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite–muscovite–quartz–kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in X _Mg as the schists develop. δ³⁴S for copper sulphides range from +2.3?‰ to +18.5?‰, with pyrite typically restricted to values between +3.9?‰ and +6.2?‰. These values are atypical of sulphides precipitated by bacteriogenic sulphate reduction. δ³⁴S data for Chimiwungo (Cu + Co) show a broader range and increased δ³⁴S values compared to the Malundwe (Cu) mineralization. The Lumwana deposits show many characteristics which distinguish them from classical Copperbelt mineralization and which suggests that they are formed by metasomatic alteration, mineralization and shearing of pre-Katangan basement. Although this style of mineralization is reported elsewhere in the Copperbelt, sometimes associated with the more widely reported stratiform ores of the Lower Roan, none of the previously reported occurrences have so far developed the tonnages of ore reported at Lumwana.     

Reynolds stress and sand transport over a foredune

Reynolds shear stress (RS = –u′ w′) and sand transport patterns over a vegetated foredune are explored using three‐dimensional velocity data from ultrasonic anemometers (at 0 · 2 and 1 · 2 m) and sand transport intensity from laser particle counters (at 0 · 014 m). A mid‐latitude cyclone on 3–4 May 2010 generated storm‐force winds (exceeding 20 m s^–1) that shifted from offshore to obliquely alongshore. Quadrant analysis was used to characterize the spatial variation of RS quadrant components (Q1 through Q4) and their relative contributions were parameterized using the flow exuberance relation, EX_FL = (Q1 + Q3)/(Q2 + Q4). The magnitudes of RS and sand transport varied somewhat independently over the dune as controlled by topographic forcing effects on flow dynamics. A ‘flow exuberance effect’ was evident such that Q2 (ejection‐like) and Q4 (sweep‐like) quadrants (that contribute positively to RS) dominated on the beach, dune toe, and lower stoss, whereas Q1 and Q3 (that contribute negatively to RS) dominated near the crest. This exuberance effect was not expressed, however, in sand transport patterns. Instead, Q1 and Q4, with above‐average streamwise velocity fluctuations (+u′), were most frequently associated with sand transport. Q4 activity corresponded with most sand transport at the beach, toe, and stoss locations (52, 60, 100%). At the crest, 25 to 86% of transport was associated with Q1 while Q4 corresponded with most of the remaining transport (13 to 59%). Thus, the relationship between sand transport and RS is not as straightforward as in traditional equations that relate flux to stress in increasing fashion. Generally, RS was poorly associated with sand transport partly because Q1 and Q4 contributions offset each other in RS calculations. Thus, large amounts of transport can occur with small RS. Turbulent kinetic energy or Reynolds normal stresses (u′², w′²) may provide stronger associations with sand transport over dunes, although challenges exist on how to normalize and compare these quantities. Copyright © 2013 John Wiley & Sons, Ltd.