Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs.     

Rapid evaluation and damage assessment of instrumented highway bridges

This study focuses on the use of strong motion data recorded during earthquakes and aftershocks to provide a preliminary assessment of the structural integrity and possible damage in bridges. A system identification technique is used to determine dynamical characteristics and high‐fidelity first‐order linear models of a bridge from low level earthquake excitations. A finite element model is developed and updated using a genetic algorithm optimization scheme to match the frequencies identified and to simulate data from a damaging earthquake for the bridge. Here, two criteria are used to determine the state of the structure. The first criteria uses the error between the data recorded or simulated by the calibrated nonlinear finite element model and the data predicted by the linear model. The second criteria compares relative displacements of the structure with displacement thresholds identified using a pushover analysis. The use of this technique can provide an almost immediate, yet reliable, assessment of the structural health of an instrumented bridge after a seismic event. Copyright © 2011 John Wiley & Sons, Ltd.     

Seismic records of late Pleistocene aridity in Lake Tanganyika,tropical East Africa

New intermediate-resolution, normal-incidence seismic reflection profiles from Lake Tanganyika’s central basin capture dramatic evidence of base-level change during two intervals of the late Pleistocene. Four seismically-defined stratigraphic sequences (A–D) tied to radiocarbon-dated sediment cores provide a chronology for fluctuating environmental conditions along the Kalya Platform. Stacked, oblique clinoforms in Sequence C are interpreted as prograding siliciclastic deltas deposited during a major regression that shifted the paleo-lake shore ∼21 km towards the west prior to ∼106 ka. The topset-to-foreset transitions in these deltas suggest lake level was reduced by ∼435 m during the period of deposition. Mounded reflections in the overlying sequence are interpreted as the backstepping remnants of the delta system, deposited during the termination of the lowstand and the onset of transgressive conditions in the basin. The youngest depositional sequence reflects the onset of profundal sedimentation during the lake level highstand. High amplitude reflections and deeply incised channels suggest a short-lived desiccation event that reduced lake level by ∼260 m, interpreted as a product of Last Glacial Maximum (32–14 ka) aridity. Paleobathymetric maps constructed for the two interpreted regressions reveal that despite the positive lake-floor topography created by the Kavala Island Ridge Accommodation Zone, Lake Tanganyika remained a large, mostly connected water body throughout the late Pleistocene. The results of this analysis further imply that Lake Tanganyika is the most drought resistant water body in the East African tropics, and may have acted as a refuge for local and migrating fauna during periods of prolonged aridity.     

Calcium levels in <Emphasis Type="Italic">Daphnia</Emphasis> ephippia cannot provide a useful paleolimnological indicator of historical lakewater Ca concentrations

Despite reductions in atmospheric sulphur emissions and the resulting decline in acidic deposition, many lakes on the Canadian Shield that have experienced acidification are either recovering at a rate slower than expected or not recovering at all. This lack of recovery is believed to be partly the consequence of the depletion of exchangeable base cations (principally calcium, Ca) from watershed soils. Although the implications of reduced Ca availability for biological communities remain poorly understood, the effects on crustacean zooplankton populations may be severe, as Ca is the primary structural component of the crustacean zooplankton exoskeleton. Because the daphniid resting egg is protected by a modified portion of the exoskeleton (ephippia) and because these ephippia are well preserved in lake sediments, we investigated whether inter-specific differences in Ca content are recoverable from Daphnia ephippia. However, using two methods, we did not find a recoverable Ca signal in the ephippia, indicating that future efforts should be focused upon sedimentary taxonomic assemblage differences, not differences in ephippial Ca levels.     

Rates of fluvial bedrock incision within an actively uplifting orogen: Central Karakoram Mountains, northern Pakistan

Terrestrial cosmogenic nuclide (TCN) ¹⁰Be surface exposure ages for strath terraces along the Braldu River in the Central Karakoram Mountains range from 0.8 to 11 ka. This indicates that strath terrace formation began to occur rapidly upon deglaciation of the Braldu valley at  11 ka. Fluvial incision rates for the Braldu River based on the TCN ages for strath terraces range from 2 to 29 mm/a. The fluvial incision rates for the central gorged section of the Braldu River are an order of magnitude greater than those for the upper and lower reaches. This difference is reflected in the modern stream gradient and valley morphology. The higher incision rates in the gorged central reach of the Braldu River likely reflect differential uplift above the Main Karakoram Thrust that has resulted in the presence of a knickpoint and more rapid fluvial incision. The postglacial fluvial incision rate (2–3 mm/a) for the upper and lower reaches are of the same order of magnitude as the exhumation rates estimated from previously published thermochronological data for the Baltoro granite in the upper catchment region and for the adjacent Himalayan regions.     

A review of penetrometers for subsurface access on comets and asteroids

Abstract— The characterization of comet and asteroid interiors will eventually require in situ exploration with drills, penetrators/penetrometers, hypervelocity impactors, excavators or other devices. Because they offer desirable scientific capabilities and relative mechanical simplicity, penetrators and penetrometers, which use only axial force to push beneath the surface, are a good choice for near‐term missions. Penetrometers are instruments, generally deployed from a larger vehicle, that measure subsurface mechanical properties and may also contain additional scientific instruments. There are three basic types: “fast” penetrometers are released from above and plunge into the surface. Static and dynamic (collectively referred to as “slow”) penetrometers use, respectively, a constant slow penetration speed and periodic hammering impulses. The low gravity environment of asteroids and comets presents a key challenge to instrument deployment and also greatly affects the mechanical properties of surface materials, and in turn penetrometer performance. The Rosetta mission, currently en route to comet 67P/Churyumov‐Gerasimenko, will be the next mission to try both fast and slow, dynamic penetrometry, when it arrives in 2014. We present some new concepts of static penetrometers for small body exploration that are adapted to the low gravity environment. The low gravity environment also presents challenges for the testing of penetrometers on Earth and a number of previous solutions are described and new methods suggested. In the next generation of missions to study comets and asteroids, penetrometers could provide important data on their mechanical, seismic, thermal, electromagnetic, and chemical characteristics, as well as sample collection.     

Hyperaccretion

I briefly review the physics of accretion at rates well above the Eddington value. In stellar-mass systems, the result is generally an ultraluminous X-ray binary, and I show how SS433 fits into this picture. Conditions are relatively less extreme in active galactic nuclei, as the greatest likely accretion rates are not far above the electron-scattering Eddington value. However, even quite modest mass inflow rates exceed the corresponding value for dust opacity. I show that the obscuring torus invoked in unified AGN schemes is the probable result, and note that the matter in the torus probably does not supply the matter accreting on to the central black hole and thus powering the AGN.     

Shape,metal abundance,chemistry, and origin of chondrules in the Renazzo (CR) chondrite

Abstract— We used synchrotron X‐ray microtomography to image in 3‐dimensions (3D) eight whole chondrules in a ?1 cm³piece of the Renazzo (CR) chondrite at ?17 μm per volume element (voxel) edge. We report the first volumetric (3D) measurement of metal/silicate ratios in chondrules and quantify indices of chondrule sphericity. Volumetric metal abundances in whole chondrules range from 1 to 37 volume % in 8 measured chondrules and by inspection in tomography data. We show that metal abundances and metal grain locations in individual chondrules cannot be reliably obtained from single random 2D sections. Samples were physically cut to intersect representative chondrules multiple times and to verify 3D data. Detailed 2D chemical analysis combined with 3D data yield highly variable whole‐chondrule Mg/Si ratios with a supra‐chondritic mean value, yet the chemically diverse, independently formed chondrules are mutually complementary in preserving chondritic (solar) Fe/Si ratios in the aggregate CR chondrite. These results are consistent with localized chondrule formation and rapid accretion resulting in chondrule + matrix aggregates (meteorite parent bodies) that preserve the bulk chondritic composition of source regions.     

New Zealand wave climate from satellite observations

Wave data derived from radar altimeters carried on four satellite missions are combined into a wave climatology for New Zealand waters. These data provide extensive observations of wave conditions around New Zealand, where the paucity of measurements has previously hindered definition of the wave climate. The data span the period 1985 to the present with the exception of a 2‐year gap in 1989–91. The spatial distribution of the long‐term mean of significant wave heights (SWH) indicates a strong latitudinal variation in the south‐west Pacific, with values of over 4 m at latitudes of 50–60°S and under 2.5 m towards the tropics. The shadowing of New Zealand is quite marked; a result of the dominant contribution of south‐westerly wave events. The annual range of the mean SWH also varies over the region; within 0.6 m in the north and 1.3 m in the south. A principal component analysis of the monthly anomalies in mean SWH identifies spatial patterns of variation. Some components vary with the local wind more than others suggesting that some anomalies are associated with wind sea and some with swell. Some patterns also appear to vary with the Southern Oscillation Index and can be related to the wind anomalies associated with El Nino events. Frequency distributions of SWH are also determined, and it is noted that in the north of the region the spatial pattern of the high waves differs considerably from the means.