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991.
Lewis Matt J. Palmer Tamsin Hashemi Resa Robins Peter Saulter Andrew Brown Jenny Lewis Huw Neill Simon 《Ocean Dynamics》2019,69(3):367-384
Ocean Dynamics - The combined hazard of large waves occurring at an extreme high water could increase the risk of coastal flooding. Wave-tide interaction processes are known to modulate the wave... 相似文献
992.
Andrew Darling Kelin Whipple Paul Bierman Brian Clarke Arjun Heimsath 《地球表面变化过程与地形》2020,45(2):312-330
Prior numerical modeling work has suggested that incision into sub-horizontal layered stratigraphy with variable erodibility induces non-uniform erosion rates even if base-level fall is steady and sustained. Erosion rates of cliff bands formed in the stronger rocks in a stratigraphic sequence can greatly exceed the rate of base-level fall. Where quartz in downstream sediment is sourced primarily from the stronger, cliff-forming units, erosion rates estimated from concentrations of cosmogenic beryllium-10 (10Be) in detrital sediment will reflect the locally high erosion rates in retreating cliff bands. We derive theoretical relationships for threshold hillslopes and channels described by the stream-power incision model as a quantitative guide to the potential magnitude of this amplification of 10Be-derived erosion rates above the rate of base-level fall. Our analyses predict that the degree of erosion rate amplification is a function of bedding dip and either the ratio of rock erodibility in alternating strong and weak layers in the channel network, or the ratio of cliff to intervening-slope gradient on threshold hillslopes. We test our predictions in the cliff-and-bench landscape of the Grand Staircase in southern Utah, USA. We show that detrital cosmogenic erosion rates in this landscape are significantly higher (median 300 m/Ma) than the base-level fall rate (~75 m/Ma) determined from the incision rate of a trunk stream into a ~0.6 Ma basalt flow emplaced along a 16 km reach of the channel. We infer a 3–6-fold range in rock strength from near-surface P-wave velocity measurements. The approximately four-fold difference between the median 10Be-derived erosion rate and the long-term rate of base-level fall is consistent with our model and the observation that the stronger, cliff-forming lithologies in this landscape are the primary source of quartz in detrital sediments. © 2020 John Wiley & Sons, Ltd. 相似文献
993.
994.
Andrew R. Hedrick Danny Marks Hans-Peter Marshall James McNamara Scott Havens Ernesto Trujillo Micah Sandusky Mark Robertson Micah Johnson Kat J. Bormann Thomas H. Painter 《水文研究》2020,34(11):2560-2574
The degree to which the hydrologic water balance in a snow-dominated headwater catchment is affected by annual climate variations is difficult to quantify, primarily due to uncertainties in measuring precipitation inputs and evapotranspiration (ET) losses. Over a recent three-year period, the snowpack in California's Sierra Nevada fluctuated from the lightest in recorded history (2015) to historically heaviest (2017), with a relatively average year in between (2016). This large dynamic range in climatic conditions presents a unique opportunity to investigate correlations between annual water availability and runoff in a snow-dominated catchment. Here, we estimate ET using a water balance approach where the water inputs to the system are spatially constrained using a combination of remote sensing, physically based modelling, and in-situ observations. For all 3 years of this study, the NASA Airborne Snow Observatory (ASO) combined periodic high-resolution snow depths from airborne Lidar with snow density estimates from an energy and mass balance model to produce spatial estimates of snow water equivalent over the Tuolumne headwater catchment at 50-m resolution. Using observed reservoir inflow at the basin outlet and the well-quantified snowmelt model results that benefit from periodic ASO snow depth updates, we estimate annual ET, runoff efficiency (RE), and the associated uncertainty across these three dissimilar water years. Throughout the study period, estimated annual ET magnitudes remained steady (222 mm in 2015, 151 mm in 2016, and 299 mm in 2017) relative to the large differences in basin input precipitation (547 mm in 2015, 1,060 mm in 2016, and 2,211 mm in 2017). These values compare well with independent satellite-derived ET estimates and previously published studies in this basin. Results reveal that ET in the Tuolumne does not scale linearly with the amount of available water to the basin, and that RE primarily depends on total annual snowfall proportion of precipitation. 相似文献
995.
Critically endangered Māui dolphin (Cephalorhynchus hectori maui) are found exclusively off the west coast of New Zealand’s North Island. One important data gap troubling efforts to reduce the current unsustainable level of bycatch is the limited information on the offshore and alongshore limits of their range. Passive acoustic monitoring studies could address this data gap, but Māui dolphin habitat is dominated by a sandy substrate that can shift greatly in the strong local currents. In February 2016, a short pilot CPOD deployment was thus attempted as a first step to see if the equipment could be deployed and recovered in the area and if the data collected would be viable, with a second unit deployed inside a harbour for comparison with earlier TPOD data. The pilot was largely successful, and roughly 11% of all minutes in the core habitat location contained detections of clicks attributed to Māui dolphin. A visual inspection of the data suggests some trends with diel and tidal patterns. Further work of this type is thus recommended. 相似文献
996.
Two silver (migratory) male freshwater eels, Anguilla dieffenbachii, were caught in a commercial trawl net in the South Taranaki Bight in April 2014. The capture date and the relatively small eye size indicated that both eels had probably only recently entered the sea. This is the first record of male A. dieffenbachii caught at sea, en route to the presumed spawning area in the South Fiji Basin. 相似文献
997.
ABSTRACTAir travel has become central to Australian academic practice, with flying increasingly seen as crucial to the progression of successful academic careers. This paper seeks to understand why academic air travel has come to be perceived as so necessary, particularly given its significant environmental, social, and economic implications. Drawing on the mobilities paradigm and social practice theory, we seek to understand how air travel practices are a key part of contemporary academic careers. We conducted an online survey of 301 academics and 24 in depth semi-structured interviews to understand academic air travel in Australia, finding that it is seen as a means to connect and collaborate within and between academic communities, and to counteract the effects of ‘remoteness'. This remoteness is experienced domestically and internationally, by Australian academics who feel they must travel to perceived centres of knowledge production to further their careers. Academics often frame their ‘need' for connections as necessarily involving physical co-presence. Air travel offers career benefits for those who can take advantage of it, and corresponding drawbacks for those ‘stuck on the ground’. We conclude by discussing the need for valuing localised forms of collaboration as markers of success, and developing imaginative alternatives to academic flying. 相似文献
998.
Julie Zurbuchen Alexander R. Simms Jonathan A. Warrick Ian M. Miller Andrew Ritchie 《Sedimentology》2020,67(5):2310-2331
Observations from ground-penetrating radar, sediment cores, elevation surveys and aerial imagery are used to understand the development of the Elwha River delta in north-western Washington, USA, which prograded as a result of two dam removals in late 2011. Swash-bar, foreshore and swale depositional elements are recognized within ground-penetrating radar profiles and sediment cores. A model for the growth and development of small mountainous river wave-dominated deltas is proposed based on observation of both the fluvial and deltaic settings. If enough sediment is available in the fluvial system, mouth-bars form after higher than average river discharge events, creating a large platform seaward of the subaqueous delta plain. Swash-bars form concurrently or within a month of mouth-bar deposition as a result of wave action. Fair-weather waves drive swash-bar migration landward and in the direction of littoral drift. The signature of swash-bar welding to the shoreline is landward-dipping reflections, as a result of overwash processes and slipface migration. However, most swash-bars are eroded by the river mouth, as only 10 of the 37 swash-bars that formed between August 2011 and July 2016 survived within the Elwha River delta. The swash-bars that do survive either amalgamate onto the shoreline or an earlier deposited swash-bar, forming a single larger barrier at the delta front. In asymmetrical deltas, the signature of swash-bar welding is more likely to be preserved on the downdrift side of the delta, where formation is more likely and accommodation behind newer swash-bars preserves older deposits. On small mountainous river deltas, welded swash-bars may be more indicative of a large sediment pulse to the system, rather than large hydrological events. 相似文献
999.
Zelia Dionnet Rosario Brunetto Alice Alon‐Toppani Stefano Rubino Donia Baklouti Ferenc Borondics Anne‐Ccile Buellet Zahia Djouadi Andrew King Tomoki Nakamura Alessandra Rotundi Christophe Sandt David Troadec Akira Tsuchiyama 《Meteoritics & planetary science》2020,55(7):1645-1664
In the near future, a new generation of sample return missions (Hayabusa2, OSIRIS‐REx, MMX, etc.) will collect samples from small solar system bodies. To maximize the scientific outcome of laboratory studies and minimize the loss of precious extraterrestrial samples, an analytical sequence from less destructive to more destructive techniques needs to be established. In this work, we present a combined X‐ray and IR microtomography applied to five Itokawa particles and one fragment of the primitive carbonaceous chondrite Paris. We show that this analytical approach is able to provide a 3‐D physical and chemical characterization of individual extraterrestrial particles, using the measurement of their 3‐D structure and porosity, and the detection of mineral and organic phases, and their spatial co‐localization in 3‐D. We propose these techniques as an efficient first step in a multitechnique analytical sequence on microscopic samples collected by space missions. 相似文献
1000.
Andrew G. Tomkins Tim E. Johnson Jennifer T. Mitchell 《Meteoritics & planetary science》2020,55(4):857-885
Here, the petrological features of numerous primitive achondrites and highly equilibrated chondrites are evaluated to review and expand upon our knowledge of the chondrite–achondrite transition, and primitive achondrites in general. A thermodynamic model for the initial silicate melting temperature and progressive melting for nearly the entire known range of oxidation states is provided, which can be expressed as Tm = 0.035Fa2?3.51Fa + 1109 (in °C, where Fa is the proportion of fayalite in olivine). This model is then used to frame a discussion of textural and mineralogical evolution of stony meteorites with increasing temperature. We suggest that the metamorphic petrology of these meteorites should be based on diffusive equilibration among the silicate minerals, and as such, the chondrite–achondrite transition should be defined by the initial point of silicate melting, not by metal–troilite melting. Evidence of silicate melting is preserved by a distinctive texture of interconnected interstitial plagioclase ± pyroxene networks among rounded olivine and/or pyroxene (depending on ?O2), which pseudomorph the former silicate melt network. Indirectly, the presence of exsolution lamellae in augite in slowly cooled achondrites also implies that silicate melting occurred because of the high temperatures required, and because silicate melt enhances diffusion. A metamorphic facies series is defined: the Plagioclase Facies is equivalent to petrologic types 5 and 6, the Sub‐calcic Augite Facies is bounded at lower temperatures by the initiation of silicate melting and at higher temperatures by the appearance of pigeonite, which marks the transition to the Pigeonite Facies. 相似文献