Links between Indo-Pacific climate variability and drought in the Monsoon Asia Drought Atlas     

Caroline C. Ummenhofer  Rosanne D. D’Arrigo  Kevin J. Anchukaitis  Brendan M. Buckley  Edward R. Cook 《Climate Dynamics》2013,40(5-6):1319-1334

Drought patterns across monsoon and temperate Asia over the period 1877–2005 are linked to Indo-Pacific climate variability associated with the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD). Using the Monsoon Asia Drought Atlas (MADA) composed of a high-resolution network of hydroclimatically sensitive tree-ring records with a focus on the June–August months, spatial drought patterns during El Niño and IOD events are assessed as to their agreement with an instrumental drought index and consistency in the drought response amongst ENSO/IOD events. Spatial characteristics in drought patterns are related to regional climate anomalies over the Indo-Pacific basin, using reanalysis products, including changes in the Asian monsoon systems, zonal Walker circulation, moisture fluxes, and precipitation. A weakening of the monsoon circulation over the Indian subcontinent and Southeast Asia during El Niño events, along with anomalous subsidence over monsoon Asia and reduced moisture flux, is reflected in anomalous drought conditions over India, Southeast Asia and Indonesia. When an IOD event co-occurs with an El Niño, severe drought conditions identified in the MADA for Southeast Asia, Indonesia, eastern China and central Asia are associated with a weakened South Asian monsoon, reduced moisture flux over China, and anomalous divergent flow and subsidence over Indonesia. Insights into the relative influences of Pacific and Indian Ocean variability for Asian monsoon climate on interannual to decadal and longer timescales, as recorded in the MADA, provide a useful tool for assessing long-term changes in the characteristics of Asian monsoon droughts in the context of Indo-Pacific climate variability.  相似文献   

Ten guiding principles for the delineation of priority habitat for endangered small cetaceans     

Peter S. Ross  Jay Barlow  Thomas A. Jefferson  Brendan E. Hickie  Tatiana Lee  Christina MacFarquhar  E. Christien Parsons  Kimberly N. Riehl  Naomi A. Rose  Elisabeth Slooten  Chia-Yang Tsai  John Y. Wang  Andrew J. Wright  Shih Chu Yang 《Marine Policy》2011

The adoption of endangered species laws in various nations has intensified efforts to better understand, and protect, at-risk species or populations, and their habitats. In many countries, delineating a portion of a species' habitat as particularly worthy of protection has become a mantra of these laws. Unfortunately, the laws themselves often provide scientists and managers with few, if any, guidelines for how to define such habitat. Conservationists and scientists may view protecting part of the habitat of an endangered species as an ineffectual compromise, while managers may be under pressure to allow a range of human activities within the species' habitat. In the case of small cetaceans, establishing boundaries for such areas can also be complicated by their mobility, the fluid nature of their environment, and the often ephemeral nature of their habitat features. The convergence of multiple human impacts in coastal waters around the world is impacting many small cetaceans (and other species) that rely on these areas for feeding, reproducing, and resting. The ten guiding principles presented here provide a means to characterize the habitat needs of small, at-risk cetaceans, and serve as a basis for the delineation of ‘priority habitat’ boundaries. This conceptual approach should facilitate a constructive discourse between scientists and managers engaged in efforts to recover endangered species. The degree to which the recovery of an at-risk species can be reconciled with sustainable economic activity will depend in part on how well these principles are incorporated into the delineation of priority habitat.  相似文献   

Contrasting sedimentation rates in Lake Illawarra and St Georges Basin,two large barrier estuaries on the southeast coast of Australia     

Craig R. Sloss  Brian G. Jones  Brendan P. Brooke  Henk Heijnis  Colin V. Murray-Wallace 《Journal of Paleolimnology》2011,46(4):561-577

Sedimentation rates over the last 100 years within two lagoons on the southeast coast of Australia, Lake Illawarra and St Georges Basin, have been quantified to determine the effects of catchment land use change and native vegetation clearance on infill rates, and spatial variations in the rate at which the estuaries have filled. Both catchments have similar lake and catchment area but have experience different degrees of modification due to land clearing for agriculture practices, urbanisation and industrialisation. Results indicate that in the heavily modified catchment of Lake Illawarra sedimentation rates close to fluvial deltas can be in excess of 16 mm/year, and between 2 and 4 mm/year in the adjacent central basin. This is approximately an order of magnitude greater than the pre-European rates. In contrast, at St Georges Basin, where the catchment has experienced much less modification, sedimentation rates in the central basin appear to have remained close to those prior to European settlement. However, sedimentation rates in the urbanized margin of St Georges Basin are relatively high (up to 4.4 mm/year). This rapid modern sedimentation in the margin of the estuarine embayments has been detected in several other estuaries in the region. However the degree of sedimentation within the bay-head deltas, and more significantly in the central basin appears proportional to the degree clearance of native vegetation (forest) in the catchment, urban expansion and development of heavy industry in the respective catchment areas.  相似文献   

Patterns of grain‐size dependent sediment transport in low‐ordered,ephemeral channels     

Brendan T. Yuill  Mary H. Nichols 《地球表面变化过程与地形》2011,36(3):334-346

Sediment data were analyzed to determine grain‐size dependant factors affecting sediment transport in a low‐ordered, ephemeral watershed. Sediment and flow samples were collected during 22 flow events at the outlet of a 4·53 ha sub‐watershed within the Walnut Gulch Experimental Watershed in south‐eastern Arizona. Measured concentrations ranged from 4191 to 115 045 mg l^?1 and included grain sizes up to 8·0 mm in diameter. Two grain‐size dependent transport patterns were observed, that of the finer grain‐size fraction (approximately < 0·25 mm) and that of a coarser grain‐size fraction (approximately ≥ 0·25 mm). The concentration of the fine fraction decreased with flow duration, peaking near the beginning of a flow event and declining thereafter. The concentration of the fine fraction showed slight trends with season and recovery period. The concentration of the coarse fraction displayed a slight negative trend with instantaneous discharge and was not correlated with event duration. These patterns typically produced a condition where the majority of the fine fraction of the sediment yield was evacuated out of the watershed before the hydrograph peak while the majority of the coarser sediment was evacuated during the falling limb of the hydrograph. Each grain‐size dependent transport pattern was likely influenced by the source of the associated sediment. At the flow event time scale, the fines were primarily wash load, supplied from the hillslopes and the coarser grains were entrained from the channel bed. Because transport patterns differ based on grain size, attempts to define the total sediment concentration and sediment yield by the behavior of a single grain‐size fraction may lead to erroneous results, especially when a large range of sediment grain sizes are present. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Highly depleted oceanic lithosphere in the Rheic Ocean: Implications for Paleozoic plate reconstructions     

J. Brendan Murphy  Brian L. Cousens  James A. Braid  Rob A. Strachan  Jaroslav Dostal  J. Duncan Keppie  R. Damian Nance 《Lithos》2011,123(1-4):165-175

The Rheic Ocean formed at ca. 500 Ma, when several peri-Gondwanan terranes (e.g. Avalonia and Carolinia) drifted from the northern margin of Gondwana, and were consumed during the Late Carboniferous collision between Laurussia and Gondwana, a key event in the formation of Pangea. Several mafic complexes ranging in age from ca. 400–330 Ma preserve many of the lithotectonic and/or chemical characteristics of ophiolites. They are characterized by anomalously high εNd values that are typically either between or above the widely accepted model depleted mantle curves. These data indicate derivation from a highly depleted (HD) mantle and imply that (i) the mantle source of these complexes displays time-integrated depletion in Nd relative to Sm, and (ii) depletion is the result of an earlier melting event in the mantle from which basalt was extracted. The extent of mantle depletion indicates that this melting event occurred in the Neoproterozoic, possibly up to 500 million years before the Rheic Ocean formed. If so, the mantle lithosphere that gave rise to the Rheic Ocean mafic complexes must have been captured from an adjacent, older oceanic tract. The transfer of this captured lithosphere to the upper plate enabled it to become preferentially preserved. Possible Mesozoic–Cenozoic analogues include the capture of the Caribbean plate or the Scotia plate from the Pacific to the Atlantic oceanic realm. Our model implies that virtually all of the oceanic lithosphere generated during the opening phase of the Rheic Ocean was consumed by subduction during Laurentia–Gondwana convergence.  相似文献   

Long-term trends in benthic habitat quality as determined by Multivariate AMBI and Infaunal Quality Index in relation to natural variability: a case study in Kinsale Harbour, south coast of Ireland     

Kennedy R  Arthur W  Keegan BF 《Marine pollution bulletin》2011,62(7):1427-1436

Benthic Ecological Quality Ratios (EQR) are important tools for assessing the ecological status of coastal and transitional water bodies. Here, we use spatial and time-series data from Kinsale Harbour, Ireland to examine the effects of sample processing methodologies on the outputs of two EQRs: Multivariate AMBI (M-AMBI) and Infaunal Quality Index (IQI).Both EQRs were robust to changes in sieve size from 1 mm to 0.5 mm, and to changes in the taxa identified in spatial calibration. Both EQRs classified habitat quality in Kinsale as generally Good or High with no evidence of significant change over the time series (1981-2006). IQI classified the ecological status as higher than M-AMBI.There was a significant relationship between IQI and M-AMBI in spatial calibration, but no significant relationship between them in time series. Further research into the behaviour of EQRs in relation to natural variability over long time-scales is needed to discriminate anthropogenic impacts reliably.  相似文献   

Crystal structures and phase transitions in Sr2InTaO6 perovskite     

Qingdi Zhou  Brendan J. Kennedy  Maxim Avdeev 《Physics and Chemistry of Minerals》2013,40(8):603-610

The preparation and crystal structure of the double perovskite oxide Sr₂InTaO₆ are reported. This oxide has a monoclinic structure in space group P2₁/n at room temperature, where In and Ta display a rock-salt type ordering with a = 5.73356(10), b = 5.74052(10), c = 8.10905(14) Å and β = 90.022(6)°. Variable temperature neutron diffraction measurements demonstrate this displays the sequence of phase transitions $ P2_{1} /n\mathop{\longrightarrow}\limits^{{605\,^\circ {\text{C}}}}I2/m\mathop{\longrightarrow}\limits^{{705\,^\circ {\text{C}}}}I4/m\mathop{\longrightarrow}\limits^{{930\,^\circ {\text{C}}}}Fm\bar{3}m $ as a consequence of the sequential loss of tilting of the corner shared octahedra upon heating. The evolution of Sr₂InTaO₆ crystal structure upon heating is analysed and described in terms of symmetry-adapted distortion modes. The GM4+ and X3+, that are responsible for anti-phase and in-phase tilting, respectively, are highly temperature dependent, with the GM4+ mode having the largest amplitude at room temperature.  相似文献   

The Galway astronomical Stokes polarimeter: an all-Stokes optical polarimeter with ultra-high time resolution     

Patrick Collins  Gillian Kyne  David Lara  Michael Redfern  Andy Shearer  Brendan Sheehan 《Experimental Astronomy》2013,36(3):479-503

Many astronomical objects emit polarised light, which can give information both about their source mechanisms, and about (scattering) geometry in their source regions. To date (mostly) only the linearly polarised components of the emission have been observed in stellar sources. Observations have been constrained because of instrumental considerations to periods of excellent observing conditions, and to steady, slowly or periodically-varying sources. This leaves a whole range of interesting objects beyond the range of observation at present. The Galway Astronomical Stokes Polarimeter (GASP) has been developed to enable us to make observations on these very sources. GASP measures the four components of the Stokes Vector simultaneously over a broad wavelength range 400–800 nm., with a time resolution of order microseconds given suitable detectors and a bright source - this is possible because the optical design contains no moving or modulating components. The initial design of GASP is presented and we include some preliminary observational results demonstrating that components of the Stokes vector can be measured to $<1$ % in conditions of poor atmospheric stability. Issues of efficiency and stability are addressed. An analysis of suitable astronomical targets, demanding the unique properties of GASP, is also presented.  相似文献   

The Burrum River estuary: identifying reference sites for Australian sub-tropical estuarine systems using paleolimnological methods   总被引：1，自引：0，他引：1  

Brendan Logan  Kathryn H. Taffs 《Journal of Paleolimnology》2011,46(4):613-622

There is a pressing need to obtain historical information on estuaries so that levels of natural variability and ecosystem thresholds can be identified. Once these factors are known, estuaries that exhibit high conservation value and minimal impact from anthropogenic activity can be acknowledged and protected. In order to understand and quantify the level of change that may have occurred due to human impact, near pristine estuaries that have the potential to act as reference sites need to be identified. However, this is often difficult due to a lack of documented knowledge of estuary variability. This paper retrospectively assesses environmental conditions in the Burrum River, a sub-tropical east Australian estuary on the coast of Queensland, using diatom and stable isotope analyses. These techniques were combined with AMS ¹⁴C dating methods to determine if this system has undergone any natural or anthropogenically induced change. Diatom assemblages have shown very little variation over the past 5,000 years, indicating minimal changes to water quality. Upper and lower limits for δ¹³C and δ¹⁵N stable isotope results also infer that the sources of carbon and nitrogen to the Burrum River estuary have remained constant over this time period. Carbon inputs have been dominated by marine autotrophic production, whilst nitrogen inputs are indicative of terrestrial sources. Hence, the Burrum River has not been altered by anthropogenic activities and is a suitable reference site for benchmarking impacted sub-tropical estuaries. This paper demonstrates that paleolimnological techniques can be applied successfully to identify estuaries that are suitable as reference sites.  相似文献   

Schmidt hammer exposure‐age dating (SHD) of late Quaternary fluvial terraces in New Zealand     

Timothy Stahl  Stefan Winkler  Mark Quigley  Mark Bebbington  Brendan Duffy  Daniel Duke 《地球表面变化过程与地形》2013,38(15):1838-1850

Schmidt hammer (SH) R‐values are reported for surface clasts from numerically dated Holocene and Pleistocene fluvial terraces in the South Island of New Zealand. The R‐values are combined with previously obtained weathering rind, radiocarbon, terrestrial cosmogenic nuclide and luminescence terrace ages to derive SH R‐value chronofunctions for greywacke clasts from four distinct locations. Our results show that different weathering rates affect the form of the SH R‐value versus Age curve, however a fundamental dependency between the two remains constant over timescales ranging from 10² to 10⁵ years. Power law scaling constants suggest changes in clast weathering rates are primarily affected by climatic (precipitation and temperature) and sedimentologic variables (source terrane petrology). Age uncertainties of ~22% of the surface age suggest that Schmidt hammer exposure‐age dating (SHD) is a reliable calibrated‐age dating technique for fluvial terraces. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献