Tide–surge interactions and their effects on total sea levels in Irish coastal waters     

Agnieszka Indiana Olbert  Stephen Nash  Conleth Cunnane  Michael Hartnett 《Ocean Dynamics》2013,63(6):599-614

The research presented in this paper involves the application of the joint probability method to the estimation of extreme water levels resulting from astronomical tides and surge residuals and the investigation of the effects of tide–surge interactions on extreme water levels. The distribution of tide peaks was analysed from field records (<20 years) and a 46-year dataset of monthly maximum tidal amplitudes. Large surges were extracted from both field records and a numerical model hindcast covering the 48 largest storm events in the Irish Sea over the period 1959–2005. Extreme storm surges and tides were independently modelled using the generalised extreme value statistical model, and derived probability distributions were used to compute extreme water levels. An important, and novel, aspect of this research is an analysis of tide–surge interactions and their effects on total water level; where interactions exist, they lead to lower total water levels than in the case of independency. The degree of decrease varies with interaction strength, magnitude of surge peak at a particular phase of tide and the distribution of peaks over a tidal cycle. Therefore, including interactions in the computation of extreme levels may provide very useful information at the design stage of coastal protection systems.  相似文献   

Multi-proxy summer and winter precipitation reconstruction for southern Africa over the last 200 years     

Raphael Neukom  David J. Nash  Georgina H. Endfield  Stefan W. Grab  Craig A. Grove  Clare Kelso  Coleen H. Vogel  Jens Zinke 《Climate Dynamics》2014,42(9-10):2713-2726

This study presents the first consolidation of palaeoclimate proxy records from multiple archives to develop statistical rainfall reconstructions for southern Africa covering the last two centuries. State-of-the-art ensemble reconstructions reveal multi-decadal rainfall variability in the summer and winter rainfall zones. A decrease in precipitation amount over time is identified in the summer rainfall zone. No significant change in precipitation amount occurred in the winter rainfall zone, but rainfall variability has increased over time. Generally synchronous rainfall fluctuations between the two zones are identified on decadal scales, with common wet (dry) periods reconstructed around 1890 (1930). A strong relationship between seasonal rainfall and sea surface temperatures (SSTs) in the surrounding oceans is confirmed. Coherence among decadal-scale fluctuations of southern African rainfall, regional SST, SSTs in the Pacific Ocean and rainfall in south-eastern Australia suggest SST-rainfall teleconnections across the southern hemisphere. Temporal breakdowns of the SST-rainfall relationship in the southern African regions and the connection between the two rainfall zones are observed, for example during the 1950s. Our results confirm the complex interplay between large-scale teleconnections, regional SSTs and local effects in modulating multi-decadal southern African rainfall variability over long timescales.  相似文献   

Fundamentals of tree‐ring research. James H. Speer.     

Stephen E. Nash 《Geoarchaeology》2011,26(3):453-455

  相似文献   

The Blacktail Creek Tuff: an analytical and experimental study of rhyolites from the Heise volcanic field,Yellowstone hotspot system     

Torsten Bolte  Francois Holtz  Renat Almeev  Barbara Nash 《Contributions to Mineralogy and Petrology》2015,169(2):15

The magma storage conditions of the 6.62 Ma Blacktail Creek Tuff eruption, belonging to the Heise volcanic field (6.62–4.45 Ma old) of the Yellowstone hotspot system, have been investigated by combining thermobarometric and experimental approaches. The results from different geothermometers (e.g., Fe–Ti oxides, feldspar pairs, apatite and zircon solubility, and Ti in quartz) indicate a pre-eruptive temperature in the range 825–875 °C. The temperature estimated using two-pyroxene pairs varies in a range of 810–950 °C, but the pyroxenes are probably not in equilibrium with each other, and the analytical results of melt inclusion in pyroxenes indicate a complex history for clinopyroxene, which hosts two compositionally different inclusion types. One natural Blacktail Creek Tuff rock sample has been used to determine experimentally the equilibrium phase assemblages in the pressure range 100–500 MPa and a water activity range 0.1–1.0. The experiments have been performed at fluid-present conditions, with a fluid phase composed of H₂O and CO₂, as well as at fluid-absent conditions. The stability of the quartzo-feldspathic phases is similar in both types of experiments, but the presence of mafic minerals such as biotite and clinopyroxene is strongly dependent on the experimental approach. Possible explanations are given for this discrepancy which may have strong impacts on the choice of appropriate experimental approaches for the determination of magma storage conditions. The comparison of the composition of natural phases and of experimentally synthesized phases confirms magma storage temperatures of 845–875 °C. Melt water contents of 1.5–2.5 wt% H₂O are required to reproduce the natural Blacktail Creek Tuff mineral assemblage at these temperatures. Using the Ti-in-quartz barometer and the Qz–Ab–Or proportions of natural matrix glasses, coexisting with quartz, plagioclase and sanidine, the depth of magma storage is estimated to be in a pressure range between 130 and 250 MPa.  相似文献   

Evaluation of the frequency of skipped spawning in Norwegian spring-spawning herring     

James Kennedy  Jon Egil Skjraasen  Richard D.M. Nash  Aril Slotte  Audrey J. Geffen  Olav S. Kjesbu 《Journal of Sea Research》2011,65(3):327-332

Based upon an under-representation of second time spawners on the spawning grounds between 1935 and 1973, researchers have suggested that Norwegian spring-spawning (NSS) herring (Clupea harengus) frequently skip their second spawning event. In order to evaluate this claim with direct evidence, herring were collected over a period of three years from statutory surveys and commercial catches over a wide area covering the feeding, over-wintering and spawning grounds. The development stage of the ovaries was assessed and the intensity of atresia quantified. Only a negligible number of the analysed herring caught were considered likely to skip spawning, thus this phenomenon does not appear to be a common feature of the NSS herring stock at present. In addition, considering the reproductive strategy of herring, it seems doubtful that skipping the second spawning event has ever frequently occurred in this stock.  相似文献   

Topographic control on the nascent Mediterranean outflow   总被引：1，自引：1，他引：0  

M. Gasser  J. L. Pelegr��  J. D. Nash  H. Peters  J. Garc��a-Lafuente 《Geo-Marine Letters》2011,31(5-6):301-314

Data collected during a 12-day cruise in July 2009 served to examine the structure of the nascent Mediterranean Outflow Water (MOW) immediately west of the Espartel Sill, the westernmost sill in the Strait of Gibraltar. The MOW is characterized by high salinities (>37.0 and reaching 38.3) and high velocities (exceeding 1?m s^?1 at 100?m above the seafloor), and follows a submerged valley along a 30?km stretch, the natural western extension of the strait. It is approx. 150?m thick and 10?km wide, and experiences a substantial drop from 420 to 530?m over a distance of some 3?km between two relatively flat regions. Measurements indicate that the nascent MOW behaves as a gravity current with nearly maximal traveling speed; if this condition is maintained, then the maximum MOW velocity would decrease slowly with distance from the Espartel Sill, remaining significantly high until the gravity current excess density is only a small fraction of its original value. The sharp pycnocline between the Mediterranean and the overlying North Atlantic Central waters is dynamically unstable, particularly where the flow interacts with the 100?m decrease in bottom depth. Here, subcritical gradient Richardson numbers coincide with the development of large interfacial undulations and billows. The very energetic downslope flow is likely responsible for the development of a narrow V-shaped channel downstream of the seafloor drop along the axis of the submerged valley, this probably being the very first erosional scour produced by the nascent MOW. The coincidence of subcritical gradient Richardson numbers with relatively high turbidity values above the channel flanks suggests it may be undergoing upstream erosion.  相似文献   

Irish estuaries: Water quality status and monitoring implications under the water framework directive     

Michael Hartnett  James G. Wilson  Stephen Nash 《Marine Policy》2011

The status of water quality of Irish estuaries is reviewed; this sheds light on the rationale behind the design of the national monitoring programme. Relative to other EU Member States, Ireland's coastal monitoring programme is relatively young and not as advanced. The monitoring programmes in Ireland pre Water Framework Directive (WFD) were structured on a salinity-based typology, with an emphasis on quantifying the variability of the component elements. Although monitoring is a significant obligation under the WFD, there is little guidance on developing monitoring protocols; Member States are developing ad hoc monitoring programme. The Irish Environmental Protection Agency (EPA), responsible authority, undertook research programmes to assist design and implementation of the WFD. A substantial new national monitoring programme was developed. However, the Irish programme is not optimised; the programme is being refined to include elements not yet covered, notably the biota. New research, by the authors, aims to develop a robust approach towards monitoring integrating data and model results. This paper presents changes in Irish marine water quality monitoring policy and some of the associated research necessary to change policy.  相似文献   

Post‐1850 changes in Glacier Benito,North Patagonian Icefield,Chile     

Vanessa Winchester  Martin Sessions  Jammie Valdivia Cerda  Olaf Wündrich  Samuel Clemmens  Neil F. Glasser  Megan Nash 《Geografiska Annaler: Series A, Physical Geography》2014,96(1):43-59

Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr^?1 with the rate increasing to 6.1 m yr^?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day^?1 and ablation averaged 0.05 m day^?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr^?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr^?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr^?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers.  相似文献   

Documentary reconstruction of monsoon rainfall variability over western India, 1781–1860     

George C. D. Adamson  David J. Nash 《Climate Dynamics》2014,42(3-4):749-769

Investigations into the climatic forcings that affect the long-term variability of the Indian summer monsoon are constrained by a lack of reliable rainfall data prior to the late nineteenth century. Extensive qualitative and quantitative meteorological information for the pre-instrumental period exists within historical documents, although these materials have been largely unexplored. This paper presents the first reconstruction of monsoon variability using documentary sources, focussing on western India for the period 1781–1860. Three separate reconstructions are generated, for (1) Mumbai, (2) Pune and (3) the area of Gujarat bordering the Gulf of Khambat. A composite chronology is then produced from the three reconstructions, termed the Western India Monsoon Rainfall reconstruction (WIMR). The WIMR exhibits four periods of generally deficient monsoon rainfall (1780–1785, 1799–1806, 1830–1838 and 1845–1857) and three of above-normal rainfall (1788–1794, 1813–1828 and 1839–1844). The WIMR shows good correspondence with a dendroclimatic drought reconstruction for Kerala, although agreement with the western Indian portion of the tree-ring derived Monsoon Asia Drought Atlas is less strong. The reconstruction is used to examine the long-term relationship between the El Nino-Southern Oscillation (ENSO) and monsoon rainfall over western India. This exhibits peaks and troughs in correlation over time, suggesting a regular long-term fluctuation. This may be an internal oscillation in the ENSO-monsoon system or may be related to volcanic aerosol forcings. Further reconstructions of monsoon rainfall are necessary to validate this. The study highlights uncertainties in existing published rainfall records for 1817–1846 for western India.  相似文献   

River flow forecasting through conceptual models part II - The Brosna catchment at Ferbane     

P. E. O'Connell  J. E. Nash  J. P. Farrell 《Journal of Hydrology》1970,10(4):317-329

An attempt to model the runoff process on the Brosna catchment is described. Different models are compared and it is found possible to account for about 80 per cent of the initial variance of the discharge by very simple models.  相似文献