Highly potassic mafic dykes from Antarctica     

J. W. Sheraton  R. N. England 《Australian Journal of Earth Sciences》2013,60(1-2):129-135

Two exceptionally potassium‐rich alkali mela‐syenite dykes from widely separated localities in Antarctica consist of microcline, phlogopite, alkali amphibole (K‐richterite and K‐arfvedsonite), apatite, and minor quartz, anatase, rutile, sphene, barite, zircon, and opaque minerals; they represent the more deep‐seated equivalents of the potassium‐rich mafic volcanic and subvolcanic rock suite. Both are characterised by extremely high TiO₂, K₂O, P₂O₅, F, Rb, Sr, Zr, Nb, Ba, La, Ce, Pb, Th, and U, but relatively low Al₂O₃, CaO, and Na₂O. The dyke from Priestley Peak, Enderby Land is relatively magnesian (mg 0.67–0.71) and probably represents a near‐primary magma; its compositional variation may be mainly explained in terms of phlogopite fractionation. The dyke from Mount Bayliss, MacRobertson Land is more evolved (mg 0.54–0.58), and a similar, more rapidly cooled specimen from nearby moraine shows textural evidence that early leucite reacted with liquid to give K‐feldspar. It also shows evidence, in the form of felsic ocelli, for liquid immisci‐bility, although it is not clear whether this was petrogenetically important or merely a late‐magmatic feature.  相似文献   

Abrupt millennial variability and interdecadal-interstadial oscillations in a global coupled model: sensitivity to the background climate state     

Olivier Arzel  Matthew H. England  Alain Colin de Verdière  Thierry Huck 《Climate Dynamics》2012,39(1-2):259-275

The origin and bifurcation structure of abrupt millennial-scale climate transitions under steady external solar forcing and in the absence of atmospheric synoptic variability is studied by means of a global coupled model of intermediate complexity. We show that the origin of Dansgaard-Oeschger type oscillations in the model is caused by the weaker northward oceanic heat transport in the Atlantic basin. This is in agreement with previous studies realized with much simpler models, based on highly idealized geometries and simplified physics. The existence of abrupt millennial-scale climate transitions during glacial times can therefore be interpreted as a consequence of the weakening of the negative temperature-advection feedback. This is confirmed through a series of numerical experiments designed to explore the sensitivity of the bifurcation structure of the Atlantic meridional overturning circulation to increased atmospheric CO₂ levels under glacial boundary conditions. Contrasting with the cold, stadial, phases of millennial oscillations, we also show the emergence of strong interdecadal variability in the North Atlantic sector during warm interstadials. The instability driving these interdecadal-interstadial oscillations is shown to be identical to that found in ocean-only models forced by fixed surface buoyancy fluxes, that is, a large-scale baroclinic instability developing in the vicinity of the western boundary current in the North Atlantic. Comparisons with modern observations further suggest a physical mechanism similar to that driving the 30–40?years time scale associated with the Atlantic multidecadal oscillation.  相似文献   

Development of a new model tool for evaluating groundwater resources within the Floridan Aquifer System in Southern Florida,USA     

Laura Bittner  Steve England  Clarissa Murray  June Mirecki  Emily Richardson  Christopher Brown  Ben Kaiman 《Environmental Earth Sciences》2017,76(20):718

The US Army Corps of Engineers (USACE) and the South Florida Water Management District (SFWMD) are partners in an ambitious plan to restore water flows throughout the Everglades ecosystem. An important component of the restoration plan involves storing excess stormwater deep underground in the Floridan Aquifer System using aquifer, storage and recovery (ASR) wells. In order to determine the optimal ASR system and to assess environmental impacts, USACE spent over 11 years and significant resources to develop a three-dimensional groundwater model of the Floridan Aquifer System covering a large portion of the Florida peninsula. This SEAWAT model is capable of evaluating changes in aquifer pressures and density-dependent flows in the entire study area. The model has been used to evaluate the Everglades ASR system already but could also be used by water managers for other important water resources studies in Florida including water supply estimates and adaptation to climate change. As part of an effort to make the model more readily available for other important studies, this study documents and summarizes the overall development of the SEAWAT model including a discussion regarding the intensive calibration and validation efforts undertaken during model development. The paper then demonstrates the use of the model using Everglades ASR project alternatives. Lastly, the paper outlines potential future uses of the model along with its overall limitations. Supplementary online resources are also included that provide researchers with further detail regarding the model development effort beyond the scope of this summary article as well as model development databases.  相似文献   

Calibration of an integrated land surface process and radiobrightness (LSP/R) model during summertime     

Jasmeet Judge  Anthony W. England  John R. Metcalfe  David McNichol  Barry E. Goodison 《Advances in water resources》2008

In this study, a soil vegetation and atmosphere transfer (SVAT) model was linked with a microwave emission model to simulate microwave signatures for different terrain during summertime, when the energy and moisture fluxes at the land surface are strong. The integrated model, land surface process/radiobrightness (LSP/R), was forced with weather and initial conditions observed during a field experiment. It simulated the fluxes and brightness temperatures for bare soil and brome grass in the Northern Great Plains. The model estimates of soil temperature and moisture profiles and terrain brightness temperatures were compared with the observed values. Overall, the LSP model provides realistic estimates of soil moisture and temperature profiles to be used with a microwave model. The maximum mean differences and standard deviations between the modeled and the observed temperatures (canopy and soil) were 2.6 K and 6.8 K, respectively; those for the volumetric soil moisture were 0.9% and 1.5%, respectively. Brightness temperatures at 19 GHz matched well with the observations for bare soil, when a rough surface model was incorporated indicating reduced dielectric sensitivity to soil moisture by surface roughness. The brightness temperatures of the brome grass matched well with the observations indicating that a simple emission model was sufficient to simulate accurate brightness temperatures for grass typical of that region and surface roughness was not a significant issue for grass-covered soil at 19 GHz. Such integrated SVAT-microwave models allow for direct assimilation of microwave observations and can also be used to understand sensitivity of microwave signatures to changes in weather forcings and soil conditions for different terrain types.  相似文献   

Heat refraction and heat production in and around granite plutons in north-east England     

P. C. England  E. R. Oxburgh  S. W. Richardson 《Geophysical Journal International》1980,62(2):439-455

Summary. Existing surface heat flow determinations in north-east England indicate a difference in thermal structure between the Alston block of the North Pennines and the coastal regions. New heat flow determinations in the Askrigg block and on the coast support the original indications of higher heat flow in the positive blocks, which are underlain by 400 Myr old granites, than in their marginal sedimentary troughs along the present coastline. Although the two blocks are geophysically and geologically similar, surface heat flow in the Alston block is 30mW m^-2 higher than it is in the Askrigg block 50km to its south. Heat flow refraction around high conductivity plutons with high heat production may significantly affect the interpretation of heat flow measurements made on a regional scale but in the present case its effect, if any, is to emphasize the heat flow difference between the two otherwise similar blocks. The chemical differences between the Wensleydale and the Weardale granites – cupolas of the granites underlying the Askrigg and Alston may be representative of the granites as a whole and the blocks respectively – difference in surface heat flows may result from a contrast in radiogenic heat production between the two granites extending to mid-crustal depths.  相似文献   

New evidence from the western Canadian Arctic Archipelago for the resubmergence of Bering Strait     

John H. England  Mark F.A. Furze 《Quaternary Research》2008,70(1):60-67

Widespread molluscan samples were collected from raised marine sediments to date the last retreat of the NW Laurentide Ice Sheet from the western Canadian Arctic Archipelago. At the head of Mercy Bay, northern Banks Island, deglacial mud at the modern coast contains Hiatella arctica and Portlandia arctica bivalves, as well as Cyrtodaria kurriana, previously unreported for this area. Multiple H. arctica and C. kurriana valves from this site yield a mean age of 11.5 ¹⁴C ka BP (with 740 yr marine reservoir correction). The occurrence of C. kurriana, a low Arctic taxon, raises questions concerning its origin, because evidence is currently lacking for a molluscan refugium in the Arctic Ocean during the last glacial maximum. Elsewhere, the oldest late glacial age available on C. kurriana comes from the Laptev Sea where it is < 10.3 ¹⁴C ka BP and attributed to a North Atlantic source. This is 2000 cal yr younger than the Mercy Bay samples reported here, making the Laptev Sea, ~ 3000 km to the west, an unlikely source. An alternate route from the North Atlantic into the Canadian Arctic Archipelago was precluded by coalescent Laurentide, Innuitian and Greenland ice east of Banks Island until ~ 10 ¹⁴C ka BP. We conclude that the presence of C. kurriana on northern Banks Island records migration from the North Pacific. This requires the resubmergence of Bering Strait by 11.5 ¹⁴C ka BP, extending previous age determinations on the reconnection of the Pacific and Arctic oceans by up to 1000 yr. This renewed ingress of Pacific water likely played an important role in re-establishing Arctic Ocean surface currents, including the evacuation of thick multi-year sea ice into the North Atlantic prior to the Younger Dryas geochron.  相似文献   

Comment: Holocene palaeoceanographic changes in Barrow Strait,Canadian Arctic: foraminiferal evidence. T. R. Gregory,C. W. Smart,M. B. Hart,G. MassÉ, L. L. Vare and S. T. Belt (2010). Journal of Quaternary Science 25: 903–910     

Mark F.A. Furze  Anna J. Pieńkowski  John H. England 《第四纪科学杂志》2010,25(7):1189-1192

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Facies and stratigraphical analyses of glacial and interglacial sediments at Morgan Bluffs,Banks Island,Canadian Arctic Archipelago     

Thomas R. Lakeman  John H. England 《Boreas: An International Journal of Quaternary Research》2014,43(4):895-913

Stratigraphical exposures of both glacial and non‐glacial sediments at Morgan Bluffs, a >6‐km long exposure on the east coast of Banks Island, comprise a discontinuous archive of Quaternary environmental change. A detailed facies analysis of the sediments and a new stratigraphical framework is incompatible with the many climatostratigraphical units proposed previously. Instead, three distinct intervals of sedimentation are recognized. The first records the progradation of a delta, followed by fluvial aggradation of a braided river valley perhaps ～1 Ma. The second documents glacigenic sedimentation, including fluctuations of a tidewater glacier margin, in a marine basin more than 0.78 Ma. The third records till deposition by the NW Laurentide Ice Sheet during the Late Wisconsinan, followed by the progradation of a deglacial, ice‐contact delta into an ice‐dammed lake ～12.8 cal. ka BP. The revised stratigraphical framework adds important new terrestrial observations to a sparse and fragmentary data set of Quaternary environmental change in the Canadian Arctic. This study challenges former references and correlations to the previously proposed climatostratigraphical framework and nomenclature.  相似文献   

The deglacial to postglacial marine environments of SE Barrow Strait,Canadian Arctic Archipelago     

Anna J. Pieńkowski  John H. England  Mark F.A. Furze  Fabienne Marret  Frédérique Eynaud  Gustav Vilks  Brian Maclean  Steve Blasco  James D. Scourse 《Boreas: An International Journal of Quaternary Research》2012,41(2):141-179

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The exaggerated radiocarbon age of deposit‐feeding molluscs in calcareous environments     

John England  Arthur S. Dyke  Roy D. Coulthard  Roger Mcneely  Alec Aitken 《Boreas: An International Journal of Quaternary Research》2013,42(2):362-373

Throughout northern Canada, live‐collected, pre‐bomb, deposit‐feeding marine molluscs from calcareous sediments yield greater apparent radiocarbon ages than do suspension feeders. We explore the size of this effect in a set of 57 paired datings of deposit feeders, mainly Portlandia arctica, and suspension feeders, mainly Hiatella arctica and Mya truncata, collected from both calcareous and non‐calcareous Holocene sediments. Deposit feeders from calcareous sediments are older than their suspension‐feeding counterparts by as much as 2240±130 ¹⁴C years. This is attributed to the uptake of ‘old’ bicarbonate derived from calcareous bedrock. The age discrepancy between suspension and deposit feeders in calcareous terrain is non‐systematic in space and time, thereby invalidating the application of a correction. In contrast, the age comparisons are concordant at sites located on the Precambrian Shield. In terrestrial environments underlain by carbonate, previous acceptance of dates on deposit feeders led to erroneous interpretations of deglaciation and relative sea‐level history, in both the North American and the Eurasian Arctic. This has prompted several researchers to exclude deposit feeders from their late Quaternary reconstructions. The same chronological problem of deposit‐feeding molluscs now needs to be more widely acknowledged by the marine community.  相似文献