Pattern,style and timing of British–Irish Ice Sheet retreat: Shetland and northern North Sea sector     

Tom Bradwell  David Small  Derek Fabel  Chris D. Clark  Richard C. Chiverrell  Margot H. Saher  Dayton Dove  S. Louise Callard  Matthew J. Burke  Steven G. Moreton  Alicia Medialdea  Mark D. Bateman  David H. Roberts  Nicholas R. Golledge  Andrew Finlayson  Sally Morgan  Colm Ó Cofaigh 《第四纪科学杂志》2021,36(5):681-722

The offshore sector around Shetland remains one of the least well-studied parts of the former British–Irish Ice Sheet with several long-standing scientific issues unresolved. These key issues include (i) the dominance of a locally sourced ‘Shetland ice cap’ vs an invasive Fennoscandian Ice Sheet; (ii) the flow configuration and style of glaciation at the Last Glacial Maximum (i.e. terrestrial vs marine glaciation); (iii) the nature of confluence between the British–Irish and Fennoscandian Ice Sheets; (iv) the cause, style and rate of ice sheet separation; and (v) the wider implications of ice sheet uncoupling on the tempo of subsequent deglaciation. As part of the Britice-Chrono project, we present new geological (seabed cores), geomorphological, marine geophysical and geochronological data from the northernmost sector of the last British–Irish Ice Sheet (north of 59.5°N) to address these questions. The study area covers ca. 95 000 km², an area approximately the size of Ireland, and includes the islands of Shetland and the surrounding continental shelf, some of the continental slope, and the western margin of the Norwegian Channel. We collect and analyse data from onshore in Shetland and along key transects offshore, to establish the most coherent picture, so far, of former ice-sheet deglaciation in this important sector. Alongside new seabed mapping and Quaternary sediment analysis, we use a multi-proxy suite of new isotopic age assessments, including 32 cosmogenic-nuclide exposure ages from glacially transported boulders and 35 radiocarbon dates from deglacial marine sediments, to develop a synoptic sector-wide reconstruction combining strong onshore and offshore geological evidence with Bayesian chronosequence modelling. The results show widespread and significant spatial fluctuations in size, shape and flow configuration of an ice sheet/ice cap centred on, or to the east of, the Orkney–Shetland Platform, between ~30 and ~15 ka BP. At its maximum extent ca. 26–25 ka BP , this ice sheet was coalescent with the Fennoscandian Ice Sheet to the east. Between ~25 and 23 ka BP the ice sheet in this sector underwent a significant size reduction from ca. 85 000 to <50 000 km², accompanied by several ice-margin oscillations. Soon after, connection was lost with the Fennoscandian Ice Sheet and a marine corridor opened to the east of Shetland. This triggered initial (and unstable) re-growth of a glaciologically independent Shetland Ice Cap ca. 21–20 ka BP with a strong east–west asymmetry with respect to topography. Ice mass growth was followed by rapid collapse, from an area of ca. 45 000 km² to ca. 15 000 km² between 19 and 18 ka BP , stabilizing at ca. 2000 km² by ~17 ka BP. Final deglaciation of Shetland occurred ca. 17–15 ka BP , and may have involved one or more subsidiary ice centres on now-submerged parts of the continental shelf. We suggest that the unusually dynamic behaviour of the northernmost sector of the British–Irish Ice Sheet between 21 and 18 ka BP – characterized by numerous extensive ice sheet/ice mass readvances, rapid loss and flow redistributions – was driven by significant changes in ice mass geometry, ice divide location and calving flux as the glaciologically independent ice cap adjusted to new boundary conditions. We propose that this dynamism was forced to a large degree by internal (glaciological) factors specific to the strongly marine-influenced Shetland Ice Cap.  相似文献   

Mapped Predictions of Manganese and Arsenic in an Alluvial Aquifer Using Boosted Regression Trees     

Katherine J. Knierim  James A. Kingsbury  Kenneth Belitz  Paul E. Stackelberg  Burke J. Minsley  J.R. Rigby 《Ground water》2022,60(3):362-376

Manganese (Mn) concentrations and the probability of arsenic (As) exceeding the drinking-water standard of 10 μg/L were predicted in the Mississippi River Valley alluvial aquifer (MRVA) using boosted regression trees (BRT). BRT, a type of ensemble-tree machine-learning model, were created using predictor variables that affect Mn and As distribution in groundwater. These variables included iron (Fe) concentrations and specific conductance predicted from previously developed BRT models, groundwater flux and age estimates from MODFLOW, and hydrologic characteristics. The models also included results from the first airborne geophysical survey conducted in the United States to target an entire aquifer system. Predictions of high Mn and As occurred where Fe was high. Predicted high Mn concentrations were correlated with fraction of young groundwater (less than 65 years) computed from MODFLOW results. High probabilities of As exceedance were predicted where groundwater was relatively old and airborne electromagnetic resistivity was high, typically proximal to streams. Two-variable partial-dependence plots and sensitivity analysis were used to provide insight into the factors controlling Mn and As distribution in groundwater. The maps of predicted Mn concentrations and As exceedance probabilities can be used to identify areas where these constituents may be high, and that could be targeted for further study. This paper shows that incorporation of a selected set of process-informed data, such as MODFLOW results and airborne geophysics, into a machine-learning model improves model interpretability. Incorporation of process-rich information into machine-learning models will likely be useful for addressing a wide range of problems of interest to groundwater hydrologists.  相似文献   

Development of management measures for the groundfish fishery in Atlantic Canada : A case study of the Nova Scotia inshore fleet     

R. G. Halliday  F. G. Peacock  D. L. Burke 《Marine Policy》1992,16(6)

Subsequent to extension of fishery jurisdiction in 1977 it was Canadian policy to favour the inshore sector in rehabilitation of the Canadian groundfish fishery. Catch allocation, limited entry licensing and vessel replacement policies were implemented, which at first allowed and then increasingly attempted to limit inshore fleet expansion, which was being encouraged through financial assistance programmes. New regulatory authorities wer obtained to deal with the increasingly difficult task of limiting annual harvests to catch quota levels. A 1986 study concluded that the licensed capacity of the Nova Scotia inshore fleet was approximately four times that required to exploit the resource at target levels. As a result of a government task force report released in January 1990, substantial changes were made in the control of fishing by inshore fleets, including establishment of an individual boat catch quota system for some sectors. This article documents the regulatory actions taken to date to control inshore fleet development and annual fishing activities, and the responses of fishermen to these, as a possible guide to the implementation of new approaches.  相似文献   

Alkoxyquinoline O-dealkylation: A new fluorimetric assay for hydrocarbon-induced cytochrome P450 in fish     

M. Danny Burke  Douglas Brown  Richard T. Mayer  Dominic F.J. Houlihan 《Marine environmental research》1995,39(1-4)

The O-dealkylation of a new series of substrates, the alkoxyquinolines, provides a new easy fluorimetric assay for measuring the induction of cytochrome P450 by polycyclic aromatic hydrocarbons and drilling mud oil in fish. Expression of the results as a ratio between the inducible butyloxyquinoline O-dealkylation (BuQOD) activity and the non-inducible benzyloxyquinoline O-dealkylation (BeQOD) activity (i.e. the ‘BuQOD:-BeQOD quotient’) maximises the degree of induction measured and minimises the degree of inter-animal variation.  相似文献   

Late Pleistocene glaciers in Darhad Basin, northern Mongolia     

Alan R. Gillespie  Raymond M. Burke  Amgalan Bayasgalan 《Quaternary Research》2008,69(2):169-187

Late Pleistocene glaciers around Darhad Basin advanced to near their maximum positions at least three times, twice during the Zyrianka glaciation (at ∼ 17-19 ka and ∼ 35-53 ka), and at least once earlier. The Zyrianka glaciers were smaller than their predecessors, but the equilibrium-line altitude (ELA) difference was < 75 m. End moraines of the Zyrianka glaciers were ∼ 1600 m asl; ELAs were 2100-2400 m asl. ¹⁴C and luminescence dating of lake sediments confirm the existence of paleolake highstands in Darhad Basin before ∼ 35 ka. Geologic evidence and ¹⁰Be cosmic-ray exposure dating of drift suggests that at ∼ 17-19 ka the basin was filled at least briefly by a glacier-dammed lake ∼ 140 m deep. However, lake sediments from that time have not yet been recognized in the region. A shallower paleolake briefly occupied the basin at ∼ 11 ka, but between ∼ 11 and 17 ka and after ∼ 10 ka the basin was probably largely dry. The timing of maximum glacier advances in Darhad appears to be approximately synchronous across northern Mongolia, but different from Siberia and western Central Asia, supporting the inference that paleoclimate in Central Asia differed among regions.  相似文献   

Deforestation, hunting and the ecology of microbial emergence     

Nathan D. Wolfe  Mpoudi Ngole Eitel  Jim Gockowski  Pia K. Muchaal  Christian Nolte  A. Tassy Prosser  Judith Ndongo Torimiro  Stephan F. Weise  Donald S. Burke 《Global Change & Human Health》2000,1(1):10-25

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Galaxy colours in high-redshift, X-ray-selected clusters – I. Blue galaxy fractions in eight clusters     

B. W.Fairley  L. R.Jones  D. A.Wake  C. A.Collins  D. J.Burke  R. C.Nichol  A. K.Romer 《Monthly notices of the Royal Astronomical Society》2002,330(3):755-767

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Giga-Pixels and Sky Surveys     

John L. Tonry  Gerald A. Luppino  Nicholas Kaiser  Barry Burke  George H. Jacoby 《Experimental Astronomy》2002,14(1):17-24

We describe a project to build a new type of astronomical CCD that should significantly decrease the cost per pixel of detectors. This device should also provide very fast readout, autoguiding capability, image motion compensation, and good red sensitivity. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The Southern SHARC catalogue: a ROSAT survey for distant galaxy clusters     

D. J. Burke  C. A. Collins  R. M. Sharples  A. K. Romer  R. C. Nichol 《Monthly notices of the Royal Astronomical Society》2003,341(4):1093-1108

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CCD Technology     

Barry Burke  Paul Jorden  Paul Vu 《Experimental Astronomy》2005,19(1-3):69-102

Charge-coupled devices (CCDs) continue to reign supreme in the realm of imaging out to 1 μm, with the steady improvement of performance and the introduction of innovative features. This review is a survey of recent developments in the technology and the current limits on performance. Device packaging for large, tiled focal-plane arrays is also described. Comparisons between CCDs and the emerging CMOS imagers are highlighted in terms of process technology and performance.  相似文献