Discussion on the paper by Denton and Hughes (1983)     

J. T. Andrews  G. H. Miller   《Quaternary Research》1985,24(3):361-364

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Rehabilitation of the inner Thames estuary     

M.J. Andrews  D.G. Rickard 《Marine pollution bulletin》1980,11(11):327-332

This article deals with a previously unreported phase in the recolonization of the inner Thames estuary which occurred between 1976–1980, and which is characterized by increases in population size, animal fecundity and species diversity. A thriving estuarine community has become established in the outfall reaches of Beckton and Crossness sewage treatment works, and can be related to the improved effluent quality of the modernized Beckton works. We reiterate the extent of the first phase, and using a few examples from our collected data, illustrate the extent of the second phase of the rehabilitation of the ecosystem and show how it marks a change from a polluted to a non-polluted regime in the critical reaches of the Thames.  相似文献   

Late Quaternary ice extent and glacial history from the Djúpáll trough, off Vestfirdir peninsula, north-west Iceland: a stacked 36 cal. Ky environmental record     

John T. Andrews  Jórunn Hardardóttir  Áslaug Geirsdóttir  Gudrún Helgadóttir 《Polar research》2002,21(2):211-226

Djúpáll is a Ø90 km long by 15 km wide trough which extends from Ísafjardardjúp to the shelf break above Blosseville Basin, north of the Denmark Strait. We present 3.5 kHz seismic profiles from this trough and data from cores collected in 1996 (JM96-1232 and −1234) and five cores collected on cruise B997. We pay particular attention to B997-338 as this core recovered sediments ranging in age between 12 and 36 cal. Ky BP. This is the first such record from the Iceland continental shelf. Dating control is provided by AMS ¹⁴C dates and the occurrence of the Saksunarvatn tephra. X-radiographs of the cores enable us to quantify the input of iceberg-rafted detritus (IRD) and to describe the lithofacies. The sediment matrix is fine-grained and might represent either rain-out of suspended sediment plumes or distal turbidites. IRD is present from ca. 12 cal. Ky BP throughout the next 24 cal. Ky with some IRD-free intervals. Using sediment magnetic properties, sampled at 1 cm (ø100 yrs/sample) resolution, we provide a stacked environmental record which includes marine isotope stages 1, 2 and part of 3. The sediment magnetic properties kARM and IRM(60), and carbonate and TOC, show multi-millennia quasi-periodic cycles, but there are no obvious events coeval with the North Atlantic Heinrich events. Our data indicate that at the Last Glacial Maximum on the Vestfirdir peninsula (VP), north-west Iceland, ice did not reach the shelf break, but was probably grounded near the mouth of Ísafjardardjúp. A rapid increase in the rate of sediment accumulation suggests that deglaciation of the VP occurred mainly between 11 and 15 cal. Ky BP.  相似文献   

A 36 Ky record of iceberg rafting and sedimentation from north-west Iceland   总被引：2，自引：0，他引：2  

Áslaug Geirsdóttir  John T. Andrews  Saedís Ólafsdóttir  Gudrún Helgadóttir  Jórunn Hardardóttir 《Polar research》2002,21(2):291-298

Evidence from north-west Iceland's shelf and fjords is used to develop a scenario for environmental change during the last 36 cal Ky. The retreat history of the Iceland Ice Cap during the last deglaciation is delineated through lithofacies studies, carbon analyses and magnetic susceptibility, and studies of ice-rafted debris (IRD) in sediment cores. Sedimentological data from lake Efstadalsvatn, Vestfirdir peninsula, trace the glacier retreat on land. In two of the high resolution shelf cores we detect near continuous IRD accumulation from 36 to 11 cal Kya. However, IRD is absent in the cores from ca. 22 to 19 cal Kya, possibly indicating more extensive landfast sea ice conditions. All cores show intensified IRD during the Younger Dryas chronozone; the fjord cores show a continuous IRD record until 10 cal Kya. Magnetic susceptibility and carbon analyses from Efstadalsvatn reveal the disappearance of local ice in the basin just before 10.5 cal Kya. No IRD was detected in the sediment cores during 10 to Ø4 cal Kya. Some indication of cooling occurs between 4 and 3 cal Kya, with a fresh input of IRD in fjord cores after 1 cal Kya.  相似文献   

Taphonomy in palaeoecological interpretations     

Y. Fernández-Jalvo  L. Scott  P. Andrews 《Quaternary Science Reviews》2011,30(11-12):1296-1302

The taphonomic history of single fossils or of fossil assemblages provides evidence additional to that given by taxonomic identification. Too often taphonomy is viewed as destructive processes biasing evidence of past life or restricting taxonomic diversity in the reconstruction of palaeoecology, but in reality it sheds light on circumstances of life and preservation of fossil organisms. Because recorded modifications of fossils are due to biotic or abiotic agents that may not be evident in a studied sequence, taphonomic modifications should be seen as providing a more dynamic view of the past rather than as destructive processes.  相似文献   

The role of the Iceland Ice Sheet in the North Atlantic during the late Quaternary: a review and evidence from Denmark Strait     

John T. Andrews 《第四纪科学杂志》2008,23(1):3-20

Investigations indicate that the Iceland Ice Sheet was reduced in size during MIS 3 but readvanced to the shelf break at the LGM. Retreat occurred very rapidly around 15 k–16 k cal. yr BP. By contrast, the margin of the ice sheet on the East Greenland shelf, north of the Denmark Strait, was at or close to the shelf break during MIS 3 and 2 and retreat starting ～17 k cal. yr BP. Quantitative X‐ray diffraction analysis of the <2 mm sediment fraction was undertaken on 161 samples from Iceland and East Greenland diamictons, and from cores on the slopes and margins of the Denmark Strait. Weight% mineralogical data are used in a principal component analysis to differentiate sediments derived from the two margins. The first two PC axes explain 52% of the variance. These associations are used to characterise sediments as being affiliated with (a) Iceland, (b) East Greenland or (c) mixed. The contribution from Iceland becomes prominent during MIS 2. The extensive outcrop of early Tertiary basalts on East Greenland between 68° and 71° N is an alternative source for basaltic clasts and North Atlantic sediments with εNd(0) values close to ±0. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Cloud Adjustment and its Role in CO2 Radiative Forcing and Climate Sensitivity: A Review     

Timothy Andrews  Jonathan M. Gregory  Piers M. Forster  Mark J. Webb 《Surveys in Geophysics》2012,33(3-4):619-635

Understanding the role of clouds in climate change remains a considerable challenge. Traditionally, this challenge has been framed in terms of understanding cloud feedback. However, recent work suggests that under increasing levels of atmospheric carbon dioxide, clouds not only amplify or dampen climate change through global feedback processes, but also through rapid (days to weeks) tropospheric temperature and land surface adjustments. In this article, we use the Met Office Hadley Centre climate model HadGSM1 to review these recent developments and assess their impact on radiative forcing and equilibrium climate sensitivity. We estimate that cloud adjustment contributes ~0.8?K to the 4.4?K equilibrium climate sensitivity of this particular model. We discuss the methods used to evaluate cloud adjustments, highlight the mechanisms and processes involved and identify low level cloudiness as a key cloud type. Looking forward, we discuss the outstanding issues, such as the application to transient forcing scenarios. We suggest that the upcoming CMIP5 multi-model database will allow a comprehensive assessment of the significance of cloud adjustments in fully coupled atmosphere–ocean-general-circulation models for the first time, and that future research should exploit this opportunity to understand cloud adjustments/feedbacks in non-idealised transient climate change scenarios.  相似文献   

Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater,Ukraine          下载免费PDF全文

Alena Ebinghaus  David W. Jolley  Steven D. Andrews  David B. Kemp 《Sedimentology》2017,64(6):1465-1487

The Boltysh meteorite impact crater, Ukraine, formed at the Cretaceous–Palaeogene boundary at ca 65·2 Ma. A borehole drilled in the central part of the crater cored a >400 m thick high‐resolution lacustrine succession that covers the Dan‐C2 hyperthermal event associated with a negative carbon isotope excursion. Continuous terrestrial records of past hyperthermals are of limited availability, which makes this record a unique case study of the continental impact of rapid climate warming. This study uses high‐resolution sedimentological core log data together with thin‐section, X‐ray diffraction, microprobe and palynological analyses to: (i) reconstruct lake sedimentological and ecological development across the carbon isotope excursion; and (ii) assess the environmental effect of hyperthermals on terrestrial ecosystems. Based on detailed facies analysis, five gradual stages of lake formation are identified, which show a strong relationship to carbon isotope shifts and associated climatic trends. Initially, sediment supply into the Boltysh lake was controlled by crater morphology. During later lake stages, sediment supply was increasingly controlled by changes in inflow–evaporation ratios which affected seasonal stratification patterns and longer term lake levels. An inferred increase in atmospheric pCO₂ related to the carbon isotope excursion, together with increasing mean annual temperatures, was probably responsible for periodic increases in biological activity of photosynthesising organisms and biomass production. These fluctuations in facies and lake settings largely correspond to orbital‐paced moisture availability oscillations. The gradual reduction in sediment supply commencing during early lake formation prior to carbon isotope excursion inception suggest that the Dan‐C2 event did not initiate sedimentary changes, but intensified sedimentary response to orbital controlled climate change.  相似文献   

Wide-band coupling of Earth's normal modes due to anisotropic inner core structure     

J. C. E. Irving  A. Deuss  J. Andrews 《Geophysical Journal International》2008,174(3):919-929

We investigate the importance of wide-band coupling of normal modes due to inner core anisotropy. We compare four different seismic models of inner core anisotropy, which were obtained by others using the splitting of Earth's normal modes. These models have been developed using a self-coupling (SC) approximation, which assumes that coupling between nearby modes through anisotropic inner core structure is negligible. We test the SC approximation by comparing the frequencies and quality factors of 90 inner core sensitive modes, computed for these models using either the SC approximation or full-coupling (FC) among large groups of modes. We find significant shifts in the quality factors and frequencies for some modes. Groups of modes which significantly couple together are constructed for six target modes. These groups are model dependent and in some cases contain large numbers of modes. Synthetic seismograms are calculated to show that the difference between SC and FC is observable on the scale of seismograms and of the same order of magnitude as the difference between synthetic and observed seismograms. Thus, future models of inner core anisotropy should take cross-coupling between large groups of modes into account.  相似文献   

Mhd Interpretation of LASCO Observations of a Coronal Mass Ejection as a Disconnected Magnetic Structure     

S. T. Wu  W. P. Guo  M. D. Andrews  G. E. Brueckner  R. A. Howard  M. J. Koomen  C. M. Korendyke  D. J. Michels  J. D. Moses  D. G. Socker  K. P. Dere  P. L. Lamy  A. Llebaria  M. V. Bout  R. Schwenn  G. M. Simnett  D. K. Bedford  C. J. Eyles 《Solar physics》1997,175(2):719-735

We present a qualitative and quantitative comparison of a single coronal mass ejection (CME) as observed by LASCO (July 28–29, 1996) with the results of a three-dimensional axisymmetric time-dependent magnetohydrodynamic model of a flux rope interacting with a helmet streamer. The particular CME considered was selected based on the appearance of a distinct ‘tear-drop’ shape visible in animations generated from both the data and the model. The CME event begins with the brightening of a pre-existing coronal streamer which evolves into a ‘tear-drop’ shaped loop followed by a Y-shaped structure. The brightening moves slowly outward with significant acceleration reaching velocities of ∼450 km s^-1 at 30 R⊙. The observed CME characteristics are compared with the model results. On the basis of this comparison, we suggested that the observed features were caused by the evacuation of a flux rope in the closed field region of the helmet streamer (i.e., helmet dome). The flux rope manifests itself as the cavity of the quasi-static helmet streamer and the whole system becomes unstable when the flux rope reaches a threshold strength. The observed ‘tear-drop’ structure is due to the deformed flux rope. The leading edge of the flux rope interacts with the helmet dome to form the typical loop-like CME. The trailing edge of this flux rope interacts with the local bi-polar field to form the observed Y-shaped structure. The model results for the evolution of the magnetic-field configurations, velocity, and polarization brightness are directly compared with observations. Animations have been generated from both the actual data and the model to illustrate the good agreement between the observation and the model. These animations can be found on the CD-ROM which accompanies this volume. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1004923016322  相似文献