Evaluation of transfer functions in spatially structured environments     

R.J. Telford  H.J.B. Birks 《Quaternary Science Reviews》2009,28(13-14):1309-1316

Transfer function training set sites close to each other tend to have similar species assemblages and environmental conditions in both oceanic and terrestrial data sets. This is unremarkable, but as this lack of independence between sites violates the assumptions of many statistical tests, it has severe consequences for transfer function evaluation, possibly resulting in inappropriate model choice and misleading and over-optimistic estimates of a transfer function's performance. In this paper, we develop a simple graphical method to test if spatial autocorrelation affects a training set, develop a Monte Carlo geostatistical simulation as a null model to test the significance of transfer functions in autocorrelated environments, and introduce a cross-validation scheme that is more robust to autocorrelation. We use these tests to show that some recently-published transfer functions have no predictive power, and strongly recommend the use of these tests to make transfer functions more robust to autocorrelation.  相似文献   

Radar images of the moon at 75 and 185 cm wavelengths     

J. E. B. Ponsonby  I. Morison  A. R. Birks  J. K. Landon 《Earth, Moon, and Planets》1972,5(3-4):286-293

The librations of the Moon allow it to be mapped using a continuous wave radar by an aperture synthesis method particularly suited to long wavelengths. Maps, as seen in the depolarised return at wavelengths of 75 and 185 cm, are presented. Both are broadly similar and show that most of the depolarised return comes from the highland regions with no significant return from the maria. Certain isolated features, such as the craters Tycho, Theophilus, and Copernicus, appear particularly prominent.Paper presented to the NATO Advanced Study Institute on Lunar Studies, Patras, Greece, September 1971.  相似文献   

The impact of the Laacher See Tephra on terrestrial and aquatic ecosystems in the Black Forest,southern germany     

A. F. Lotter  H. J. B. Birks 《第四纪科学杂志》1993,8(3):263-276

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11000 yr BP) have been analysed for pollen and diatoms at two sites (Hirschenmoor, Rotmeer) in the montane belt of the Black Forest (southern Germany) in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota. The pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition, whereas the pollen of aquatic macrophytes do not show any consistent pattern. Partial redundancy analysis and Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically. The diatom assemblages at both sites changed after the deposition of the LST and diatominferred pH estimates suggest a short but non-significant excursion towards lower values. Multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the LST and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically. However, owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the LST or by lithological changes.  相似文献   

Winifred Tutin (1915–2007)     

H. J. B. Birks  Hilary H. Birks 《Journal of Paleolimnology》2007,38(4):601-605

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Holocene sediments of Sägistalsee, a small lake at the present-day tree-line in the Swiss Alps     

A.F. Lotter  H.J.B. Birks 《Journal of Paleolimnology》2003,30(3):253-260

Sägistalsee is a small lake located at the modern tree-line in the Swiss Alps. A 13.5 m long core taken in the central part of the 9.5 m deep basin consists of clayey silts and sands and dates back to about 9000 cal. BP. These sediments have a low organic content that steadily increases from 4–8% loss-on-ignition at 550 °C towards the top of the core, whereas the carbonate content decreases from 20 to about 10% loss-on-ignition at 950 %C. We outline the aims of an interdisciplinary research project centred on the Holocene sediments of Sägistalsee. We also present information about the lake, its sediments, and its catchment that forms the basis for different biotic and abiotic multi-proxy studies carried out on the sediments of Sägistalsee.  相似文献   

Recent Environmental Change and Human Impact on Svalbard: The Lake-Sediment Geochemical Record   总被引：1，自引：1，他引：1  

J.F. Boyle  N.L. Rose  P.G. Appleby  H.J.B. Birks 《Journal of Paleolimnology》2004,31(4):515-530

As part of a broader investigation into recent environmental change on Svalbard, the inorganic geochemical record of six lake-sediment cores was analysed. The major temporal trends in sediment elemental composition are driven by variations in two contrasting sediment components, both derived from catchment soils: (1) mineral matter, and (2) soil organic matter (SOM), enriched in Fe and Mn oxides and heavy metals. Two environmental impacts are recorded in most or all of the lake sediment sequences. An up-core increase in organic matter can be partly attributed to diagenetic effects, but also requires an enhanced supply of SOM relative to mineral matter. In addition, the central and southern sites all show a ca. 1970 event characterised by an enhanced mineral matter accumulation rate. This requires either an enhanced allochthonous supply or an enhanced mobilisation of littoral sediments. In either case a regional-scale driving force, such as a shift in climate, is required. At five of the lakes the sediment heavy metal concentration profiles can be explained entirely by natural factors. However, at Tenndammen (U), situated close to the Svalbard’s largest settlement at Longyearbyen, possible anthropogenic Pb enrichment is found. Comparison of observed and expected heavy metal profiles (based on Greenland ice-core data) shows that the lakes are generally too insensitive to have recorded a long-transported heavy metal pollution signal.  相似文献   

The Dynamics of Chironomidae (Insecta: Diptera) Assemblages in Response to Environmental Change during the past 700 years on Svalbard   总被引：8，自引：4，他引：8  

Stephen J. Brooks  H.J.B. Birks 《Journal of Paleolimnology》2004,31(4):483-498

The impact of recent natural and human-induced environmental change on chironomid faunas on Svalbard has been investigated. The modern chironomid fauna was studied from surface-sediment samples collected from 23 lakes in western Svalbard. A total of 18 taxa was found, of which three had not been recorded previously from Svalbard. The influence of water chemistry and physical variables on the distribution and abundance of the modern chironomid assemblages was investigated using correspondence analysis and multiple regression. The chironomid assemblages fall into four groups, which are primarily influenced by pH, nutrient concentrations, water temperature, and water depth. Sediment cores were taken from three lakes to investigate changes in chironomid assemblages over the last 700 years. At two of the sites there is evidence for a response to regional climatic change occurring about 200 years ago and may have been associated with the ‘Little Ice Age’. At the third site there is a response to local catchment changes, probably brought about, initially, by the establishment of a human settlement close to the lake 70 years ago, and subsequently, as a result of the abandonment of this settlement in 1988.  相似文献   

Recent paleolimnology of three lakes in Northwestern Minnesota     

Hilary H. Birks  M.C. Whiteside  Donna M. Stark  R.C. Bright 《Quaternary Research》1976,6(2):249-IN11

A paleolimnological study was undertaken to investigate changes in three Minnesota lakes over the last 100 years and to demonstrate the stratigraphic effects of cultural eutrophication in two of them. The study combined the analysis of the lake sediment from short cores with stratigraphic analyses of pollen, plant macrofossils, mollusks, diatoms and certain other algae, chydorid Cladocera, and Daphnia ephippia.The rise of Ambrosia type pollen (ragweed) marks the onset of interference with the landscape by European man, which can be closely dated. Calculations of sedimentation rates from this base gave reasonable correlations of other stratigraphic events with historical events.Elk Lake is considered “unpolluted” today and was chosen as a control. Man's effects are limited to logging some of the surrounding forest and to the construction of a dam. Small changes in the lake's fauna and flora are demonstrated, showing the sensitivity of the lake to changes in its catchment area.Lake Sallie and St. Clair Lake, in the same watershed as the city of Detroit Lakes, have been affected not only by logging but also by addition of nutrients from agricultural runoff and sewage effluent. Considerable responses by the lake organisms are apparent. In Lake Sallie the changes were gradual, but in St. Clair Lake they were very abrupt because the lake was partially drained at the same time and the water volume was thereby reduced.The merits of such an integrated study, the types of information gained from the analyses of the various fossils, and the wider application of the results are discussed.  相似文献   

Diatom assemblages from Adirondack lakes (New York,USA) and the development of inference models for retrospective environmental assessment   总被引：5，自引：0，他引：5  

Sushil S. Dixit  Brian F. Cumming  H. J. B. Birks  John P. Smol  John C. Kingston  Allen J. Uutala  Donald F. Charles  Keith E. Camburn 《Journal of Paleolimnology》1993,8(1):27-47

Detrended canonical coreespondence analysis (DCCA) was used to examine the relationships between diatom species distributions and environmental variables from 62 drainage lakes in the Adirondack region, New York (USA). The contribution of lakewater pH, Al_m (monomeric Al), NH₄, maximum depth, Mg, and DOC (dissolved organic carbon) were statistically significant in explaining the patterns of variation in the diatom species composition. Twenty-three and sixteen diatom taxa were identified as potential indicator species for pH and Al_m, respectively (i.e. a taxon with a strong statistical relationship to the environmental variable of interest, a well defined optimum, and a narrow tolerance to the variable of interest). Using weighted-averaging regression and calibration, predictive models were developed to infer lakewater pH (r ²=0.91), Al_m (r ²=0.83), DOC (dissolved organic carbon) (r ²=0.64), and ANC (acid neutralizing capacity; r ²=0.90). These variables are of key importance in understanding watershed acidification processes. These predictive models have been used in the PIRLA-II (Paleoecological Investigation of Recent Lake Acidification-II) project to answer policy-related questions concerning acidification, recovery, and fisheries loss.  相似文献   

New age estimates and climatostratigraphic correlations for the Borrobol and Penifiler Tephras: evidence from Abernethy Forest,Scotland     

I. P. Matthews  Hilary H. Birks  A. J. Bourne  S. J. Brooks  J. J. Lowe  A. MacLeod  S. D. F. Pyne‐O'Donnell 《第四纪科学杂志》2011,26(3):247-252

The emerging tephrostratigraphy of NW Europe spanning the last termination (ca. 15–9 ka) provides the potential for synchronizing marine, ice‐core and terrestrial records, but is currently compromised by stratigraphic complications, geochemical ambiguity and imprecise age estimates for some layers. Here we present new tephrostratigraphic, radiocarbon and chironomid‐based palaeotemperature data from Abernethy Forest, Scotland, that refine the ages and stratigraphic positions of the Borrobol and Penifiler tephras. The Borrobol Tephra (14.14–13.95 cal ka BP) was deposited in a relatively warm period equated with Greenland Interstadial sub‐stage GI‐1e. The younger Penifiler Tephra (14.09–13.65 cal ka BP) is closely associated with a cold oscillation equated with GI‐1d. We also present evidence for a previously undescribed tephra layer that has a major‐element chemical signature identical to the Vedde Ash. It is associated with the warming trend at the end of the Younger Dryas, and dates between 11.79 and 11.20 cal ka BP. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献