Les C. Cwynar

An event stratigraphy for the Last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group.

It is suggested that the GRIP Greenland ice-core should constitute the stratotype for the Last Termination. Based on the oxygen isotope signal in that core, a new event stratigraphy spanning the time interval from ca. 22.0 to 11.5 k GRIP yr BP (ca. 19.0-10.0 k 14 C yr BP) is proposed for the North Atlantic region. This covers the period from the Last Glacial Maximum, through Termination 1 of the deep-ocean record, to the Pleistocene-Holocene boundary, and encompasses the Last Glacial Late-glacial of the traditional northwest European stratigraphy. The isotopic record for this period is divided into two stadial episodes, Greenland Stadials 1 (GS-1) and 2 (GS-2), and two interstadial events, Greenland Interstadials 1 (GI-1) and 2 (GI-2). In addition, GI-1 and GS-2 are further subdivided into shorter episodes. The event stratigraphy is equally applicable to ice-core, marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon-dated chronostratigraphy that has been used hitherto.

Geographical Variation of Lodgepole Pine in Relation to Population History

Relation des caracteristiques genetiques et morphologiques des populations de Pinus contorta ssp. latifolia depuis leur origine

Isotopic &events' in the GRIP ice core: a stratotype for the Late Pleistocene

An event stratigraphy for the Last Termination, based on the stratotype of the GRIP ice-core record, has been outlined for the North Atlantic region. It is suggested that such an approach to stratigraphic subdivision may o!er a more satisfactory alternative to conventional stratigraphical procedures for those parts of the recent Quaternary record that are characterised by rapid and/or short-term climatic #uctuations. ( 1999 Elsevier Science Ltd. All rights reserved.

An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada

AbstractUsing an expanded surface sample data set, representing lakes distributed across a transect from southernmost Canada to the Canadian High Arctic, a revised midge-palaeotemperature inference model was developed for eastern Canada. Modelling trials with weighted averaging (with classical and inverse deshrinking; with and without tolerance downweighting) and weighted averaging partial least squares (WA-PLS) regression, with and without square-root transformation of the species data, were used to identify the best model. Comparison of measured and predicted temperatures revealed that a 2 component WA-PLS model for square-root transformed percentage species data provided the model with the highest explained variance (r

Rapid and widespread vegetation responses to past climate change in the North Atlantic region.

_{jack}^2

THE AMPHI-ATLANTIC OSCILLATION - A PROPOSED LATE-GLACIAL CLIMATIC EVENT

= 0.88) and the lowest error estimate (RMSEPjack = 2.26 °C). Comparison of temperature inferences based on the new and old models indicates that the original model may have seriously under-estimated the magnitude of late-glacial temperature oscillations in Atlantic Canada. The new inferences suggest that summer surface water temperatures in Splan Pond, New Brunswick were approximately 10 to 12 °C immediately following deglaciation and during the Younger Dryas. During the Allerod and early Holocene, surface water temperatures of 20 to 24 °C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.

Accelerator-mass spectrometer ages for late-glacial events at Ballybetagh, Ireland

A 403—cm core was recovered from Hanging Lake in unglaciated northern Yukon. Twenty—one radiocarbon dates indicate that the section is at least 25 000 and possibly 33 000 yr old; they permit the calculation of pollen influxes for the full—glacial in eastern Beringia. Numerical methods were used to divide the pollen stratigraphy into five zones. From prior to 33 000 to 18 450 BP, a herb zone was dominant (zone HL 1) with high percentages of Gramineae, Artemisia, and Cruciferae. However, the low pollen influx, ranging from 5—100 grains°cm—2°yr—1, the low organic content of the sediment, and the occurrence of open—ground taxa all indicate that the vegetation cover was sparser than it is today. The arctic—alpine affinities of the herb pollen show that generically the vegetation was akin to modern arctic plant communities. Modern fellfield communities in the northern Yukon and Siberia have a rich and endemic Artemisia flora and they can produce pollen spectra comparable to that of the herb zone. Percent and influx values for spruce, alder, and birch increased slightly during subzone H 1B (21 680—18 450 BP); this subzone probably represents an interstadial. From 18 450 to 14 600 BP, a Salix—Cyperaceae zone (HL 2) occurred, suggesting the development of snowbed and willow scrub communities in sheltered areas. Between 14 600 and 11 100 BP Betula pollen dominated (zone HL 3) indicating the spread of dwarf birches, but the influx data show that this initial increase was modest compared with the subsequent zone and thus dwarf birches were probably restricted at this time to more favorable habitats. The spread of birch together with the increased total pollen influx, the higher organic content of the sediment, and the increased richness of herb pollen indicates that the local flora was more diverse and that the vegetative cover increased. The climate must have warmed. Zone HL 4 (Ericales zone) spanned the period from 11 100 to 8900 BP. Wet heath communities became locally abundant, poplar was more abundant at the beginning of this zone than at any subsequent time, the ranges of Typha latifolia and Myrica gale were greater than today, and pollen influx and sedimentation rate both increased greatly. Spruce became regionally abundant. These varied changes are probably in response to a warmer and wetter climate; they provide evidence for a late Pleistocene to early Holocene warm interval initially recognized by McCulloch and Hopkins (1966). Zone HL 5 (Alnus crispa zone) has been dated from 8900 BP to the present; it reflects the regional expansion of Alnus crispa on organic soils.

Alnus as an indicator taxon of the Younger Dryas cooling in eastern North America

Ongoing anthropogenic perturbations to the atmosphere and biosphere increase the risk of future abrupt changes in the climate system and generate concern about the ability of natural ecosystems to respond to rapid climate change. Study of past climatic events and biotic responses can inform us about potential future change. Qualitatively fast local responses of plant taxa to abrupt late glacial climate oscillations have been reported from individual records and attributed to short migration distances in areas of high topographic relief. By using quantitative time-series analyses, we show that vegetation responses to late glacial climate change around the North Atlantic were rapid and widespread and occurred in areas of differing relief. Cross-correlation analysis of 11 high-resolution lacustrine records in eastern North America and Europe indicates vegetation-response times consistently of ,200 yr and often ,100 yr, despite regional differences in physiography and species composition. Vegetation lags of ,200 yr confirm theoretical predictions, and the apparently tight coupling between vegetation and atmosphere suggests that recent climatic trends may already have begun to affect plant population abundances and distributions.