J. John Lowe

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.

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.

Temperature gradients in northern Europe during the last glacial-Holocene transition (14-9 14C kyr BP) interpreted from coleopteran assemblages.

Late-glacial and early Holocene climatic conditions have been reconstructed for northern Europe using the mutual climatic range (MCR) palaeoclimate method based on fossil coleopteran assemblages. Altogether, beetle faunas from 77 sites have been analysed ranging from Ireland in the west to Poland and Finland in the east, and MCR estimates calculated. The results are plotted on 16 maps, each representative of a selected time-slice covering the period from 14.5 14C kyr BP to 9.0 14C kyr BP. Eight of the maps show the MCR estimates of Tmax (mean temperature of the warmest month) derived from each site for which data are available, while the remainder show estimated Tmax isotherms interpolated from these values. It can be demonstrated that at times the thermal climate was fairly uniform throughout the study area, whereas at others temperature gradients were much steeper than they are in the region today. There also appears to be a distinct contrast between cold periods, when contours trended NW–SE, and warmer periods, when contours trend W–E or even NE–SW. The pattern of climatic changes that emerges is shown to be very different from the traditional view that has been used up to now as a template for classifying Late-glacial climatic events on a wide, even global, scale. The suddenness and intensity of changes in the thermal climate may have been partially responsible for an apparent lack of equilibrium between the flora and fauna of the time and the physical environment in which they lived.

The use of microtephra horizons to correlate Late‐glacial lake sediment successions in Scotland

Evidence is presented to show that two measurable concentrations of microtephra particles can be detected in deposits of Late Devensian Late-glacial age in three sites in Scotland. One layer is attributed to the Vedde Ash, a marker horizon within the Younger Dryas chronozone. The second is a new tephra reported for the first time, which we name the Borrobol Tephra. This occurs consistently near the base of the Late-glacial Interstadial organic sediments at each site, and is thought to date to around 12.5 14C ka BP. Geochemical determinations using an electron microprobe confirm the identification of the Vedde Ash, suggest the Borrobol Tephra to have an Icelandic origin, and demonstrate the consistency of the geochemical signals at all three sites.

Volcanic ash layers illuminate the resilience of Neanderthals and early modern humans to natural hazards

Marked changes in human dispersal and development during the Middle to Upper Paleolithic transition have been attributed to massive volcanic eruption and/or severe climatic deterioration. We test this concept using records of volcanic ash layers of the Campanian Ignimbrite eruption dated to ca. 40,000 y ago (40 ka B.P.). The distribution of the Campanian Ignimbrite has been enhanced by the discovery of cryptotephra deposits (volcanic ash layers that are not visible to the naked eye) in archaeological cave sequences. They enable us to synchronize archaeological and paleoclimatic records through the period of transition from Neanderthal to the earliest anatomically modern human populations in Europe. Our results confirm that the combined effects of a major volcanic eruption and severe climatic cooling failed to have lasting impacts on Neanderthals or early modern humans in Europe. We infer that modern humans proved a greater competitive threat to indigenous populations than natural disasters.

Sub-millennial scale climatic oscillations in the central Adriatic during the Lateglacial: palaeoceanographic implications

Abstract A multi-proxy study of a sedimentary core obtained from the central Adriatic basin provides evidence of short-term events of palaeoceanographic variability during the last glacial Lateglacial period (GRIP event stages GI-1 and GS-1). Comparison of the Adriatic results with other Mediterranean records reveals a common sequence of changes in palaeoceanographic conditions. Variations in foraminiferal assemblage data and in stable isotopic compositions indicate two short-term cold oscillations, which interrupted an overall cooling trend that commenced at the beginning of the Greenland GI-1 episode (Bolling/Allerod episode). These cold events, considered to be contemporaneous with GI-1b and GI-d of the GRIP ice-core record, are indicated by distinctive foraminiferal assemblages, which reflect episodes of high productivity under relatively restricted water circulation, with (in particular) reduced vertical mixing during winter. Differences in the foraminiferal assemblages indicate that the younger of the two cold spells is characterized by reduced ventilation of bottom waters. Our results, combined with published data from neighbouring marine basins, suggest a widespread reduction in deep-water formation in the central Mediterranean which commenced during the GI-1b episode and reached its maximum effect during the onset of the GS-1 (Younger Dryas) episode. Moreover, three intervals with reduced vertical mixing correspond to the two cold spells during GI-1 and the lower phase of the GS-1 episode and show close similarities with the palaeoceanographic changes reported for the North Atlantic. This similarity indicates that the Mediterranean and North Atlantic may have been responding more-or-less synchronously to common forcing mechanisms.

The Devensian (Weichselian) Lateglacial palaeoenvironmental record from Gransmoor, East Yorkshire, England: A contribution to the ‘North Atlantic seaboard programme’ of IGCP-253, ‘Termination of the Pleistocene’

Abstract Palynological and coleopteran data are described from a section through Late Devensian (Weichselian) deposits at Gransmoor, East Yorkshire, England. The pollen evidence shows that, following an initial open-habitat episode, first Juniperus scrub and later Betula woodland became established in the area during the Lateglacial Interstadial. This woodland was replaced during the Loch Lomond (Younger Dryas) Stadial by a predominatly herbaceous flora with arctic/alpine, steppe and halophytic elements. The coleopteran evidence indicates a similar local environment and that the thermal maximum of the Interstadial, when mean July temperatures may well have exceeded 18°C, occurred prior to the deposition of the earliest polleniferous sediments. By the time of the Juniperus expansion, summer temperatures had fallen by 2–4°C to levels comparable with those of the present day. A further temperature decline followed the expansion of Betula during the later Interstadial and another fall occurred at the Lateglacial Interstadial/Loch Lomond Stadial boundary. During the Loch Lomond Stadial mean July temperatures of 9–11°C are implied, with winter temperatures as low as −15 to −20°C. Collectively the evidence reemphasises the point that for the first 1000 years or so of the Lateglacial Interstadial, there was a disequilibrium between the palynological and coleopteran records in terms of climatic signal. During the later Interstadial, however, a closer relationship is apparent between both proxy data sources. Of particular significance in this respect is the fluctuation in reconstructed summer and winter temperatures, and a rise and subsequent fall in Betula pollen frequencies. This may be the correlative of one of the pre-Younger Dryas climatic oscillations recorded in other proxy data sources including palynological records from Britain and eastern Canada, oxygen isotope traces from Swiss lake sediments, isotopic and electrical conductivity profiles from the Greenland ice sheet, and diatom and foraminiferal records in cores from the Norwegian Sea and the North Atlantic Ocean.

Towards a European tephrochronological framework for Termination 1 and the Early Holocene

The record of deposition of tephras in Europe and the North Atlantic during the period 18.5–8.0 14C ka BP (the Last Termination and Early Holocene) is reviewed. Altogether, 34 tephras originating from four main volcanic provinces (Iceland, the Eifel district, the Massif Central and Italy) have been identified so far in geological sequences spanning this time–interval. Most of the records have been based, until very recently, on observations of visible layers of tephras. Here, we report on the potential for extending the areas over which some of the tephras can be traced by the search for layers of micro–tephra, which are not visible to the naked eye, and on the use of geochemical methods to correlate them with known tephra horizons. This approach has greatly extended the area in Northern Europe over which the Vedde Ash can be traced. The same potential exists in southern Europe, which is demonstrated for the first time by the discovery of a distinct layer of micro–tephra of the Neapolitan Yellow Tuff in a site in the Northern Apennines in Italy, far to the north of the occurrences of visible records of this tephra. The paper closes by considering the potential for developing a robust European tephrostratigraphy to underpin the chronology of records of the Last Termination and Early Holocene, thereby promoting a better understanding of the nature, timing and environmental effects of the abrupt climatic changes that characterized this period.

A re-evaluation of the vegetation history of the eastern Pyrenees (France) from the end of the last glacial to the present

Abstract Fourteen pollen records obtained from 10 sites in the eastern Pyrenees are presented along with the results of 40 new radiocarbon dates of samples obtained from these sites. The data (784 pollen spectra) provide a more comprehensive evaluation of the vegetation history of the region than has hitherto been possible. The salient elements of the regional plant succession are described in the light of a study of regional pollen rain/vegetation relationships. Vegetational developments during the last glacial-interglacial transition and the Holocene are compared with those of other regions in France and the western Mediterranean. This approach therefore provides a new synthesis of published and unpublished information over a large area. A consistent and coherent pattern emerges and the new evidence indicates a number of previously-held views on the vegetation history of the Pyrenees to be erroneous.

The chronology of palaeoenvironmental changes during the Last Glacial-Holocene transition: towards an event stratigraphy for the British Isles

The overall aim of the TIGGER IIb project is to increase our understanding of the manner and rates by which ecosystems responded to climate changes during the Last Glacial-Holocene transition. Success in this venture requires better constrained palaeoenvironmental reconstructions than have been achieved thus far, and the TIGGER project focused, in particular, on three main aims: (1) off-setting the limitations of conventional radiocarbon dating, in order to provide a more secure chronology of events; (2) increasing the resolution and precision of palaeoclimatic reconstructions; (3) widening the scope of site-specific palaeoecological investigations. In this paper we focus on the first of these strategies, and describe the progress made in developing a more coherent timescale for the climate history of the Lateglacial period. This has been achieved by using a number of independent methods, including calibration of AMS radiocarbon dates obtained from terrestrial plant macrofossils, MCR estimates of summer temperatures based on coleopteran records, analysis of stable carbon isotope ratios in terrestrial plant macrofossils and tephrochronology. Following Björck et al.s 1998 recommendations, we integrate the new results to construct a provisional event stratigraphy for the Last Glacial-Holocene transition in the British Isles, which is based on a sequence of features that are believed to be time-parallel. This approach is considered to provide a more coherent framework for direct comparison of the palaeoenvironmental evidence from Britain with that from elsewhere.