We used 5704 14C, 10Be, and 3He ages that span the interval from 10,000 to 50,000 years ago (10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an increase in northern summer insolation, providing the source for an abrupt rise in sea level. The onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent with evidence that this was the primary source for an abrupt rise in sea level approximately 14.5 ka.

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 14C 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) and2 (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. © 1998 John Wiley & Sons, Ltd.

On the basis of synchronization of three carbon-14 (14C)-dated lacustrine sequences from Sweden with tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta14C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.

The Les Echets sediment sequence has recently been the subject of a high-resolution, multi-proxy study which revealed shifts in lake productivity linked to Greenland stadials and interstadials over the last 40 ka . Rapid ecosystem response to abrupt climate changes during the last glacial period in western Europe, 40-16 ka. Geology 36: 407-410). Here we present new elemental data for this sequence as acquired using an X-ray fluorescence core scanning system which provides in situ high-resolution, continuous, multi-element analyses. It was found that the strength of associations between the studied elements (Ti, Rb, K, Zr, Si, Ca, Sr, Mn and Fe) varied over time with changes in lake status which are ultimately driven by changes in climate. Increases in fine-grained, detrital input (as indicated by Ti, Rb, K and Zr/Rb) overlap with independently established periods of lower lake productivity and are interpreted to represent more arid conditions. Several of these arid periods are coincident with low diatom concentrations and the timing of Heinrich events H4, H3 and H2. The duration of the environmental impacts linked to the H events varied by proxy with elemental data (Ti and Zr/Rb) estimating shorter events than the diatom data. Periods of lower detrital input and coarser grain sizes agreed in time with periods of higher lake productivity. The elemental data provide new insights into hydrological changes and related sediment processes within the catchment, and highlight the need for multi-element and multi-proxy approaches when reconstructing climate change using lacustrine sediment sequences.

Analyses of two infilled lakes in Blekinge, southeast Sweden, indicate the presence of at least three tephra horizons of Termination 1 and early Holocene age. Geochemical analyses confirm the presence of the Borrobol Tephra, the Askja Tephra (10,000 14C yr B.P.), and one previously unreported tephra of Icelandic origin. Extending the limits of the Borrobol Tephra to Scandinavia illustrates that this ash is far more widespread than previously realized and is therefore, an important marker horizon for determining the rate and timing of the initial warming at the start of Greenland Interstade 1 (GI-1) within Europe. The relatively unknown Askja Tephra and the newly discovered Hässeldalen Tephra are stratigraphically placed at the Younger Dryas/Preboreal transition. This paper demonstrates the suitability and success associated with the extraction techniques for tracing microtephra horizons in areas distal to volcanic sources.

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The sediment sequence from Hässeldala port in southeastern Sweden provides a unique Lateglacial/early Holocene record that contains five different tephra layers. Three of these have been geochemically identified as the Borrobol Tephra, the Hässeldalen Tephra and the 10-ka Askja Tephra. Twenty-eight high-resolution 14 C measurements have been obtained and three different age models based on Bayesian statistics are employed to provide age estimates for the five different tephra layers. The chrono-and pollen stratigraphic framework supports the stratigraphic position of the Borrobol Tephra as found in Sweden at the very end of the Older Dryas pollen zone and provides the first age estimates for the Askja and Hässeldalen tephras. Our results, however, highlight the limitations that arise in attempting to establish a robust, chronologically independent lacustrine sequence that can be correlated in great detail to ice core or marine records. Radiocarbon samples are prone to error and sedimentation rates in lake basins may vary considerably due to a number of factors. Any type of valid and 'realistic' age model, therefore, has to take these limitations into account and needs to include this information in its prior assumptions. As a result, the age ranges for the specific horizons at Hässeldala port are large and calendar year estimates differ according to the assumptions of the age-model. Not only do these results provide a cautionary note for overdependence on one age-model for the derivation of age estimates for specific horizons, but they also demonstrate that precise correlations to other palaeoarchives to detect leads or lags is problematic. Given the uncertainties associated with establishing age-depth models for sedimentary sequences spanning the Lateglacial period, however, this exercise employing Bayesian probability methods represents the best possible approach and provides the most statistically significant age estimates for the pollen zone boundaries and tephra horizons.