Pollen-stratigraphic Evidence Research Articles

On the timing of retreat of the Loch Lomond (‘Younger Dryas’) Readvance icefield in the SW Scottish Highlands and its wider significance

It has long been assumed that the last glacier expansion in the Scottish Highlands, the Loch Lomond Readvance (LLR), resulted from a cold reversal that was broadly coeval with the ‘Younger Dryas’ episode. This view has recently been challenged, with the suggestion that glacier ice had disappeared from Rannoch Moor, one of the main ice accumulation centres in the SW Scottish Highlands, by as early as 12.5 ka, i.e. within the first half of the ‘Younger Dryas’. Here we present new radiocarbon, tephrostratigraphical and pollen-stratigraphical evidence from one of the key sites on Rannoch Moor, the results of an experiment designed to test this hypothesis. Our results not only contradict that concept, but are fully compatible with other evidence from the SW Scottish Highlands that suggests that the LLR glaciers in this area continued to expand until towards the end of the ‘Younger Dryas’ period, and may have persisted in some places after the onset of the Holocene. We consider the possible reasons for this marked divergence in chronology, a matter that is crucial to resolve because the precise timing of the demise of the LLR glaciers has important palaeoclimatic and other implications. In the wider context, we also draw attention to problems with the general use of the term ‘Younger Dryas’ and why we regard the Greenland stratotype unit and term ‘Greenland Stadial 1’ (GS-1) a more secure stratigraphic comparator.

8800 years of high-altitude vegetation and climate history at the Rutor Glacier forefield, Italian Alps. Evidence of middle Holocene timberline rise and glacier contraction

Sedimentary archives at or near the timberline ecotone in Alpine glaciated areas contain records to study Holocene climate change and the interplay between climate, ecosystems, and humans. We focused on records of timberline and glacier oscillations in the Rutor Glacier forefield (Western Italian Alps) in the last 8800 years. Human activity in this area was negligible for most of the Holocene. We adopted an integrative stratigraphic approach including proxies for glacier advance and timberline estimation, sedimentary events, and reconstructed temperatures. Changes in timberline ecotone correlate to climate until the Middle Ages. Pollen-stratigraphic evidence of a primary plant succession highlights a lag beween local deglaciation and the first reliable 14C age. The radiocarbon chronology points to a prolonged phase of glacier contraction between 8.8 and 3.7 ka cal BP. Even later the glacier remained within its LIA limits. Between 8.4 and 4 ka cal BP MAT-inferred TJuly fluctuated near 12.4 °C, ca. 3.1 °C higher than today. During this period, a Pinus cembra forest belt grew at 2600 m asl with an upper limit of tree groves placed 434 ± 310 m above the current open forest limit. This Holocene phase of thermal maximum ended between 3.98 and 3.51 ± 70 ka cal BP and with a substantial rearrangement of forest composition; temperature reconstruction shows a decrease of 1.8 °C. This climate deterioration concluded the Subboreal thermal optimum, mirroring glacial advances widely documented in the Alps. The Rutor Glacier advanced at ca. AD 1093 ± 65, and remained inside the LIA maximum extent. The LIA started since AD 1594, and culminated between AD 1751 and 1864.

Did large ice caps persist on low ground in north‐west Scotland during the Lateglacial Interstade?

AbstractRecent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived 10Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.

Data on mid-Holocene climatic, vegetation and anthropogenic interactions at Stanshiel Rig, southern Scotland

Pollen, microscopic charcoal and peat humification analyses were applied to radiocarbon-dated peat cores to examine environmental change before and after the mid-Holocene transition from hunter-gatherer (Mesolithic) to agricultural (Neolithic) communities in presently marginal upland pasture at Stanshiel Rig, Annandale, southern Scotland. The Mesolithic-Neolithic transition in northern Britain is characterised by a number kf key environmental changes as well as economic shifts, including temporal patterns of fire and the Ulmus decline. Deliberate vegetation modification by Mesolithic communities is not demonstrable at Stanshiel Rig, and openings in the woodland canopy may have been promoted by grazing by wild animals or have been a consequence of climate change. Changes in fire frequency are also correlated with peat- and pollen-stratigraphic evidence for shifts to a drier climate in the late Mesolithic, probably mediated through pedological and biomass-storage change. A single Ulmus decline occurred between ca. 5650 and 5600 cal B. P., and is related here to climate change. Neolithic-age impacts on the woodland were limited, and no cereal-type pollen were found. The difference between hunter-gatherer and opportunistic farmer/hunter-gatherer at this locally is argued to be insignificant, or not detectable palynologically.

Pollen-stratigraphic evidence of human activity at Dieng, Central Java

The pollen stratigraphy of a small lake at 2000 m elevation in the Dieng Highlands of Central Java, where a large Hindu-Javanese religious center flourished from about 1250 to 700 B.P., indicates substantial and nearly continuous clearance of the montane forest since about 1350 B.P. A core to the base of organic sediments is 14 m long and has a basal date of 1340 B.P. A zone of abundant pollen of the weedy herb Plantago major corresponds well in time with the occupation of the religious center. After about 700 B.P., the pollen of secondary forest species shifted in composition, suggesting a different pattern of vegetation use in the highlands. In the mid-19th century, European observers reported that the forest on the mountains at Dieng was closed and mature, but evidence in the pollen is lacking. By the 1920s, the expanding human population had stripped the landscape of trees, and the first pollen of cultivated plants appears in the stratigraphy. Because of local protection and forest replanting, trees have again increased on the steepest slopes, and the pollen assemblage today differs in composition from the previous zones.

Pollen-stratigraphical evidence of Holocene hydrological change in northern Fennoscandia supported by independent isotopic data

Pollen records from 21 sites were used to reconstruct Holocene hydrological changes in northern Fennoscandia. The inferred dominance of maritime-type Betula-forests from c. 9600 BP onwards indicate an oceanic climate in the region during the early Holocene, with high amounts of precipitation and low seasonal contrasts. This interpretation is supported by oxygen isotope records obtained on lacustrine carbonates from Abisko, northern Sweden. Enrichment of O-18 during the early Holocene suggests enhanced zonal circulation and a pronounced influence of Atlantic air-masses in northern Sweden. The pattern of Pinus expansion in the area was time-transgressive, ranging from 9200-8000 BP in the extreme north-east to 7900-5500 BP in the western and south-western parts of the region. The replacement of Betula-forests by Pinus-forests indicates a climatic change towards drier summers and increased seasonality. At Abisko, a close correlation between regional Pinus expansion and depletion of (1)8O in lacustrine carbonates suggests that the expansion of Pinus was triggered by a gradual attenuation of the influence of westerlies. Thus, in large-scale palaeohydrological terms, the early expansion of Pinus in the north-easternmost parts of Fennoscandia as compared to the successively later expansion in the west and south-west may reflect a gradually decreasing influence of Atlantic air-masses in northern Fennoscandia during the early and mid Holocene. (Less)

Holocene evolution of a lowland Scottish landscape: Kirkpatrick Fleming. Part I, peat- and pollen-stratigraphic evidence for raised moss development and climatic change

This series of papers addresses the principal natural and anthropogenic environmental changes that have transformed a typical lowland Scottish landscape during the Holocene. Sediment- and pollen- stratigraphic techniques, together with radiocarbon dating, are applied in this paper to the stratigraphy of a raised bog at Burnfoothill Moss, eastern Dumfriesshire, to deduce changes in groundwater levels within the bog, and by inference, changes in effective precipitation. The basin, initially a shallow pond, was rapidly colonized by fen peat at 9600 BP, possibly during a phase of drier climate, which ended at c. 8700 BP. Short-lived fluctuations in bog-surface wetness are identified before a major change to a wetter bog surface at around 7700 cal. BP, representing the transformation from fen peat to raised moss. Anthropogenic interference with surrounding woodland is believed to have destabilized the water balance within the peat. Drier bog-surface conditions occur at c. 6700 cal. BP, and a shift to a wetter climate at around 5250 cal. BP, but a perhaps more substantial wet shift is recorded at c. 4000 cal. BP. At c. 1900 cal. BP a dry climate shift is recognized, ending at c. 1200 cal. BP. Slightly prior to the 'Little Ice Age', represented by a very wet phase before c. 400 cal. BP, is a dry period between c. 600 and 400 cal. BP.

Wisconsinan Late‐glacial environmental change in Newfoundland: A regional review

AbstractThe distribution of 75 lake and bog sites, from which pollen stratigraphical evidence relevant to the late Quaternary of Newfoundland has been obtained, is presented. The detailed records of lithology, pollen and diatoms, supplemented by geochemical data, are discussed for three of the sites — Southwest Brook Lake, Woody Hill Brook Pond and Leading Tickles — and interpretations made are based on vegetational history, relative climatic changes and extent of ice cover. Radiocarbon data from 14 sites are summarised. A summary chart of Late‐glacial environmental changes, including a qualitative palaeotemperature curve, is provided.

New pollen-stratigraphic evidence for the deglaciation and lake drainage chronology of the Glen Roy-Glen Spean area

Synopsis Pollen-stratigraphic evidence is presented from a number of sites in Glen Roy and lower Glen Treig. The new data do not support the chronology of the Glen Roy-Loch Laggan proglacial lake drainage proposed by Macpherson (1978). The evidence also has a bearing on the controversy over the age of outwash fan deposits in upper Glen Roy, and this problem is re-examined here. Since no Late Devensian Lateglacial deposits are found anywhere in the region, whereas early Flandrian (Holocene) successions are found in several basins, the evidence as a whole is interpreted as indicating that the outwash deposits at the Roy–Turret confluence are of Loch Lomond Stadial age.

A reinterpretation of the Lateglacial environmental history of the Isle of Skye, Inner Hebrides, Scotland

AbstractThis paper presents a major revision of the Late Devensian Lateglacial environmental history of the Isle of Skye, Scotland, based upon a combination of geomorphological, biostratigraphical and radiocarbon evidence. The distribution of glacial and periglacial landforms, and of raised shorelines, suggests that there was only one extensive readvance of local glaciers in southern Skye following the wastage of the Late Devensian ice sheet. Pollen‐stratigraphic evidence from 10 sites inside and 4 sites outside the mapped ice limits indicates that this readvance occurred during the Loch Lomond Stadial. At that time over 180km2 of the uplands of south‐central Skye were covered by glacier ice, a much more extensive glaciation than previously envisaged. Palynological evidence from four Lateglacial profiles implies that degree of exposure to strong westerly winds was the principal factor determing vegetational contrasts on the island, and that regional differences in vegetational type were less pronounced than has hitherto been suggested. The glacial and palaeobotanical reconstructions reported here are more compatible with Lateglacial data from the Scottish mainland and Hebridean islands than were the previously‐published accounts for the Isle of Skye.

A critical evaluation of pollen-stratigraphic investigations of pre-Late Devensian sites in Scotland

This paper reviews pollen-stratigraphic evidence from proposed interglacial and pre-Late Devensian interstadial sites in Scotland. The paper has two major parts. In the first the stratigraphic details of each of the sites are summarised and discussed. The sites are classified as ‘interglacial’ or ‘interstadial’ according to the interpretations adopted by recent authors, though as discussed in later sections such distinction is problematic and somewhat arbitrary. In the second part general problems of interpretation are discussed in the light of the stratigraphic details. Problems of dating and correlation are severe since most of the sediments lie close to or beyond the limit of conventional radiocarbon dating. Thus the normal approach has been to use pollen-stratigraphic comparisons with type-sites in southern or eastern England. This practice is considered questionable. Problems of assessing the provenance of pollens and spores are perhaps even more important, and at some sites are so severe as to render pollen assemblages of limited value. The problems discussed are: (a) secondary reworking of pollen; (b) long-distance wind transport of nonregional pollen; (c) pollen deterioration and (d) low pollen concentrations. Many of the problems discussed are of general significance being applicable to late Quaternary pollen diagrams from other regions. In the concluding section of the paper certain procedures are proposed that may permit a clearer assessment of potential problems of taphonomy in pollen stratigraphy.

Lateglacial and early Flandrian chronology of the Isle of Mull, Scotland

The Isle of Mull, which lies off the west coast of Scotland (Fig. 1), was partially over-ridden by ice from the mainland during the build-up of the late Devensian ice sheet1 but, in common with the adjacent islands of Rum2 and Skye3, supported smaller ice masses, including independent valley and cirque glaciers during the Loch Lomond Stadial4,5 (approximately equivalent with the Younger Dryas of Scandinavia6,7). However, although the recent glacial history of Mull is understood, at least in general terms, little is known about the nature and timing of the major environmental changes that preceded and succeeded the Loch Lomond Stadial on the island. We present here pollen–stratigraphical evidence supported by 15 radiocarbon dates which provide new information on landscape changes on the Isle of Mull from the wastage of the last Scottish ice sheet to the early part of the Flandrian period. The radiocarbon dates are of particular significance as they form the basis for the first Lateglacial and early Flandrian chronology for the islands of the Scottish Inner Hebrides.

The early Postglacial environment of Scotland: Evidence from a site near Tyndrum, Perthshire

Pollen‐stratigraphic evidence is presented from a site in the Grampian Highlands of Scotland in which a detailed record is preserved of early Postglacial plant succession in an area previously occupied by glacier ice. Following an initial period of open habitat conditions during which sedge‐moss communities were interspersed with large areas of bare, disturbed ground, the area around the site was colonised first by Empetrum heath, and then successively by juniper scrub, birch, and then birch‐hazel woodland. On a local scale, the biostratigraphic record implies a rapid shallowing of lake waters during the early Postglacial, due possibly to relatively dry climatic conditions which prevailed in the area after ca. 9000 B.P. Radiocarbon dates were obtained from the basal sediments in the site, but these are regarded as aberrant due to groundwater contamination. In view of the poor resolution associated with the radiocarbon‐dating of Lateglacial and early Flandrian events in Britain, a method is proposed here whereby pollen stratigraphic evidence at widely separated sites can be employed to gauge the extent to which deglaciation at the end of the Loch Lomond (Younger Dryas) Stadial was time‐transgressive across the Highlands of Scotland

Late-Glacial history of the Brecon Beacons, South Wales

In the uplands of the Brecon Beacons, Black Mountains, Fforest Fawr area of South Wales, small arcuate moraines and/or protalus ramparts are found below steep escarpments and in glacial cirques1–3. The freshness and distinctive morphology of many of these features have led to the suggestion that they are not a product of the late Devensian ice sheet, but may have been formed during the Loch Lomond Stadial of the Late-Glacial period (Fig. 1), the last occasion when glaciers existed in the British Isles. I present here pollen-stratigraphic evidence and radiocarbon dates which form the basis for the first Late-Glacial chronology for this area of South Wales, and which prove that the features described above developed during the Loch Lomond Stadial (approximately equivalent with the Younger Dryas of Scandinavia4–6).