Late‐glacial and Holocene record of vegetation and climate from Cynthia Bay,Lake St Clair,Tasmania

A Late‐glacial–Holocene pollen record was obtained from a 3.96 m sediment core taken from Lake St Clair, central Tasmania. Modern vegetation and pollen analyses formed the basis for interpretation of the vegetation and climate history. Following deglaciation and before ca. 18450 yr BP Podocarpus lawrencei coniferous heath and Astelia–Plantago wet alpine herbfield became established at Lake St Clair. A distinct Poaceae‐Plantago peak occurs between 18450 and 11210 yr BP and a mean annual temperature depression from ca. 6.2°C to 3°C below present is inferred for this period. The marked reduction in Podocarpus and strong increase of Poaceae suggests reduced precipitation levels during the period of widespread deglaciation (ca. 18.5–11 kyr BP). The local Late Pleistocene–Holocene non‐forest to forest biostratigraphical boundary is dated at 11.2 kyr BP. It is characterised by expansion of the subalpine taxa Athrotaxis/Diselma with Nothofagus gunnii, and by the establishment of Nothofagus cunninghamii with Eucalyptus spp. A ‘Phyllocladus bulge’ prior to the expansion of Nothofagus cunninghamii, reported at other Tasmanian sites, is not present at Lake St Clair. Nothofagus cunninghamii cool temperate rainforest peaked at 7800 yr BP, probably under wetter climatic conditions than present. The maximum development of rainforest in the early–middle Holocene may indicate that the temperature was slightly warmer than present, but the evidence is not definitive. The expansion of Eucalyptus spp. and Poaceae after 6000 yr BP may be partly a disclimax effect as a result of Aboriginal burning, but appears also to reflect reduced precipitation. The changes in vegetation and inferred climate can be explained by major changes in synoptic patterns of southern Australia and the adjacent southwest Pacific. Copyright © 2000 John Wiley & Sons, Ltd.     

Late‐glacial and early Holocene changes in vegetation and lake‐level at Hauterive/Rouges‐Terres,Lake Neuchâtel (Switzerland)

Palynological and sedimentological analyses of a sedimentary sequence sampled at Hauterive/Rouges‐Terres, Lake Neuchâtel (Switzerland) provide documentation of changes in vegetation and lake‐level during the Bølling, Younger Dryas and Preboreal pollen zones, and have allowed a comparison with sequences covering the same period from other sites located in the western part of the Swiss Plateau. The Juniperus–Hippophaë zone (regional pollen assemblage zone (RPAZ) CHb‐2, first part of the Bølling, ca. 14 650–14 450 cal. yr BP) was characterised by a generally low lake‐level. A weak rise occurred during this zone. The Juniperus–Hippophaë to Betula zone transition coincided with a lake‐level lowering, interrupted by a short‐lived but marked phase of higher lake‐level recorded at the neighbouring site of Hauterive‐Champréveyres, but not present at Hauterive/Rouges‐Terres owing to an erosion surface. Shortly after the beginning of the Betula zone (RPAZ CHb‐3, second part of the Bølling, ca 14 450–14 000 cal. yr BP), a marked rise in lake‐level occurred. It was composed of two successive periods of higher level, coinciding with high values of Betula, separated by a short episode of relatively lower lake‐level associated with raised values in Artemisia and other non‐arboreal pollen. The last part of RPAZ CHb‐3 saw a fall in lake‐level. The lower lake‐levels during RPAZ CHb‐2 to early RPAZ CHb‐3 can be correlated with the abrupt warming at the beginning of the Greenland Interstadial (GI) 1e thermal maximum. The successive episodes of higher lake‐level punctuating the GI 1e might be linked to the so‐called Intra‐Bølling Cold Oscillations identified from several palaeoclimatic records in the North Atlantic area, and also documented in oxygen‐isotope data sets from Swiss Plateau lakes. The Hauterive/Rouges‐Terres lake‐level record provides evidence for marked climatic drying through the second part of the Younger Dryas event (GS1), during the GS1–Preboreal (RPAZ CHb‐4b–4c) transition (except for a rise at ca. 11 450–11 400 cal. yr BP), and at the RPAZ CHb‐4c–5 (Preboreal–Boreal) transition, following the Preboreal Oscillation (after 11 150 cal. yr BP). The Preboreal Oscillation coincided with higher lake‐levels, its end being followed by a rapid expansion of Corylus, Quercus, Ulmus and Tilia. The Hauterive/Rouges‐Terres lake‐level record suggests that radiocarbon plateau at 12 600, 10 000 and 9500 ¹⁴C yr BP corresponded to periods of generally lower lake‐level. This suggests that an increase in solar activity may have contributed to both climatic dryness and a decrease in atmospheric radiocarbon content. Copyright © 2002 John Wiley & Sons, Ltd.     

Millennial‐scale climate variability in northwest Patagonia over the last 15 000 yr

A pollen record from Lago Condorito (41°45'S, 73°07'W) shows prominent vegetation and climate changes at millennial time‐scales, superimposed on multimillennial trends in temperature and westerly activity in northwest Patagonia during the past 15 000 yr. The record shows that evergreen temperate rainforests have dominated the landscape over this interval, with floristic changes ranging from cold‐resistant North Patagonian forests with podocarp conifers to Valdivian forests with thermophilous, summer‐drought resistant species. The long‐term trend shows that cool‐temperate and humid conditions prevailed between 15 000 and 11 000 cal. yr BP, followed by an extreme warm and dry phase between 11 000 and 7600 cal. yr BP, and subsequent cooling events and increase in precipitation that peaked at ca. 5000 cal. yr BP, when Southern Hemisphere alpine glaciers achieved their first Neoglacial maximum. Modern conditions were established at ca. 1800 cal. yr BP, following a warm and dry phase between ca. 2900 and 1800 cal. yr BP. These results suggest that millennial‐scale climate variability during deglacial and post‐glacial times also affected the mid‐latitude region of the South Pacific, supporting the idea that changes in the tropical Pacific might be a key factor in the initiation and/or propagation of millennial‐scale climate variability at regional, hemispheric and global scales. Copyright © 2004 John Wiley & Sons, Ltd.     

A Late‐glacial chironomid record from Hawes Water,northwest England

This paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ¹⁸O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ¹⁸O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.     

A high resolution,multiproxy Late‐glacial record of climate change and intrasystem responses in northwest England

A lacustrine carbonate sequence from Hawes Water, Lancashire, UK, has been studied using stable isotopic, lithological, pollen and mineral magnetic analysis. The data reveal four abrupt climatic oscillations in the Late‐glacial Interstadial leading up to the onset of the Loch Lomond Stadial. The data also point to climatic warming relatively early within the stadial, ca. 12 500 GRIP yr, prior to the onset of the Holocene. The oxygen isotope record is taken as a signature of climate forcing against which the response of the lake‐system can be monitored. By adopting this approach it is revealed that the response of the biological system to the rapid climatic oscillations is non‐linear and primarily a function of the antecedent conditions. A significant end‐Devensian isotopic excursion (A) is matched by only minor changes in the cold‐adapted floras and faunas. During the warmer interstadial, the response of the biological ecosystem (events B–D) is clearly influenced by thresholds: major changes in the catchment vegetation associated with relatively minor oscillations in the isotopic signature. The stratigraphical patterns reveal significant lag effects between the onset of climate deterioration and resulting changes in vegetation. Copyright © 2002 John Wiley & Sons, Ltd.     

A high‐resolution record of mire development and climatic change spanning the Late‐glacial–Holocene boundary at Church Moss,Davenham (Cheshire,England)

Excavations of deposits filling a closed basin within glacial drift at Church Moss, Davenham, near Northwich (Cheshire, England) revealed a sequence of Late‐glacial and Early Holocene sediments. Analyses of pollen and plant and invertebrate macrofossils were undertaken, together with loss‐on‐ignition analyses and a programme of AMS radiocarbon dating, to provide a record of changing biostratigraphy and climatic and ecological regimes. The infilling of features identified as frost‐cracks in the till flooring the basin gave remains that reflected conditions of extreme cold towards the end of the Devensian. The pollen record from a 3.5 m sequence of peat towards the deepest part of the basin, supported by radiocarbon dates, shows that organic deposition was initiated during the Late‐glacial Interstadial and continued into the early part of the Holocene. There was some evidence for a cool episode during the interstadial, with amelioration prior to the rapid onset of the tundra conditions of the Loch Lomond Stadial. Following the stadial, amelioration was rapid. There was evidence from both central and marginal sequences for a mosaic of fen dominated by sedges and often also mosses, with short‐lived small pools through much of the succession. Change to terrestrial conditions proceeded intermittently, probably as a result of subsidence caused by solution of underlying salt‐bearing strata. Copyright © 2000 John Wiley & Sons, Ltd.     

Chironomid‐inferred Late‐glacial air temperatures at Whitrig Bog,Southeast Scotland

This paper presents the first chironomid‐inferred mean July air temperature reconstruction for the Late‐glacial in Britain. The reconstruction suggests that the thermal maximum occurred early in the interstadial, with temperatures reaching about 12°C. There was then a gradual downward trend to about 11°C, punctuated by four distinct cold oscillations of varying intensity. At the beginning of the Younger Dryas, mean July temperatures fell to about 7.5°C but gradually increased to about 9°C before a rapid rise at the onset of the Holocene. The chironomid‐inferred temperature curve agrees closely, both in general trends and in detail, with the GRIP ice‐core oxygen‐isotope curve. The reconstructed temperatures are 2–4°C lower than coleopteran‐inferred temperatures but are closer to those inferred from plant macrofossils and glacial equilibrium‐line altitudes during the Younger Dryas. Copyright © 2000 John Wiley & Sons, Ltd.     

The Late‐glacial reoccupation of the British Isles and the Creswellian

This paper presents a review of AMS radiocarbon dating evidence for human occupation of Britain during the Late‐glacial Interstadial. The dates are all on humanly modified materials, including artefacts, and on human bone. The CalPal program is used to test whether the earliest evidence of human presence shows any correlation with more widespread climatic events, and if the British chronology differs significantly from that of neighbouring regions of northwest Europe. In the second part of the paper a number of well‐dated sites with British Late Upper Palaeolithic ‘Creswellian’ technology are examined and compared with lithic assemblages from The Netherlands and Belgium. The main conclusions of this work are that expansion of human populations into the northern edge of the upland zone just before or at the beginning of GI‐1 was followed by repopulation of the British Isles possibly with very little time‐lag. The British Creswellian sites offer evidence of this earliest resettlement, which is mainly focused on the upland margins of western and central Britain. Copyright © 2003 John Wiley & Sons, Ltd.     

A speleothem record of Holocene climate variability from southwestern Mexico

A paleoclimate reconstruction for the Holocene based upon variations of δ¹⁸O in a U-Th dated stalagmite from southwestern Mexico is presented. Our results indicate that the arrival of moisture to the area has been strongly linked to the input of glacial meltwaters into the North Atlantic throughout the Holocene. The record also suggests a complex interplay between Caribbean and Pacific moisture sources, modulated by the North Atlantic SST and the position of the ITCZ, where Pacific moisture becomes increasingly more influential through ENSO since ~ 4.3 ka. The interruption of stalagmite growth during the largest climatic anomalies of the Holocene (10.3 and 8.2 ka) is evidenced by the presence of hiatuses, which suggest a severe disruption in the arrival of moisture to the area. The δ¹⁸O record presented here has important implications for understanding the evolution of the North American Monsoon and climate in southwestern Mexico, as it represents one of the most detailed archives of climate variability for the area spanning most of the Holocene.     

The use of caddisfly fauna (Insecta: Trichoptera) to characterise the Late‐glacial River Trent,England

Trichoptera have been utilised infrequently in palaeoecological studies despite their value as environmental indicators of freshwater habitat structure and quality, via their aquatic larvae, and catchment macroclimate conditions, via the aerial adults. Two sites, dated ca. 11 600 ¹⁴C yr BP, in the middle reaches of the River Trent (England) supported caddisfly (Trichoptera) assemblages indicative of a dynamic braided river with extensive floodplain development. At the first, Barrow‐upon‐Trent, the caddisfly assemblage was dominated by taxa indicative of a medium to large gravel‐bed river (Lepidostoma hirtum, Micrasema setiferum and taxa from the family Hydropsychidae). At the second site, Hemington, the caddisfly fauna was dominated by taxa from the families Limnephilidae and Phryganeidae. These usually occur in slow flowing and standing waters and are indicative of cut‐off channels on the floodplain. Micrasema setiferum does not occur in the contemporary UK fauna and has a modern distribution across central Europe and Fennoscandia. A gridded climatology extracted for those geographical areas where M. setiferum occurs today indicated a greater degree of continentality than currently prevailing in the Trent catchment. The value of Trichoptera in palaeoecological studies is explored and a model of channel evolution for the River Trent is presented based on caddisfly data. Copyright © 2003 John Wiley & Sons, Ltd.     

Holocene vegetation and land‐use changes in response to climatic changes in the forelands of the southwestern Alps,Italy

The Holocene sediment of Lago Piccolo di Avigliana (Piedmont, Italy, 356 m a.s.l.) was dated by ¹⁴C and analysed for pollen to reconstruct the vegetation history of the area. The early‐ and mid‐Holocene pollen record shows environmental responses to centennial‐scale climatic changes as evidenced by independent palaeoclimatic proxies. When human impact was low or negligible, continental mixed‐oak forests decreased at ca. 9300 BC in response to the early‐Holocene Preboreal climatic oscillation. Abies alba expanded in two phases, probably in response to higher moisture availability at ca. 6000 and ca. 4000 BC , while Fagus expanded later, possibly in response to a climatic change at 3300 BC . During and after the Bronze Age five distinct phases of intensified land use were detected. The near synchroneity with the land‐use phases detected in wetter regions in northern and southern Switzerland points to a common forcing factor in spite of cultural differences. Increasing minerogenic input to the lake since 1000 BC coincided with Late Bronze—Iron Age technical innovations and probably indicate soil erosion as a consequence of deforestation in the lake catchment. The highest values for cultural indicators occurred at 700–450 and at 300–50 BC , coinciding with periods of high solar activity (inferred from Δ¹⁴C). This suggests that Iron Age land use was enhanced by high solar activity, while re‐occupation of partly abandoned areas after crises in earlier periods match better with the GRIP stable isotope record. On the basis of our data and comparison with independent palaeoclimatic proxies we suggest that precipitation variation was much more important than temperature oscillations in driving vegetation and societal changes throughout the Holocene. Copyright © 2006 John Wiley & Sons, Ltd.     

Holocene climate changes in southern Greenland: evidence from lake sediments

A Holocene lake sediment record is presented from Lake N14 situated on Angissoq Island 15 km off the main coast of southern Greenland. The palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica, clastic material, organic material and sulphur as well as sedimentation rate, moss content and magnetic susceptibility. A total of 43 radiocarbon dates has ensured a reliable chronology. It is argued that varying sediment composition mainly reflects changing precipitation. By analogy with the present meteorological conditions in southern Greenland, Holocene climate development is inferred. Between 11 550 and 9300 cal. yr BP temperature and precipitation increase markedly, but this period is climatically unstable. From 9300 yr BP conditions become more stable and a Holocene climatic optimum, characterised by warm and humid conditions, is observed from 8000 to 5000 cal. yr BP. From 4700 cal. yr BP the first signs of a climatic deterioration are observed, and from 3700 cal. yr BP the climate has become more dry and cold. Superimposed on the climatic long‐term trend is climate variability on a centennial time‐scale that increases in amplitude after 3700 cal. yr BP. A climatic scenario related to the strength and position of the Greenland high‐pressure cell and the Iceland low‐pressure cell is proposed to explain the Holocene centennial climate variability. A comparison of the Lake N14 record with a terrestrial as well as a marine record from the eastern North Atlantic Ocean suggests that the centennial climate variability was uniform over large areas at certain times. Copyright © 2004 John Wiley & Sons, Ltd.     

Evidence for Holocene climate variability from the sediments of a Scottish remote mountain lake

High resolution sampling of sediment cores covering approximately the last 4000 yr from Lochan Uaine, a small corrie loch in the Scottish Cairngorm Mountains, show quasi‐periodic cycles in organic matter (measured as percentage loss on ignition). Analysis of these cycles show correspondences between loss on ignition, δ¹³C values and chironomid head capsule abundance. We interpret the changes as reflecting changes in lake productivity and hypothesise that they are driven by climate variability. However, it is not yet clear whether the periods of relatively high organic matter production and preservation are associated with colder or with warmer conditions. Nevertheless the results indicate the value of using sediments from remote, undisturbed mountain lakes as recorders of Holocene climate variability. Copyright © 2001 John Wiley & Sons, Ltd.     

Response of chironomids to Late Quaternary environmental change in the Taitao Peninsula,southern Chile

An Erratum has been published for this article in Journal of Quaternary Science 17(7) 2002, 721. There is conflicting evidence concerning the extent and timing of late Quaternary climate variability in southern South America and how this may be linked to climate change in the Northern Hemisphere. Critical unresolved questions include whether or not a cool period occurred in southern South America during the Younger Dryas Chronozone (YDC) (11 000–10 000 ¹⁴C yr BP; 13 000–11 200 yr BP), and the timing of wet and dry phases during the Holocene. To date most evidence is from glacial, pollen and beetle records but, in an attempt to resolve these questions, we have used chironomid midges as an independent proxy in one of the first studies of its kind in Patagonia. We investigated the dynamics of midge assemblages during the Late‐glacial and Holocene at Lago Stibnite on the Taitao Peninsula, southern Chile (46°S). Changes in the midge assemblage suggest that the climate may have become cooler and drier during the YDC. During the Holocene there were cyclical changes in the midge assemblage that may have been in response to trophic change and/or to changes in precipitation when conditions appear to have been drier than today at 9400–6300 ¹⁴C yr BP and 2400–1600 ¹⁴C yr BP. Copyright © 2002 John Wiley & Sons, Ltd.     

River sediments,great floods and centennial‐scale Holocene climate change

A new analysis of all 346 published ¹⁴C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd.     

Two decadally resolved records from north‐west European peat bogs show rapid climate changes associated with solar variability during the mid–late Holocene

Two ¹⁴C accelerator mass spectrometry (AMS) wiggle‐match dated peat sequences from Denmark and northern England record changes in mire surface wetness reconstructed using plant macrofossil and testate amoebae analyses. A number of significant mid–late Holocene climatic deteriorations (wet shifts) associated with declines in solar activity were recorded (at ca. 2150 cal. yr BC, 740 cal. yr BC, cal. yr AD 930, cal. yr AD 1020, cal. yr AD 1280–1300, cal. yr AD 1640 and cal. yr AD 1790–1830). The wet shifts identified from ca. cal. yr AD 930 are concurrent with or lag decreases in solar activity by 10–50 years. These changes are replicated by previous records from these and other sites in the region and the new records provide improved precision for the ages of these changes. The rapidly accumulating (up to 2–3 yr cm^?1, ～1310 yr old, 34 ¹⁴C dates) Danish profile offers an unprecedented high‐resolution record of climate change from a peat bog, and has effectively recorded a number of significant but short‐lived climate change events since ca. cal. yr AD 690. The longer time intervals between samples and the greater length of time resolved by each sample in the British site due to slower peat accumulation rates (up to 11 yr cm^?1, ～5250 yr old, 42 ¹⁴C dates) acted as a natural smoothing filter preventing the clear registration of some of the rapid climate change events. Not all the significant rises in water table registered in the peat bog archives of the British and Danish sites have been caused by solar forcing, and may be the result of other processes such as changes in other external forcing factors, the internal variability of the climate system or raised bog ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.     

Late‐glacial to Holocene depositional architecture of the Ombrone palaeovalley system (Southern Tuscany,Italy): Sea‐level,climate and local control in valley‐fill variability

The Ombrone palaeovalley was incised during the last glacial sea‐level fall and was infilled during the subsequent Late‐glacial to Holocene transgression. A detailed sedimentological and stratigraphic study of two cores along the palaeovalley axis led to reconstruction of the post‐Last Glacial Maximum valley‐fill history. Stratigraphic correlations show remarkable similarity in the Late‐glacial to early‐Holocene succession, but discrepancy in the Holocene portion of the valley fill. Above the palaeovalley floor, about 60 m below sea‐level, Late‐glacial sedimentation is recorded by an unusually thick alluvial succession dated back to ca 18 cal kyr bp . The Holocene onset was followed by the retrogradational shift from alluvial to coastal facies. In seaward core OM1, the transition from inner to outer estuarine environments marks the maximum deepening of the system. By comparison, in landward core OM2, the emplacement of estuarine conditions was interrupted by renewed continental sedimentation. Swamp to lacustrine facies, stratigraphically equivalent to the fully estuarine facies of core OM1, represent the proximal expression of the maximum flooding zone. This succession reflects location in a confined segment of the valley, just landward of the confluence with a tributary valley. It is likely that sudden sediment input from the tributary produced a topographic threshold, damming the main valley course and isolating its landward segment from the sea. The seaward portion of the Ombrone palaeovalley presents the typical estuarine backfilling succession of allogenically controlled incised valleys. In contrast, in the landward portion of the system, local dynamics completely overwhelmed the sea‐level signal, following marine ingression. This study highlights the complexity of palaeovalley systems, where local morphologies, changes in catchment areas, drainage systems and tributary valleys may produce facies patterns significantly different from the general stratigraphic organization depicted by traditional sequence‐stratigraphic models.