Glacial Vegetation Research Articles

Small changes in the sea surface temperature during the last 20,000 years: Molecular evidence from the western tropical Pacific

One of the most controversial problems of glacial paleoclimatology is the conservative change in tropical sea surface temperature (SST) in contrast with the large high altitude temperature change in the western tropical Pacific. In this report SST was estimated for the last 20,000 years using alkenones preserved in marine sediments recovered from a site 800 km north of New Guinea. The UK37 (unsaturation degree of long‐chain alkenones synthesized by planktonic prymnesiophyte algae) record suggests that SST decreased at most 1.5°C at the last glacial maximum. This small changes in SST of the western tropical Pacific is concordant with results previously reported in UK37 studies from the eastern equatorial Pacific and the equatorial Atlantic. The UK37‐based SST estimates are in good agreement with the CLIMAP results and planktonic foraminifera δ18O, but much smaller than those (ca. −5°C) obtained from coral Sr/Ca and δ18O thermometries and glacial vegetation reconstruction.

Long Pleistocene pollen sequences from the Velay Plateau (Massif Central, France)

In June 1988, a 50-m-deep boring was made in the lacustrine infilling of the explosion crater of Ribains (Haute-Loire). On the basis of pollen analyses the following chronology is proposed for this sequence: 0–5.10 m, Holocene and Lateglacial (hiatus); 5.70–17.48 m, last pleniglacial; 17.48–27.70 m, early glacial; 27.70–31.55 m: last interglacial, referred to as the Ribains Interglacial; 31.55–53.50 m, penultimate glaciation. The zone between 32.0 and 22.5 m, corresponding to a thick diatomite layer, provided a detailed record of the last interglacial and the early glacial vegetation succession. This enabled precise correlations with the neighbouring site of Lac du Bouchet and other long European sequences, confirming the proposed chronology. In particular, the temperate phase correlated with the St-Germain I of Grande Pile is well characterized, as at Lac du Bouchet, by the presence of an abrupt cooling corresponding to the Montaigu Event. In contrast, the last pleniglacial deposits contain great amounts of reworked pollen from earlier temperate phases, this making a comparison with Lac du Bouchet impossible. The thick sequence representing the penultimate glaciation is also affected by sediment loss during coring. However, several cold episodes are recorded that are characterized either by a total absence of vegetation or by a treeless steppe vegetation or a Pinus woodland, like the successions observed in the last pleniglacial at Lac du Bouchet.

Glacial to interglacial vegetation changes in the northern and southern Pyrénées: Deglaciation, vegetation cover and chronology

New palynological investigations have been carried out in the southern, northern and Mediterranean part of the Pyrenean chain. Pollen percentage and concentration diagrams are compared for a period including the end of the glacial period, the Late Glacial and Postglacial periods. From the new results and from comparisons with previous published data, the steppe and semi-desert vegetation of the end of the last glacial period are described, as well as the plant communities of the period 15-13 ka. A dry climate was responsible for the early glacial retreat before 30 ka. Deglaciation was continuous up to about 15-14 ka, without any readvance around 20-18 ka. Different aspects of the Late Glacial vegetation are studied and the first stages of the Postglacial are described. The Younger Dryas event is found everywhere, but particularly clearly in the Mediterranean area. The most important 14C dates are discussed, and a plateau of 14C ages is clearly visible around 10,000 BP.

Late Pleistocene/Holocene radiolarian and pollen records from sediments in the Sea of Okhotsk

In two cores with oxygen isotope stratigraphy from the southern Okhotsk Sea, marine pollen and siliceous microfauna record concurrent late glacial through Holocene variations in regional terrestrial and marine environments. Glacial vegetation around the southern Okhotsk basin, which resembles the present tundra/steppe of the northwest coast of this marginal sea, yields to spruce‐dominated boreal forests during the glacial/interglacial transition. Temperate forest components, such as oak, peak during the mid‐Holocene. Decreasing oak accompanied by increasing spruce reflects the effect of global cooling on local vegetation during the last 4 kyr. Although the radiolarian fauna in the Okhotsk Sea samples is similar to that present in the northwest Pacific, the dominant species in both regions differ. Concentrations of radiolarians are low in latest glacial samples, with higher concentrations occurring above and below this interval. Cycladophora davisiana, the dominant radiolarian species in the majority of Holocene Okhotsk Sea sediments, is present at lower percentages in late glacial samples from our two sites. Thus, this species' Holocene/latest Pleistocene abundance pattern in Sea of Okhotsk sediments is the reverse of that recorded in high‐latitude open ocean sites. The combined marine pollen and radiolarian records indicate changes in the Sea of Okhotsk's physical oceanographic conditions and surrounding vegetation during the late glacial which were associated with this region's response to global climate change.

Holocene Paleoecology of the Boreal Forest and Great Lakes‐St. Lawrence Forest in Northern Ontario

This paper presents pollen and macrofossil stratigraphies derived from sediment cores taken near the deepest parts of Nina Lake (46°36' N, 81°30' W), Jack Lake (47°19' N, 81°46' W), and Lake Six (48°24' N, 81°19' W), which are situated along a transect across the ecotone between the boreal forest and the Great Lakes—St. Lawrence forest in northern Ontario. Paleoecological data from this region of steep climatic gradient and varied landforms provide sensitive records of postglacial vegetational and climatic changes. These data are used to evaluate questions concerning the occurrence of late—glacial vegetation communities without modern analog. Hypsithermal ecotonal movements, and individualistic species response to climatic change and soil development. The early postglacial boreal forest that colonized the Canadian Shield upland after ca. 10 000 BP was dominated by white spruce with little or no black spruce, and probably contained more oak, elm, poplar, and heliophytic herbs and shrubs than its modern counterpart. Its lack of modern analog is probably due to the widespread occurrence of fresh, unleached soil in a newly deglaciated landscape. Spruce declined and was replaced by jack pine after ca. 9000 BP as the climate continued to warm. The boreal forest was enriched floristically by the successive immigration of species such as Myrica. Alnus crispa, and A. rugosa. Boreal forest was transformed into Great Lakes—St. Lawrence forest ca. 7400 yr ago when white pine, beech, and hemlock immigrated to Nina Lake. Species of the Great Lakes—St. Lawrence forest responded individualistically to Hypsithermal climatic changes. White pine populations continued to spread northward during ca. 7000—3000 BP, causing the boreal forest/Great Lakes—St. Lawrence forest ecotone to advance ca. 140 km north of its present position, only constrained by the physiographic boundary between the Clay Belt and the Canadian Shield upland. During 6000—4500 BP northern white cedar proliferated in the Clay Belt lowlands due to a warmer and drier climate. The regional water table was lowered, permitting Thuja populations that were otherwise restricted to the margins of swamps and open peatlands to spread to the center. This vegetation response was landform selective, being more pronounced in the Clay Belt than on the Canadian Shield upland. The predominance of calcareous substrates and wetland habitats in the Clay Belt was favorable to the expansion of Thuja under a suitable climate. Neoglacial cooling decimated the populations of northern white cedar in the Clay Belt and those of white pine in the whole region. Spruce, jack pine, and balsam fir increased over the last 4000 yr. The ecotone retreated from near Lake Six after 3000 BP, reaching Jack Lake at ca. 2600 BP, and was stabilized in its modern position during the last millennium.

Last Glacial loess and early Last Glacial vegetation history of Wairarapa Valley, New Zealand

Abstract The upper Quaternary stratigraphic and physiographic record of Wairarapa Valley, southern North Island, is one of the most complete sequences for this time period in New Zealand. Wairarapa Valley is situated within an active tectonic belt, and opens to the south on a coastline that has been rapidly deformed during the Quaternary. Warm climate and high eustatic sea level are reflected by a sequence of five well-preserved marine benches, and by lacustrine environments in Wairarapa Valley. Cold climate (and low eustatic sea level) are reflected by erosion, fluvial aggradation, and loess production. Three loess units deposited on Last Interglacial marine benches are widely preserved around the coastal part of the valley, and on fluvial aggradation gravels older than the Last Interglacial, further inland. At several other sites, the three loess units are preserved conformably on lacustrine sediments containing pollen and diatoms. At one site, Bidwill Hill, a well-preserved pollen and diatom flora reco...

Guatemalan forest synthesis after Pleistocene aridity

Sediments from two lakes in the Peten Department, Guatemala, provide palynological evidence from Central America of late Pleistocene aridity and subsequent synthesis of mesic forests. Late Glacial vegetation consisted of marsh, savanna, and juniper scrub. An early Holocene temperate forest preceded a mesic tropical forest with Brosimum (ramon). Thus "primeval" rain forests of Guatemala are no older than 10,000 to 11,000 years and are considerably younger in the Peten due to Mayan disturbances. Among dated Neotropical sites, the Peten has the most mesic vegetation yet shown to have supplanted xeric vegetation present during the Pleistocene. The arid late Glacial-humid early Holocene transition appears to have been pantropical in the lowlands. The Peten was not a Pleistocene refugium for mesophytic taxa, as has been suggested. Thus genesis of extant rain forests in northern Central America and southern Mexico remains unexplained.

Late Quaternary Vegetational History of Illinois

Pollen diagrams from the Prairie Peninsula in Illinois record the climatically related vegetation shifts that have occurred since the late Pleistocene. They indicate that the major period of prairie development started between 8500 and 7900 BP, apparently occurring first along the southern margin. These events mark the beginning of the Hypsithermal interval and are correlated with the final disintegration of the Laurentide ice sheet and the establishment of the postglacial system of atmospheric circulation over North America. The late—glacial vegetation was spruce woodland in the north and open spruce woodland/tundra in central Illinois. These vegetation communities disappeared from the state in a northward direction between 14 000 and 10 900 BP. They were followed in northern Illinois by Pinus, Abies, Betula, and Fraxinus; in central Illinois Fraxinus expanded in the lowlands while the uplands remained relatively treeless. These assemblages, which persisted longer in the south than in the north, were subsequently replaced first by a mixture of cool temperate, then warm temperate deciduous trees as climatic amelioration continued. By 9000 BP, Illinois was dominated by deciduous forest. In response to Hypsithermal climatic stress, prairie vegetation began replacing deciduous forest about 8300 BP on the uplands in central Illinois and by 7900 BP xeric oak—hickory forest became dominant in northern Illinois. This is the beginning of the Prairie Peninsula as a discrete floristic area in Illinois. About 5000 BP the southern border of the Prairie Peninsula experienced increased moisture and renewed forest development suggesting a western contraction of the prairie margins. Central Illinois, however, remained grassland to the present. Between 900 and at least 400 yr ago an indicated trend toward cooler temperatures is correlated with late stages of the Neoglacial. Pollen evidence from northern Illinois and adjacent Lake Michigan indicates the reappearance or increase in Betula, Pinus, Picea and Larix. This short cool episode appears to end prior to the beginning of large—scale historic land clearance, about 140 yr ago, as the evidence for a vegetational readjustment to warmer climate is truncated by the logging of the forests, the plowing of the prairies and the resultant dramatic increase in Ambrosia pollen.

Contributions to the Quaternary history of the New Zealand flora 8. Interglacial and glacial vegetation in the Westport District, South Island

Abstract Pollen analysis of organic layers exposed in quarries and road cuttings provides the framework for an understanding of vegetation and climate history during and since the last (Oturi) interglacial in the Westport district. The early and late Oturi are separated by a stadial of unknown duration when forest was replaced by grassland-shrubland. During the early Oturi Nothofagus forest was dominant, but during the late Oturi Dacrydium cupressinum was dominant until it was replaced by Nothofagus. The Otiran record, like the Oturian, is incomplete, but an interstadial characterised by shrubland and by minor spread of Nothofagus began earlier than 31 000 yr B.P. and ended c. 26 000 yr B.P. Subsequently vegetation of grassland or grassland-shrubland remained dominant until the post-glacial spread of forest. The transition from grassland to forest was abrupt and not preceded by the shrubland phase common to the early post-glacial in most areas investigated in New Zealand; there is no evidence of a break i...

Omaha Kinship Terminology and Spruce-Fir Pollen

AbstractTwo points raised in a review of Indian Life in the Upper Great Lakes are discussed. The points questioned were statements about Winnebago social organization and the late glacial and early postglacial vegetation of the Upper Great Lakes. A review of the available evidence suggests that the Winnebago had an Omaha type of kinship system and that the late glacial and early post-glacial vegetation included spruce and fir or spruce and deciduous trees with coeval differences of vegetation being due to factors of soil, drainage, light, elevation, and pioneering ability instead of climate.