Characterization of the Soil Hydromorphic Conditions in a Paludified Dunefield during the Mid-Holocene Hemlock Decline near Québec City, Québec

The mid-Holocene eastern hemlock [Tsuga canadensisL. (Carr.)] decline has been recently attributed to the activity of insect defoliators. N. Bihiry and L. Filion,Quaternary Research45,312–320 (1996). In this study, soil hydromorphic conditions were investigated for the period 6800–3200 yr B.P. using micromorphological data from a peat section from a swale in a paludified dunefield in southern Québec. After a short period of plant colonization in shallow pools between 6800 and 6400 yr B.P., mesic conditions predominated in the interdune before the decline (6400–4900 yr B.P.), as evidenced by strong bioturbation and abundance of excrements from the soil fauna. During the decline, a shift from mesic to wet conditions occurred (4900–4100 yr B.P.), although xeric to mesic conditions persisted on dune ridges until at least 4200 yr B.P. Wetness culminated when beaver occupied the site (4100–3750 yr B.P.). Hemlock needles with chewing damage typical of hemlock looper (Lambdina fiscellaria) feeding were identified at levels dated 4900, 4600, and 4200 yr B.P., respectively, implying that the hemlock decline was associated with at least three defoliation events. The ca. 400-yr interval between these events likely represents the time required for this late-sucessional tree species to recover.     

Boreal peatland margins as repository sites of long-term natural disturbances of balsam fir/spruce forests

A multidisciplinary, high-resolution paleoecological study (Lepidoptera and plant remains, macroscopic charcoal, pollen) was conducted on a 4000-yr peat monolith extracted from the margin of an ombrotrophic peatland on Anticosti Island (Gulf of St. Lawrence, eastern Canada) to reconstruct the long-term natural disturbances (insect outbreaks, forest fires) of a balsam fir/spruce forest. We hypothesized that an activity of insect defoliators (spruce budworm, hemlock looper) was the main disturbance factor of conifer forests during the Late Holocene. The earliest remains of spruce budworm and hemlock looper were found ca. 3220 and 2350 cal yr BP, respectively. Peaks of insect head capsules occurred from ca. 1640 to ca. 625 cal yr BP. Low balsam fir pollen concentrations during this period suggest a lengthy episode ( 1000 yr) of high insect activity, resulting in extensive fir dieback and mortality. The long-term dynamics of the pristine balsam fir/spruce forests were mainly governed by the activity of insect defoliators. The limited extent and possibly the low occurrence of forest fires in the maritime environment of Anticosti Island allowed the development of mature coniferous stands propitious for insect infestations. Insect head capsules appeared to be a useful and effective tool for establishing insect presence and activity during the Holocene.     

Quaternary palynology of the Pacific slope of Washington

Quaternary deposits on the Pacific slope of Washington range in age from the earliest known interglaciation, the Alderton, through the Holocene. Pollen stratigraphy of these deposits is represented by 12 major pollen zones and is ostensibly continuous through Zone 8 over more than 47,000 radiocarbon yr. Before this, the stratigraphy is discontinuous and the chronology less certain. Environments over the time span of the deposits are reconstructed by the comparison of fossil and modern pollen assemblages and the use of relevant meteorological data. The Alderton Interglaciation is characterized by forests of Douglas fir (Pseudotsuga menziesii), alder (Alnus), and fir (Abies). During the next younger interglaciation, the Puyallup, forests were mostly of pine, apparently lodgepole (Pinus contorta), except midway in the interval when fir, western hemlock (Tsuga heterophylla), and Douglas fir temporarily replaced much of the pine. Vegetation outside the limits of Salmon Springs ice (>47,00034,000 yr BP) varied chiefly between park tundra and forests of western hemlock, spruce (Picea), and pine. The Salmon Springs nonglacial interval at the type locality records early park tundra followed by forests of pine and of fir. During the Olympia Interglaciation (34,00028,000 yr BP), pine invaded the Puget Lowland, whereas western hemlock and spruce became manifest on the Olympic Peninsula. Park tundra was widespread during the Fraser Glaciation (28,00010,000 yr BP) with pine becoming more important from about 15,000 to 10,000 yr BP. Holocene vegetation consisted first of open communities of Douglas fir and alder; later, closed forests succeeded, formed principally of western hemlock on the Olympic Peninsula and of western hemlock and Douglas fir in the Puget Lowland. Over the length of the reconstructed environmental record, climate shifted between cool and humid or relatively warm, semihumid forest types and cold, relatively dry tundra or park tundra types. During times of glaciation, average July temperatures are estimated to have been at least 7°C lower than today. Only during the Alderton Interglaciation and during the Holocene were temperatures higher for protracted periods that at present.     

Fossil Arthropods from a Full-Glacial Site in Northeastern Italy

Fossil remains of beetles and oribatid mites from a peat deposit dated 18,870 ± 300 yr B.P. near Verona, northeastern Italy, represent the first insect fauna of its kind from the last glacial maximum to be described from Italy. The assemblage includes the ground beetle Amara alpina, whose distribution today in Europe is restricted to mountains in Scandinavia and Scotland. Ecological requirements and geographic distribution of recent populations of the identified species suggest mesic habitats with standing water and peat bogs during the glacial maximum. The paleoenvironment was comparable to present-day lowland moors in Scandinavia or mesic environments above 1000 m altitude on the southern slopes of the Alps. The climate is inferred to have been colder and wetter than today. Mean July temperature may have been 8-9°C lower than at present.     

Constructing Seasonal Climograph Overlap Envelopes from Holocene Packrat Midden Contents, Dinosaur National Monument, Colorado

Five Neotoma spp. (packrat) middens are analyzed from Sand Canyon Alcove, Dinosaur National Monument, Colorado. Plant remains in middens dated at approximately 9870, 9050, 8460, 3000, and 0 ¹⁴C yr B.P. are used to estimate Holocene seasonal temperature and precipitation values based on modern plant tolerances published by Thompson et al. (1999a, 1999b). Early Holocene vegetation at the alcove shows a transition from a cool/mesic to a warmer, more xeric community between 9050 and 8460 ¹⁴C yr B.P. Picea pungens, Pinus flexilis, and Juniperus communis exhibit an average minimum elevational displacement of 215 m. Picea pungens and Pinus flexilis are no longer found in the monument.Estimates based on modern plant parameters (Thompson et al., 1999a) suggest that average temperatures at 9870 ¹⁴C yr B.P. may have been at least 1° to 3°C colder in January and no greater than 3° to 10°C colder in July than modern at this site. Precipitation during this time may have been at least 2 times modern in January and 2 to 3 times modern in July. Discrepancies in estimated temperature and precipitation tolerances between last occurrence and first occurrence taxa in the midden record suggest that midden assemblages may include persisting relict vegetation.     

Expansion of Magellanic Moorland during the late Pleistocene: Palynological evidence from northern Isla de Chiloé, Chile

The late Quaternary vegetation of northern Isla de Chiloé is inferred from palynological analysis of a section in the Río Negro drainage (42°03′S, 73°50′W). At ca. 30,500 yr B.P., maxima of Astelia and Donatia occurred, suggesting wetland development. From that time until ca. 27,000 yr B.P., steppe indicators such as Compositae/Gramineae dominated, suggesting drier conditions. After 27,000 yr B.P., the moorland shrub Dacrydium gradually increased, reaching a maximum by 18,000 yr B.P. At this time Astelia increased again, suggesting development of cushion bog during cold and wet conditions. The glacial-postglacial transition is characterized by a marked change from peaty sediments to clays, a decrease in the cushion bog flora, and the prevalence of Gramineae/ Compositae and swamp taxa. This vegetation prevailed until ca.7000 yr B.P. when forest taxa became dominant. The floristic pattern inferred from the pollen spectra of the Rio Negro section suggests that the late Pleistocene vegetation of Chiloé resembled modern Magellanic Moorland vegetation (52°–56°lat S). Based on climatic conditions presently associated with Magellanic Moorland, its occurrence in Chiloé at low elevations during the late Pleistocene implies a decrease in average temperature of at least 4°C and an increase in annual precipitation of at least 1500 mm.     

An insect assemblage of early Flandrian age from Lea Marston, Warwickshire, and its bearing on the contemporary climate and ecology

An extensive insect fauna is described from an organic deposit occurring in a gravel pit at Lea Marston, Warwickshire, England. This organic deposit was lying beneath approximately 2.5 m of alluvial clay and directly above gravels which had provided organic material ¹⁴C dated at 11,700 ± 200 yr BP. The insect fauna was indicative of a temperate oceanic climate similar to that found today in southern England or south Sweden and suggested the presence of deciduous woodland. The six radiocarbon dates, however, agreed in giving the deposit an age of around 9500 yr BP which is earlier than the arrival of the principal broad-leaved trees. The pollen assemblage was consistent with the radiocarbon dates in showing, in addition to herbaceous pollen, only the presence of Betula, Salix, and small amounts of Pinus. As the insect faunas known from midland Britain at the close of the Devensian period, barely 500 yr before, are aretic in aspect and entirely devoid of thermophilous species a very rapid climatic amelioration is postulated which permitted the immigration of the very mobile insect fauna well in advance of the more slowly migrating trees.     

Tectonic plate motion and deformation inferred from very long baseline interferometry

We inverted 76 rates of change of baseline lengths measured with very long baseline interferometry (VLBI) during the period 1979–1989 to estimate the parameters of motions of the North American (noam) and Eurasian (eura) plates relative to the Pacific (pcfc) plate. We considered two types of plate motion models, namely, rigid and non-rigid models. In the non-rigid models, we simultaneously determined the non-rigid motions of several stations near plate boundaries due to intraplate deformation. Intraplate deformation in the regions far away from plate boundaries is assumed to be negligible.Among several models considered, a non-rigid model called M2 is found to fit most closely to the observed data. In this model, six stations are assumed to be capable of the non-rigid motion; those are goldvenu, hatcreek, mojave12, ovro 130 and vndnberg, in the southwestern United States and kashima, in Japan. M2 gives parameter sets of 0.827 ± 0.035°/m.y., about 50.5 ± 1.2°N, 78.5 ± 5.3°W and 0.889 ± 0.049°/m.y., about 59.7 ± 1.9°N, 85.1 ± 7.4 °W, representing the noam-pcfc and eura-pcfc relative motions. The plate motion parameters of M2 are nearly identical to those of the newest global-scale plate motion model nuvel-1. The noam-pcfc and eura-pcfc rotation rates of M2 respectively deviate only 0.044°/m.y. and 0.010°/m.y. from those of nuvel-1 (these deviations are only about 6% and 1%, respectively, of the rotation rates themselves). The noam-pcfc and eura-pcfc poles of M2 both lie only 2° from those of nuvel-1 (within a 2σ error ellipse of each pole). nuvel-1 is determined from spreading rates at mid-ocean ridges, azimuths of transform faults and earthquake slip vectors. Since the spreading rates are estimated from marine magnetic anomalies integrated over a geological timescale, nuvel-1 gives the plate motions averaged over this timescale. Thus, we may conclude that there is no appreciable difference between the plate motions averaged over a geological timescale (millions of years) and those in a recent short period ( ~ 10 yr).M2 also gives the horizontal non-rigid motions of VLBI stations in the southwestern United States at rates of 6–9 mm/yr and roughly in opposite direction to the rigid motion of each station associated with plate motion. hatcreek, located near the northern part of the Basin and Range Province (B&R), also shows additional westward motion of about 9 mm/yr, suggesting crustal stretching in the northern B&R. The US VLBI stations show subsidence at rates of about 5–7 mm/yr, except for goldvenu and ovro 130, whose subsidence is negligible. The Japanese VLBI station, kashima, has a horizontal non-rigid motion of about 20 mm/yr in the west-northwest direction, roughly opposite to the direction of the rigid motion. kashima also shows subsidence at a rate of about 12 mm/yr, which is larger than that deduced from geodetic data but consistent with the result from GPS.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Sea-level estimates during the last deglaciation based on δO and accelerator mass spectrometry C ages measured in Globigerina bulloides

Coupled measurements of δ¹⁸O and accelerator mass spectrometry (AMS) ¹⁴C in a particular species of planktonic foraminifera may be used to calculate sea-level estimates for the last deglaciation. Of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth, which can be provided by δ¹⁸O measurements of modern shells (core tops, plankton tows). Isotopic (δ¹⁸O, AMS-¹⁴C dating) and faunal records (transfer function sea surface temperature) were obtained from two cores in the North Atlantic at about 37°N. The locations were chosen to obtain high sedimentation rate records removed from the major ice-melt discharge areas of the last deglaciation. Based upon Globigerina bulloides data, four δ¹⁸O-based sea-level estimates were calculated: −67 ± 7 m at 12,200 yr B.P. and −24 ± 8 m at about 8200 yr B.P. for core SU 81-18; −83 ± 10 m at 12,200 yr B.P. and −13 ± 11 m at about 8500 yr B.P. for core SU 81-14. Using a second working hypothesis concerning the seasonability of G. bulloides growth, it is suggested that the sea-level rose by about 40 m during the millennium which followed 14,500 yr B.P.     

Sedimentologic and palynologic records of the last deglaciation and Holocene from Ballston Lake, New York

Continuous pollen and sediment records from two ∼8.5-m-long cores document late Pleistocene and Holocene sedimentation and vegetation change in the Ballston Lake basin, eastern New York State. Pebbles at the base of both cores and the geomorphology of the watershed reflect the presence of the Mohawk River in the basin prior to ∼12,900 ± 70 cal yr B.P. Ballston Lake formed at the onset of the Younger Dryas (YD) by an avulsion of the Mohawk River. The transition from clay to gyttja with low magnetic susceptibility (MS), low bulk density, and high organic carbon indicates rapid warming and increased lake productivity beginning 11,020 cal yr B.P. MS measurements reveal that the influx of magnetic particles, associated with pre-Holocene clastic sedimentation, ceased after ∼10,780 cal yr B.P. The pollen record is subdivided into six zones: BL1 (12,920 to 11,020 cal yr B.P.) is dominated by boreal forest pollen; BL2 (11,020 to 10,780 cal yr B.P.) by pine (Pinus) forest pollen; BL3 (10,780 to 5290 cal yr B.P.) by hemlock (Tsuga) and mixed hardwood pollen; BL4 (5290 to 2680 cal yr B.P.) by mixed hardwood pollen; BL5a (2680 cal yr B.P. to 1030 cal yr B.P.) by conifer and mixed hardwood pollen; and BL5b (1030 cal B.P. to present) by increasing ragweed (Ambrosia) pollen. A 62% decrease in spruce (Picea) pollen in <320 cal years during BL1 reflects rapid warming at the end of the YD. Holocene pollen zones record more subtle climatic shifts than occurred at the end of the YD. One of the largest changes in the Holocene pollen spectra began ∼5300 cal yr B.P., and is characterized by a marked decline in hemlock pollen. This has been noted in other pollen records from the region and may record preferential selection of hemlock by a pathogen or parasites.     

Late Quaternary Vegetation and Climate of the Wind River Range, Wyoming

Sediments from Rapid Lake document glacial and vegetation history in the Temple Lake valley of the Wind River Range, Wyoming over the past 11,000 to 12,000 yr. Radiocarbon age determinations on basal detrital organic matter from Rapid Lake (11,770 ± 710 yr B.P.) and Temple Lake (11,400 ± 630 yr B.P.) bracket the age of the Temple Lake moraine, suggesting that the moraine formed in the late Pleistocene. This terminal Pleistocene readvance may be represented at lower elevations by the expansion of forest into intermontane basins 12,000 to 10,000 yr B.P. Vegetation in the Wind River Range responded to changing environmental conditions at the end of the Pleistocene. Following deglaciation, alpine tundra in the Temple Lake valley was replaced by a Pinus albicaulis parkland by about 11,300 ¹⁴C yr B.P. Picea and Abies, established by 10,600 14C yr B.P., grew with Pinus albicaulis in a mixed conifer forest at and up to 100 m above Rapid Lake for most of the Holocene. Middle Holocene summer temperatures were about 1.5°C warmer than today. By about 5400 ¹⁴C yr B.P. Pinus albicaulis and Abies became less prominent at upper treeline because of decreased winter snowpack and higher maximum summer temperatures. The position of the modern treeline was established by 3000 ¹⁴ C yr B.P. when Picea retreated downslope in response to Neoglacial cooling.     

Late Pleistocene Glaciations in the Northwestern Sierra Nevada, California

Pleistocene fluvial landforms and riparian ecosystems in central California responded to climate changes in the Sierra Nevada, yet the glacial history of the western Sierra remains largely unknown. Three glacial stages in the northwestern Sierra Nevada are documented by field mapping and cosmogenic radionuclide surface-exposure (CRSE) ages. Two CRSE ages of erratic boulders on an isolated till above Bear Valley provide a limiting minimum age of 76,400±3800 ¹⁰Be yr. Another boulder age provides a limiting minimum age of 48,800±3200 ¹⁰Be yr for a broad-crested moraine ridge within Bear Valley. Three CRSE ages producing an average age of 18,600±1180 yr were drawn from two boulders near a sharp-crested bouldery lateral moraine that represents an extensive Tioga glaciation in Bear Valley. Nine CRSE ages from striated bedrock along a steep valley transect average 14,100±1500 yr and suggest rapid late-glacial ice retreat from lower Fordyce Canyon with no subsequent extensive glaciations. These ages are generally consistent with glacial and pluvial records in east-central California and Nevada.     

Late Quaternary vegetation, fire and climate history reconstructed from two cores at Cerro Toledo, Podocarpus National Park, southeastern Ecuadorian Andes

The last ca. 20,000 yr of palaeoenvironmental conditions in Podocarpus National Park in the southeastern Ecuadorian Andes have been reconstructed from two pollen records from Cerro Toledo (04°22'28.6"S, 79°06'41.5"W) at 3150 m and 3110 m elevation. Páramo vegetation with high proportions of Plantago rigida characterised the last glacial maximum (LGM), reflecting cold and wet conditions. The upper forest line was at markedly lower elevations than present. After ca. 16,200 cal yr BP, páramo vegetation decreased slightly while mountain rainforest developed, suggesting rising temperatures. The trend of increasing temperatures and mountain rainforest expansion continued until ca. 8500 cal yr BP, while highest temperatures probably occurred from 9300 to 8500 cal yr BP. From ca. 8500 cal yr BP, páramo vegetation re-expanded with dominance of Poaceae, suggesting a change to cooler conditions. During the late Holocene after ca. 1800 cal yr BP, a decrease in páramo indicates a change to warmer conditions. Anthropogenic impact near the study site is indicated for times after 2300 cal yr BP. The regional environmental history indicates that through time the eastern Andean Cordillera in South Ecuador was influenced by eastern Amazonian climates rather than western Pacific climates.     

Fire and Vegetation History from the Coastal Rain Forest of the Western Oregon Coast Range

High-resolution charcoal and pollen analyses were used to reconstruct a 4600-yr-long history of fire and vegetation near Taylor Lake in the wettest forests of coastal Oregon. Today, fires in these forests are rare because the season of ignition does not coincide with months of dry fuels. From ca. 4600 to 2700 cal yr B.P. fire episodes occurred at intervals of 140±30 yr while forest vegetation was dominated by disturbance-adapted taxa such as Alnus rubra. From ca. 2700 cal yr B.P. to the present, fire episodes have become less common, occurring at intervals of 240±30 yr, and fire-sensitive forest taxa, such as Tsuga heterophylla and Picea sitchensis, have become more prominent. Fire occurrence during the mid-Holocene was similar to that of the more xeric forests in the eastern Coast Range and suggests that summer drought was widespread. After ca. 2700 cal yr B.P., a decrease in fire episode frequency suggests that cooler conditions and possibly increased summer fog allowed the establishment of present-day Picea sitchensis forests within the watershed. These results provide evidence that fire has been an important disturbance agent in the Coast Range of Oregon, and variations in fire frequency and climate have led to the establishment of present-day forests.     

Plant and insect remains from the Wisconsinan interstadial/stadial transition at Wedron, north-central Illinois

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ± 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated by Picea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, including Picea, Larix laricina, and the moss Campylium stellatum; subarctic species including Betula glandulosa, Empetrum nigrum, and Selaginella selaginoides; along with the predominantly arctic Vaccinium uliginosum var. alpinum, Dryas integrifolia, and Rhododendron lapponicum. The insect fauna contains the western montane ground beetle Opisthius richardsoni; several arctic-subarctic ground beetles including Diacheila polita, Helophorus sibiricus, and Pterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation.     

Drought-Related Changes in Two Hunter–Gatherer California Populations

Skeletal remains from two California cemeteries bracketing a severe drought that began around 1200 yr B.P. are analyzed to determine drought-related quality of life changes in Native Americans. Cemetery 1 predates the drought at 2895±160 yr B.P. to 1845±90 yr B.P. and Cemetery 2 dates it at 1100±90 yr B.P. to 1220±200 yr B.P. Quality of life was assessed through femoral computerized tomography scan measures of cortical thickness, age at adult death, and pathology/trauma frequency. After controlling for age and sex differences, changes from Cemetery 1 to Cemetery 2 showed decreases in cortical thickness and age at death and increases in pathology and trauma frequency.     

14,000 Years of Sediment, Vegetation, and Water-Level Changes at the Makepeace Cedar Swamp, Southeastern Massachusetts

Data from a transect of four cores collected in the Makepeace Cedar Swamp, near Carver, Massachusetts, record past changes in deposition, vegetation, and water level. Time series of palynological data provide a 14,000-yr record of regional and local vegetation development, a means for biostratigraphic correlation and dating, and information about changes in water level. Differences in records among cores in the basin show that water level decreased at least 1.5 m between 10,800 and 9700 cal yr B.P., after which sediment accumulation was slow and intermittent across the basin for about 1700 yr. Between 8000 and 5600 cal yr B.P., water level rose 2.0 m, after which slow peat accumulation indicates a low stand about the time of the hemlock decline at 5300 ± 200 cal yr B.P. Dry conditions may have continued after this time, but by 3200 cal yr B.P., the onset of peat accumulation in shallow cores indicates that water level had risen to close to its highest postglacial level, where it is today. Peat has accumulated across the whole basin since 3200 cal yr B.P. Data from Makepeace and the Pequot Cedar Swamp, near Ledyard, Connecticut, indicate an early Holocene dry interval in southern New England that began 11,500 yr ago near the end of the Younger Dryas interval. The dry conditions prevailed between 10,800 and 8000 cal yr B.P. and coincide with the arrival and later rise to dominance of white pine trees (Pinus strobus) both regionally and near the basins. Our results indicate a climatic cause for the “pine period” in New England.     

Southern Westerlies during the last glacial maximum

Vegetation and climate over approximately the past 13,000 yr are reconstructed from fossil pollen in a 9.4-m mire section at Caleta Róbalo on Beagle Channel, Isla Navarino (54°56′S, 67°38′W), southern Tierra del Fuego. Fifty surface samples reflecting modern pollen dispersal serve to interpret the record. Chronologically controlled by nine radiocarbon dates, fossil pollen assemblages are: Empetrum-Gramineae-Gunnera-Tubuliflorae (zone 3b, 13,000–11,850 yr B.P.), Gramineae-Empetrum-assorted minor taxa (zone 3a, 11,850-10,000 yr B.P.), Nothofagus-Gramineae-Tubuliflorae-Polypodiaceae (zone 2, 10,000–5000 yr B.P.), Nothofagus-Empetrum (zone 1b, 5000-3000 yr B.P.), and Empetrum-Nothofagus (zone 1a, 3000-0 yr B.P.). Assemblages show tundra under a cold, dry climate (zone 3), followed by open woodland (zone 2), as conditions became warmer and less dry, and later, with greater humidity and lower temperatures, by closed forest and the spread of mires (zone 1). Comparisons drawn with records from Antarctica, New Zealand, Tasmania, and the subantarctic islands demonstrate broadly uniform conditions in the circumpolar Southern Hemisphere. The influences of continental and maritime antarctic air masses were apparently considerable in Tierra del Fuego during cold late-glacial time, whereas Holocene climate was largely regulated by interplay between maritime polar and maritime tropical air.     

Tropical Rain Forest and Climate Dynamics of the Atlantic Lowland, Southern Brazil, during the Late Quaternary

Palynological analysis of a core from the Atlantic rain forest region in Brazil provides unprecedented insight into late Quaternary vegetational and climate dynamics within this southern tropical lowland. The 576-cm-long sediment core is from a former beach-ridge “valley,” located 3 km inland from the Atlantic Ocean. Radio-carbon dates suggest that sediment deposition began prior to 35,000 ¹⁴C yr B.P. Between ca. 37,500 and ca. 27,500 ¹⁴C yr B.P. and during the last glacial maximum (LGM; ca. 27,500 to ca. 14,500 ¹⁴C yr B.P.), the coastal rain forest was replaced by grassland and patches of cold-adapted forest. Tropical trees, such as Alchornea, Moraceae/Urticaceae, and Arecaceae, were almost completely absent during the LGM. Furthermore, their distributions were shifted at least 750 km further north, suggesting a cooling between 3°C and 7°C and a strengthening of Antarctic cold fronts during full-glacial times. A depauperate tropical rain forest developed as part of a successional sequence after ca. 12,300 ¹⁴C yr B.P. There is no evidence that Araucaria trees occurred in the Atlantic lowland during glacial times. The rain forest was disturbed by marine incursions during the early Holocene period until ca. 6100 ¹⁴C yr B.P., as indicated by the presence of microforaminifera. A closed Atlantic rain forest then developed at the study site.