A Holocene climatic record denoted by geochemical indicators from Barkol Lake in the northeastern Xinjiang,NW China

The Barkol Lake, as a closed inland lake, is located at the northeast Xinjiang in northwest China. A combination of geochemical indicators including δ¹⁸O and δ¹³C of carbonate, TOC, carbonate contents, as well as grain size proxies and magnetic susceptibility of sediments obtained from a newly recovered section at this lake, provides a high-resolution history of climatic change in the past 9400 years. Multi-indicators reflect that Holocene climatic change in the study region generally follows the Westerly Wind pattern of Holocene, and three climatic periods can be identified. Between 9400 and 7500 cal a B.P., climate was characterized by relatively drier and colder condition. From 7500 to 5800 cal a B.P., a relatively warmer and moister climate prevailed, but between 5800 and 3500 cal a B.P., climate shifted towards warmer and drier conditions. A relatively colder and wetter climate prevailed during 3500∼1000 cal a B.P., then it changed towards cold and dry between 1000 and 500 cal a B.P.; after 500 cal a B.P., climate changed towards warm and dry conditions again. This study reflects that during the Middle Holocene (from ca 7000 to 3500 cal a B.P.), variations of carbonate δ¹⁸O of sediments from several lakes in the northern Xinjiang were synchronous with that of Qinghai Lake, where was strongly influenced by the South Asian monsoon; however, after 3500 cal a B.P. this consistency was interrupted, possibly resulting from a re-domination of the Westerly Wind and the retreat of South Asian monsoon in the northern Xinjiang.     

Mid to late holocene climate evolution of the lake telmen basin, north central mongolia, based on palynological data

Palynological and sedimentological data from Lake Telmen, in north-central Mongolia, permit qualitative reconstruction of relative changes in moisture balance throughout the mid to late Holocene. The climate of the Atlantic period (7500–4500 yr ago) was relatively arid, indicating that Lake Telmen lay beyond the region of enhanced precipitation delivered by the expanded Asian monsoon. Maximum humidity is recorded between 4500 and 1600 cal yr B.P., during the Subboreal (4500–2500 yr ago) and early Subatlantic (2500 yr–present) periods. Additional humid intervals during the Medieval Warm Epoch (1000–1300 A.D. or 950–650 ago) and the Little Ice Age (1500– 1900 A.D. or 450–50 yr B.P.) demonstrate the lack of long-term correlation between temperature and moisture availability in this region. A brief aridification centered around 1410 cal yr B.P. encompasses a decade of cold temperatures and summer frost between A.D. 536 and 545 (1414–1405 yr B.P.) inferred from records of Mongolian tree-ring widths. These data suggest that steppe vegetation of the Lake Telmen region is sensitive to centennial- and decadal-scale climatic perturbations.     

Clay Minerals in Soils as Evidence of Holocene Climatic Change, Central Indo-Gangetic Plains, North-Central India

Clay mineral assemblages of a soil chrono-association comprising five fluvial surface members (QGH1 to QGH5) of the Indo-Gangetic Plains between the Ramganga and Rapti rivers, north-central India, demonstrate that pedogenic interstratified smectite–kaolin (Sm/K) can be considered as a potential indicator for paleoclimatic changes during the Holocene from arid to humid climates. On the basis of available radiocarbon dates, thermoluminescence dates, and historical evidence, tentative ages assigned to QGH1 to QGH5 are <500 yr B.P., >500 yr B.P., >2500 yr B.P., 8000 TL yr B.P., and 13,500 TL yr B.P., respectively. During pedogenesis two major regional climatic cycles are recorded: relatively arid climates between 10,000–6500 yr B.P. and 3800–? yr B.P. were punctuated by a warm and humid climate. Biotite weathered to trioctahedral vermiculite and smectite in the soils during arid conditions, and smectite was unstable and transformed to Sm/K during the warm and humid climatic phase (7400–4150 cal yr B.P.). When the humid climate terminated, vermiculite, smectite, and Sm/K were preserved to the present day. The study suggests that during the development of soils in the Holocene in alluvium of the Indo-Gangetic Plains, climatic fluctuations appear to be more important than realized hitherto. The soils older than 2500 yr B.P. are relict paleosols, but they are polygenetic because of their subsequent alterations.     

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.     

Holocene Monsoon Changes Inferred from Lake Sediment Pollen and Carbonate Records, Northeastern Cambodia

Major Holocene monsoon changes in continental Southeast Asia are reconstructed from analysis of ¹⁴C-dated changes in pollen and organic/inorganic carbon in sediment cores taken from permanent, closed-basin, volcanic lakes in Ratanakiri Province, northeastern Cambodia. Analysis focuses on the nature and timing of monsoon changes, inferred from changes in vegetation and lake conditions. These data provide the first well-dated palynological record, covering most of the Holocene and continuous up to the present, from a terrestrial site in mainland Southeast Asia. The record from a 15-m core retrieved from Kara Lake, representing the last 9300 years, shows that the late Glacial conditions ended about 8500 ¹⁴C yr B.P., more than 1000 years later than sites in southwest China. Summer monsoon intensity increased over the period ca. 8400–5300 ¹⁴C yr B.P., similar to most other sites in the Asian monsoon region. A subsequent expansion of secondary forests at the expense of dense semievergreen forests suggest a drier climate leading to more frequent fire disturbance. After ca. 3500 ¹⁴C yr B.P. disturbance frequency may have increased further with increasing seasonality. From ca. 2500 ¹⁴C yr B.P. to the present, dense forest has recovered in a mosaic with annually burned dry forest, but climate may not be the main control on local vegetation dynamics in the late Holocene.     

Environmental Change and Terrestrial Resource Use by the Thule and Inuit of Labrador,Canada

The object of this study is to document how the Inuit on the northern coast of Labrador, Canada used terrestrial resources such as peat and wood during the Little Ice Age (LIA; A.D. 1500–1870). Paleoecological investigations consisting of pollen and macrofossil analyses were undertaken in conjunction with archaeological excavations at the Inuit winter settlement sites of Oakes Bay 1, located in the Nain region of north‐central Labrador. Our data indicate that the major changes in terrestrial ecosystems of this coastal region were triggered by climate change. From ca. 5700 to 3000 cal. yr B.P., climatic conditions were relatively warm and moist. At ca. 3000 cal. yr B.P. conditions became significantly drier and colder, which corresponds to broader climatic trends during the Neoglacial period. At ca. 1000 cal. yr B.P., the reappearance of hygrophilic species and the establishment of Larix laricina provide evidence of a return to more humid conditions that in turn triggered the onset of the paludification of sandy terraces in the Dog Island region. Peat accumulation persisted after ca. 580 cal. yr B.P. likely due to the elevation of the frost table during the LIA. Elevated frost tables contributed to water saturation of the surface during the spring, creating conditions that were conducive to the preservation of organic material. Natural resources such as trees and peat were therefore readily available and more abundant during the LIA and extensively used by the Inuit for house construction and heating in the Dog Island region.     

Late Quaternary Variations in the Level of Paleo-Lake Malheur, Eastern Oregon

The highest shoreline features of paleo-Lake Malheur are undated gravelly barrier beaches south of Harney Lake that lie ca. 3.5 m higher than the hydrographic outlet of Harney Basin at Malheur Gap (1254 m). The earliest Quaternary record for Lake Malheur consists of occurrences of water-deposited tephra dated to ca. 70,000–80,000 yr ago. The next identified lake interval is dated by shells with ages of ca. 32,000 and 29,500 yr B.P. No dates are available for the terminal-Pleistocene Lake Malheur. Lake(s) were present between ca. 9600 and 7400 yr B.P., although periodic low levels or desiccation are suggested by a paleosol dated as ca. 8000 yr B.P. The lake system probably dried further after 7400 yr B.P., although dates are lacking for the period between ca. 7400 and 5000 yr B.P. Dune deposits on the lake floor are ca. 5000 yr old and indicate generally dry conditions. Fluctuating shallow lakes have probably characterized the last 2000 years. A date of 1000 yr B.P. gives a maximum age for beach deposits at 1254 m, near the basin threshold elevation. Thus, the Malheur Lake system may have drained to the Pacific Ocean by way of Malheur Gap during the latest Holocene.     

The Holocene thermal maximum and late-Holocene cooling in the tundra of NE European Russia

To investigate the Holocene climate and treeline dynamics in the European Russian Arctic, we analysed sediment pollen, conifer stomata, and plant macrofossils from Lake Kharinei, a tundra lake near the treeline in the Pechora area. We present quantitative summer temperature reconstructions from Lake Kharinei and Lake Tumbulovaty, a previously studied lake in the same region, using a pollen–climate transfer function based on a new calibration set from northern European Russia. Our records suggest that the early-Holocene summer temperatures from 11,500 cal yr BP onwards were already slightly higher than at present, followed by a stable Holocene Thermal Maximum (HTM) at 8000–3500 cal yr BP when summer temperatures in the tundra were ca. 3°C above present-day values. A Picea forest surrounded Lake Kharinei during the HTM, reaching 150 km north of the present taiga limit. The HTM ended with a temperature drop at 3500–2500 cal yr BP associated with permafrost initiation in the region. Mixed spruce forest began to disappear around Lake Kharinei at ca. 3500 cal yr BP, with the last tree macrofossils recorded at ca. 2500 cal yr BP, suggesting that the present wide tundra zone in the Pechora region formed during the last ca. 3500 yr.     

Holocene ethnobotanical and paleoecological record of human impact on vegetation in the Little Tennessee River Valley, Tennessee

Human occupation and utilization of plant resources have affected vegetation in the lower Little Tennessee River Valley of East Tennessee for 10,000 yr. Changes in Indian cultures and land use are documented by radiocarbon chronologies, lithic artifacts, ceramics, settlement patterns, and ethnobotanical remains from 25 stratified archaeological sites within the Holocene alluvial terrace. The ethnobotanical record consists of 31,500 fragments (13.7 kg) of wood charcoal identified to species and 7.7 kg of carbonized fruits, seeds, nutshells, and cultigens from 956 features. Pollen and plant macrofossils from small ponds both in the uplands and on lower stream terraces record local vegetational changes through the last 1500 to 3000 yr. Human impact increased after cultigens, including squash and gourd, were introduced ca. 4000 yr B.P. during the Archaic cultural period. Forest clearance and cultivation disturbed vegetation on both the floodplain and lower terraces after 2800 yr B.P., during the Woodland period. Permanent Indian settlements and maize and bean agriculture extended to higher terraces 1.5 km from the floodplain by the Mississippian period (1000 to 300 yr B.P.). After 300 yr B.P., extensive land clearance and cultivation by Historic Overhill Cherokee and Euro-Americans spread into the uplands beyond the river valley.     

An 8000-year record of vegetation, climate, and human disturbance from the Sierra de Apaneca, El Salvador

An ∼8000-cal-yr stratigraphic record of vegetation change from the Sierra de Apaneca, El Salvador, documents a mid-Holocene warm phase, followed by late Holocene cooling. Pollen evidence reveals that during the mid-Holocene (∼8000-5500 cal yr B.P.) lowland tropical plant taxa were growing at elevations ∼200-250 m higher than at present, suggesting conditions about 1.0°C warmer than those prevailing today. Cloud forest genera (Liquidambar, Juglans, Alnus, Ulmus) were also more abundant in the mid-Holocene, indicating greater cloud cover during the dry season. A gradual cooling and drying trend began by ∼5500 cal yr B.P., culminating in the modern forest composition by ∼3500 cal yr B.P. A rise in pollen from weedy plant taxa associated with agriculture occurred ∼5000 cal yr B.P., and pollen from Zea first appeared in the record at ∼4440 cal yr B.P. Human impacts on local vegetation remained high throughout the late Holocene, but decreased abruptly following the Tierra Blanca Joven (TBJ) eruption of Volcán Ilopango at ∼1520 cal yr B.P. The past 1500 years are marked by higher lake levels and periodic depositions of exogenous inorganic sediments, perhaps indicating increased climatic variability.     

Contiguous multi‐proxy analyses (X‐radiography,diatom, pollen,and microcharcoal) of Holocene archaeological features at Kuk Swamp,Upper Wahgi Valley,Papua New Guinea

Contiguous multi‐proxy analyses (X‐radiography, diatom, pollen, and microcharcoal) have been conducted on the fills of early, mid‐, and mid‐late Holocene features at Kuk Swamp, Upper Wahgi Valley, Papua New Guinea. The features are associated with key periods of archaeological interest: plant exploitation (ca. 10,000 cal yr B.P.), earliest cultivation (6950–6440 cal yr B.P.), and earliest ditches (ca. 4000 cal yr B.P.). The analyses are designed to clarify uncertainties regarding the reliability and association of different samples within feature fills for the interpretation of human activities on the wetland in the past. Methodologically, these investigations have clarified site formation processes, including pedogenesis within feature fills, which enable a better determination of archaeological associations for different samples within those fills. Substantively, the results provide higher resolution interpretations of paleoenvironments and past human activities on the wetland margin. © 2009 Wiley Periodicals, Inc.     

A late quaternary pollen record from the Transvaal bushveld, South Africa

Pollen spectra from cores of organic spring deposits from the Transvaal provide evidence for the climatic evolution of the province during the last 35,000 yr B.P. or more. The past climatic phases are derived from palynological reconstructions of past vegetation types by comparison of fossil pollen data with modern surface pollen spectra from various localities. Evidence is provided for an early moist, cool phase with relatively mesic bushveld and expanded montane forest in the central Transvaal, followed by a drier period with drier bushveld which probably lasted until approximately 25,000 yr B.P. During the next phase, which at the latest ended about 11,000 yr B.P., the temperatures were probably 5°–6°C cooler than at present. At that time bushveld vegetation in the central Transvaal was replaced by open grassland with macchia elements. Climatic amelioration came and semiarid savanna returned to the plains, at first gradually and then developing into a warm Kalahari thornveld-type vegetation. After 6000 yr B.P. it apparently became slightly wetter and a more broad-leafed bushveld developed. About 4000 yr B.P. it again became cooler and slightly wetter and the bushveld vegetation on the central and northern plains was comparable to present open upland types. After 2000 yr B.P. conditions gradually became warner until about 1000 yr B.P., when the modern climate of the central Transvaal bushveld originated.     

Postglacial fire, vegetation, and climate history in the Clearwater Range, Northern Idaho, USA

The environmental history of the Northern Rocky Mountains was reconstructed using lake sediments from Burnt Knob Lake, Idaho, and comparing the results with those from other previously published sites in the region to understand how vegetation and fire regimes responded to large-scale climate changes during the Holocene. Vegetation reconstructions indicate parkland or alpine meadow at the end of the glacial period indicating cold-dry conditions. From 14,000 to 12,000 cal yr B.P., abundant Pinus pollen suggests warmer, moister conditions than the previous period. Most sites record the development of a forest with Pseudotsuga ca. 9500 cal yr B.P. indicating warm dry climate coincident with the summer insolation maximum. As the amplification of the seasonal cycle of insolation waned during the middle Holocene, Pseudotsuga was replaced by Pinus and Abies suggesting cool, moist conditions. The fire reconstructions show less synchroneity. In general, the sites west of the continental divide display a fire-frequency maximum around 12,000–8000 cal yr B.P., which coincides with the interval of high summer insolation and stronger-than-present subtropical high. The sites on the east side of the continental divide have the highest fire frequency ca. 6000–3500 cal yr B.P. and may be responding to a decrease in summer precipitation as monsoonal circulation weakened in the middle and late Holocene. This study demonstrated that the fire frequency of the last two decades does not exceed the historical range of variability in that periods of even higher-than-present fire frequency occurred in the past.     

Environmental history since 11,000 C yr B.P. of the northeastern Pampas, Argentina, from alluvial sequences of the Luján River

Sedimentological, malacological, and pollen analyses from ¹⁴C-dated alluvial sections from the Luján River provide a detailed record of environmental changes during the Holocene in the northeastern Pampas of Argentina. From 11,200 to 9000 ¹⁴C yr B.P., both sedimentary and biological components suggest that the depositional environment was eutrophic, alkaline, and freshwater to brackish shallow water bodies without significant water circulation. During this time, bioclastic sedimentation was dominant and the shallow water bodies reached maximum development as the climate became more humid, suggesting an increase in precipitation. Short-term fluctuations in climate during the last stage of this interval may have been sufficient to initiate changes in the water bodies, as reduction of the volume alternated with periods of flooding. The beginning of the evolution of shallow swamps in the wide floodplain or huge wetlands was contemporaneous with a sea level lower than the present one. From 9000 and 7000 ¹⁴C yr B.P., mesotrophic, alkaline, brackish, probably anoxic swamps existed. Between 7000 and 3000 ¹⁴C yr B.P., anoxic calcareous swamps were formed, with subaerial exposure and development of the Puesto Berrondo Soil (3500-2900 ¹⁴C yr B.P.). A trend to a reduction of water bodies is recorded from 9000 to ca. 3000 ¹⁴C yr B.P., with a significant reduction after ca. 7000 ¹⁴C yr B.P. A shift to subhumid-dry climate after 7000 ¹⁴C yr B.P. appears to be the main cause. During this time, an additional external forcing toward higher groundwater levels was caused by Holocene marine transgression causing changes in the water bodies levels. The climate became drier during the late Holocene (ca. 3000 yr B.P.), when clastic sedimentation increased, under subhumid-dry conditions. Flood events increased in frequency during this time. From ca. A.D. 1790 to present, the pollen record reflects widespread disturbance of the vegetation during the European settlement.     

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.     

Vegetation, Climate, and Sea Level in the Past 55,000 Years, Hanjiang Delta, Southeastern China

Pollen in Quaternary deposits from the subtropical Hanjiang Delta records three major phases in the local vegetation and climate history during the last 55,000 yr: (1) a prevalent cool-to-temperate and humid climate at ca. 24,000 ¹⁴C yr B.P. is indicated by abundant pollen of temperate trees including conifers; (2) between 20,000 and 15,000 ¹⁴C yr B.P., a cold, dry environment was associated with low sea level during the last glaciation, leading to subaerial exposure, weathering, and interruption of sedimentation, as well as departure from the region of Dacrydium and Sonneratia; (3) a short-term expansion of grassland at ca. 10,300 ¹⁴C yr B.P. reduced the predominant Lauraceae-Fagaceae evergreen forest, possibly corresponding to the Younger Dryas cooling. The combined data indicate a maximum sea-level rise in the mid-Holocene (7500–4000 ¹⁴C yr B.P.) and a marine influence in the late Pleistocene at 45,000–20,000 ¹⁴C yr B.P. The Holocene warming, however, did not bring back moisture-sensitive taxa, indicating high seasonal aridity probably caused by renewed monsoon conditions.     

Fluctuations of Outlet and Valley Glaciers in the Southern Andes (Argentina) during the Past 13,000 Years

In the southern Argentine Andes, ten advances of valley glaciers were used to reconstruct the late-glacial and Holocene glacier history. The accumulation areas of these glaciers lie in the Precordillera and are thus independent of fluctuations of the South Patagonian Icefield. Like the Viedma outlet glacier, the valley glaciers advanced three times during late-glacial time (14,000–10,000 yr B.P.). The youngest advance correlates with the Younger Dryas Stade, based on two minimum AMS¹⁴C dates of 9588 and 9482 yr B.P. The second oldest advance occurred before 11,800 yr B.P. During the first half of the Holocene, (ca. 10,000–5000 yr B.P.), advances culminated about 8500, 8000–7500, and 5800–5500 yr B.P. During the second half of the Holocene, advances occurred between ca. 4500 and 4200 yr B.P., as well as between 3600 and 3300 yr B.P. In the Río Cóndor valley three subsequent advances have been identified.     

23,000 yr of vegetation history of the Upper Lerma, a tropical high-altitude basin in Central Mexico

Pollen analysis on a 9.54-m sediment core from lake Chignahuapan in the upper Lerma basin, the highest intermontane basin in Central Mexico (2570 m asl), documents vegetation and limnological changes over the past ∼23,000 ¹⁴C yr. The core was drilled near the archaeological site of Santa Cruz Atizapán, a site with a long history of human occupation, abandoned at the end of the Epiclassic period (ca. 900 AD). Six radiocarbon AMS dates and two well-dated volcanic events, the Upper Toluca Pumice with an age of 11,600 ¹⁴C yr B.P. and the Tres Cruces Tephra of 8500 ¹⁴C yr B.P., provide the chronological framework for the lacustrine sequence. From ca. 23,000 ¹⁴C yr B.P. to ca. 11,600 ¹⁴C yr B.P. the plant communities were woodlands and grasslands based on the pollen data. The glacial advances MII-1 and MII-2 correlate with abundant non-arboreal pollen, mainly grasses, from ca. 21,000 to 16,000 ¹⁴C yr B.P., and at ca. 12,600 ¹⁴C yr B.P. During the late Pleistocene, lake Chignahuapan was a shallow freshwater lake with a phase of lower level between 19,000 and 16,000 ¹⁴C yr B.P. After 10,000 ¹⁴C yr B.P., tree cover in the area increased, and a more variable lake level is documented. Late Holocene (ca. 3100 ¹⁴C yr B.P.) deforestation was concurrent with human population expansion at the beginning of the Formative period (1500 B.C.). Agriculture and manipulation of the lacustrine environment by human lakeshore populations appear at 1200 ¹⁴C yr B.P. (550 A.D.) with the appearance of Zea mays pollen and abundant charcoal particles.     

A 10,000-year high-resolution diatom record from Pilkington Bay, Lake Victoria, East Africa

A new diatom record from Lake Victoria’s Pilkington Bay, subsampled at 21- to 25-year intervals and supported by 20 AMS dates, reveals a ∼10,000 calendar year environmental history that is supported by published diatom and pollen data from two nearby sites. With their chronologies adjusted here to account for newly documented ancient carbon effects in the lake, these three records provide a coherent, finely resolved reconstruction of Holocene climate change in equatorial East Africa. After an insolation-induced rainfall maximum ca. 8800-8300 cal yr B.P., precipitation became more seasonal and decreased abruptly ca. 8200 and 5700 yr B.P. in apparent association with northern deglaciation events. Century-scale rainfall increases occurred ca. 8500, 7000, 5800, and 4000 yr B.P. Conditions after 2700 yr B.P. were generally similar to those of today, but major droughts occurred ca. 1200-600 yr B.P. during Europe’s Medieval Warm Period.     

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.