Early Holocene Transition Research Articles

A 40,000‐year woodrat‐midden record of vegetational and biogeographical dynamics in north‐eastern Utah, USA

AbstractAim A conspicuous climatic and biogeographical transition occurs at 40–45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time‐scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat‐midden record northward into the lowlands of the central Rocky Mountains.Location Woodrat middens were collected from crevices and rock shelters on south‐facing slopes of Dutch John Mountain (2000–2200 m, 40°57′ N, 109°25′ W), situated on the eastern flanks of the Uinta Mountains in north‐eastern Utah. The site is near the regional limits for Pinus ponderosa, P. edulis, P. contorta, Cercocarpus ledifolius var. intricatus, Abies concolor, Ephedra viridis and other important western species.Methods We analysed pollen and plant macrofossils from the 40,000‐year midden sequence. The middens represent brief, depositional episodes (mostly years to decades). Four middens represent the early to full‐glacial period (40,000–18,000 cal‐yr bp), eight middens are from the late‐glacial/early Holocene transition (13,500–9000 cal yr bp), and 33 middens span the mid‐to‐late Holocene (last 7500 years). Temporal density of our Holocene middens (one every c. 210 years) is comparable with typical Holocene pollen sequences from lake sediments.Results Early to full‐glacial assemblages are characterized by low diversity and occurrence of montane conifers (Picea pungens, Pseudotsuga menziesii, P. flexilis, Juniperus communis) absent from the site today. Diversity increases in the late‐glacial samples with the addition of J. scopulorum, J. horizontalis, C. montanus, C. ledifolius var. intricatus and mesic understory species. The coniferous trees and J. communis declined and J. osteosperma appeared during the late‐glacial/Holocene transition. Juniperus osteosperma populations have occupied the site throughout the Holocene. Pinus ponderosa was established by 7500 cal‐yr bp, and has occurred at least locally ever since. Montane conifers and J. horizontalis persisted until c. 5500 cal‐yr bp. The signature events of the late Holocene were the invasions of P. edulis and Ephedra viridis and establishment of pinyon–juniper woodland in the last 800 years.Main conclusions The Dutch John Mountain midden record adds to an emerging picture in which mid‐elevation conifers (P. flexilis, Pseudotsuga menziesii, Picea pungens, J. scopulorum, J. communis) dominated vegetation over a wide area of the Colorado Plateau and adjacent Rocky Mountains. Rather than being fragmented, as often assumed in phylogeographical studies, these species had broader and more‐connected distributions than they do in the region today. Paradoxically, subalpine conifers (Picea engelmannii, A. lasiocarpa) occurred at higher elevations to the south, possibly representing declining precipitation from south to north owing to southward displacement of the polar jet stream. The Dutch John Mountain record displays a series of extinction and invasion events. Most of the extinctions were local in scale; nearly all constituents of fossil midden assemblages occur within a few kilometres of Dutch John Mountain, and some occur at least locally on its slopes. The sole exception is J. horizontalis, which is regionally extinct. In contrast to extinctions, Holocene invasions were regional in scale; J. osteosperma, P. ponderosa, P. edulis and Ephedra viridis immigrated from glacial‐age source populations far to the south.

Tree-Ring Records of Near-Younger Dryas Time in Central North America—Preliminary Results from the Lincoln Quarry Site, Central Illinois, Usa

The abrupt millennial-scale changes associated with the Younger Dryas (YD) event (“chronozone”) near the dawn of the Holocene are at least hemispheric, if not global, in extent. Evidence for the YD cold excursion is abundant in Europe but fairly meager in central North America. We are engaged in an investigation of high-resolution environmental changes in mid-North America over several millennia (about 10,000 to 14,000 BP) during the Late Glacial–Early Holocene transition, including the YD interval. Several sites containing logs or stumps have been identified and we are in the process of initial sampling or re-sampling them for this project. Here, we report on a site in central Illinois containing a deposit of logs initially thought to be of YD age preserved in alluvial sands. The assemblage of wood represents hardwood (angiosperm) trees, and the ring-width characteristics are favorable to developing formal tree-ring chronologies. However, 4 new radiocarbon dates indicate deposition of wood may have taken place over at least 8000 14C yr (6000–14,000 BP). This complicates the effort to develop a single floating chronology of several hundred years at this site, but it may provide wood from a restricted region over a long period of time from which to develop a sequence of floating chronologies, the timing of deposition and preservation of which could be related to paleoclimatic events and conditions.

Rapid climatic changes during the Greenland stadial 1 (Younger Dryas) to early Holocene transition on the Norwegian Barents Sea coast

A pollen‐based quantitative climate reconstruction from a lake‐sediment core on the Norwegian Barents Sea coast provides insights about climatic change over the Greenland stadial 1 (GS‐1) to early‐Holocene transition. GS‐1 was characterized by low July mean temperatures (c. 6.0°C) and dry conditions probably resembling modern arctic deserts. The increase in July mean temperatures to the Holocene level (10.0–12.0°C) took place in a two‐step pattern interrupted by a short cool period with July mean temperatures of c. 8.0°C during the early Preboreal at c. 11450–11200 cal. yr BP. The reconstruction also suggests two other early‐Holocene coolings of c. 1.5°C, dating to 10900–10800 cal. yr BP and 10400–10200 cal. yr BP, synchronously with short‐term decreases in δ18O values in the Greenland ice cores. These results reflect the highly unstable nature of the early‐Holocene climate in northernmost Fennoscandia. Apart from the cooling at 10900–10800 cal. yr BP, the reconstructed cold events correlate with fluxes of fresh water to the North Atlantic and related reductions of North Atlantic deep‐water formation, suggesting that the rapid climate changes resulted from the dynamics of the North Atlantic thermohaline circulation and oceanic energy transport during the GS‐1 to early‐Holocene transition.

Rapid climatic changes during the Greenland stadial 1 (Younger Dryas) to early Holocene transition on the Norwegian Barents Sea coast

Rapid climatic changes during the Greenland stadial 1 (Younger Dryas) to early Holocene transition on the Norwegian Barents Sea coast

Vegetation invasions into absolute desert: A 45;th000 yr rodent midden record from the Calama–Salar de Atacama basins, northern Chile (lat 22°–24°S)

Research Article| March 01, 2002 Vegetation invasions into absolute desert: A 45;th000 yr rodent midden record from the Calama–Salar de Atacama basins, northern Chile (lat 22°–24°S) Claudio Latorre; Claudio Latorre 1Laboratorio de Palinología, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Ñuñoa, Santiago, Chile Search for other works by this author on: GSW Google Scholar Julio L. Betancourt; Julio L. Betancourt 2Desert Laboratory, U.S. Geological Survey, 1675 West Anklam Road, Tucson, Arizona 85745, USA Search for other works by this author on: GSW Google Scholar Kate A. Rylander; Kate A. Rylander 2Desert Laboratory, U.S. Geological Survey, 1675 West Anklam Road, Tucson, Arizona 85745, USA Search for other works by this author on: GSW Google Scholar Jay Quade Jay Quade 3Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Claudio Latorre 1Laboratorio de Palinología, Departamento de Biología, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Ñuñoa, Santiago, Chile Julio L. Betancourt 2Desert Laboratory, U.S. Geological Survey, 1675 West Anklam Road, Tucson, Arizona 85745, USA Kate A. Rylander 2Desert Laboratory, U.S. Geological Survey, 1675 West Anklam Road, Tucson, Arizona 85745, USA Jay Quade 3Desert Laboratory, Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Publisher: Geological Society of America Received: 14 Nov 2000 Revision Received: 02 Aug 2001 Accepted: 18 Sep 2001 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2002) 114 (3): 349–366. https://doi.org/10.1130/0016-7606(2002)114<0349:VIIADA>2.0.CO;2 Article history Received: 14 Nov 2000 Revision Received: 02 Aug 2001 Accepted: 18 Sep 2001 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Claudio Latorre, Julio L. Betancourt, Kate A. Rylander, Jay Quade; Vegetation invasions into absolute desert: A 45;th000 yr rodent midden record from the Calama–Salar de Atacama basins, northern Chile (lat 22°–24°S). GSA Bulletin 2002;; 114 (3): 349–366. doi: https://doi.org/10.1130/0016-7606(2002)114<0349:VIIADA>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Plant macrofossils, percentage abundance of grass taxa, fecal-pellet δ13C, and plant-cuticle contents from 49 fossil rodent middens dated by 14C record changes in local vegetation and precipitation since 45 ka (calibrated or measured to thousands of calendar years before present) in the central Atacama Desert (lat 22°–24°S) of northern Chile. The midden sites are along the hyperarid upper margin (2400–3100 m) of the “absolute desert,” in an extreme environment sparsely vegetated by annual herbs and halophytic shrubs. Conditions between 40 and 22 ka may have been at least intermittently dry, and possibly cooler, as implied by four middens with low species richness. We infer a large increase in summer rainfall between 16.2 and 10.5 ka on the basis of the lowering of steppe grasses by as much as 1000 m, prominence of C4 grasses and summer annuals, high species richness, and displacement of northern species at least 50 km south of their modern ranges. The precipitation increase was greatest for a cluster of middens between 11.8 and 10.5 ka. Abrupt drying, evident in a dramatic decrease in grass abundance, occurred after 10.5 ka at all four midden localities. Increased percentages of grass, higher species richness, and extralocal taxa record slightly wetter conditions between 7.1 and 3.5 ka. The present hyperarid conditions were established after 3 ka.Present-day variability of summer precipitation in the central Atacama Desert and adjacent Altiplano is related to the intensity and position of upper air circulation anomalies, which in turn respond to Pacific sea-surface temperature anomalies. Summer insolation over the central Andes (lat 20°S) was at its minimum during the latest glacial to early Holocene transition, so regional insolation forcing cannot account for intensified pluvial conditions in the central Atacama. Summer precipitation collapsed abruptly between 10.5 and 10 ka, indicating either nonlinear relationships with seasonal insolation or a change in intensity of upper air circulation over the Altiplano, effectively blocking moisture transport to the Atacama Desert. Here, we suggest that precipitation variations on millennial time scales in the central Atacama are the result of extraregional forcing of the South American Summer Monsoon through intensified Walker Circulation (stronger easterlies) and La Niña–like conditions operating through insolation anomalies (i.e., departures in insolation values) directly over central Asia and the equatorial Pacific. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Chemical and isotopic composition of modern water bodies in the Lake Kopais Basin, central Greece: analogues for the interpretation of the lacustrine sedimentary sequence

Stable-isotope measurements and modern aquatic chemistry are used to aid the reconstruction of past hydrological changes recorded in a 126 ka-long sediment core from Lake Kopais, Greece. This is the most southeasterly European site with a long Late Quaternary sequence. Although the lake has been artificially drained, calcareous sediments from the centre of the basin, 38°26′16ʺN, 23°03′01ʺE, provide a continuous record from the early part of the last interglacial to the Early Holocene. Because the physiography and hydrology are complex, modern analogues for past environmental conditions are essential. The modern waters are of Ca–Mg–HCO3 or Mg–Ca–HCO3 type, reflecting the prevalence of limestones and metamorphic rocks in the catchment. They show a clear evolutionary trend in δ18O and δD values from the source areas to the modern lakes. However, the modern water bodies are less evolved than the palaeolake. A larger evaporating surface, higher values of δ18O in precipitation, decreased precipitation/evaporation ratios and hydrological closure increased the δ18O values of endogenic carbonates at different times in the past. However, Palaeolake Kopais never desiccated completely or became saline. Analyses of the organic fraction from the core show that: (i) it is mainly of algal origin; (ii) productivity and carbon cycling in the lake waters were relatively stable through time; and (iii) the bulk δ13C values vary between −29‰ and −25‰, indicating that the lake waters were never appreciably carbon-limited and that C4 plants did not invade the catchment. Although significant shifts in the δ18O and δ13C values of endogenic low-Mg calcite are attributable mainly to past variations in water balance, weak δ18O–δ13C covariance during marine isotope stages (MIS) 5e–5c suggests that the palaeolake leaked significantly through karstic sinkholes. Since it was effectively operating as an open system, δ18O may have retained the isotopic imprint of increased summer precipitation. Between MIS 5a and MIS 4, strong isotopic covariance suggests minimal outflow and drier conditions than today. After an increase in winter snowmelt during MIS 3, the climate again became cold and dry in the full-glacial (MIS 2). A fluctuating increase in moisture occurred during the late-glacial to early Holocene transition (MIS 2–1).

Visualisation of luminescence excitation‐emission timeseries: Palaeoclimate implications from a 10,000 year stalagmite record from Ireland

Stalagmite luminescence excitation emission wavelength timeseries can provide high‐resolution palaeoclimate records. Here, we employ multidimensional visualisation techniques in order to interpret a 10,000 year luminescence record from a stalagmite from Crag Cave, SW Ireland. Our results demonstrate three periods of distinct luminescence properties: (1) 0–4,000 BP, when they are affected by overlying agriculture. (2) 4,000–9,600 BP, where there is a strong correlation between luminescence and 13C isotopic variations; we suggest the correlation demonstrates a vegetation response to climate change, (3) Before 9,600 BP, where a strong early Holocene transition is visible. Our results suggest that it took about 400–600 years for soils above the cave to stabilise after significant climate or environmental change, and that there was a complex vegetation response between 8,000 and 7,100 BP that my have been a lagged response to the “8.2 ka event”.

Environmental and sea-level changes in London from 10 500 BP to the present: a case study from Silvertown

Results of stratigraphic and palaeoecological studies carried out on deposits at Silvertown in east London are discussed in relation to current models of Late glacial and Holocene alterations to river form, relative sea-level change, vegetation development and archaeology in the lower Thames. The data indicate that the braided bedform typical of British cold stage rivers evolved into a lower energy meandering form around 10 500 BP, a process that caused channel cut-off. The fill of one of these contained organic sediments and in-washed sands dating from 10 500-9300 BP in which there was palynological evidence for the replacement of Late Devensian tundra by early Holocene pine forest. Biostratigraphic evidence for the period 9000-5500 BP was limited owing to the absence of organic sediments and, instead, deposition was of in-channel sands. Peat formation began at c. 5500 bp , and these organic sequences contain evidence of the elm decline at 5010±70 BP and the lime decline at 3070±60 BP. The latter event was accompanied by forest clearance for Bronze Age agriculture and a consequent alteration to both the marsh and dry ground flora. Around 2500 bp the peats were submerged beneath estuarine muds as a result of further sea-level rise. A series of age/altitude points relating to Holocene sea-levels were constructed from the site data and were found to fit relatively well with current ideas of sea-level change in the post-glacial period. The results from Silvertown reflect data from shorter sequences in the London area, combining evidence of the Late glacial to early Holocene transition, with information on river development, changes in sea-level tendency and human-induced vegetation change.

Vegetation and climate changes during the last 21 000 years in S.W. Africa based on a marine pollen record

A high resolution marine pollen record from site GeoB1023, west of the northern Namib desert provides data on vegetation and climate change for the last 21 ka at an average resolution of 185 y. Pollen and spores are mainly delivered to the site by the Cunene river and by surface and mid-tropospheric wind systems. The main pollen source areas are located between 13°S and 21°S, which includes the northern Namib desert and semi-desert, the Angola-northern Namibian highland, and the north-western Kalahari. The pollen spectra reflect environmental changes in the region. The last glacial maximum (LGM) was characterised by colder and more arid conditions than at present, when a vegetation with temperate elements such as Asteroideae, Ericaceae, and Restionaceae grew north of 21°S. At 17.5 ka cal. B.P., an amelioration both in temperature and humidity terminated the LGM but, in the northern Kalahari, mean annual rainfall in the interval 17.5-14.4 ka cal. B.P. was probably 100–150 mm lower than at present (400–500 mm/y). The Late-glacial to early Holocene transition includes two arid periods, i.e. 14.4–12.5 and 10.9–9.3 ka cal. B.P. The last part of the former period may be correlated with the Younger Dryas. The warmest and most humid period in the Holocene occurred between 6.3 and 4.8 ka cal. B.P. During the last 2000 years, human impact, as reflected by indications of deforestation, enhanced burning and overgrazing, progressively intensified.

Vegetation dynamics in central Africa since 18,000 yr BP: pollen records from the interlacustrine highlands of Burundi, Rwanda and western Uganda

A standardized analysis of palaeoecological data, in the form of six pollen sequences and forty‐ four radiocarbon ages, has permitted a region‐wide reconstruction of Late Quaternary vegetation dynamics for the interlacustrine highlands of central Africa.A landscape widely dominated by ericaceous scrub and grasslands, but also supporting sparse patches of open‐canopied montane forest, possibly in those areas with a topography most favourable to the growth of trees, is indicated for the last glacial maximum of 18,000 yr bp. Major expansions in the extent of upper altitudinal forms of montane forest occurred from around 12,500 yr bp, while lower moist montane forest—the expected climax for much of the region today—did not become prominent until 11,000 yr bp to 10,000 yr bp. From the palaeoecological evidence at least, it appears that the major east Central forest refuge, proposed by some workers on the basis of current species’ distribution patterns, did not extend to the eastern flanks of the Albertine Rift.A late glacial–early Holocene transition is only fully chronicled in two of the sites. However, it appears that the expansion of lower montane forest had a time‐transgressive pattern across the region, and was not simply from low to high altitude. The composition of forests during the early Holocene appears to have been different to that in the later stages of the present interglacial, as taxa presently associated with wetter and/or more open forest types were much more common. Pollen data also indicate that higher altitude parts of the interlacustrine highlands were more attractive to the earliest (possibly Bantu‐speaking) farmers and metal‐workers. There is evidence of wide‐spread forest clearance around the beginning of the present millennium, possibly as a result of substantial changes in socio‐economic conditions, and patterns of settlement, associated with the onset of the Late Iron Age.

Glacial and climatic events in iceland reflecting regional north atlantic climatic shifts during the Pleistocene-Holocene transition

This paper presents a summary of the evidence for glacial and climatic changes during the late Pleistocene-early Holocene transition in Iceland. The deglaciation during the Bølling-Allerød event was interrupted by a short-lived Older Dryas glacial advance. A biostratigraphical record from northern Iceland shows significant climate warming in late Allerød, when mean July temperatures were at least as warm as those of today. An abrupt cooling marked the beginning of the Younger Dryas event. It was characterised by a cold and stable polar climate and an extensive glaciation, before the postglacial warming of climate set in. The Icelandic paleoclimatic record is discussed in the light of climatic oscillations recorded from the GRIP ice-core, from the Greenland Inland Ice, and with reference to major shifts in the oceanic front systems, recorded in the Troll 8903 marine sediment core from the North Sea. The Vedde Ash gives a unique opportunity to address the chronological problems and correlate event stratigraphies of the different proxies. It is concluded that the Icelandic record of glacial and climatic changes during the late Pleistocene—early Holocene transition largely reflects the climatic development in the North Atlantic region.

Century scale paleoclimatic reconstruction from Moon Lake, a closed‐basin lake in the northern Great Plains

Estimates of past lake‐water salinity from fossil diatom assemblages were used to infer past climatic conditions at Moon Lake, a climatically sensitive site in the northern Great Plains. A good correspondence between diatom‐inferred salinity and historical records of mean annual precipitation minus evapotranspiration (P ‒ ET) strongly suggests that the sedimentary record from Moon Lake can be used to reconstruct past climatic conditions. Century‐scale analysis of the Holocene diatom record indicates four major hydrological periods: an early Holocene transition from an open freshwater system to a closed saline system by 7300 b.p., which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate; a mid‐Holocene period of high salinity from 7300 to 4700 b.p., indicating low effective moisture (P ‒ ET); a transitional period of high salinity from 4700 to 2200 b.p., characterized by poor diatom preservation; and a late Holocene period of variable lower salinity during the past 2,200 yr, indicating fluctuations in effective moisture.

Late quaternary paleogeography of Middle Europe and the Northcentral United States: A framework for comparative studies of prehistoric man‐land relationships

AbstractThe work summarized in this paper is an important component of a larger study concerned with the responses of prehistoric hunting‐gathering cultures to long term environmental change. the general approach involves comparing cultural systems and their transformations in Middle Europe and the northcentral United States during the late Pleistocene and early Holocene transition from glacial to interglacial conditions. This paper is specifically aimed at identifying ecological factors that may help account for similarities and differences in the cultural successions on opposite sides of the Atlantic. We conclude that, despite broadly similar environmental histories in both regions, important differences are evident in, for example, trajectories of climatic amelioration. These, together with differences in human demography, can be seen to have contributed toward shaping divergent cultural adaptations in Europe and North America.

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.