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

1999 ◽  
Vol 51 (3) ◽  
pp. 238-247 ◽  
Author(s):  
Gerd Wenzens
Keyword(s):  
Younger Dryas ◽  
Late Glacial ◽  
The South ◽  
Southern Andes ◽  
Outlet Glacier ◽  
The Holocene ◽  
The Past ◽  
Late Glacial And Holocene ◽  
Glacial Time

AbstractIn 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 Rı́o Cóndor valley three subsequent advances have been identified.

scholarly journals How dry was the Younger Dryas? Evidence from a coupled <i>δ</i><sup>2</sup>H–<i>δ</i><sup>18</sup>O biomarker paleohygrometer applied to the Gemündener Maar sediments, Western Eifel, Germany

2019 ◽  
Vol 15 (2) ◽  
pp. 713-733 ◽  
Author(s):  
Johannes Hepp ◽  
Lorenz Wüthrich ◽  
Tobias Bromm ◽  
Marcel Bliedtner ◽  
Imke Kathrin Schäfer ◽  
...  
Keyword(s):  
Isotope Composition ◽  
Younger Dryas ◽  
Late Glacial ◽  
Climatic Conditions ◽  
Leaf Water ◽  
Early Holocene ◽  
Unexpected Finding ◽  
Temperature Dependent ◽  
The Past ◽  
Natural Climate

Abstract. Causes of the Late Glacial to Early Holocene transition phase and particularly the Younger Dryas period, i.e. the major last cold spell in central Europe during the Late Glacial, are considered to be keys for understanding rapid natural climate change in the past. The sediments from maar lakes in the Eifel, Germany, have turned out to be valuable archives for recording such paleoenvironmental changes. For this study, we investigated a Late Glacial to Early Holocene sediment core that was retrieved from the Gemündener Maar in the Western Eifel, Germany. We analysed the hydrogen (δ2H) and oxygen (δ18O) stable isotope composition of leaf-wax-derived lipid biomarkers (n-alkanes C27 and C29) and a hemicellulose-derived sugar biomarker (arabinose), respectively. Both δ2Hn-alkane and δ18Osugar are suggested to reflect mainly leaf water of vegetation growing in the catchment of the Gemündener Maar. Leaf water reflects δ2H and δ18O of precipitation (primarily temperature-dependent) modified by evapotranspirative enrichment of leaf water due to transpiration. Based on the notion that the evapotranspirative enrichment depends primarily on relative humidity (RH), we apply a previously introduced “coupled δ2Hn-alkane–δ18Osugar paleohygrometer approach” to reconstruct the deuterium excess of leaf water and in turn Late Glacial–Early Holocene RH changes from our Gemündener Maar record. Our results do not provide evidence for overall markedly dry climatic conditions having prevailed during the Younger Dryas. Rather, a two-phasing of the Younger Dryas is supported, with moderate wet conditions at the Allerød level during the first half and drier conditions during the second half of the Younger Dryas. Moreover, our results suggest that the amplitude of RH changes during the Early Holocene was more pronounced than during the Younger Dryas. This included the occurrence of a “Preboreal Humid Phase”. One possible explanation for this unexpected finding could be that solar activity is a hitherto underestimated driver of central European RH changes in the past.

scholarly journals A major hydrobiological change in Dasht-e Arjan Wetland (southwestern Iran) during the late glacial – early Holocene transition revealed by subfossil chironomids

2019 ◽  
Vol 56 (8) ◽  
pp. 848-856
Author(s):  
Cyril Aubert ◽  
Morteza Djamali ◽  
Matthew Jones ◽  
Hamid Lahijani ◽  
Nick Marriner ◽  
...  
Keyword(s):  
Lake Level ◽  
Regional Scale ◽  
Younger Dryas ◽  
Late Glacial ◽  
Early Holocene ◽  
Geochemical Data ◽  
The Holocene ◽  
Chironomus Plumosus ◽  
Subfossil Chironomids ◽  
Southwestern Iran

The late glacial – early Holocene transition is a key period in the earth’s history. However, although this transition is well studied in Europe, it is not well constrained in the Middle East and palaeohydrological records with robust chronologies remain scarce from this region. Here we present an interesting hydrobiological record showing a major environmental change occurring in the Dasht-e Arjan Wetland (southwestern Iran, near to Persepolis) during the late glacial – early Holocene transition (ca. 11 650 years cal BP). We use subfossil chironomids (Insecta: Diptera) as a proxy for hydrological changes and to reconstruct lake-level fluctuations. The Arjan wetland was a deep lake during the Younger Dryas marked by a dominance of Chironomus plumosus/anthracinus-type, taxa adapted to anoxic conditions of deep waters. At the beginning of the Holocene, a drastic decrease (more than 80% to less than 10%) of Chironomus plumosus/anthracinus-type, combined with diversification of littoral taxa such as Polypedilum nubeculosum-type, Dicrotendipes nervosus-type, and Glyptotendipes pallens-type, suggests a lake-level decrease and a more vegetalized aquatic environment. We compare and contrast the chironomid record of Arjan with a similar record from northwestern Iran. The palaeoclimatic significance of the record, at a local and regional scale, is subsequently discussed. The increase in Northern Hemisphere temperatures, inferred by geochemical data from NGRIP, at the beginning of the Holocene best explains the change from the Younger Dryas highstand to early Holocene lowstand conditions in the Dasht-e Arjan wetland. However, a contribution of the meltwater inflow from small local glaciers in the catchment basin is not excluded.

Late glacial to Recent stratigraphy, paleontology, and sedimentary processes: Newfoundland continental slope and rise

1985 ◽  
Vol 22 (2) ◽  
pp. 266-282 ◽  
Author(s):  
C. T. Schafer ◽  
F. C. Tan ◽  
D. F. Williams ◽  
J. N. Smith
Keyword(s):  
Late Glacial ◽  
Turbidity Current ◽  
Western Boundary ◽  
Sedimentary Processes ◽  
Suspended Particulate ◽  
Labrador Current ◽  
Current Water ◽  
Late Wisconsinan ◽  
Late Glacial And Holocene ◽  
Glacial Time

Micropaleontology, pollen, sediment, and δ18O studies point to considerable variation in sedimentary processes and water-mass characteristics on the northeast Newfoundland slope and rise during late glacial and Holocene time. Allochthonous shelf and upper slope foraminiferal species suggestive of turbidity current activity occur relatively frequently in rise sediments during a postglacial interval, dated by extrapolation from a probable 9300 year old ash horizon. A single late glacial turbidity current deposit involved a much larger volume of sediment than that noted for the earlier events and it appears to have originated primarily on the middle slope. In conjunction with a widespread late glacial interval of fecal pellet deposition, this larger event suggests an increased flux of material in the form of suspended particulate matter to the continental margin following the late Wisconsinan glacial maximum. Oceanographic conditions during late glacial time appear to have stimulated the productivity of zooplankton in the waters off northeastern Newfoundland.Within the late Holocene interval of the rise sediments, there is some micropaleontological and sedimentological evidence for an intensification of the Western Boundary Undercurrent that appears to have started about 1000–2000 years BP. Over the same period of time, the surface water circulation seaward of the northeast Newfoundland shelf appears to have changed from a mode that was dominated occasionally by a northern component of relatively warm North Atlantic drift water to one that is dominated today exclusively by Labrador Current water.

Paleoenvironmental Changes and Glacial Stades of the Last 50,000 Years in the Cordillera Central, Colombia

1996 ◽  
Vol 46 (1) ◽  
pp. 1-18 ◽  
Author(s):  
Jean-Claude Thouret ◽  
Thomas Van der Hammen ◽  
Barry Salomons ◽  
Etienne Juvigné
Keyword(s):  
Late Glacial ◽  
Equilibrium Line Altitude ◽  
Cordillera Central ◽  
The Past ◽  
Paleoenvironmental Changes ◽  
Tephra Layers ◽  
Using Data ◽  
Glacial Time ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Using data from glacial geomorphology, tephra-soil stratigraphy and mineralogy, palynology, and radiocarbon dating, a sequence of glacial and bioclimatic stades and interstades has been identified for the past ca. 50,000 yr in the Ruı́z-Tolima massif, Cordillera Central. Six cold stades separated by warmer interstades occurred before 48,000, between 48,000 and 33,000, between 28,000 and 21,000, from ≥16,000 to ca. 14,000, ca. 13,000–12,400, and ca. 11,000–10,000 yr B.P. Although the radiocarbon ages are minimum-limiting ages obtained from tephra layers on top of tills, the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections. Two minor moraine stages likely reflect glacier pauses during cold intervals ca. 7400 yr B.P. and slightly earlier. Finally, glaciers readvanced between the 17th and 19th centuries. In contrast to the glacier cover (ca. 34 km2) on volcanoes of the massif during the last glacial maximum (LGM) the ice cover expanded to 1200 km2 and was still 800 km2 during late-glacial time (LGT). Glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude (ELA) by ca. 1100 m during the LGM and 500–600 m during LGT relative to the modern ELA which lies at ca. 5100 m in the Cordillera Central. Glaciers in this region apparently reached their greatest extent when the climate was cold and moist, e.g., during stades corresponding to marine isotope stage 3; glaciers were still expanding during the LGM ca. 28,000–21,000 yr B.P., but they shrank considerably after 21,000 yr B.P. because of greatly reduced precipitation.

Climatic, Solar, Oceanic, and Geomagnetic Influences on Late-Glacial and Holocene Atmospheric 14C/12C Change

1991 ◽  
Vol 35 (1) ◽  
pp. 1-24 ◽  
Author(s):  
Minze Stuiver ◽  
Thomas F. Braziunas ◽  
Bernd Becker ◽  
Bernd Kromer
Keyword(s):  
Ocean Circulation ◽  
Time Scale ◽  
Late Glacial ◽  
Minor Role ◽  
Activity Levels ◽  
Data Set ◽  
The Holocene ◽  
Spectral Interpretation ◽  
Late Glacial And Holocene ◽  
A Minor

AbstractLate-glacial and Holocene 14C/12C ratios of atmospheric CO2 vary in magnitude from a few per mil for annual/decadal pertubations to more than 10% for events lasting millennia. A data set illuminating 10- to 104-yr variability refines our understanding of oceanic (climatic) versus geomagnetic or solar forcing of atmospheric 14C/12C ratios. Most of the variance in the Holocene atmospheric 14C/12C record can be attributed to the geomagnetic (millennia time scale) and solar (century time scale) influence on the flux of primary cosmic rays entering the atmosphere. Attributing the observed atmospheric 14C/12C changes to climate alone leads to ocean circulation and/or global wind speed changes incompatible with proxy records. Climate-(ocean-)related 14C redistribution between carbon reservoirs, while evidently playing a minor role during the Holocene, may have perturbed atmospheric 14C/12C ratios measurably during the late-glacial Younger Dryas event. First-order corrections to the radiocarbon time scale (12,000–30,000 14C yr B.P.) are calculated from adjusted lake-sediment and tree-ring records and from geomagnetically defined model 14C histories. Paleosunspot numbers (100–9700 cal yr B.P.) are derived from the relationship of model 14C production rates to sunspot observations. The spectral interpretation of the 14C/12C atmospheric record favors higher than average solar activity levels for the next century. Minimal evidence was found for a sun-weather relationship.

scholarly journals Reconstruction of vegetation in the foothills of the Carpathian Mountains, Gorgany region, in the late glacial (based on pollen data of peat-bog Pidluzhia)

2015 ◽  
pp. 333-340
Author(s):  
Natalia Chumak
Keyword(s):  
Key Words ◽  
Radiocarbon Dating ◽  
Environmental Changes ◽  
Younger Dryas ◽  
Late Glacial ◽  
Peat Bog ◽  
Pollen Data ◽  
Carpathian Mountains ◽  
The Holocene ◽  
Short Period

The environmental changes on short-period stages of the Late Glacial were reconstructed based on pollen data of peat-bog Pidluzhia deposits and their radiocarbon dating. There are the Older and Younger Dryas, the Allerod (three phases) are allocated on palynological data in the Late Glacial. Vegetation had evolved from cold meadows to pine forest during this time. The transition from the Late Glacial to the Holocene was identified by the emergence of broad-leaved trees (elm, oak and linden), the spreading of spruce and disappearance of xerophytic elements. Key words: paleovegetation, paleoclimate, palinology, the Late Glacial, the foothills of the Carpathian Mountains.

scholarly journals Vegetation history and palaeoclimate at Lake Dojran (FYROM/Greece) during the Late Glacial and Holocene

2017 ◽  
Author(s):  
Alessia Masi ◽  
Alexander Francke ◽  
Caterina Pepe ◽  
Matthias Thienemann ◽  
Bernd Wagner ◽  
...  
Keyword(s):  
Roman Empire ◽  
Vegetation History ◽  
Late Glacial ◽  
Mediterranean Area ◽  
Human Presence ◽  
The Past ◽  
Age Model ◽  
Late Glacial And Holocene ◽  
Yugoslavian Republic ◽  
Southern Balkans

Abstract. A new high-resolution pollen and NPPs (Non-Pollen Palynomorphs) analysis has been performed on the sediments of Lake Dojran, a transboundary lake located at the border between Greece and Former Yugoslavian Republic of Macedonia (FYROM). The sequence covers the last 12 500 years and provides information on vegetational dynamics of the Late Glacial and Holocene for southern Balkans. A robust age-model, sedimentological, diatom, and biomarker analyses published previously have been the base 5 for a multi-perspective interpretation of the new palynological data. Pollen analysis revealed that the Late Glacial is characterized by steppic taxa with prevailing Amaranthaceae, Artemisia and Poaceae. The arboreal vegetation starts to rise after 11 500 yr BP, taking a couple of millennia to be definitively attested. Holocene vegetation is characterized by the dominance of mesophilous plants. Quercus robur type and Pinus are the most abundant taxa followed by Quercus cerris type, Quercus ilex type and Ostrya/Carpinus orientalis. The first attestation of human presence can be presumed at 5000 yr BP for the 10 contemporary presence of cereals, Juglans and Rumex. A drop of both pollen concentration and influx together with a δ18Ocarb shift indicates increasing aridity and precedes clear and continuous human signs since 4000 yr BP. Also a correlation between Pediastrum boryanum and fecal stanol suggests that the increase of nutrient in the water is related to human presence and pasture. An undoubted expansion of human-related plants occurs since 2600 yr BP when cereals, arboreal cultivated and other synanthropic non-cultivated taxa are found. A strong reduction in arboreal vegetation occurred at 2000 yr BP, when the strong 15 Roman Empire impacted on a landscape undergoing climate dryness in the whole Mediterranean area. In recent centuries the human impact still remains high but spots of natural vegetation are preserved. The Lake Dojran multi-proxy analysis including pollen data provide a valuable contribution to the palaeoenvironmental reconstruction and the comprehension of the past vegetation dynamics of southern Balkans.

12,000–11,700 cal BP

2017 ◽  
Author(s):  
Ofer Bar-Yosef ◽  
Miryam Bar-Matthews ◽  
Avner Ayalon
Keyword(s):  
Spatial Organization ◽  
Younger Dryas ◽  
Late Glacial ◽  
Glacial Maximum ◽  
Food Sources ◽  
Climatic Fluctuations ◽  
The Holocene ◽  
Fertile Crescent ◽  
First Millennium ◽  
Terminal Pleistocene

We take up the question of “why” cultivation was adopted by the end of the Younger Dryas by reviewing evidence in the Levant, a sub-region of southwestern Asia, from the Late Glacial Maximum through the first millennium of the Holocene. Based on the evidence, we argue that the demographic increase of foraging societies in the Levant at the Terminal Pleistocene formed the backdrop for the collapse of foraging adaptations, compelling several groups within a particular “core area” of the Fertile Crescent to become fully sedentary and introduce cultivation alongside intensified gathering in the Late Glacial Maximum, ca. 12,000–11,700 cal BP. In addition to traditional hunting and gathering, the adoption of stable food sources became the norm. The systematic cultivation of wild cereals begun in the northern Levant resulted in the emergence of complex societies across the entire Fertile Crescent within several millennia. Results of archaeobotanical and archaeozoological investigations provide a basis for reconstructing economic strategies, spatial organization of sites, labor division, and demographic shifts over the first millennium of the Holocene. We draw our conclusion from two kinds of data from the Levant, a sub-region of southwestern Asia, during the Terminal Pleistocene and early Holocene: climatic fluctuations and the variable human reactions to natural and social calamities. The evidence in the Levant for the Younger Dryas, a widely recognized cold period across the northern hemisphere, is recorded in speleothems and other climatic proxies, such as Dead Sea levels and marine pollen records.

The extent, timing and palaeoclimatic significance of Late-glacial and Holocene snowpatches and glaciers in the Marrakech High Atlas, Morocco

2021 ◽  
Author(s):  
Benjamin Bell ◽  
Philip Hughes ◽  
William Fletcher ◽  
Roger Braithwaite ◽  
Henk Cornelissen ◽  
...  
Keyword(s):  
Little Ice Age ◽  
Late Glacial ◽  
Ice Age ◽  
High Atlas ◽  
The Holocene ◽  
Exposure Dating ◽  
Ground Water Recharge ◽  
Late Glacial And Holocene ◽  
High Level ◽  
Snow And Ice

&lt;p&gt;Pleistocene glaciers were extensive in the Marrakech High Atlas, Morocco. Today, semi-permanent snowpatches survive in topoclimatic settings and there is evidence of niche glaciers as recently as the Little Ice Age and early 20&lt;sup&gt;th&lt;/sup&gt; Century. However, little is known about the state of permanent snow and niche glaciers through the Holocene. One hypothesis is that Little Ice Age glaciers were the largest snow and ice masses since the end of the Late-glacial (Younger Dryas 12.9-11.7 ka). Another possibility is that snow and ice expanded to similar or greater extents at other points in the Holocene.&lt;/p&gt;&lt;p&gt;To test these hypotheses, moraine boulders have been sampled on moraine successions in the highest parts of the High Atlas, including moraine successions in front of the n&amp;#233;v&amp;#233; permanent below the north-facing cliffs of Tazaghart (3890 m a.s.l.), a semi-permanent snowpatch that survives many summers today. This site is bounded by prominent moraine ridges with no soil development and no lichens on surface boulders. Several other high-level sites have been targeted and over 40 samples are currently being processed for &lt;sup&gt;10&lt;/sup&gt;Be and &lt;sup&gt;36&lt;/sup&gt;Cl exposure dating. Establishing the relative difference in extent and altitude of Late-glacial and the most recent glaciers in the High Atlas is important for understanding landscape and climate evolution in high mountain areas in the subtropics (31&amp;#186;N).&lt;/p&gt;&lt;p&gt;The dated geomorphological records for late-lying snow and glaciers will be compared to high-resolution &lt;sup&gt;14&lt;/sup&gt;C dated continuous parasequences from sediment cores from marshes at the Yagour Plateau and Ouka&amp;#239;meden, both high-level sites in the High Atlas (~2700 m a.s.l.). The proximity of these sites (5-30 km, respectively) from the snowpatch/glacier sites will provide an important independent record of environmental change, spanning the Late-glacial and Holocene. This geomorphological record of former glaciers and snowpatches (moraines and pronival ramparts) is inherently fragmentary in time and the continuous core records from these alpine marshes will provide crucial insights into changing moisture conditions over time, which at these altitudes are closely related to the extent and volume of snowpack.&lt;/p&gt;&lt;p&gt;The climates associated with perennial snow cover and niche glaciers, and the associated annual snowpack melt, will be quantified using degree-day modelling. This allows melt rates to be predicted and this can be compared against observed modern climate in the High Atlas region. This involves interrogation of existing meteorological datasets from across the High Atlas and the development of algorithms for interpolation and extrapolation to ungauged higher altitudes.&lt;/p&gt;&lt;p&gt;Changes in the nature of the cryosphere through time in the High Atlas Mountains is crucial for understanding human activity and socioeconomic development in the wider region. Today, snowmelt from the High Atlas represents the most important ground water recharge used for a wide variety of purposes. Understanding changes in snow conditions, and as a consequence the behaviour of niche glaciers, in the High Atlas through the Holocene has important implications not only for water supply for humans but also for biological refugia and the evolution of cold-adapted flora and fauna.&lt;/p&gt;

Late-Glacial to Holocene Changes in Winds, Upwelling, and Seasonal Production of the Northern California Current System

1992 ◽  
Vol 38 (3) ◽  
pp. 359-370 ◽  
Author(s):  
Constance Sancetta ◽  
Michell Lyle ◽  
Linda Heusser ◽  
Rainer Zahn ◽  
J.Platt Bradbury
Keyword(s):  
Late Pleistocene ◽  
Climate Model ◽  
Current System ◽  
Younger Dryas ◽  
California Current ◽  
Late Glacial ◽  
California Current System ◽  
The Past ◽  
Northern California Current ◽  
Continental Interior

AbstractA core 120 km off the coast of southern Oregon was examined for changes in lithology, diatoms, and pollen over the past 30,000 yr. Primary production during the late Pleistocene was about half that of the Holocene. Evidence from diatoms and pollen indicates that summer upwelling was much weaker, implying an absence of strong northerly winds. Early Pliocene diatoms found throughout the late Pleistocene section were probably derived from diatomites east of the Cascades and provide evidence for strong easterly winds over a dry continental interior. The findings verify predictions of a climate model based on glacial maximum conditions. There is no compelling evidence for a climatic reversal corresponding to the European Younger Dryas chron. During the early Holocene (9000−7000 yr B.P.) there may have been years when winds were insufficiently strong to support upwelling, so that warm stratified waters lay closer to the coast.

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