LOESS SPATIAL CHARACTERISTICS ESTIMATE PALEOWIND PATTERNS DURING AND AFTER LATE GLACIAL MAXIMUM IN WISCONSIN, USA

2016 ◽  
Author(s):  
Randall Schaetzl ◽  
2010 ◽  
Vol 226 (1-4) ◽  
pp. 29-41 ◽  
Author(s):  
William C. Mahaney ◽  
Volli Kalm ◽  
John Menzies ◽  
Michael W. Milner
Keyword(s):  

Biologia ◽  
2006 ◽  
Vol 61 (4) ◽  
Author(s):  
Anton Petrík ◽  
Zuzana Dúbravcová ◽  
Ivan Jarolímek ◽  
Ján Kliment ◽  
Jozef Šibík ◽  
...  

AbstractWe present a syntaxonomic account of the communities of the alliances of Oxytropido-Elynion Br.-Bl. 1949 and Festucion versicoloris Krajina 1933 from Western Carpathians. Both alliances comprise naked-rush, cushion form and dwarf-shrub heath communities typical of wind-exposed habitats occurring at the highest altitudes of the Tatra Mts. They represent a relic vegetation of the cold stages of the Pleistocene (probably Late Glacial Maximum) and they can be classified within the class of Carici rupestris-Kobresietea bellardii Ohba 1974. A set of relevés was subject to numerical-classification analysis. Floristics and ecology of the communities were characterised and the relationships to similar syntaxa were discussed.The Oxytropido-Elynion is restricted to the extreme ridge positions in the highest altitudes of the Belianske Tatry Mts. Five associations were distinguished, such as the Pyrolo carpaticae-Salicetum reticulatae, the Festuco versicoloris-Oreochloetum distichae, the Festucetum versicoloris, the Oxytropido carpaticae-Elynetum myosuroides and the Drabo siliquosae-Festucetum versicoloris.The Festucion versicoloris is limited to the mylonite zone of the alpine and subnival belt of the Vysoké Tatry and Západné Tatry Mts (and found as rare in the Nízke Tatry Mts). The stands of these communities prefer terraces of steep rocky faces and cliffs and stabilised small-grained screes below the cliffs. Within this alliance, three associations were described, including the Agrostio alpinae-Festucetum versicoloris, the Silenetum acaulis and the Salicetum kitaibelianae.


2021 ◽  
Author(s):  
Brent Goehring ◽  
Brian Menounos ◽  
Gerald Osbron ◽  
Adam Hawkins ◽  
Brent Ward

Abstract. We present a new in situ produced cosmogenic beryllium-10 and carbon-14 nuclide chronology from two sets (outer and inner) of alpine glacier moraines from the Grey Hunter massif of southern Yukon Territory, Canada. The chronology potential of moraines deposited by alpine glaciers outside the limits of the Last Glacial Maximum (LGM) ice sheets potentially provide a less-ambiguous archive of mass balance, and hence climate than can be inferred from the extents of ice sheets themselves. Results for both nuclides are inconclusive for the outer moraines, with evidence for pre-LGM deposition (beryllium-10) and Holocene deposition (carbon-14). Beryllium-10 results from the inner moraine are suggestive of canonical LGM deposition, but with relatively high scatter. Conversely, in situ carbon-14 results from the inner moraines are tightly clustered and suggestive of terminal Younger Dryas deposition. We explore plausible scenarios leading to the observed differences between nuclides and find that the most parsimonious explanation for the outer moraines is that of pre-LGM deposition, but many of the sampled boulder surfaces were not exhumed from within the moraine until the Holocene. Our results thus imply that the inner and outer moraines sampled pre- and post-date the canonical LGM and that moraines dating to the LGM are lacking likely due to overriding by the subsequent Late Glacial/earliest Holocene advance.


Author(s):  
Ofer Bar-Yosef ◽  
Miryam Bar-Matthews ◽  
Avner Ayalon

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.


2021 ◽  
Author(s):  
Hans Fernández ◽  
Juan-Luis García ◽  
Samuel U. Nussbaumer ◽  
Alessa Geiger ◽  
Isabelle Gärtner-Roer ◽  
...  

<p>The geochronological and geomorphological reconstruction of glacier fluctuations is required to assess the timing and structure of climate changes of the last glacial cycle in the subtropical Andes of Chile. The scarcity of data in this region limits the knowledge related to the timing of glacial landscape changes during this long-term period. To provide a new framework to better understand the climate history of the semiarid Andes of Chile, we have reconstructed the glacial history of the Universidad glacier (34° S).</p><p>Our mapping shows the existence of four moraine belts (UNI I to UNI IV, from outer to inner) that are spatially unequally distributed along the 13 km of the valley between ~2500 and ~1400 m a.s.l. We applied <sup>10</sup>Be cosmogenic surface exposure dating to 26 granodioritic boulders on moraines and determined the age of the associated glacial advances. UNI I moraine represents the distal glacier advance between 20.8±0.8 and 17.8±0.8 kyr ago (number of <sup>10</sup>Be samples = 11). Other two significative glacier advances terminated one and four km up-valley from the UNI I moraine, respectively, formed 16.1±0.9 kyr (n=1) (UNI II) and 14.6±1 to 10±0.5 kyr ago (n=3) (UNI III). A sequence of six distinct and smaller moraine ridges has been identified in the proglacial area. They are part of last significative glacier advances labeled as UNI IV. The four distal ridges have been dated to between 645-150 years ago (n=11), while the most proximal moraines coincide with mid-20<sup>th</sup> century and 1997 aerial photographs.</p><p>The results indicate that the Universidad glacier advanced during the Last Glacial Maximum (LGM) (UNI I). Deglaciation was punctuated by glacier readvances during the Late Glacial when the UNI II and UNI III moraines were deposited. Finally, UNI IV moraine shows six glacier fluctuations developed between the 14th and 20<sup>th</sup> centuries.</p><p>Our data suggest that the glacier advances by the Universidad glacier were triggered by intensified southern westerly winds bringing colder and wetter conditions to subtropical latitudes in the SE Pacific. Moreover, our data indicate that more or less in-phase Late-Glacial advances along the tropical and extratropical Andes occurred. We discuss different climate forcings that explain these glacier changes. Finally, we illustrate the influence of the “Little Ice Age” in the Semiarid Andes.</p>


2014 ◽  
Vol 8 (2) ◽  
pp. 607-621 ◽  
Author(s):  
T. Zwinger ◽  
M. Schäfer ◽  
C. Martín ◽  
J. C. Moore

Abstract. We use a full-Stokes thermo-mechanically coupled ice-flow model to study the dynamics of the glacier inside Scharffenbergbotnen valley, Dronning Maud Land, Antarctica. The domain encompasses a high accumulation rate region and, downstream, a sublimation-dominated bare ice ablation area. The ablation ice area is notable for having old ice at its surface since the vertical velocity is upwards, and horizontal velocities are almost stagnant there. We compare the model simulation with field observations of velocities and the age distribution of the surface ice. No satisfactory match using an isotropic flow law could be found because of too high vertical velocities and much too high horizontal ones in simulations despite varying enhancement factor, geothermal heat flux and surface temperatures over large ranges. However, the existence of a pronounced ice fabric may explain the observed present-day surface velocity and mass balance distribution in the inner Scharffenbergbotnen blue ice area. Near absence of data on the temporal evolution of Scharffenbergbotnen since the Late Glacial Maximum necessitates exploration of the impact of anisotropy using prescribed ice fabrics: isotropic, single maximum, and linear variation with depth, in both two-dimensional and three-dimensional flow models. The realistic velocity field simulated with a noncollinear orthotropic flow law, however, produced surface ages in significant disagreement with the few reliable age measurements and suggests that the age field is not in a steady state and that the present distribution is a result of a flow reorganization at about 15 000 yr BP. In order to fully understand the surface age distribution, a transient simulation starting from the Late Glacial Maximum including the correct initial conditions for geometry, age, fabric and temperature distribution would be needed. This is the first time that the importance of anisotropy has been demonstrated in the ice dynamics of a blue ice area and demonstrates the need to understand ice flow in order to better interpret archives of ancient ice for paleoclimate research.


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