scholarly journals Implications of present ground temperatures and relict stone stripes in the Ethiopian Highlands for the palaeoclimate of the tropics

2020 ◽  
Author(s):  
Alexander R. Groos ◽  
Janik Niederhauser ◽  
Luise Wraase ◽  
Falk Hänsel ◽  
Thomas Nauss ◽  
...  
Keyword(s):  
Air Temperature ◽  
Ground Temperature ◽  
Seasonal Temperature ◽  
Ethiopian Highlands ◽  
Last Glacial ◽  
Exposure Dating ◽  
Ice Cap ◽  
The Tropics ◽  
Temperature Depression ◽  
The Last Glacial

Abstract. Large sorted patterned grounds are the most prominent features of periglacial and permafrost environments of the mid and high latitudes, but have not yet been verified for the tropics. Here, we report on relict large sorted polygons (up to 8 m in diameter) and large sorted stone stripes (up to 1000 m long, 15 m wide, and 2 m deep) on the ~ 4000 m high Sanetti Plateau in the Bale Mountains, southern Ethiopian Highlands. For a systematic investigation of past and present frost-related processes and landforms in the Bale Mountains, we conducted geomorphological mapping both in the field and on satellite images. The sorted stone stripes were studied in more detail by applying aerial photogrammetry, ground-penetrating radar measurements, and 36Cl surface exposure dating. In addition, we installed 29 ground temperature data loggers between 3493 and 4377 m to analyse present frost occurrence and seasonal temperature variations from 2017 to 2020. Finally, we ran a simple experiment and combined recent ground temperature measurements with meteorological data in a statistical model to assess the air temperature depression needed for the past formation of deep seasonal frost and cyclic freezing and thawing on the plateau. Our results show that relict and modern periglacial landforms are common in the Bale Mountains. Nocturnal superficial ground frost on the plateau occurs at 35–90 days per year, but the mean annual ground temperature (~ 11 °C) is far off from seasonal or permanent frost conditions. The modelling experiment suggests a minimum air temperature depression on the plateau of 7.6 ± 1.3 °C for the emergence of several decimetre deep seasonal frost. The stone stripes probably formed under periglacial conditions in proximity of a palaeo ice cap on the plateau during the coldest period(s) of the last glacial cycle. We hypothesise that the slightly inclined and unglaciated areas of the plateau, the coexistence of regolith and large blocks, the occurrence of deep seasonal frost, as well as relatively dry conditions beyond the ice cap provided ideal conditions for frost heave and sorting and the formation of large sorted patterned grounds. The presence of these landforms and the associated air temperature depression provide further evidence for an amplified cooling of high tropical mountains during the last glacial period that is yet not well captured in global climate models.

The enigma of large sorted stone stripes in the tropical Ethiopian Highlands

2020 ◽  
Author(s):  
Alexander Raphael Groos ◽  
Janik Niederhauser ◽  
Naki Akçar ◽  
Heinz Veit
Keyword(s):  
Active Layer ◽  
Late Pleistocene ◽  
Small Scale ◽  
Mean Annual Temperature ◽  
Seasonal Temperature ◽  
Ethiopian Highlands ◽  
Tropical Mountains ◽  
Freeze Thaw ◽  
Exposure Dating ◽  
Ice Cap

<p>The Bale Mountains in the southern Ethiopian Highlands (7-8°N) are formed of multiple superimposed flood basalts and comprise Africa’s largest plateau above 4000 m. Glacial and periglacial landforms are well-preserved and facilitate the reconstruction of the paleoclimate and landscape of the afro-alpine environment. During the Late Pleistocene, an ice cap covered the central part of the plateau and outlet glaciers extended down into the northern valleys. A striking geomorphological feature on the plateau are large sorted stone stripes that consist of hardly-weathered columnar basalt and are up to 2 m deep, 15 m wide and 200 m long. The stone stripes are located between 3850 and 4050 m at gentle slopes (4-8°) of two volcanic plugs 3-5 km south of the highest peak (Tullu Dimtu, 4377 m) and in the far west of the plateau. Sorted patterned grounds of similar size are characteristic for periglacial environments of the high latitudes, but unique for tropical mountains since their formation requires permafrost and a deep active layer. While diurnal freeze-thaw cycles in tropical mountains are sufficient for the genesis of small-scale patterned grounds, the sorting of large basalt columns (length >2 m, diameter >40 cm) assumes seasonal (or multi-annual) freeze-thaw cycles and a deep active layer. When and under which climatic conditions the sorted stone stripes in the Bale Mountains formed, remains an unsolved mystery. The stone stripes might have developed during the Late Pleistocene under periglacial conditions in close proximity to the ice cap or after deglaciation (~15-14 ka). To assess the timing of the final stagnation of the stone stripes, we determined the age of six basalt columns from two different stripes using <sup>36</sup>Cl surface exposure dating. In addition, we installed temperature data logger in 2, 10 and 50 cm depth across the plateau and between the stone stripes to investigate the present thermal conditions and diurnal and seasonal temperature variations in the ground. The difference between the measured mean annual temperature and presumed average ground temperature for permafrost (≤0°C) indicates an extreme temperature depression on the plateau of ≥10°C during the formation period of the sorted stone stripes. Such a Late Pleistocene cooling would be unprecendented in the tropical mountains. Finally, we applied a simple statistical model forced with meteorological data from a nearby weather station to simulate ground temperatures and test which climatic preconditions are necessary for the formation of sporadic permafrost in the Bale Mountains.</p>

II.—On the very Recent and Rapid Elevation of the Highlands of Eastern Asia

1891 ◽  
Vol 8 (4) ◽  
pp. 156-163
Author(s):  
Henry H. Howorth
Keyword(s):  
Geological Survey ◽  
Glacial Period ◽  
Eastern Asia ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Ice Cap ◽  
The Last Glacial

These opinions of Mr. Campbell, however clearly and precisely stated, are so strong and emphatic, that I wish to confirm them by those of another experienced geologist, who worked much among the Himalayas, namely, General McMahon. In “Notes of a Tour through Hangrang and Spiti,” published in the twelfth volume of the Eecords of the Geological Survey of India, he describes the existing glaciers and their remains in the district, and then says: “I do not know whether any one has ever supposed that the Himalayas were covered during the last Glacial period with an ice-cap, but I may note that whilst I saw nothing to favour such, an idea, I saw much to negative it. The contour of the hills and valleys in those parts of the interior of the Himalayas that I have visited is sharp and angular, and where rounded outlines are seen, they are sufficiently explained by the action of subaeiial forces on comparatively soft and friable rocks.

Thermodynamic Scaling of the Hydrological Cycle of the Last Glacial Maximum

2012 ◽  
Vol 25 (3) ◽  
pp. 992-1006 ◽  
Author(s):  
William R. Boos
Keyword(s):  
Water Vapor ◽  
Last Glacial Maximum ◽  
Climate Models ◽  
Hydrological Cycle ◽  
High Latitudes ◽  
Last Glacial ◽  
The Tropics ◽  
The Last Glacial Maximum ◽  
Circulation Changes ◽  
The Last Glacial

Abstract In climate models subject to greenhouse gas–induced warming, vertically integrated water vapor increases at nearly the same rate as its saturation value. Previous studies showed that this increase dominates circulation changes in climate models, so that precipitation minus evaporation (P − E) decreases in the subtropics and increases in the tropics and high latitudes at a rate consistent with a Clausius–Clapeyron scaling. This study examines whether the same thermodynamic scaling describes differences in the hydrological cycle between modern times and the last glacial maximum (LGM), as simulated by a suite of coupled ocean–atmosphere models. In these models, changes in water vapor between modern and LGM climates do scale with temperature according to Clausius–Clapeyron, but this thermodynamic scaling provides a poorer description of the changes in P − E. While the scaling is qualitatively consistent with simulations in the zonal mean, predicting higher P − E in the subtropics and lower P − E in the tropics and high latitudes, it fails to account for high-amplitude zonal asymmetries. Large horizontal gradients of temperature change, which are often neglected when applying the scaling to next-century warming, are shown to be important in large parts of the extratropics. However, even with this correction the thermodynamic scaling provides a poor quantitative fit to the simulations. This suggests that circulation changes play a dominant role in regional hydrological change between modern and LGM climates. Changes in transient eddy moisture transports are shown to be particularly important, even in the deep tropics. Implications for the selection and interpretation of climate proxies are discussed.

scholarly journals III.—Essays on Speculative Geology. 2.—Probable Changes of Latitude

1886 ◽  
Vol 3 (7) ◽  
pp. 300-308
Author(s):  
R. D. Oldham
Keyword(s):  
Glacial Period ◽  
Coal Field ◽  
Last Glacial Period ◽  
Last Glacial ◽  
The Face ◽  
The Tropics ◽  
Glacial Periods ◽  
The Last Glacial

In my last essay I had occasion to refer to the former existence of icebergs in localities which now lie in latitudes lower than those in which glacial action is known to have reached, even during the last Glacial period. But, surprising as it may be to find evidence of glacial action within a few degrees of, and, as in the case of the Eowen Eiver Coal-field, a few degrees within, the tropics, this sinks into insignificance in the face of the evidences of repeated Glacial periods that may be found in India, and especially in the Himalayas.

scholarly journals The last Glacial Period: rapid changes in air temperature and ocean hydrology

PAGES news ◽  
1997 ◽  
Vol 5 (2) ◽  
pp. 15-16
Author(s):  
E Cortijo ◽  
M Elliot ◽  
L Vidal ◽  
L Labeyrie ◽  
C Kissel ◽  
...  
Keyword(s):  
Air Temperature ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Rapid Changes ◽  
The Last Glacial

Last Glacial Maximum to near present 10Be chronology of the Universidad glacier fluctuations in the Subtropical Chilean Andes (34° S): paleoclimate implications  

2021 ◽  
Author(s):  
Hans Fernández ◽  
Juan-Luis García ◽  
Samuel U. Nussbaumer ◽  
Alessa Geiger ◽  
Isabelle Gärtner-Roer ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Late Glacial ◽  
Glacial Maximum ◽  
Ice Age ◽  
Climate History ◽  
Last Glacial ◽  
Exposure Dating ◽  
Glacier Fluctuations ◽  
History Of ◽  
The Last Glacial

<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>

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