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Complex erosion patterns produced by the Haizishan paleo-ice cap
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Purdue University.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Determining patterns and rates of glacial erosion is important in understanding landscape evolution, topographic relief production, geochemical cycles, climate change, and glacial thermal regimes of paleo glaciers and ice sheets. Combining in situ $^{10}$Be and $^{26}$Al apparent exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4 000 km$^2$ Haizishan paleo-ice cap on the southeastern Tibetan Plateau. Our results show that ice caps developed several times on the low relief Haizishan Plateau and produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with last deglaciation, complete resetting of the cosmogenic exposure age clock indicates that more than 2 m of glacial erosion occurred during the last major glaciation (which in this area correlates with the global Last Glacial Maximum (gLGM)).  However, older apparent exposure ages on bedrock and in saprolites profiles in areas known to have been covered by the paleo ice cap during gLGM indicate inheritance and thus limited or no erosion by the last ice cap in several areas, including the central zone of the paleo ice cap and at the head of an outlet glacier. Similarly, cosmogenic radionuclide depth profiles in saprolites show erosion of $>$2 m in an outlet valley bottom and in the mountains that make up the northern border of the paleo ice cap, while samples from saprolites in areas of otherwise scoured terrain have a large nuclide inheritance indicating limited erosion. As patterns of glacial erosion intensity are largely driven by basal thermal regime, our results are consistent with a hypothesis of complex thermal regimes for the paleo Haizishan ice cap during gLGM that was proposed previously on the basis of landform patterns. Future work, including glaciological modeling, is required to fully understand the implications and mechanisms of the complex thermal regime of this paleo ice cap.

Keyword [en]
Paleoglaciology, Tibetan Plateau, cosmogenic nuclide, Last Glacial Maximum, basal thermal regime
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-95140OAI: oai:DiVA.org:su-95140DiVA: diva2:658659
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2013-10-30Bibliographically approved
In thesis
1. Paleoglaciology of Shaluli Shan, southeastern Tibetan Plateau
Open this publication in new window or tab >>Paleoglaciology of Shaluli Shan, southeastern Tibetan Plateau
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes. This work focuses on the paleoglaciology of the Shaluli Shan Mountain area in the southeastern Tibetan Plateau. Multiple approaches, including geomorphological mapping, field assessment, cosmogenic nuclide exposure dating, and numerical glacier modeling are employed to reconstruct the extent, timing, erosion patterns, basal thermal regime, and ice dynamic of past glaciation of the Shaluli Shan. Detailed geomorphological mapping and analysis provide evidence for multiple past glaciations involving valley glaciers and small ice fields in the high mountains and ice caps on low-relief plateaus at intermediate elevations. Ice cap glaciation on the low-relief Haizishan Plateau produced glacial landforms in a zonal pattern, suggesting that the Haizishan paleo-ice cap had a complex basal thermal regime. 10Be exposure ages for glacial erratics and till depth profiles constrain three major glaciations in the Shaluli Shan: pre global Last Glacial Maximum (gLGM) (with minimum ages at 102.3 ± 10.0 – 183.6 ± 17.0 ka), gLGM (21.6 ± 2.0 ka), and Late Glacial (13.0 ± 1.2 – 17.1 ± 1.6 ka) . Extensive glacier expansion in the Shaluli Shan during Marine Isotope Stage (MIS) 6 and gLGM, and the lack of evidence of glaciation during MIS 4 and 3, suggests that the extent and timing of glaciations in the southeastern Tibetan Plateau are synchronized with northern Hemisphere climate changes. The glacial erosion depth constraints based on 10Be and 26Al concentrations in bedrock, glacial erratics, and till depth profiles indicate a complex glacial erosion pattern during the gLGM and Late Glacial, consistent with the hypothesis of complex basal thermal regime of Haizishan paleo-ice cap. Numerical model simulations of a Haizishan ice cap also predict a complex basal thermal regime and indicate high sensitivity of the ice cap to past temperature.

 

Abstract [sv]

Rekonstruktioner av Tibetanska platåns paleoglaciologi är av stor vikt för att förstå kopplingen mellan regionala och globala klimatförändringar. Det här arbetet fokuserar på paleoglaciologin i Shaluli Shan-bergen i sydöstra delen av den Tibetanska platån, där syftet har varit att rekonstruera utbredning, ålder, erosions-mönster, subglacial temperatur och isdynamik under tidigare nedisningsperioder i området. De metoder som använts har varit geomorfologisk kartering med hjälp av satellitbilder och höjdmodeller, fältkartering och -provtagning, ytexponerings-datering och numerisk modellering av glaciärer. Den detaljerade geomorfologiska karteringen av nedisningsspår visar att tidigare nedisningar framför allt har förekommit i form av tillväxt av dalglaciärer och små isfält i de höga bergsområdena samt platåisar på flacka platåytor på mellanhöga höjder. De platåisar som har vuxit till på den flacka Haizishan-platån har skapat glaciala landformer med en utbredning som tyder på att Haizishan-isen hade ett komplext mönster av bottentemperatur med både varm- och kallbottnade delar. Kosmogen ytexponerings-datering, baserad på koncentration av 10Be-isotoper i flyttblock och morän-profiler, visar tre perioder av nedisning i Shaluli Shan: tidig isexpansion med minimi-åldrar på 102.3 ± 10.0 – 183.6 ± 17.0 ka (ka=1000 år före nu), nedisning under det senaste globala glaciala maximat (gLGM) vid 21.6 ± 2.0 ka, samt  en sen fas av tillväxt av glaciärer vid  13.0 ± 1.2 – 17.1 ± 1.6 ka. Utbredd nedisning under perioden 102-184 ka och under gLGM, samt bristen på spår av nedisning under perioden däremellan, tyder på att nedisningen av den sydöstra Tibetanska platån sker i takt med de klimatförändringar och perioder av glaciärtillväxt som förekommit på övriga norra halvklotet under samma tid. Omfattningen av den glaciala erosionen, vilken analyserats med hjälp av koncentrationer av 10Be- och 26Al-isotoper i berggrund, flyttblock och morän-profiler, tyder på att platåisarna hade ett komplext erosionsmönster under gLGM och den sista delen av nedisningen. Detta stödjer den tidigare slutsatsen om en komplex subglacial temperaturfördelning under den tidigare platåisen på Haizishan. Även numerisk glaciologisk modellering av nedisningen på Haizishan-platån visar på en komplex subglacial temperatur-regim, vilket i sin tur tyder på en hög temperaturkänslighet för tidigare platåisar i området.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2013. 30 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 39
Keyword
Paleoglaciology, Tibetan Plateau, geomorphological mapping, cosmogenic nuclide, Last Glacial Maximum, glacial erosion, basal thermal regime, paleoglaciologi, Tibetanska platån, geomorfologisk kartering, kosmogena isotoper, senaste glaciala maximat, glacial erosion, subglacial temperatur
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-94204 (URN)978-91-7447-803-7 (ISBN)
Public defence
2013-12-03, De Geer lecture hall, The Geoscience building, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2013-11-11 Created: 2013-09-30 Last updated: 2013-11-04Bibliographically approved

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