Paleoglaciation of the Tibetan Plateau and surrounding mountains based on exposure ages and ELA depression estimates

Abstract

The Tibetan Plateau holds an ample record of past glaciations, and there is an extensive set of glacial deposits dated by exposure dating. Here a compilation is presented of 10 Be exposure ages from 485 glacial deposits with 1855 individual samples on the Tibetan Plateau, and ELA depression estimates for the glacial deposits based on a simple toe to headwall ratio approach. To recalculate the Tibetan Plateau exposure ages, 10Be production rates from 24 calibration sites across the world are compiled and recalibrated yielding an updated global reference 10 Be production rate. The recalculated exposure ages from the Tibetan Plateau glacial deposits are then divided into three groups based on exposure age clustering, to discriminate good (well-clustered) from poor (scattered) deglaciation ages. A major part of the glacial deposits have exposure ages affected by prior or incomplete exposure, complicating exposure age interpretations. The well-clustered deglaciation ages are primarily from mountain ranges along the margins of the Tibetan Plateau with a main peak between 10 and 30 ka, indicating glacial advances during the global LGM. A large number of deglaciation ages older than 30 ka indicates maximum glaciation predating the LGM, but the exposure age scatter generally prohibits accurate definition of the glacial chronology. The ELA depression estimates scatter significantly, but the main part is remarkably low. Average ELA depressions of 337 ± 197 m for the LGM and 494 ± 280 m for the pre-LGM indicate restricted glacier expansion.

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…Several recent 10 Be production rate calibration studies have reported 5-15% lower reference 10 Be production rates (e.g. Balco et al, 2009;Young et al, 2013;Heyman, 2014) compared to the original CRONUS production rates (e.g. Balco et al, 2008), implying that many exposure ages are likely to be thousands of years older than previously reported.…”

“…A series of investigations have documented evidence for extensive erosion of the Arctic Ocean seafloor caused by ice at modern water depths of up to 1,000 m, as well as glacial landforms on individual ridge crests and plateaus where water depths are shallower (Vogt et al, 1994;Jakobsson, 1999, Polyak et al, 2001. These data, together with chronological information retrieved from sediment cores, have been taken to imply that the most extensive ice shelf complex existed in the Amerasian basin of the Arctic Ocean during Marine Isotope Stage (MIS) 6 2014).…”

<sup>10</sup>Be depth profiles in glacial sediments on the Swiss Plateau: deposition age, denudation and (pseudo-) inheritance

“…Apart from the measured 10 Be concentrations at specific depths, critical input parameters are the allowed age range (time, t), ranges for denudation rate (cm a −1 ) and inheritance (atoms g −1 ), as well as a denudation threshold. We used a reference production rate for neutrogenic spallation of 3.93 atoms g −1 a −1 (Heyman, 2014) and the scaling model by Lal (1991) and Stone (2000) to calculate the production rate for each site. Because the standard files for calculating muogenic production rate after Heisinger et al (2002a, b) yield too-high values (Braucher et al, 2003(Braucher et al, , 2013Phillips et al, 2016), we used the .m files provided Ruszkiczay-Rüdiger et al (2016).…”

“…For this purpose, we here briefly summarize the currently available data and the state of knowledge. All exposure ages have been (re)calculated using the CRONUS web calculator with the time-dependent scaling model by Lifton et al (2014) and a reference production rate of 3.93 (±0.1) atoms g −1 a −1 (Heyman, 2014).…”

Weichselian phases and ice dynamics of the Scandinavian Ice Sheet in northeast Germany: a reassessment based on geochronological and geomorphological investigations in Brandenburg

“…The recalibration of previously published cosmogenic exposure ages from glacigenic boulders with an up-to-date 10 Be production rate (Heyman, 2014) resulted in a considerable increase of the ages (9-15 %; Hardt and Böse, 2017). In combination, the OSL ages and the cosmogenic nuclide exposure ages now provide a consistent geochronology of the Weichselian ice dynamics in Brandenburg.…”