Fluctuation history of the interior East Antarctic Ice Sheet since mid-Pliocene

Abstract

Cosmogenic 10 Be and 26 Al measurements from bedrock exposures in East Antarctica provide indications of how long the rock surface has been free from glacial cover. Samples from the crests of Zakharoff Ridge and Mount Harding, two typical nunataks in the Grove Mountains, show minimum 10 Be ages of 2.00 AE 0.22 and 2.30 AE 0.26 Ma, respectively. These ages suggest that the crests were above the ice sheet at least since the Plio -Pleistocene boundary. Adopting a 'reasonable' erosion rate of 5 -10 cm Ma -1 increases the exposure ages of these two samples to extend into the mid-Pliocene. The bedrock exposure ages steadily decrease with decreasing elevation on the two nunataks, which indicates~200 m decrease of the ice sheet in the Grove Mountains since mid-Pliocene time. Seven higher elevation samples exhibit a simple exposure history, which indicates that the ice sheet in the Grove Mountains decreased only~100 m over a period as long as 1 -2 Ma. This suggests that the East Antarctic Ice Sheet (EAIS) was relatively stable during the Pliocene warm interval. Five lower elevation samples suggest a complex exposure history, and indicate that the maximum subsequent increase of the EAIS was only 100 m higher than the present ice surface. Considering the uncertainties, their total initial exposure and subsequent burial time could be later than mid-Pliocene, which may not conflict with the stable mid-Pliocene scenario.

Late Miocene ice sheet elevation in the Grove Mountains, East Antarctica, inferred from cosmogenic 21Ne–10Be–26Al

“…Table 1 gives the cosmogenic 10 Be, 26 Al and 21 Ne concentrations for the samples. Concentrations of 10 Be and 26 Al in R9201 and R9204 were also measured in our earlier study (Huang et al, 2008). The two samples were prepared and determined again and the concentrations of 10 Be and 26 Al obtained in this study are consistent within 10% to those reported in Huang et al (2008).…”

“…In an earlier study, we determined bedrock exposure ages in the Grove Mountains, East Antarctica, with the cosmogenic nuclides 10 Be and 26 Al (Huang et al, 2008). The 10 Be-inferred minimum exposure ages for the crests of the Zakharoff Ridge and Mount Harding, two typical nunataks in the Grove Mountains, are 2.0 Ma and 3.89 Ma, respectively.…”

Cosmogenic 21Ne concentrations and exposure ages of summit bedrocks in the Grove Mountains, Antarctica

“…The crest is 2300 m a.s.l., 200 m higher than the current ice sheet level. Detailed geological and geomorphic descriptions can be found in Huang et al [4]. The two samples R9202 and R9203 studied in this work were taken from smooth granulite bedrock, which are 8 and 15 m below the crest.…”

“…Cosmogenic radio-nuclides are normally determined with AMS, and radio-nuclides with long half-life such us 10 Be, 26 Al can be used to date exposure age [4] and burial age [5,6] up to million years. For exposure ages over 3-5 Ma, the concentrations of 10 Be and 26 Al are close to saturation, thus they cannot provide precise ages.…”

“…Among common stable cosmogenic nuclides (i.e., 3 He, 4 He, 21 Ne, 22 Ne, 38 Ar, 83 Kr), 3 He and 21 Ne are more often applied to study surface exposure histories [8][9][10]. As the diffusion coefficients of 3 He in quartz are much larger than 21 Ne, 3 He is not closed in quartz for million years at normal Earth surface temperatures; in contrast, 21 Ne can be quantitatively retained in quartz for million years [11].…”