A pre-Pliocene origin of the glacial trimline in the Ellsworth Mountains and the prevalence of old landscapes at high elevations in West Antarctica

Abstract

A glacial trimline at high elevations in West Antarctica informs on previous warm-based glaciation that occurred during an earlier stage of Antarctic Ice Sheet evolution. A multi-million-year history of theses landscapes has previously been evidenced in a few disparate locations. Here we present new cosmogenic nuclide analyses (¹⁰Be and ²⁶Al) from a total of 60 samples (clasts and bedrock) at high elevations in several hard-to-access locations across the interior of West Antarctica. In the Sentinel Range of the Ellsworth Mountains this trimline occurs at the highest elevations of any sites in West Antarctica (~3000 m asl). These new data reveal that clasts and bedrock, both above and below the trimline, have long exposure histories with minimum exposure-burial histories of 0.9–2.6 Ma. Accounting for low rates of erosion extends these exposure-burial histories to 2.7–4.8 Ma. Under the assumption of cyclical exposure-burial for proportions of glacial-interglacial cycles we show that some of our samples have exposure-burial histories extending back to the Miocene. We also present new data from the nearby Heritage Range where our new data supports previous work potentially extends the inferred persistence of the location of the West Antarctic ice sheet divide to >2.1 Ma. Finally, we present new data from two isolated nunataks (Mount Woollard and Mount Johns) located deep in the interior of the West Antarctic Ice Sheet near the main ice divide. Paired nuclide analyses of samples from these nunataks also shows long exposure histories and unambiguous evidence of past burial within the last ~100 ka. Such a thickening is not currently represented in ice-sheet models.