Cosmogenic exposure age record of emerged nearshore erratic boulders on the western Antarctic Peninsula

Abstract

The retreat of the Antarctic Peninsula Ice Sheet since the Last Glacial Maximum provides key insights into ice-sheet dynamics, climate interactions and sea-level fluctuations. Terrestrial cosmogenic nuclide (TCN) dating of glacial deposits on the western Antarctic Peninsula (WAP) offers valuable temporal and spatial information regarding this retreat. However, many erratic deposits are found near the present sea level on the WAP archipelagos, limiting the applicability of TCN dating. This is because some of these deposits were previously submerged and later emerged due to ongoing post-glacial isostatic uplift and global sea-level rise. Here, for the first time on the Antarctic Peninsula, we present TCN dating results for emerged erratic boulders and bedrock samples located below the post-glacial marine limit of the WAP. Samples were collected from three islands along a latitudinal range from 64 degrees S to 68 degrees S: Nansen Island in Wilhelmina Bay (n = 4), Galindez Island in the Argentine Islands-Kyiv Peninsula region (n = 5) and Horseshoe Island on the northern coast of Marguerite Bay (n = 1). Our study indicates that nearshore boulder emergence occurred sometime between 1.4 +/- 0.3 and 3.8 +/- 0.3 ka ago on the WAP. The bedrock samples on Galindez Island provide somewhat older ages (17.9 +/- 2.8 and 11.8 +/- 1.9 ka), indicating the earliest emergence following deglaciation of the WAP. We discuss the challenges associated with sampling emerged erratic boulders along the Antarctic Peninsula shorelines and propose methods for overcoming these complications.