Abstract
The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60°22′ W, 62°40’ S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 10Be exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at ∼22 ka but intense glacial shrinking occurred from ∼18 to ∼13 ka, when the nunataks became exposed, being particularly intense at the end of this period (∼14–13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).
Highlights
Nunataks, ice-free areas protruding from glaciers, are unique environments that allow to study past glacial dynamics such as glacial retreat in a vertical perspective (Small et al, 2019)
Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at ~22 ka but intense glacial shrinking occurred from ~18 to ~13 ka, when the nunataks became exposed, being intense at the end of this period (~14 e13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR)
Geografico del Ejercito’ (1991) e based on in-situ classical topographic measurements in 1989e1990 and 1990e1991 (RodríguezCielos, 2014) e, and GNSS measurements of the glacier margin performed in 2000e2001 (Recio-Blitz, 2019) all show this area as ice-free, so there is no risk of that surface being covered by the ice at Sample name Latitude (DD) Longitude (DD) Elevation (m a.s.l.)a Vertical distance from the summit (m) Topographic shielding factor
Summary
Ice-free areas protruding from glaciers, are unique environments that allow to study past glacial dynamics such as glacial retreat in a vertical perspective (Small et al, 2019) These islands of land surrounded by ice are found in mountain glaciers, ice caps and ice sheets. Nunataks have important implications for post-glacial geomorphic and environmental dynamics during the paraglacial phase, such as for vegetation colonization (Ruiz-Fernandez et al, 2019) They have been suggested to provide refugia to biodiversity during past glaciations, being pioneering sites for vegetation re-colonization following glacial retreat (Jørgensen et al, 2012) and key spots for species dispersal across migration routes from ice-free areas in the Maritime Antarctica to the interior of the continent (Convey et al, 2020). A more accurate picture of the age of deglaciation and nunatak development in the Antarctic Peninsula region can be useful to better understand the pattern of colonization
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