Holocene deglaciation and glacier readvances on the Fildes Peninsula and King George Island (Isla 25 de Mayo), South Shetland Islands, NW Antarctic Peninsula

Pablo Heredia Barión, Stephen J Roberts , Cornelia Spiegel, Steven A. Binnie, Lukas Wacker, Joanna Davies, Imogen Gabriel, Vivienne J. Jones, Simon Blockley, Emma J Pearson, Louise Foster, Sarah J Davies, Thomas P Roland, Emma Hocking, Michael J Bentley, Dominic A Hodgson, Chris L Hayward, Robert D McCulloch, Jorge A Strelin, Gerhard Kuhn

To provide insights into glacier-climate dynamics of the South Shetland Islands (SSI), NW Antarctic Peninsula, we present a new deglaciation and readvance model for the Bellingshausen Ice Cap (BIC) on Fildes Peninsula and for King George Island/Isla 25 de Mayo (KGI) ~62°S. Deglaciation on KGI began after c. 15 ka cal BP and had progressed to within present-day limits on the Fildes Peninsula, its largest ice-free peninsula, by c. 6.6–5.3 ka cal BP. Probability density phase analysis of chronological data constraining Holocene glacier advances on KGI revealed up to eight 95% probability ‘gaps’ during which readvances could have occurred. These are grouped into four stages – Stage 1: a readvance and marine transgression, well-constrained by field data, between c. 7.4–6.6 ka cal BP; Stage 2: four probability ‘gaps’, less well-constrained by field data, between c. 5.3–2.2 ka cal BP; Stage 3: a well-constrained but restricted ‘readvance’ between c. 1.7–1.5 ka; Stage 4: two further minor ‘readvances’, one less well-constrained by field data between c. 1.3–0.7 ka cal BP (68% probability), and a ‘final’ well-constrained ‘readvance’ after <0.7 ka cal BP. The Stage 1 readvance occurred as colder and more negative Southern Annular Mode (SAM)-like conditions developed, and marginally stronger/poleward shifted westerly winds led to more storms and precipitation on the SSI. Readvances after c. 5.3 ka cal BP were possibly more frequent, driven by reducing spring/summer insolation at 62°S and negative SAM-like conditions, but weaker (equatorward shifted) westerlies over the SSI led to reduced storminess, restricting readvances within or close to present day limits. Late Holocene readvances were anti-phased with sub-aquatic moss layers in lake records unaffected by glaciofluvial inputs. Retreat from ‘Neoglacial’ glacier limits and the recolonisation of lakes by sub-aquatic moss in the post-bomb era (>1950 CE) is associated with recent warming/more positive SAM-like conditions.