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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 1950 CE) is associated with recent warming/more positive SAM-like conditions.

Assessing seismic and tsunami hazards commonly relies on historical accounts of past events, but aside from limitations where such chronicles are too short to account for variability in earthquake size, rupture style, tsunamigenesis and the existence of supercycles, even where long written histories exist, records may be biased by temporal gaps due to historical circumstances. We demonstrate that this is the case for the area affected by the magnitude 9.5 1960 Chile earthquake. Historical records document four great earthquakes (M8+) in the last 450 years in this region, but while devastating tsunamis are known to have accompanied earthquakes in 1575, 1837 and 1960 CE, there is no such record of inundation in 1737. The lack of reports of tsunami inundation from the 1737 south-central Chile earthquake has been attributed to either civil unrest or a small tsunami due to deep fault slip below land. Here we cross-check the historical record using a coastal sedimentary record from Chaihuín, a tidal marsh 15 km southwest of Valdivia, close to the region of maximum 1960 slip. Tidal marshes are low energy intertidal settings that may preserve evidence for abrupt co-seismic changes in land level and inundation by extreme waves. We conduct sedimentological and diatom analyses of tidal marsh sediments within the 1737 rupture area and find evidence for a locally-sourced tsunami consistent in age with this event. The evidence is a laterally-extensive sand sheet coincident with abrupt, decametric-scale subsidence. Coupled dislocation-tsunami models place the causative fault slip mostly offshore rather than below land, as had previously been assumed from the absence of historical accounts of a tsunami. Whether associated or not with the 1737 earthquake, our findings reduce the average recurrence interval of tsunami inundation derived from historical records alone, highlighting the importance of combining geological and historical records in order to obtain robust long-term patterns to inform seismic and tsunami hazard assessment.