Cosmogenic 10Be constraints on deglacial snowline rise in the Southern Alps, New Zealand

Geochronological dating of glacial landforms, such as terminal and lateral moraines, is useful for determining the extent timing past glaciation reconstructing magnitude rate climate changes. In Southern Alps New Zealand, well-dated geomorphological records constrain last cycle across much Waitaki River basin (e.g. Ōhau, Pukaki, Tekapo) but its southern sector Ahuriri valley remains comparatively unconstrained. Recently, there has been debate on scale rapidity mountain glacier retreat during termination, particularly 20–17 ka period in Zealand. Missing from this well-constrained equilibrium-line altitude (ELA) associated temperature reconstructions, over around 17 ka, which can help us to develop a more complete picture how changes drove retreat. Here we report first chronology dataset Last Glacial Maximum (LGM) subsequent deglaciation valley, Alps, Zealand (44°23′54″S, 169°39′48″E) based 38 beryllium-10 (10Be) surface-exposure ages moraine systems glaciated bedrock situated at lower middle sections valley. Our results show that former Glacier reached maximum 19.8 ± 0.3 coincides with global Maximum. By 16.7 had ∼18 km up-valley suggesting least ∼43% glacier-length loss relative full LGM extent. This was accompanied by formation shallow proglacial lake. Using accumulation area ratio (AAR) method, estimate ELA than present ∼880 m (∼1120 a.s.l.) ∼770 (∼1230 ka. Applying an lapse rate, anomaly implies local air 5 1 °C colder (1981–2010) while it 4.4 0.9 assuming no change precipitation. The substantial response relatively small accompanying increases (110 m) (0.6 °C) may have result high sensitivity system due low gradient ice surface. warming differs markedly other studies, specifically Rakaia reports larger increase onset deglaciation. precisely-dated record along reconstructed proxies atmospheric conditions, provides new insight into post behaviour conditions