Under what climate conditions were the New Zealand subantarctic islands glaciated?

Mountain glaciers are highly sensitive to climatic changes, making them key indicators for reconstructing past climate conditions. This study focuses on the New Zealand subantarctic Auckland and Campbell archipelagos, where geomorphological evidence of past glaciation provides rare insights into past terrestrial climate in the Southern Ocean. Using a 2D glacier model, we explored the temperature, precipitation, and seasonality conditions necessary for different glaciation extents on these islands. Our findings suggest that the Auckland Islands, with higher topography and greater precipitation, are more prone to glaciation than Campbell Island. We find that the most recent period of glaciation occurred in a climate that was 6–7 °C below mid-20th century levels, while the islands were covered by ice caps at temperatures more than 8 °C lower (assuming present day precipitation). Increased temperature seasonality relative to present requires further temperature reductions to achieve equivalent ice volumes, underscoring the sensitivity of glacier mass balance to summer temperatures. Our results provide a refined understanding of glaciation in the southwest Pacific sector of the Southern Ocean and offer a framework for assessing global climate model simulations of past climates. However, the climatic implications of the glacial record in these islands remain uncertain without precise dating of past glaciation events. • 2D glacier modelling experiments covering Auckland Islands and Campbell Island. • Cirque and valley glaciation occurs at temperatures 5–7 °C below modern. • Ice caps form when temperatures are colder than 8 °C below modern. • Increased seasonality relative to present reduces equilibrium ice volumes. • Greater geological and chronological control of past ice extent needed.