Ocean warming caused by Late Ordovician glacial onset in a coupled climate-ice sheet simulation

The Late Ordovician marks the first major continental ice sheet event in the Phanerozoic Eon, despite high CO ₂ levels, coinciding with a dramatic global temperature drop and one of the largest mass extinctions. However, the critical role of ice sheet-climate feedbacks in driving the Late Ordovician glaciation remains poorly understood. Using an asynchronous coupling approach, we capture the critical feedback of the ice sheet on large-scale processes such as atmospheric circulation and accurately reproduce regional cooling processes driven by the strong ice albedo positive feedback. We then reveal a key positive feedback loop: ice sheet growth triggers katabatic winds, which in turn promote further ice sheet expansion. Results show a 1.4 °C decrease in global mean surface temperature caused by ice sheet onset, with significant cooling over mid- to high-latitude continents while warming over the ocean. In contrast, the impact on tropical ocean temperatures remained limited. The high-latitude ocean warming is driven by the atmospheric stationary wave triggered by the massive ice sheet on the Gondwana continent. Our findings highlight the complex interactions between ice sheet dynamics, atmospheric and ocean circulation, emphasizing the importance of incorporating coupled ice sheet-climate feedbacks in palaeoclimate simulations.