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Heinrich Stadial 1 (HS1) was the major climate event at the onset of the last deglaciation associated with rapid cooling in Greenland and lagged, slow warming in Antarctica. Although it is widely believed that temperature signals were triggered in the Northern Hemisphere and propagated southward associated with the Atlantic meridional overturning circulation (AMOC), understanding how these signals were able to cross the Antarctic Circumpolar Current (ACC) barrier and further warm up Antarctica has proven particularly challenging. In this study, we explore the physical processes that lead to the Antarctic warming during HS1 in a transient isotope-enabled deglacial simulation iTRACE, in which the interpolar phasing has been faithfully reproduced. We show that the increased meridional heat transport alone, first through the ocean and then through the atmosphere, can explain the Antarctic warming during the early stage of HS1 without notable changes in the strength and position of the Southern Hemisphere midlatitude westerlies. In particular, when a reduction of the AMOC causes ocean warming to the north of the ACC, increased southward ocean heat transport by mesoscale eddies is triggered by steeper isopycnals to warm up the ocean beyond the ACC, which further decreases the sea ice concentration and leads to more absorption of insolation. The increased atmospheric heat then releases to the Antarctic primarily by a strengthening zonal wavenumber-3 (ZW3) pattern. Sensitivity experiments further suggest that a ∼4°C warming caused by this mechanism superimposed on a comparable warming driven by the background atmospheric CO₂rise is able to explain the total simulated ∼8°C warming in the West Antarctica during HS1.

Insolation changes play an important role in driving monsoon changes at orbital time scales. One key issue that has remained outstanding is whether the Asian monsoon is driven by local insolation from the Northern Hemisphere (NH) or remote insolation from the Southern Hemisphere (SH) at orbital band. Here, we perform a set of sensitivity experiments to quantify the impacts of local and remote insolation changes on the Afro‐Asian summer monsoon at 11 ka BP relative to the present. We show that the Afro‐Asian summer monsoon is overwhelmingly driven by the precession induced local insolation change in the tropical‐subtropical NH. The insolation from NH high latitudes also affects the Afro‐Asian summer monsoon. In contrast, the insolation from SH plays a negligible role. Our model experiments support the idea that the Afro‐Asian summer monsoon are driven predominantly by the direct forcing of NH low latitudes summer insolation for the Holocene.