Abstract
The Southern Ocean is a key driver of global climate variability, yet its dynamics during the Mid-Pleistocene Transition (MPT; ∼1.25–0.7 Ma) remain poorly understood, especially in the South Pacific sector. The Polar Frontal Zone (PFZ) underwent significant latitudinal shifts during this critical period of climate reorganization. Here, we present new diatom records from four sediment cores along a north-south transect (54°S–60°S) in the central Pacific Southern Ocean, aimed at tracing spatial and temporal changes in the positions of the SAF and the PF across the MPT. We use the relative abundance of the diatom species Thalassiothrix antarctica as a proxy for frontal movement, along with diatom-based transfer functions, to reconstruct winter sea-ice (WSI) extent and summer sea surface temperatures (SSSTs). Results indicate a gradual northward displacement of the PFZ beginning at around 1.4 Ma, followed by a return to near-modern position at 700 ka. These frontal changes were driven by significant sea-ice expansion and SSST cooling, contributing to temperate interglacials during the MPT. Additionally, frontal migrations in the Pacific Southern Ocean might be topographically steered by the regional bathymetry, that is, the East Pacific Rise.