Reconstructing Late Neogene Oceanographic Changes in the Southern Ocean: Latitudinal Migration of the Subantarctic Zone

Abstract

Reconstructing the late Neogene (5.5 – 0.5 Ma) migration of frontal systems will help understand the regional climate of the Southern Ocean (SO). This study investigates frontal latitudinal shifts at Ocean Drilling Program (ODP) Site 1171, located on the South Tasmanian Rise between the Subtropical Front (STF) and Subantarctic Front (SAF). A new age model was developed by integrating recalibrated bio- and magnetostratigraphy with new bulk δ¹⁸O and δ¹³C isotope data. Dinoflagellate cyst assemblages were analyzed through cluster analysis to trace frontal shifts over time. The results indicate that the SAF remained south of Site 1171 throughout the study interval, while STF migrations were present but less pronounced than at more northerly sites like ODP Site 1168. These findings suggest that the STF was more flexible and responsive to climate variability than the SAF. Cross-validation with isotope trends and rarefaction analysis reinforces the interpretation of a stable SAF and a climatically sensitive STF. This study contributes to a more detailed understanding of SO frontal evolution and highlights the need for site-specific, multiproxy approaches to predict future changes under ongoing anthropogenic warming.