Ventilation of the abyssal Southern Ocean during the late Neogene: A new perspective from the subantarctic Pacific

Abstract

Benthic foraminiferal stable carbon isotope records from the South Atlantic show significant declines toward more "Pacific-like" values at ∼7 and ∼2.7 Ma, and it has been posited that these shifts may mark steps toward increased CO 2 sequestration in the deep Southern Ocean as climate cooled over the late Neogene. We generated new stable isotope records from abyssal subantarctic Pacific cores MV0502-4JC and ELT 25-11. The record from MV0502-4JC suggests that the Southern Ocean remained well mixed and free of vertical or interbasinal δ 13 C gradients following the late Miocene carbon shift (LMCS). According to the records from MV0502-4JC and ELT 25-11, however, cold, low δ 13 C bottom waters developed in the Southern Ocean in the late Pliocene and persisted until ∼1.7 Ma. These new data suggest that while conditions in the abyssal Southern Ocean following the LMCS were comparable to the present day, sequestration of respired CO 2 may have increased in the deepest parts of the Southern Ocean during the late Pliocene, a critical period for the growth and establishment of the Northern Hemisphere ice sheets.