Late Pliocene growth of the West Antarctic Ice Sheet to near-modern dimensions

Abstract Accurate prediction of West Antarctic Ice Sheet (WAIS) collapse and its impact on sea level in future warmer climate states remains uncertain1. Understanding the Pliocene-Pleistocene ice sheet behaviour provides an opportunity to evaluate the role of forcing factors for ice mass gain/loss, determine the tipping points of WAIS growth/collapse and its impact on future sea level rise. Here, we provide evidence for the transition from a dynamic2 and smaller-sized WAIS during the warm Pliocene to a relatively stable and expanded ice sheet closer to its modern configuration during the Pleistocene based on the longest sedimentary geochemical records from Amundsen Sea, in proximity to modern maximum ice loss3. This transition coincided with initiation of orbitally paced 40-ka glacial-interglacial (G-I) cycles and atmospheric pCO2 drop, thus suggests that major tipping points for the growth and stability of the WAIS lies within atmospheric-oceanic conditions encountered during the Pliocene-Pleistocene transition. Despite large G-I variations in global temperature (+4 to -10 °C) and pCO2 (~180 – 280 ppm)4, the observation of relatively stable Pleistocene WAIS is contrary to model observations5,6 and questions its contribution to late Pleistocene sea level change. These findings have significant implications for predicting future ice sheet behavior and its impact on sea level rise.