An Antarctic stratigraphic record of stepwise ice growth through the Eocene-Oligocene transition

Abstract

Earth's current icehouse phase began ~34 million years ago with the onset of major Antarctic glaciation at the Eocene-Oligocene Transition (EOT). Changes in ocean circulation and a decline in atmospheric greenhouse gas levels were associated with step-wise cooling and ice growth at southern high latitudes.The Antarctic cryosphere plays a critical role in the ocean-atmosphere system, but its early evolution is still poorly known. With a near-field record from Prydz Bay, Antarctica, we demonstrate that Antarctic ice growth was stepwise and had an earlier onset than previously suggested. Prydz Bay lies downstream of a major East Antarctic ice-sheet drainage system and its sedimentary records uniquely constrain the timing of ice-sheet advance onto the continental shelf. We investigate a detrital record extracted from three Ocean Drilling Program drill holes within a new depositional and chronological framework spanning the late Eocene to early Oligocene (~36-33 Ma). The chemical index of alteration (CIA) and the S-index, calculated from the major element geochemistry of bulk samples, yield estimates of chemical weathering intensities and mean annual temperature (MAT) on the East Antarctic continent. We document evidence for late Eocene mountain glaciation along with transient warm events at 35.8-34.8 Ma. From 34.4 Ma, associated with the EOT-1  18 O excursion, glaciers advanced into Prydz Bay, coincident with a decline in chemical weathering and temperature. We conclude that Antarctic continental ice growth commenced with the EOT-1 "precursor" glaciation, during a time of Subantarctic surface ocean cooling and a decline in atmospheric pCO 2 . These results call for dynamic high-latitude feedbacks that are currently poorly represented in Earth system models and emphasize the need for additional near-field glaciosedimentological, high-latitude SST, and pCO2 records across the EOT.

Changes in the high-latitude Southern Hemisphere through the Eocene–Oligocene transition: a model–data comparison

“…Higher-resolution modelling and better representation of climate feedbacks offer some potential improvements in this regard (Huber and Caballero, 2011;Baatsen et al, 2018), and the current Deep-MIP modelling effort might provide further insights into the causes of this common model bias. It should also be noted that these simulations were run with relatively arbitrary pCO 2 levels (although they are of a plausible magnitude; Pearson et al, 2009;Pagani et al, 2011;Foster et al, 2017), and these could be refined to provide a slightly better absolute fit to the data. Orbital variability does not appear to have a major impact on the comparison, as shown by the relatively minor impact on the results in the FOAM simulations and due to the length of the averaged periods of the proxy records.…”

Changes in the high latitude Southern Hemisphere through the Eocene-Oligocene Transition: a model-data comparison

“…A number of studies have suggested there was cooling in the several million years prior to the EOT, particularly at high latitudes (e.g. Raine & Askin, 2001;Petersen & Schrag, 2015;Passchier et al, 2016;Carter et al, 2017;Pound & Salzmann, 2017). Even in the high Northern Hemisphere changes have been identified occurring prior to the EOT (e.g.…”

Equilibrium state and sensitivity of the simulated middle-to-late Eocene climate

“…Significant swings in global temperature thus occurred prior to the EOT. Yet, conditions only allowed the growth of a continental-scale Antarctic ice sheet after 34Ma, although indications for significant ice volume in the late Eocene have been 40 found (Scher et al, 2014;Passchier et al, 2017;Carter et al, 2017). It remains a question to what extent continental geometry (e.g.…”