Deep water inflow slowed offshore expansion of the West Antarctic Ice Sheet at the Eocene-Oligocene transition

Abstract

The stability of the West Antarctic Ice Sheet is threatened by the incursion of warm Circumpolar Deepwater which flows southwards via cross-shelf troughs towards the coast there melting ice shelves. However, the onset of this oceanic forcing on the development and evolution of the West Antarctic Ice Sheet remains poorly understood. Here, we use single- and multichannel seismic reflection profiles to investigate the architecture of a sediment body on the shelf of the Amundsen Sea Embayment. We estimate the formation age of this sediment body to be around the Eocene-Oligocene Transition and find that it possesses the geometry and depositional pattern of a plastered sediment drift. We suggest this indicates a southward inflow of deep water which probably supplied heat and, thus, prevented West Antarctic Ice Sheet advance beyond the coast at this time. We conclude that the West Antarctic Ice Sheet has likely experienced a strong oceanic influence on its dynamics since its initial formation.

Late Eocene signals of oncoming Icehouse conditions and changing ocean circulation, Antarctica

“…The vigorous current systems in the Southern Ocean play a critical role in redistributing glacially-derived sediments and depositing them in sediment drifts that contain records of long-term environmental change. Depositional signatures in sedimentary successions along the Antarctic margin provide Neogene records of Antarctic glaciation and its relationship with global climatic and oceanographic change (Escutia et al, 2005;Hernández-Molina et al, 2009;Gohl et al, 2013;Huang and Jokat, 2016;Huang et al, 2022;Uenzelmann-Neben et al, 2022). However, detailed knowledge of the timing and paleoenvironmental implications of ice growth and ocean circulation during the transition from greenhouse to icehouse are limited (Lear et al, 2008;Galeotti et al, 2016).…”

A large-scale transcontinental river system crossed West Antarctica during the Eocene

“…The overlying seismostratigraphic unit was drilled at MeBo site PS104_21-3 ~40 km further north ( Fig. 2 ) and was dated as earliest Oligocene (~34 Ma) ( 20 ). Hence, the Polarstern Sandstone was deposited between the middle Eocene and the latest Eocene (~44 to –34 Ma).…”

“…Numbered examples in white boxes are described in the legend. The seismic horizons and units are adopted from Gohl et al ( 21 ) with ages modified to lower to middle Cretaceous for unit ASS-1, middle to upper Eocene for unit ASS-2, and Oligocene for unit ASS-3 according to the stratigraphy of the MeBo70 drill cores ( 4 , 20 ; this study). Thin black lines mark interpreted faults.…”

“…Thin black lines mark interpreted faults. MeBo70 drill site PS104_20-2 (containing the Polarstern Sandstone) is located at the intersection of the three seismic profiles, while the position of site PS104_21-3 [containing Early Oligocene strata ( 20 )] is projected from the real drill location ~5 km to the west. IBCSO-v2 bathymetric map [upper right; ( 74 )] shows the locations of the seismic profiles and the MeBo70 drill sites as well as the modern flow directions of Pine Island Glacier, Thwaites Glacier, and neighboring glaciers (blue arrows).…”

West Antarctic Ice Sheet Dynamics in the Amundsen Sea Sector since the Late Miocene—Tying IODP Expedition 379 Results to Seismic Data

“…This results in sub-ice-shelf melting and marine ice sheet instability (Whitworth et al, 1998;Pritchard et al, 2012). It has been hypothesized that these processes also occurred during the Late Eocene/Early Oligocene (Uenzelmann-Neben et al, 2022), the Pliocene under the influence of warmer-thanpresent NADW (1-2 °C higher than recent) (Billups et al, 1998), and during Holocene retreat phases (Hillenbrand et al, 2017).…”