The deep glacial trough and hinterland of the Denman Glacier (East Antarctica) makes the area around the Shackleton ice shelf sensitive to ice loss due to warmer deep water intruding onto the continental shelf in the near future. In addition, the configuration of the ocean currents offshore is an important factor in priming the local and regional vulnerability to warm water intrusions. Here, we use reflection seismic data sets from the Bruce Rise offshore the Denman-Shackleton region to investigate the Cenozoic history of the ocean bottom current configurations offshore and their influence on the Cenozoic sedimentation patterns of the Denman-Shackleton region. On the Bruce Rise, sediment drift building, and erosional features indicate three distinct ocean current configurations, (a) the production of dense shelf waters in times of a smaller East Antarctic Ice Sheet (EAIS), (b) periods dominated by a strong Antarctic Slope Current (ASC) and (c) periods with a weak ASC. During the early establishment of the EAIS, the Denman-Shackleton area contributed to the production of Antarctic Bottom Water, a process which stabilizes the regional ice sheet. With a growing icesheet, the ASC strengthened representing an effective barrier between the continental shelf and the warmer water masses of the deeper ocean during most of the times of an extended EAIS. The transition in the paleoceanographic setting from a strong, erosive ASC, toward a weak ASC increases the vulnerability of the Denman-Shackleton continental shelf to deep water intrusions as we are observing today.
Today, warm salty water flows across the continental shelf of the Denman-Shackleton region in East Antarctica, causing increased melting and the retreat of the local ice sheet. We are investigating based on the sediment archive, how likely these intrusions have been in the geological past. Our analysis shows, that most likely, the Denman-Shackleton region has not experienced warm water intrusions for the majority of the Antarctic glaciation. During the early presence of the icesheet, the region contributed to the production of Antarctic bottom water, the globally dominating bottom water mass, a process which is not observed since and blocks intruding warm waters. With the transition to colder climates, the strength of the westward flowing ocean currents along the continental slope are managing the barrier between the cold shelf waters and the warmer waters of the deep sea. With a weakening of the current, the intrusion of warm waters onto the continental shelf become more common. This highlights, that the Denman/Shackleton region underwent a complete reversal of the ocean bottom current system throughout the history of the Antarctic ice sheet from the export of denser shelf waters to an increased potential of frequent warm waters on the continental shelf.
The Denman-Shackleton region contributes to Antarctic bottom water formation during the early Antarctic glaciation The Denman-Shackleton region's ocean current behavior changed dramatically during the late Cenozoic Exploration of sediment drift building on the Bruce Rise as record of pre-conditioning for warm water intrusions in the Shackleton region