Oceanography (Sep 2012)
Glacial Intensification During the Neogene: A Review of Seismic Stratigraphic Evidence from the Ross Sea, Antarctica, Continental Shelf
Abstract
Seismic stratigraphic and drill data from Antarctic continental margins have provided much direct evidence concerning ice sheet evolution as Earth's climate cooled from the warmth of the Eocene. Seismic facies analyses and correlations to sediment cores from Deep Sea Drilling Project Leg 28 drill sites show that the Ross Sea, the southwestern Pacific gateway of West Antarctica, was still mostly free of grounded ice for ~ 6 million years after Oi-1, the large-amplitude oxygen-isotope shift that signaled the abrupt onset of the current Antarctic glaciation. In the Ross Sea, our analysis shows that West Antarctic glaciation had begun by the late Oligocene, much earlier than usually interpreted from the paleoceanographic proxy data. Continental ice probably existed on Marie Bird Land and other highland areas of the West Antarctica. In the central Ross Sea, ice caps nucleated on the subaerially elevated basement horst blocks of the Central and Coulman Highs. Ice caps waxed and waned across the shallow-marine platforms rimming these broad basement uplifts. These temperate glacial systems delivered much sediment to the surrounding deepwater shelf basins. Ice cap oscillations during the early and middle Miocene also included significant intervals of grounded ice retreat and resumption of widespread marine sedimentation. By the end of the middle Miocene, glaciation intensified, local ice caps coalesced, and grounded ice with cross-shelf ice streams eventually extended across the entire Ross Sea continental shelf. Antarctic climate shifted from polar to temperate conditions during this time and ice streams advanced to the shelf edge. Full-bodied West Antarctic Ice Sheet advances continued and even occurred during the warmer-than-present early Pliocene. As a consequence of widespread and progressive glacial erosion, the shelf overdeepened in the latest Miocene. The surprisingly few advances of grounded ice preserved in Plio-Pleistocene strata suggest that the record is amalgamated and/or otherwise below the resolution of seismic data.
