Evidence for a dynamic East Antarctic ice sheet during the mid-Miocene climate transition

Abstract

The East Antarctic ice sheet underwent a major expansion during the Mid-Miocene Climate Transition, around 14 Ma, lowering sea level by ∼60 m. However, direct or indirect evidence of where changes in the ice sheet occurred is limited. Here we present new insights on timing and locations of ice sheet change from two drill sites offshore East Antarctica. IODP Site U1356, Wilkes Land, and ODP Site 1165, Prydz Bay are located adjacent to two major ice drainage areas, the Wilkes Subglacial Basin and the Lambert Graben. Ice-rafted detritus (IRD), including dropstones, was deposited in concentrations far exceeding those known in the rest of the Miocene succession at both sites between 14.1 and 13.8 Ma, indicating that large amounts of IRD-bearing icebergs were calved from independent drainage basins during this relatively short interval. At Site U1356, the IRD was delivered in distinct pulses, suggesting that the overall ice advance was punctuated by short periods of ice retreat in the Wilkes Subglacial Basin. Provenance analysis of the mid-Miocene IRD and fine-grained sediments provides additional insights on the movement of the ice margin and subglacial geology. At Site U1356, the dominant 40Ar/39Ar thermochronological age of the ice-rafted hornblende grains is 1400–1550 Ma, differing from the majority of recent IRD in the area, from which we infer an inland source area of this thermochronological age extending along the eastern part of the Adélie Craton, which forms the western side of the Wilkes Subglacial Basin. Neodymium isotopic compositions from the terrigenous fine fraction at Site U1356 imply that the ice margin periodically expanded from high ground well into the Wilkes Subglacial Basin during periods of MMCT ice growth. At Site 1165, MMCT pebble-sized IRD are sourced from both the local Lambert Graben and the distant Aurora Subglacial Basin drainage area. Together, the occurrence and provenance of the IRD and glacially-eroded sediment at these two marine drill sites proximal to the Antarctic continent provide a previously undocumented record of dynamic ice margin change during the 14.1–13.8 Ma interval in three major East Antarctic drainage basins

The Role of Lithospheric Flexure in the Landscape Evolution of the Wilkes Subglacial Basin and Transantarctic Mountains, East Antarctica

“…The presence of oscillatory and erosive ice sheets between 34 and 14 Ma, which were strongly sensitive to climate forcing, has also been inferred in the Aurora Subglacial Basin, where inland fjord systems associated with a dynamic early EAIS have been described (Aitken et al, ; Young et al, ). Oscillatory behavior of the EAIS during warm periods of the Miocene is supported by ice sheet model results (Gasson et al, ), and the age and provenance of terrigenous sediment on the Wilkes Land margin (Pierce et al, ). In addition, terrestrial palynomorphs and soil material in offshore sediment cores indicate the presence of temperate vegetation in the absence of ice near the WSB coast during the mid‐Miocene climatic optimum (Sangiorgi et al, ).…”

Bedrock Erosion Surfaces Record Former East Antarctic Ice Sheet Extent

“…Wilkes Land offshore sediment records indicate that the majority of the volume of glacially eroded terrigenous material was removed by erosion prior to and/or during the expansion of the EAIS at ca. 14 Ma (supporting information; Escutia et al, ; Pierce et al, ; Tauxe et al, ). A slowdown in source‐area erosion rates at ca.…”

“…The scale of these basins, alongside potential field modeling, implies that they are superimposed on pre‐existing tectonic features (Aitken et al, ; Ferraccioli et al, ; Jordan et al, ). These subbasins were likely overdeepened beneath dynamic ice sheets that expanded over the northern WSB during cooler periods during the Oligocene‐Neogene (Jamieson et al, ; Mengel & Levermann, ; Pierce et al, ) and exploited the pre‐existing topographic depressions.…”

Neogene Modifications of Circulation in the Northeastern African‐Southern Ocean Gateway

“…The occurrence of abyssal sheeted drifts in the deeper basin suggests a more tabular, nonfocused flow of AABW in the south of the study area (Faugères et al, ; Faugères & Stow, ; Rebesco et al, ). According to Schlüter and Uenzelmann‐Neben (), modifications of the Antarctic Circumpolar Current in response to the mid‐Miocene cooling and the strong expansion of the Antarctic ice sheets (Cramer et al, ; Flower & Kennett, ; Pierce et al, ; Shevenell et al, ; Zachos et al, ) resulted in a northeastward flow of AABW into the Transkei Basin through a passage east of the Agulhas Plateau. We hypothesize that these modifications caused the initiation of current‐controlled sedimentation in depths similar to modern AABW in the area of the southern MozR.…”