Relative sea-level rise around East Antarctica during Oligocene glaciation

Abstract

Antarctic glaciation was abruptly established during the EoceneOligocene transition (EOT) in two ∼200-kyr-spaced phases between 34.0 Myr and 33.5 Myr ago, as recorded by the oxygen isotope composition of marine biogenic calcite 3,4,9 (δ 18 O). The first shift (EOT-1) is believed to represent a transient glaciation [10][11][12] , later followed by the establishment of a continental-scale ice sheet across the Oligocene isotope event-1 33.7 Myr ago; ref. 4). This is consistent with Northern Hemisphere ocean-sediment cores, which indicate a 60 ± 20 m relative sea level (rsl) fall across the EOT (refs 13-15). Under isostatic equilibrium conditions, the observed regression nearly corresponds to the rsl drop expected from glacioeustasy 6 . Along the Antarctic margins, however, the rsl changes accompanying the glaciation are expected to strongly deviate from the eustatic, because of large crustal and gravitational perturbations induced by the ice sheet on the deformable Earth 6 . Furthermore, strong regional rsl change gradients would be maintained long after the ice-sheet stabilization, by the flexure of lithosphere 16 . This necessitates self-consistent physical models for rsl change to compare near-field sedimentary sequences with far-field ice-sheet volume estimates.Here we evaluate the regionally varying rsl changes in response to glacial expansion and their effects on glaciomarine facies 17 around East Antarctica with a numerical model for glacial-hydro isostatic adjustment (GIA). Our model is based on the solution of the gravitationally self-consistent sea-level equation 7,8 for a prescribed Antarctic ice-sheet chronology 18 and a linear viscoelastic rheology for the solid Earth (Methods and Supplementary Information). We compare the model results with sedimentary records from the Wilkes Land Margin (Fig. 1a) The ice-sheet model employed in our GIA computations is characterized by a 2.2 Myr growth phase caused by a combination of decreasing CO 2 and orbital forcing that drives summer temperatures below the threshold for glaciation 18 but uses a new reconstruction of Antarctic topography 24 at EOT time (Methods). The ice-sheet volume at the glacial maximum corresponds to ∼69.0 m of equivalent sea level in this model, ∼14.0 m more than previous modelling results 18 , probably owing to larger Antarctic land surface 24 .We run a reference simulation (Fig. 1a-d) for an Earth model defined by an elastic lithosphere thickness (LT) of 100 km, and by a viscosity profile (RVP) that is discretized into a lower mantle (LM), a transition zone (TZ) and an upper mantle (UM) and is characterized by viscosities of 1.0 × 10 22 , 5.0 × 10 20 and 2.5 × 10 20 Pa s respectively (RVP-100 km-LT simulation). To evaluate how the GIA signal varies according to the mantle viscosity, we perform simulations for an ensemble of viscosity profiles (EVPs) characterized by viscosities varying in the range of

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica – Part 2: Insights from Oligocene–Miocene dinoflagellate cyst assemblages

“…In particular, the Antarctic continental shelf exhibits a consistently high relative abundance of Selenopemphix antarctica. In addition to the sur- face samples of Prebble et al (2013), this is also evident at the Wilkes Land margin proper (IODP Site U1357; Julian D. Hartman, Peter K. Bijl, and Francesca Sangiorgi, personal observation), at Prydz Bay (Storkey, 2006), in the Weddell (Harland and Pudsey, 1999) and Ross seas (Julian D. Hartman, Peter K. Bijl, and Francesca Sangiorgi, personal observation), and in the southern Indian Ocean (Marret and De Vernal, 1997): samples all contain very abundant to dominant (> 50 to 90 %) S. antarctica. The dominance of this species becomes even stronger when considering that assemblages in these surface samples often include cysts that are not easily preserved in older sediments such as that of Polarella glacialis.…”

Coastal staircase sequences reflecting sea-level oscillations and tectonic uplift during the Quaternary and Neogene

“…Such a development was likely to have occurred during the onset of the ice sheet in Antarctica, the impact of which is currently being verified in terms of sea level (e.g. Stocchi et al, 2013). The staircase shaping of coasts increased during the Pliocene and Pleistocene as a consequence of the intensification of eustatic sea-level oscillations, as inferred from the isotopic record (Lisiecki and Raymo, 2005).…”

“…Indeed, such cycles were initially identified as part of the most recent geological period affected by glacial events and bracketed at~2.6 Ma, but possibly may extend further into the past in association with the onset of earlier glaciations during the Cenozoic (as for instance during the buildup of the ice sheet in East Antarctica, e.g. Stocchi et al, 2013). Such sea-level oscillations interact with tectonic uplift that promotes the preservation of emerged fossil strandlines.…”

Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

“…Second, over longer timescales the viscous response of the upper mantle and crust produce a redistribution of (bedrock) mass that also affects the gravitational pull on ocean water 39 . Together, these two effects may locally modify eustatic sea level by several metres, which under some scenarios may be sufficient to stabilize or slow the retreat of marine-based ice sheets 38,39 , or in the case of a growing ice-sheet, may lead to locally increased sea level and therefore slow the advance of grounding lines 40 . By neglecting these effects in our simulations, we implicitly smooth out any grounding-line migrations that might occur in response to small (o5 m) changes in sea level.…”