Relative sea-level rise around East Antarctica during Oligocene glaciation

During the middle and late Eocene (∼48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarcticainduced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rosedespite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an icesheet grounding line

Drilling to decipher long-term sea-level changes and effects - A joint consortium for ocean leadership, ICDP, IODP, DOSECC, and Chevron Workshop

No abstract available. doi:10.2204/iodp.sd.6.02.2008</a

The amplitude and origin of sea-level variability during the Pliocene epoch

Earth is heading towards a climate that last existed more than three million years ago (Ma) during the 'mid-Pliocene warm period'(1), when atmospheric carbon dioxide concentrations were about 400 parts per million, global sea level oscillated in response to orbital forcing(2,3) and peak global-mean sea level (GMSL) may have reached about 20 metres above the present-day value(4,5). For sea-level rise of this magnitude, extensive retreat or collapse of the Greenland, West Antarctic and marine-based sectors of the East Antarctic ice sheets is required. Yet the relative amplitude of sea-level variations within glacial-interglacial cycles remains poorly constrained. To address this, we calibrate a theoretical relationship between modern sediment transport by waves and water depth, and then apply the technique to grain size in a continuous 800-metre-thick Pliocene sequence of shallow-marine sediments from Whanganui Basin, New Zealand. Water-depth variations obtained in this way, after corrections for tectonic subsidence, yield cyclic relative sea-level (RSL) variations. Here we show that sea level varied on average by 13 +/- 5 metres over glacial-interglacial cycles during the middle-to-late Pliocene (about 3.3-2.5 Ma). The resulting record is independent of the global ice volume proxy(3) (as derived from the deep-ocean oxygen isotope record) and sea-level cycles are in phase with 20-thousand-year (kyr) periodic changes in insolation over Antarctica, paced by eccentricity-modulated orbital precession(6) between 3.3 and 2.7 Ma. Thereafter, sea-level fluctuations are paced by the 41-kyr period of cycles in Earth's axial tilt as ice sheets stabilize on Antarctica and intensify in the Northern Hemisphere(3,6). Strictly, we provide the amplitude of RSL change, rather than absolute GMSL change. However, simulations of RSL change based on glacio-isostatic adjustment show that our record approximates eustatic sea level, defined here as GMSL unregistered to the centre of the Earth. Nonetheless, under conservative assumptions, our estimates limit maximum Pliocene sea-level rise to less than 25 metres and provide new constraints on polar ice-volume variability under the climate conditions predicted for this century

Phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs

A spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the Earth's surface, and hence the marine inundation of continents. For past periods of high sea level, the predicted geographical pattern of flooding correlates well with the geological record. The high spatial correlation may result from increased plate velocities at these times, leading to increased rates of subduction, subsidence and inundation at convergent margins

Bounds on global dynamic topography from Phanerozoic flooding of continental platforms

The movement of continents with respect to a large-scale pattern of dynamic topography and geoid, imposed by convection in the mantle, must contribute to the flooding of continental platforms. Here I investigate this phenomenon, using a one-dimensional model in which a continent moves from a high to a low of dynamic topography (and geoid), and in the process is partially exposed and then flooded. If the dynamic topography is greater than about 150 metres, the model continent is flooded by more than 3 0%—the maximum amount of flooding experienced by North America during the entire Phanerozoic eon1. The model suggests that a large-scale pattern of dynamic topography must have an amplitude of less than 150 metres, and that the admittance, the ratio of geoid to dynamic topography, may be greater than 0.3. Recent models of global mantle dynamics 2,3 which predict the long-wavelength geoid from mantle seismic structure are apparently inconsistent with Phanerozoic flooding