Sea Level During Past Warm Periods – Unraveling Interactions Between Climate, Ice, Crust, and Mantle
Tuesday, 15 December 2015: 17:00
3002 (Moscone West)
Changes in sea level, whether rapid or gradual, influence the style and preservation of shorelines and near-shore features including fossil reefs, paleo-sea cliffs and scarps, as well as intertidal and subtidal facies and biota. Using insight from modern shoreline systems, members of the PLIOMAX FESD project have mapped mid-Pliocene, MIS11, and MIS5e shorelines at numerous localities around the world and then modeled the effects of subsequent glacial isostatic adjustment on their current position. For MIS5e we find evidence for a rapid rise in sea level in the later phase of the interglacial, consistent with a collapse of the West Antarctic Ice Sheet. Estimates for maximum sea level during MIS5e, between 6 and 9 m, are in agreement with other studies and imply mass loss from ice sheets at both poles. For MIS11, which appears to have been slightly warmer than MIS5e, our best estimate of sea level rise is 6-13 m, a value subsequently narrowed to 8.5-12 m. Recent advances in ice sheet models also illustrate the potential for a substantial Antarctic contribution to elevated sea-level during MIS5e and other Pliestocene interglacials including MIS11. For the Pliocene interval around 3 Ma, we cannot place useful bounds on sea level because shoreline features have been vertically displaced many tens of meters by mantle dynamic topographic changes of uncertain magnitude and, probably to a lesser degree, by flexure associated with sediment redistribution. However, these once horizontal shorelines, which are sometimes hundreds of kilometers long, provide useful targets against which to measure the performance of time-dependent mantle convection models. Ultimately, the paleo-shoreline data is telling us that when global climate warming is more than 2°C (relative to pre-industrial, or >1°C relative to today), significant loss of ice mass occurs at high latitudes equivalent to a minimum rise in sea level of 6m.