LATE PLEISTOCENE, HOLOCENE AND PRESENT SEA-LEVELS - CONSTRAINTS ON FUTURE CHANGE

Late Pleistocene and Holocene sea-levels exhibit considerable temporal and spatial variation around the globe when compared with present-day sea-levels. This is the result of volumetric changes of the ocean produced by the melting of the Pleistocene ice sheets, the response of the crust to these redistributed surface loads, and to tectonic movements of the shore lines of other than glacio-hydro-isostatic origin. By examining the sea-level records from geographically well-distributed areas over time spans covering the past 10,000 years, and by avoiding records from tectonically unstable regions, it becomes possible to effect a separation of the major parameters contributing to the sea-level change. Geomorphological observations of sea-level change at sites far from the former ice sheet margins provide constraints on the total volume of Late Pleistocene meltwater and on the rate at which this meltwater has been added into the oceans. The Laurentide and Fennoscandian ice sheets appear to have been inadequate to explain the observed sea-level rise of about 130 m from 18,000 to 6000 years ago. Some contribution (congruent-to 10-15 m) from the Barents-Kara seas may have occurred as well. Antarctic contributions to the rise in sea-level appear to have been important and occurred at about the same time as or slightly after the Arctic ice sheet decay. The Antarctic melting continued, at slow rates, up to the present. Tide guage records over the past few decades also exhibit spatial variations in the rates of increase. The global average is about 1.2 mm/year but a pronounced zonal variation also occurs. About 50% of the global average rise may be the result of on-going melting of mountain and Antarctic glaciers and part of the spatial variation is the result of the ongoing glacial rebound. The long-wavelength spatial variation suggests that surface warming occurs in equatorial regions at a faster rate than middle and high latitudes and that Pacific-Indian Oceans warming occurs at a faster rater than the Atlantic Ocean.