GLOBAL GLACIAL ISOSTATIC ADJUSTMENT: HIGHSTANDS AND LOWSTANDS IN POSTGLACIAL VARIATIONS IN THE LEVEL OF THE SEA

Issues posed by the nature of "extrema" in the variations of relative sea level(RSL) continue to elicit comment and to energize debate. For example, the connection between the LGM lowstand of the sea recorded at Barbados and on the Sunda Shelf, and the volume of the ice load that was then in place upon the continents, has been a recent focal point of discussion. Of similar importance are the so-called mid-Holocene highstands of the sea recorded at both continental coastline and island locations in the far field of the LGM ice sheets. Especially significant among the issues surrounding such extrema, perhaps, is that concerning the geographical origin of the meltwater pulse that caused the sharp rise of sea level at approximately 14.2 ka.

Insight into the nature and ultimate cause of each of these sea level extrema is provided through application of the formal theory of the global process of glacial isostatic adjustment. Recent advances are especially important in this regard. In particular it has been shown that there are three distinct influences that may contribute importantly to the understanding of such features of RSL records. These influences include: (1) the migration of the coastline, (2) the history of accretion and disintegration of land ice prior to LGM, and (3) the feedback onto sea level history of co-variations in Earth rotation. I will provide examples of the action of each of these subtle effects. It is easily shown, and is in fact expected, that the impact of migration of the coastline will be extremely important in locations such as the Indonesian Archipelago where shelf exposure was pronounced at LGM. The impact of rotational feedback onto sea level history, on the other hand, is well exemplified by observations from the coast of Argentinian Patagonia where the mid-Holocene highstand is found at unusually high elevation. Observations from the Western Mediterranean Basin, well to the south of the ancient Fennoscandian ice load, provide an excellent example of the errors in the inference of mantle viscosity that one would be forced to make if one were to neglect all three of these subtle influences. Finally, it proves interesting to enquire as to what constraints may be placed upon the geographical source(s) of meltwater pulse 1a through the use of the relative amplitude of this event recorded at Barbados and on the Sunda Shelf.