IN SEARCH OF STAGE 11 SEA LEVEL: TRACES ON THE GLOBAL SHORE

Given similar orbital configurations for oxygen isotope stage 11 and the Holocene, the former may be a window for evaluating present and future sea level. Palaeoceanographers have used Mg/Ca ratios on benthic ostracoda to eliminate the temperature term in d¹⁸O measurements, allowing inferences to be drawn about sea level variability. These suggest a stage 11 sea level of ~ 10 m within a confidence band between ~ +20 m and ~ -8 m. But on world shorelines, stage 11 corals, marine sediments, and shoreline angles generally occur at higher elevations. Some believe, especially in `stable` regions, that these indicate sea levels up to 30 m; but most ascribe such elevations to regional uplift, so that estimates of stage 11 water level require separation of uplift and water level terms. Critically, the quality of stage 11 shoreline data compares unfavourably with the wealth of data for late Pleistocene and Holocene sea levels, so that method relies on extrapolation of 'uplift correction curves' based on average uplift rates derived from estimates of the 5e (5.5) water level. Estimates of this vary between 0 to ~ 10 m above 'sea level'; and related geodetic datum is sometimes ambiguous. So too is the exact age of the 5e high water (possibly multiple), with a range of up to 13 ka. Thus uplift rates often depend on arbitrary initial assumptions, highlighting a desirability for a common protocol. Similarly, stage 11 marine lithofacies does not always provide unambiguous markers for water levels; and there are relatively few reliable age estimates (ESR, TL, U-series, aminostratigraphy). Notwithstanding such uncertainty, however, `uplift correction curves` have provided estimates for a stage 11 water level between -3 to + 13 m, which lies within the band proposed by palaeoceanographers. Does this presage the future? Using examples from the Americas, Europe, Australasia, and Asia, further reconciliation of palaeoceanographical and shoreline evidence is attempted.