Spatial and temporal variability of the Late Holocene sea-level and trace element ratios in the South-Central Pacific based on U/Th dated corals of Bora Bora, Huahine and Moorea, Society Islands, French Polynesia

Fossil micro atolls precisely constrain the timing and amplitude of sea-level variations at and after the 'Holocene Sea Level Maximum, HSLM' because micro atolls grow close or even directly at the current sea-level position. We found that sea level reached a subsidence corrected position of at least ~1.5 m above present sea level (apsl) at ~5.4 ka relative to Huahine island before present (BP) and a maximum amplitude of at least ~2 m apsl at ~2 ka BP relative to Moorea. In between 5.4 and 2 ka minimum sea level oscillated between 1.5 and 2 m for ~3 ka but then declined to the present position after ~2 ka BP. Based on statistical arguments on the coral age distribution HSLM is constrained to an interval of 3.5 × 0.8 ka. Former studies being in general accord with our data show that sea level in French Polynesia was ~1 m higher than present between 5,000 and 1,250 yrs BP and that a high stand was reached between 2,000 and 1,500 yrs BP (Pirazzoli and Montaggioni, 1988) and persisted until 1,200 yrs BP in the Tuamotu Archipelago (Pirazzoli and Montaggioni, 1986). Modeling of the Late Holocene sea-level rise performed during the course of this study taking glacio-isostatic and the ocean syphoning effect into account predicts a Late Holocene sea-level high stand of ~1 m apsl at ~4 ka BP for Bora Bora which is in general accord with the statistical interpretation of our empirical data. However, the modeled HSLM amplitude of ~1 m apsl is considerably smaller than predicted by the empirical data indicating amplitudes of more than 2 m. Furthermore, the theoretical model predicts a continuously falling sea level after ~4 ka to the present. This is in contrast to the empirical data indicating a sea level remaining above at least ~1 m apsl between 5 ka and 2 ka then followed by a certain drop of the Late Holocene sea level to its present position. We further use the corals as an archive for sea surface temperature (SST) reconstructions in order to estimate the influence of SST change on the sea level amplitude. In addition, diagenetic alteration of young corals and its influence on our proxy data is also discussed. Pirazzoli, P.A. and Montaggioni, L.F., 1986, Quaternary Research, v. 25, p. 350-368. Pirazzoli, P.A. and Montaggioni, 1988, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 68, p. 153-175.