British Geological Survey, United Kingdom

The history of sea level and sea-surface temperature (SST) variation associated with the last deglaciation is of prime interest to understanding dynamics of large ice sheets and their effects on Earth's isostasy. So far, the only sea level record that encompasses the whole deglaciation is based on offshore drilling of Barbados coral reefs that overlie an active subduction zone, implying that the apparent sea level record may be biased by tectonic movements. This proposal seeks to establish the course and effects of the last deglaciation in a reef setting that developed in a tectonically inactive area at sites located far away from glaciated regions in Tahiti (French Polynesia). At each site, we propose to sample a transect of several offshore drill holes using a dynamically positioned drilling vessel. The study will have three major objectives. The first objective will be to reconstruct the deglaciation curve for the period 20.00-10.00 ka in order to establish the minimum sea level during the Last Glacial Maximum (LGM) and to assess the validity, timing, and amplitude of meltwater pulses (so-called meltwater pulse 1A and 1B [MWP-1A and MWP-1B] events; approximately 13.80 and 11.30 ka, respectively) that are thought to have disturbed the general thermohaline oceanic circulation and, hence, global climate. Second, we will establish the SST variation accompanying the transgression at each transect. These data will allow us to examine the impact of sea level changes on reef growth, geometry, and biological makeup, especially during reef drowning events, and will help improve the modeling of reef development. The third major objective will be to identify and establish patterns of short-term paleoclimatic changes that are thought to have punctuated the transitional period between present-day climatic conditions following the LGM. We propose to quantify the variations of SSTs based on high-resolution isotopic and trace element analyses on massive coral colonies. When possible, we will try to identify specific climatic phenomena such as the El Nino-Southern Oscillation (ENSO) in the time frame prior to 10.00 ka.