The timing and course of sea-level rise during the last deglaciation is an essential component for understanding the dynamics of large ice sheets and their effects on Earth’s isostasy. Moreover, the disappearance of glacial ice sheets was responsible for dramatic changes in the freshwater fluxes to the oceans, which disturbed ocean thermohaline circulation and, hence, global climate. Coral reefs are excellent sea-level indicators, and their accurate dating by mass spectrometry is critical for constraining the timing, rate and amplitude of deglaciation events and thus for understanding of the mechanisms driving glacial-interglacial, millennial and centennial cycles.
Furthermore, scleractinian coral colonies can monitor seasonal sea-surface temperatures (SSTs) and record past SSTs. So far, the only published sea-level and climate record that encompasses the whole deglaciation is based on offshore drilling of Barbados fossil coral reefs which overlie an active subduction zone, implying that the apparent sea-level record may be biased by tectonic movements. Tahiti and the Australian Great Barrier Reef represent key locations to address these problems as they are in tectonically inactive areas far away from glaciated regions.
Submerged fossil coral reefs are common but poorly studied features along the shelf edge of the Great Barrier Reef. At several key sites along 5 transects in 3 regions it is proposed to drill offshore shallow penetration drill holes using a Mission Specific Platform. The drilling targets include the successive reef terraces, relict reefs and the slope, from ~40 to 200 m water depth. The scientific aims of the project are to:
1. Establish the course of sea-level rise during the last deglaciation (~20-10 ka).
2. Reconstruct the nature and magnitude of seasonal-millennial scale climate variability (ie. sea surface temperature and sea surface salinity).
3. Determine the biologic and geologic response of the Great Barrier Reef to abrupt sea-level and climate changes in the past as a possible template to improve predictions of ecosystem response to future global climate changes.