Hawaiian Drowned Reefs (Expedition 389)

Summary from the Scientific Prospectus: Shallow marine corals are highly sensitive to sea level and global climate change and preserve a reliable record of past sea level and climate conditions. Knowledge of sea level and global climate variations over the past half a million years is severely limited because of a lack of continuous fossil coral records over this time. To address the critical need for coral records, this project focuses on the submerged fossil reefs around the island of Hawaii. Frequent and large volcanic eruptions formed and continue to grow the volcanic island of Hawaii, and the island and surrounding shallow coral reefs are pushed down at a rapid and nearly constant rate because of the weight of the volcanic rock erupted onto the land. As the land and coral reefs subside, coral reef growth can match the subsidence rate, and changes in sea level and global climate are preserved in a unique and near-continuous fossil coral record covering the last half a million years. Scientific drilling of these reefs will provide a new record of climate and sea level change, including several key time periods where sea level and climate conditions are poorly known. The project has four major scientific objectives: (1) to measure the extent of sea level change over the past half a million years, (2) to investigate why sea level and climate change through time, (3) to investigate how coral reefs respond to abrupt sea level and climate changes, and (4) to improve scientific knowledge of the growth and subsidence of Hawaii over time.

NW Greenland Glaciated Margin (Expedition 400)

Summary from the Scientific Prospectus: Sea-level consequences of anthropogenic climate forcing hinge on how the polar ice sheets respond to global warming. If fully melted, the Greenland Ice Sheet has the potential to raise sea level by >7 meters, yet we know very little about its long-term responses to past climate warming or its role in Earth’s climate system. Expedition 400 seeks to address current knowledge gaps in the evolution and variability of the northern Greenland Ice Sheet by analyzing sedimentary archives of warm and cold periods of the last ~30 million years, including times when the greenhouse gas content of the atmosphere was higher than it is today.

Sediment archives will be obtained by drilling at seven sites to depths of 300–1000 meters below seafloor along a transect crossing the northwest Greenland margin into Baffin Bay. The seven sites will provide a composite stratigraphic succession that includes preglacial settings, a record of first growth of the northern Greenland Ice Sheet, and glacial and interglacial cycles when the ice sheet grew to its maximum positions at the shelf edge and retreated toward land, possibly melting nearly completely.