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Octopus DNA reveals timing of the most recent collapse of the West Antarctic Ice Sheet 

This chapter documents the primary shipboard procedures and methods employed by various operational and scientific groups during the offshore and onshore phases of International Ocean Discovery Program (IODP) Expedition 389. Methods for postexpedition research conducted on Expedition 389 samples and data will be described in individual scientific contributions to be published after the Onshore Science Party (OSP). Detailed drilling and engineering operations are described in Operations in each site chapter. 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025). Summary operational information for Holes M0096A–M0096F is provided in Table T1. All times stated are in Hawaiian Standard Time (HST). 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all Expedition 389 sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Site M0101 is provided in Table T1. All times stated are in Hawaiian Standard Time (HST). 

Our understanding of the mechanisms controlling eustatic sea level and global climate changes has been hampered by a lack of appropriate fossil coral records over the last 500 ky, particularly into and out of the glacial periods. This problem was addressed by International Ocean Discovery Program Expedition 389, which drilled a unique succession of Hawaiian drowned coral reefs now at 110–1300 meters below sea level (mbsl). The four objectives are to investigate (1) the timing, rate, and amplitude of sea level variability to examine cryosphere and geophysical processes, including the assessment of abrupt sea level change events; (2) the processes that determine changes in mean and high-frequency (seasonal–interannual) climate variability from times with different boundary conditions (e.g., ice sheet size, pCO2, and solar forcing); (3) the response of coral reef systems to abrupt sea level and climate changes; and (4) the variations through space and time of the subsidence and the volcanic evolution of the island. To achieve these objectives, 35 holes at 16 sites in water depths ranging 131.9–1241.8 mbsl were drilled during the expedition. A total of 425 m of core was recovered, comprising reef (83%) and volcanic (17%) material. Average core recoveries were 66%, with recoveries >90% in numerous intervals characterized by very well preserved coralgal and microbialite frameworks. Some science-critical shallow sites were not drilled due to a failure to secure permits to operate in Hawaiian state waters. Furthermore, apart from one site, the target penetration depths were not achieved. Preliminary radiometric dates indicate that the recovered reef deposits are from 488 to 13 ka in age. The Onshore Science Party took place in February 2024. Cores were computed tomography (CT) scanned and then opened and hyperspectral scanned and described. Standard measurements were made, and samples were taken for postcruise research. Preliminary assessment of the age and quality of the reef and volcanic cores suggest that many of the expedition objectives will be met. 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Holes M0097A–M0097D is provided in Table T1. All times stated are in Hawaiian Standard Time (HST). 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all Expedition 389 sites, dynamic positioning (DP) was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Site M0100 is provided in Table T1. All times stated are in Hawaiian Standard Time (HST). 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Hole M0098A is provided in Table T1. All times stated are in Hawaii Standard Time (HST). 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all Expedition 389 sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Hole M0103A is provided in Table T1. All times stated are in Hawaiian Standard Time (HST). 

The multipurpose vessel MMA Valour was used as the drilling platform throughout Expedition 389. At all Expedition 389 sites, dynamic positioning was used to provide accurate positions throughout operations and water depth was established using a Sound Velocity Profiler (SVP) placed on the top of the PROD5 drilling system. For more detail on acquisition methods, see Introduction in the Expedition 389 methods chapter (Webster et al., 2025a). Summary operational information for Site M0099 is provided in Table T1. All times stated are in Hawaiian Standard Time (HST).