Geomorphology and oceanography of central-eastern Indian Ocean seamounts

The marine region around Christmas Island and Cocos (Keeling) Islands in the eastern Indian Ocean includes a large number of under-researched seamounts. Here novel geomorphological and oceanographic data from the RV Investigator IN2021_V04 and IN2022_V08 expeditions to the region are presented to demonstrate the variety of form, size and height of these seamounts, and their spatial and bathymetric relationship to the various water masses present in the region. This includes the discovery of a large extinct caldera (‘Eye of Sauron’) at 3100–3700 m depth southeast of Christmas Island and a circular volcanic crater south of Cocos (Keeling) Islands at 3800–4000 m. Eleven seamounts were mapped for the first time, and mapping was completed or extended for a further 23, including the massive Muirfield seamount that summits at 17 m below sea-level. The presence is documented of another relatively shallow seamount (‘Green-eye’, summit 438 m) at the southernmost end of the Cocos (Keeling) Islands Territory. The new data emphasises the scarcity of shallow habitat (above 2000 m) for benthic biodiversity from the region, and the eastern Indian Ocean in general, and its importance for conservation.