Deep-Sea Habitats of the Cook Islands

A surprising fact: abyssal plains cover over 50% of Earth’s surface. But when it comes to this habitat, what we don’t know far outweighs what we do. In the Cook Islands, ROV dives have surveyed over dense areas of round abyssal nodules. These slow-growing rock formations carry the unique chemistry of the local ocean as dissolved minerals in seawater come out of solution. In one of Earth's slowest geological processes, nodules form from layers of rock deposition, like layers of a gumball, growing at only millimeters per million years. As the team visits these very deep ocean areas, join in the scientific exploration learning about the environmental conditions plus biological diversity and density within this habitat type in the Cook Islands.
 

On the NA176 expedition exploring the deep ocean around the Cook Islands, our Corps of Exploration is using both ROV Hercules and a smaller vehicle known as ROV Little Hercules. Learn the differences between these two pieces of ocean exploration technology with this fun infographic.
 

During the NA176 expedition, OET is partnering with Deep-Sea Power & Light (DSPL) to field test a new ultra-high resolution video camera on ROV Hercules and ROV Little Hercules. Developed in partnership by DSPL and MBARI, the MxD SeaCam is a cutting-edge 4K imaging system, purpose-built for the most demanding subsea missions. The MxD's design features a custom Sony HDC-50 compact broadcast camera and a custom-built titanium housing with a borosilicate dome rated down to 7,000 meters. 

The 15 islands that make up the Cook Islands are distributed across two broad groups with distinct geologic histories. The northern islands consist entirely of low-lying atolls. These features are within longer seamount chains and are often capped by thick coral carbonates that developed over millions of years as features drifted away from their volcanic sources. The southern islands are generally younger and include several volcanic islands. Rarotonga, the largest and youngest of the high islands, is believed to have formed independently from nearby hotspot tracks, instead representing a unique mantle plume not linked to regional chains.

Making its first appearance of the 2025 season, the NA176 team will explore with ROV Little Hercules in tandem with ROV Atalanta to reach the depths of the Cook Islands, below what ROV Hercules can reach. Little Hercules will focus on visual surveys of abyssal plain habitats north of Aitutaki at depths below 4,500 meters, approaching 15,000 feet. Learn more about ROV Little Hercules here.
 

Located in the South-Central Pacific, the large ocean state of Cook Islands comprises 15 islands surrounded by nearly 2 million square kilometers of ocean, the vast majority of which remains unmapped and unexplored. This #deepsea region contains extensive abyssal plains, plateaus, and seamounts, and is one of the largest territories managed by a single Pacific nation. Together, these habitats are part of Marae Moana, a large-scale marine managed area that spans the entire Cook Islands Exclusive Economic Zone, established to balance conservation with economic development. The Cook Islands EEZ is one of the top 20 largest in the world- about the same size as Mexico!