2026 Cook Islands ROV Exploration

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Dive 04 of the 2026 Cook Islands ROV Exploration cruise took place on the western ridge of a seamount, dubbed “Seamount B1,” located along the Cook Island’s western boundary with American Samoa. The dive started at a depth of 2,900 meters (1.8 miles), with the remotely operated vehicle working its way up the slope of the seamount. Throughout the dive, the seafloor was littered with small rocks that are potential polymetallic nodules. Glass sponges were frequently spotted attached to nodules, with their stalks rising into the water column. Macrobiology overall was limited, but we also spotted a few other invertebrates, including corals, sea cucumbers, and crinoids. Two larger polymetallic nodules were collected for further geochemical analyses, along with one “scoop” sample that included numerous small polymetallic nodules that will be analyzed for geochemistry, microbiology, sedimentology, and benthic ecology. One primnoid octocoral was collected in its entirety; upon retrieval at the surface, it was partitioned for use as a DNA voucher specimen, an archival specimen, and isotopic analysis. The team also collected five water samples–one for environmental DNA (eDNA) analysis and four for stable carbon isotopic analysis.

This was the first of six dives planned in this region as we explore seamounts and abyssal plains that reach depths of nearly 6,000 meters (3.7 miles).

Polymetallic nodules covered the seafloor throughout Dive 04 of the 2026 Cook Islands ROV Exploration cruise. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 630 KB).

This crinoid was observed attached to a sponge stalk during the fourth dive of the 2026 Cook Islands ROV Exploration cruise. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 783 KB).

Remotely operated vehicle Deep Discoverer traverses a nodule-covered seafloor during Dive 04 of the 2026 Cook Islands ROV Exploration cruise. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 382 KB).

Glass sponges dotted the nodule-covered seafloor during the fourth dive of the 2026 Cook Islands ROV Exploration cruise. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 535 KB).

This sea cucumber was observed during Dive 04 of the 2026 Cook Islands ROV Exploration cruise. Image courtesy of NOAA Ocean Exploration, 2026 Cook Islands ROV Exploration. Download largest version (jpg, 1.2 MB).