Dive 08: Clipperton Fracture Zone
May 8, 2017
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Dive 08: Sea Cucumber Serenity

This sea cucumber was seen gracefully swimming through the water column during exploration of the far western limits of the Clipperton Fracture Zone, as it crosses the Line Islands, at a depth of 4,500 meters (2.8 miles). While we often see these sea cucumbers on the seafloor, they do swim when they need to move to another location. Video courtesy of the NOAA Office of Ocean Exploration and Research, Mountains in the Deep: Exploring the Central Pacific Basin. Download (mp4, 68.5 MB)

While we've been targeting seamounts for nearly all of the previous dives, today we dove along the far westernmost edge of the Clipperton Fracture Zone. Deep Discoverer (D2) descended to a depth of 4,500 meters (~14,765 feet) – our greatest depth on this expedition. This feature is among the longest tectonic structures on Earth, extending from the Line Islands more than 7,000 kilometers (4,350 miles) east to the Clipperton Transform on the East Pacific Rise – that's further than the distance from Honolulu to Chicago!

It was an exciting descent as we transited through the water column. There was a surprising amount of marine snow and particles throughout the full water column – surprising because typically much of this organic material has been decomposed by bacteria by the time it sinks below ~2,000 meters (~6,560 feet) – the water was relatively clear below that. On the descent, a Dana octopus squid followed us for a while. We saw a layer of fish and siphonophores at mesopelagic depths of 200-1000 meters (660-3,280 feet). From 1,000-1,500 meters (3,280-4,920 feet), we saw chaetognaths, fish, and many large red copepods. We did not see much fauna in the water column below ~1,500 meters (4,920 feet).

When D2 reached maximum depth, we immediately saw several black corals. Not far from the black corals, we saw large aggregations of small sediment-colored spheres or spherules, like those we saw during the Deepwater Exploration of the Marianas expedition. Nearby, sediment feeders had left trails on the seafloor. Other biological highlights were bamboo corals, including the second deepest ever collected; several holothurians (sea cucumbers); bryzoans; anemones; chitons; carnivorous tunicates (sea squirts); brisingid sea stars; crinoids; scale worms (polynoid polychaete); tube-dwelling fanworms (sabellid polychaete); sea stars; a carniverous starburst sponge; shrimp; chimera; and a deep ocean lizardfish with highly reflective eyes.

Because the sun set during our ascent, many of the midwater animals had migrated toward the surface as part of their diel vertical migration. By the time we transited through the water column, a very active layer of jellies, siphonophores, and fish started around 600 meters (1,970 feet) and extended into the epipelagic zone, which extends from 200-1,000 meters (~655-3,280 feet) deep.