North Carolina's Submarine Canyons: Keller, Hatteras and Pamlico, Where Currents Collide

About 35 miles off North Carolina, the continental shelf drops from about 200 meters (656 feet) to more than 2,000 meters (6,561 feet), down toward the continental rise and the flat abyssal plain. From North Carolina to Canada, 40 undersea canyons, 16 to 160 kilometers (10 to 100 miles) long and some deeper than the Grand Canyon, are cut into this edge. USGS research geneticist Cheryl Morrison described three of them before the DEEP SEARCH expedition set out to explore them.

Why canyons teem with life

Canyons offer many habitats: steep walls, rocky outcrops and ledges where fragile deep-sea corals live, and muddy floors where other fish and invertebrates thrive. Strong currents, including upwelling and tides, stir up sediment and organic matter, bringing plenty of food, and animals of the open water mix with those on the bottom to feed.

Where the currents meet

The North Carolina canyons may be unlike those farther north because of where they lie. Here the cold Labrador Current from the north meets the warm Gulf Stream and Virginia currents from the south, which are turned offshore at Cape Hatteras. The collision makes one of the sharpest temperature boundaries known in the world's coastal oceans, and the fish, invertebrates and corals differ north and south of it, probably because the temperature change acts as a barrier. By recording species on both sides and sampling their DNA, scientists can test whether the currents block animals from spreading, knowledge that matters for managing these resources. Most canyon research has been farther north, from Virginia to New England; these three had barely been explored.

Illex squid above a Bathypolypus octopus in Keller Canyon. Image from NOAA Ocean Exploration, Windows to the Deep 2018.

Keller Canyon

Keller is the only one of the three that cuts into the shelf, though less than canyons farther north. Images from the autonomous vehicle Sentry showed octocorals and anemones, and in 2018 the ROV Deep Discoverer surveyed a ridge inside it, finding white nephtheid corals, sea pens, hydroids, sea spiders, squid and octopuses. Mapping has picked up diffuse gas venting at depths of 50 to 930 meters.

Keller Canyon, 200 to 1,600 meters deep, with its main channel cutting the shelf (dark red) and many tributaries. Image by Jason Chaytor, USGS.

Shrimps, snipe eels and squid feeding over a ridge inside a canyon off Pea Island. Image from NOAA Ocean Exploration, Windows to the Deep 2018.

Hatteras Canyon

Research submersibles explored Hatteras Canyon nearly half a century ago and noted sea pens, sea stars and sea cucumbers. More recently Sentry found octocorals on its walls at 1,500 meters, mapping detected gas venting at 180 to 375 meters, and the 2018 expedition saw bacterial mats, a sign of methane seeping.

Bacterial mats, a sign of methane seepage, in a canyon off Pea Island. Image from NOAA Ocean Exploration, Windows to the Deep 2018.

Pamlico Canyon

South of Hatteras, Pamlico Canyon is the least explored of the three, though Sentry recorded octocorals on its walls in 2016. It barely cuts the shelf break about 20 miles off the Outer Banks; its main axis runs about 17 miles from 400 to 3,000 meters deep and then continues more than 100 miles offshore to 5,000 meters. It may hold the greatest variety of corals, invertebrates and fish, which made it a top target.

The expedition planned to use the ROV Jason to explore the steep rock walls, which record the canyons' geological history, to sample corals and any seep animals, collect sediment and water, and log temperature, salinity and depth along the way.

Sources

• Cheryl Morrison, USGS, "North Carolina Submarine Canyons," NOAA Ocean Exploration, DEEP SEARCH expedition; rewritten in hubnx's own words. Images from NOAA Ocean Exploration and the USGS; a photograph copyrighted by the Woods Hole Oceanographic Institution is left out.