Summiting an Underwater Mountain

Greg Stone is currently participating in a National Geographic expedition exploring seamounts off the coast of Costa Rica. Check out his previous posts from the trip.

Some of the team in the submarine Deep See, about to descend. (© CI/Photo by Greg Stone)

Costa Rica’s equatorial sun streams through the clear dome of the submarine Deep See. A diver appears, smiles through the Plexiglas, and quickly puts a cover over the sphere so that we do not overheat as we are towed back to the ship after a successful dive to the seamount.

I’ve finally made it to Argo, the mother ship for Deep See, and I’m here with a terrific crew headed by the storied Avi Klapfer. We also have a team of accomplished scientists like Dr. Jorge Cortes from the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) and Dr. Larry Madin from Woods Hole Oceanographic Institution.

I am also very happy to have two good friends on board: Alan Dynner and Mike Velings. Mike and I share a passion for chess; he has brought along a board, and we play during the few moments we can find in the days that are richly filled with submarines, ROVs and scuba diving — usually making quick moves as we run out the door to dive.

We are anchored above the Las Gemelas seamounts, 340 miles [547 kilometers] off the coast of Costa Rica. The water is still, there is no wind. Conditions are perfect. Down below, I feel like the scenes of underwater wilderness will never end. Deep-sea sharks, groupers, salps and jellyfish surround us.

Argo, the ship hosting the seamount expedition team. (©CI/Photo by Greg Stone)

So far we have made three bluewater scuba dives to study the animals near the surface. Bluewater diving is so called because once in the water, it is blue in all directions — except straight below us, where the seafloor is some 5,000 feet [1,524 meters] down. There, it fades to pitch black.

On this expedition, we have made five dives so far in our “one atmosphere” submarine. Once the hatch closes, it maintains the normal pressure of Earth at sea level. We can dive up to 1,500 feet [457 meters] without worrying about decompression sickness. During these dives, we are tethered together for safety in a rig called a trapeze.

Dr. Larry Madin is an expert on pelagic invertebrates; he and I have been diving together for over 20 years. On this trip, Larry and I have already identified a number of mid-water animals, including ctenophores, jellyfish and salps. These drifting, soft bodied, jelly-like animals are among the most common creatures on Earth, yet we know little about them. Today, Larry said with a laugh, “If a spaceship from another world landed here, their first impression might be that Earth is inhabited by salps.”

As the submarine dives, taking us to another world, we see an underwater mountain, a magnificent formation rising 3,000 feet [914 meters] from the seafloor. We dive down to its summit, about 600 feet [183 meters] from the surface.

It is amazing that a mere 600 feet can take you to such a different place, but that is how the ocean works. At this depth the pressure is 18 times greater than the surface. The light is a lovely green, blue, black tint; we call this region the twilight zone of the ocean. The peaks of the Las Gemelas seamount live perpetually in this zone, a wonderful place with prickly sharks; snowy, olive and sailfin groupers; calcareous hydroids; and several species of deep corals.

Greg Stone

Tonight we have launched the ROV and saw lanternfish, a type of deep-sea fish with the ability to generate its own light. Occasionally they make excursions to shallower water at night. Which reminds me, it’s now midnight, and I need to get some sleep because photographer Brian Skerry and I will be diving first thing in the morning.

Greg Stone is CI’s chief scientist for oceans. This expedition is supported in part by the National Science Foundation under Grant No. DRL-1114251. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the writer and do not necessarily reflect the views of the National Science Foundation. Check out the next post in this series.

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