Turtle Rock is tucked in the back corner of Erebus Bay, which itself is tucked in a back corner of McMurdo Sound in Antarctica’s Ross Sea. The seasonal fast-ice was approximately 8 feet thick in that area in 2008, and though that was more than sufficient for vehicles, it was still in motion. The clockwise currents in the sound slowly drive the entire cap of sea ice toward Turtle Rock, and the ice had crumpled and piled up on top of itself on the north-facing shore, forming a jumble of 25-foot-high uplifted ridges. The moving sea ice also breaks around the corner of the island to form a long, wide crack in nearly the same spot every year, providing predictable surface access for Turtle Rock’s Weddell seal colony. The seals raised their heads off the ice to watch the procession of strange buglike vehicles approach.
The blue door of the orange hut stood propped open as we hauled the equipment inside. In the center of the floor, the dive hole stared up, unblinking, like a giant eye. We had returned to Turtle Rock. We suited up and dropped straight through the iris of the eye, squeezing through the tunnel and down into an ethereal concert. Beneath the veil of white is a world of cyan shadows, and there in the blue light, the seals sing.
The song seems to start as semiconscious thought, a memory of wind whistling through a drafty window, sharp and sweet. It has no direction or source, and it cuts cleanly through the shadows of the mind until the tone starts to accelerate and deepen, crossing fully into consciousness. The long, descending note breaks abruptly into thumping vibration, almost too deep to hear. Weddells are among the most vocal of seals, with 34 different varieties of trills, chirps, knocks, glugs and growls. Overlapping calls filled the water as if the sounds themselves had weight, and we swam suspended in the unearthly music.
The perennial sea-ice crack originating from the corner of the island was 50 yards east of the hole. Although invisible topside to the untrained eye, underneath the crack was arched like a railroad tunnel, perhaps 20 feet across and extending into the distance as far as I could see. In the center of the arch, a line of irregularly shaped seal holes glowed hard white.
Weddell seals range farther south than any other mammal in the world. Adélie penguins, whales and petrels all migrate north in the dark winter. But the Weddells stay, braving the fierce winter storms, temperatures of -40°F and below, and more than four months of night. They are, in fact, the only air-breathing vertebrates that live in the Ross Sea year-round, and their ability to do so is entirely dependent on the cracks. On the coldest days of winter, the water can be almost 100°F warmer than the air, and the seals spend all of their time under the ice, surfacing only to breathe. But even the predictable cracks freeze over, so the seals must continually maintain their portals, raking their teeth across the edges to keep the holes from freezing shut. They survive by literally eating their way through the ice.
A dagger of light cut down through one of the holes, piercing the black water and illuminating a patch of the seafloor 230 feet below. As we approached the crack, a seal slipped smoothly through another hole, pausing for a curious look at us before turning head-down and gliding into the black depths and out of sight.
There was no telling when the seal would return. Weddells are superb divers, having been known to dive to more than 2,300 feet, where the pressure is in excess of 1,000 psi. Besides dealing with that pressure, the seal has had to solve two basic problems to maximize its diving potential. First, it had to manage decompression stress. Under high pressures like those encountered when diving deep, more nitrogen dissolves into the bloodstream from air in the lungs. When pressure returns to normal, as it does on ascent, the excess dissolved nitrogen can come out of solution, forming gas bubbles in the blood. These bubbles can damage vessels, and, in severe cases, cause a stroke or heart attack. Neither seal nor diver wants the bends. To solve this issue, the seal actually exhales right before a dive. But Weddells go even further. Shortly after starting a dive, the seal collapses its lungs, squeezing air out of the alveoli and into the bronchial tubes in an effort to move the air away from its blood. Shortly before surfacing, the seal’s lungs begin to reinflate from the throat-full of air in preparation for the next full breath at the surface.
Collapsing its lungs also helps the seal get down to depth. With a lower volume of gas, the seal sinks faster and will glide for up to 10 minutes, using very little energy on the trip down. Once down, however, the seal must contend with a second, and obvious, problem: lack of oxygen. Several adaptations work in concert to overcome this basic hurdle. First, Weddells have a lot of blood — three times as much as humans per kilogram of muscle — and they have nearly twice the number of red blood cells per liter. Thus, a seal can store six times more oxygen than a human in its blood alone. The seal also stores oxygen in its muscles and has 20 times a human’s concentration of myoglobin, the muscle protein that absorbs oxygen. But an increased capacity for storing oxygen is just the start of the seal’s adaptations.
Oxygen keeps the cellular fires burning, enabling the transformation of food into energy. Aerobic metabolism consumes oxygen and releases mainly carbon dioxide. Without oxygen, cells can still function, but they must produce energy in a different way, resorting to anaerobic metabolism. In this oxygen-deprived state, cells start to consume their own organic acids, which ferment, creating energy at the cost of lactic acid buildup, which can be problematic for cells. The seals minimize the challenge of lactic acid buildup by using oxygen with maximum efficiency.
As a seal starts its dive, it reduces its heart rate to half of normal. With the immense amount of oxygen in its blood, this is more than sufficient to supply normal amounts of oxygen to the brain and nervous system, but blood flow to most other organs slows to a trickle. Finally, it slows, but does not stop, blood flow to its muscles. As the muscles burn through their oxygen and become hypoxic, muscle cells start to absorb the oxygen bound to myoglobin around them. By balancing its oxygen use, the seals ensure that stores in the blood and muscles are depleted at the same rate. With these adaptations, Weddell seals can substantially limit reliance on anaerobic metabolism for up to 20 minutes on a hunting trip. Thus, the seals can make long series of 20-minute dives with little buildup of lactic acid, diving again and again for up to 12 hours with very little time between dives.
Twenty-minute dives are routine for a Weddell. But the seal can also push its limits by somehow informing its body that a long dive is ahead and cutting off blood flow entirely to its muscles and nonessential organs at the start of the dive. Its kidneys cease all function, and its muscles quickly deplete their own oxygen stores and switch to anaerobic processes. With no blood flow, the anaerobic muscle cells are sequestered from the rest of the body, keeping the building lactic acid out of the seal’s circulatory system and away from its organs until it resurfaces. The seal also carries its own internal scuba tank: It keeps more than half of its oxygen-rich red blood cells in its spleen. Over the course of the dive, the seal slowly releases more and more of the oxygenated cells into its bloodstream, keeping oxygen levels high for its vital organs. With this system of oxygen management, the seal can stay submerged for up to 80 minutes, but after such a dive, as you might expect, the seal needs to rest.
As the seal disappeared below us, we turned our attention back to the crack and followed it toward the island. Every few minutes a seal would either ascend from the depths or drop out of the sky. Some just dropped in and swam the length of the tunnel, making brief forays under the ice to hunt for hidden prey.
The bottom of the sea ice is not smooth like the surface, but a complex of loosely packed crystals, or platelet ice, that provides a labyrinth of diminutive hiding places. Tiny fish like Pagothenia borchgrevinki, the “bork,” live hidden in the platelets. The seals dive down and look up at the ice, identifying these little fish as they move from place to place, black silhouettes against the glowing blue. Once a seal hones in on a bork, it rises and blows bubbles of air into the platelet ice to force the small fish out of hiding. Deep-diving Weddells may use a similar technique — diving down and looking up to see dark shapes moving against the distant ice, high above. It is even suggested that the seals continue the strategy through the winter, hunting by moonlight during the four-month-long night.
I followed the seal’s lead, dropping down 50 feet, then stabilized and looked back up. Silhouetted against the ice were a mother and pup, just entering the water. The pup swam cautiously under the ice after its mother. A few feet from their hole, the pup reared back, apparently scared, and made a quick escape back to the surface. The mother seal swam lazily back, and a few minutes later she managed to lure the pup back into the water. This trip was a little longer than the first, but once again the pup made a hasty exit. The first dives into the frigid water, it seems, are hard even for a seal.
The daggers of light had changed locations over the course of the dive as the sun had slowly circled westward, aligning with one seal hole, then another. We headed back to our own hole, surfaced, handed our equipment up to the dive tenders and kicked out of the hole to sitting positions on the floor of the hut. I didn’t want to come up. Had it not been for the fact that my hands and feet had nearly lost all function, I might have stayed longer. But surface I did, and free from the gear but still in my suit, I walked outside into the still air. We lay down on the surface of the ice, looking up at the sky. The sun warmed our black suits, and we baked, blood flowing back into fingers and toes. Below us, through the ice, we could still hear the chorus of seals trilling, chirping and glugging.
Over the course of the season I watched as the mother and pup, which I quickly learned to recognize, made longer and longer trips under the ice. Near the end of my stay, the pup was nearly independent. Big males started their rut, and I witnessed confrontations under the crack. Females came back into heat, and the process of renewal began again. All in all, I had 10 precious dives at Turtle Rock, 10 chances to watch the graceful seals cruise the crack, 10 chances to drop through the iris of the giant eye and swim in the blue light through the cathedral of sound.
The Last Ocean
To meet the needs of a growing world population hungry for fish, the global fishing industry has pressed south. In 1996, a single long-line boat, carrying a 9-mile-long line of hooks, finally cut its way through the ice and into the most isolated body of water on earth. In addition to the challenges presented by a changing climate, the Ross Sea ecosystem must now contend with a commercial fishery that targets its largest fish. The fishery is international and takes 3,000 tons of Antarctic toothfish from the Ross Sea every year. The deep-dwelling Antarctic toothfish — the shark of the Southern Ocean — now supports the most remote fishery on earth.
The Ross Sea toothfish fishery is playing with fire in the last intact large marine ecosystem on earth. The seals that eat their way through the ice, the birds that hold eggs on their feet through months of darkness, the fish that make their own antifreeze and all the other organisms that have conquered the cold are unique triumphs of life. Ross Sea denizens already face an uncertain future, and growing evidence indicates that the fishery is already compounding these challenges. The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is charged with managing Antarctic ecosystems under the directive of “rational use.” There doesn’t seem to be anything more rational than protecting these vulnerable creatures as they fight for their lives in a fast-changing world.
But the argument for Ross Sea protection goes far beyond the question of whether this fishery is sustainable or not. While we squabble over a few thousand tons of fish — 1/300th of 1 percent of the global catch — ocean health continues to decline precipitously. We need to take a stand. We need to open the door to a new age of enlightenment, a new global ocean culture. I believe the Ross Sea is the key.
Having failed to act on its promises to deliver a network of marine protected areas by 2012, CCAMLR will have another chance next year to make a resounding, global statement about what is, and is not, rational. We must call on our national governments and demand decisive action. Jane Lubchenco, administrator of the U.S. National Oceanic and Atmospheric Administration, once remarked, “If we can’t protect the Ross Sea, what can we protect?” But her insight has two sides. We must also ask, “What if we can protect it?”
Imagine the 25 member nations of CCAMLR speaking as one to proclaim the Ross Sea, the “last ocean,” as a no-take marine protected area, an international marine wilderness, a rejection of the culture of overuse, a gift to the future. Imagine that voice amplified across the Antarctic by an entire network designed to protect the Antarctic core. We have the opportunity to set the stage for sweeping changes in the way we manage the ocean. Imagine what we could do if we take this next step.
An Ecosystem in Context
Scientists have identified the Ross Sea as the most intact large marine ecosystem on earth. The Ross Sea comprises only 3.2 percent of the Southern Ocean, but it is home to a hugely disproportionate number of animals — 38 percent of all Adélie penguins, 26 percent of all emperor penguins, 30 percent of all Antarctic petrels, 45 percent of Weddell seals in the Pacific Sector of the Antarctic, and the list goes on.
In stark contrast to the Antarctic Peninsula and to the high Arctic on the other end of the globe, where sea ice has been disappearing at an extreme rate in all locales, the extent of sea ice around the Antarctic as a whole has actually been increasing recently. Scientists believe that this counterintuitive trend is due to heat loss from the upper atmosphere through the Antarctic ozone hole.
Climate models predict that the average temperature of our planet will have increased by 2°C over pre-industrial levels by the year 2050. Antarctic creatures will pay the price. Their homes will literally melt away. With two degrees of warming, scientists estimate that loss of ice habitat will eliminate nearly half of the emperor penguin colonies and 75 percent of the Adélie penguin colonies around Antarctica.
Since 2002, scientists and policy institutions all over the world have added their support to a bold proposal voiced at the World Summit on Sustainable Development (WSSD) in South Africa — a worldwide network of no-take marine protected areas, strategically placed to protect the biological core of the ocean as a whole. Researchers believe that if we could protect up to 30 percent of our oceans, and complement those protections with appropriate fisheries management elsewhere, we might be able to reverse the downward spiral of ocean health.
© Alert Diver — Q1 Winter 2013