The National Zoo's Antarctica Expedition is sponsored by the National Science Foundation's Office of Polar Programs.
All photographs depicting Weddell seals were taken under NMFS Permit No. 763-1485-00 issued under the authority of the Marine Mammal Protection Act.
Call of the Seal
October 20, 2006
|Wind swirling around the Pistin Bully|
We are at sea. Although our home on the ocean is stationary, we have finally left the harbor of McMurdo Station and come to where we longed to be. Outside, the storm sings in the rigging of the tents and makes the wind generator whine and growl like a crazed double-decker plane. The wind has been blowing hard for several days now. Strong winds are our doldrums, as they severely restrict outside activities and confine us to the shelter of huts and closed vehicles. It is not very cold (10˚F), but the wind snatches away body heat with breathtaking speed.
Wind Chill and a Flying Cooler
Like heat and humidity, people here say it’s not the cold that gets you, it’s the wind chill. The greater the wind speed, the faster the heat loss from objects warmer than the ambient temperature. Extreme wind speeds are common in the Antarctic, so wind-chill tables are a familiar sight—I have a small one hanging from a key chain on the zipper of my parka. In Antarctica, the rather theoretical phenomenon of convective heat loss that I encountered in undergrad physics takes on a whole new relevance. A wind of only 35 miles per hour transforms a fairly balmy -10˚F to an effective temperature of -40˚F. Under those conditions, exposed skin will freeze in ten minutes or less. I don’t know what the wind speed is outside but am willing to bet that it is quite a bit more than 35 miles per hour.
Wind chill and its threat to life and equipment have put a damper on field work for the time being. I am quite glad to have this brief respite, and am working to get the lab hut ready for processing samples for the next two months. Looking for my gloves and perhaps some food (I seem to be perpetually hungry), I walk into the kitchen hut next door. I look out the window just in time to see a large cooler take off into the sky, flapping its lid with wild abandon and strewing its contents over the ice. By the time I get outside, cooler and contents are merrily racing in the general direction of the Transantarctic Mountains.
I set off after them at a run but have to slow down almost immediately. Outside of the protective circle of our camp, the wind has stripped the snow and exposed the beautiful blue-hued but slick sea ice. I walk gingerly, keeping my eyes on the wanton cooler. My hope is that its flight will be arrested by one of the pressure ridges and give me a chance to catch up. This is when the wind arrests me instead. A sudden gust slams into my back and sends me flying. On blue ice and without crampons, wearing a large red parka, I am a bowling pin for the wind to play with. After hitting the ice (no harm done—that parka is mighty useful), I lie still for a moment and think about the last time, only a few weeks ago, when I hit the ice out here in McMurdo Sound, Antarctica. more about ice
Learning About Ice
We were traveling past the landmarks the first explorers wrote of in their diaries. Hut Point, Castle Rock, Turtle Rock, Mt. Discovery behind us and Mt. Erebus looming ahead, filling a large part of the sky and seeming close enough to touch in the clear sharp air. We are out on a training course to learn about the sea ice. Our whole team is here and we are traveling in two tracked Pisten Bullies that drown the soft hissing of the wind with the rustic putter of their diesel engines. Our first destination today is our field site, a stretch of flat sea ice below a rocky outcrop known as Hutton Cliffs. The cliffs provide the third basic color of the Antarctic landscape, deep dark brown that offsets the shades of white and blue. Much has changed since I was here in 1998. Where there was smooth ice stretching all the way north to the Erebus Glacier Tongue, there is now a wild profusion of pressure ridges, depressions, frozen pools and healed cracks intersecting in a seemingly random pattern.
|A giant iceberg in McMurdo Sound, photo courtesy of NASA|
In normal years (one could argue humans have not been here long enough to figure out what is normal for this place, but I digress), the sea ice in McMurdo Sound breaks out in summer and re-forms in winter. In 2000 and again in 2002, two icebergs the size of small European countries calved off the Ross Ice Shelf. Fragments of these ’bergs blocked McMurdo Sound and interrupted the annual cycle of the sea ice. The ice, trapped inside McMurdo Sound, thickened year after year until it is now 17 feet tick, and more in some places. The forces of wind and tides continually drive this old, incredibly massive sea ice against the coast of Ross Island, causing it to crack, buckle, and fold into the surreal icescape that we see before us.
The area between Turtle Rock (a tiny island that looks like a tortoise when viewed from the north) and Hutton Cliffs is famous for its large, active, and treacherous crack systems. More than one vehicle has fallen through the ice in this area. Thus, it is the perfect destination for our sea ice course, exhibiting all the features one may hope to encounter (or avoid) when traveling on sea ice. Of course, seals love this place—cracks provide the vital link between the air and the ocean that they need to survive.
Trill, Whistle, and Boom
Next, our instructor, Erik, takes us to the vicinity of one of the main cracks radiating north from Turtle Rock. We start shoveling to remove four feet of snow and expose the surface of the ice, and soon find what we came here for: a large, active crack that was completely obscured by snow. Next we drill the different levels of the crack to determine the thickness of the layers of ice where the crack successively opened and refroze. It is this repeated opening and closing of an active crack that keeps the ice thin and hazardous for travelers.
Having taken a turn shoveling and drilling, I wander off a little ways to see whether I can detect any signs that might betray the crack in this innocent landscape. Underneath the sounds of engines and people, there are voices on the wind. I try to dismiss them, but the subliminal calling stubbornly tugs at my memory. Suddenly, the pattern match is complete: The eerie sounds are made by a seal below the ice, no doubt having come to investigate the circle of light that appeared when we dug out the crack. I drop down onto the snow and press my ear to the surface. The others soon notice me lying on the ground and offer witty comments, disbelieving my excited assertion that there is a seal! Then somebody else hears the call and like large red pins felled all at once, the group drops to ground. All except Erik, who is probably wondering whether this is an example of bizarre beaker humor he has been warned about. He hovers, uncertain, until he hears the call, and believes. “This is the coolest sound I have ever heard!”
|Weddell seal near our ice camp|
The call of the Weddell seal is arguably one of the more interesting sounds produced by mammals, or any animal, for that matter: they trill, whistle, and boom in a completely inorganic way that one is more likely to associate with experimental electronic music than a chubby, not very bright-looking pinniped. The surreal quality of its calls has to be heard to be believed.
Considerable research has been conducted on the social and biological significance of vocalizing in the Weddell seal, and the nature of the variation between different populations (for example (Pahl, Terhune, et al. 1997). It is thought that seals call to communicate: for example, males patrolling their underwater territories call to announce their presence to potential rivals, and they can be heard above the ice on calm days. I remember it well. I used to hear it in my sleeping bag at night, in our tent out on the sea ice.
Dawn of the Seals' Summer
|Under the ice|
And now I have come back, following the call of the seal, and landed on my back running after an errant cooler. There is something irresistibly comical about being picked up and tossed like that, especially if it does not hurt. It happens once more before I give up on the cooler and turn into the wind to fight my way back into camp in a sideways, low-slung crab-like gait. While this is sort of funny close to camp and in perfect visibility and wearing highly sophisticated ECW, I can feel the danger lurking just below the surface of this situation. Had I run out in a blizzard, I might have never returned.
While we work hard at being able to be here and maybe also do some science, the seals lie on the ice in supreme serenity. This is the dawn of their summer, of the season of light and warmth. Since we have arrived, we have conducted daily head counts of the seals at Hutton Cliffs. We tread carefully among the spires and cracks of their colony and find them at home in this landscape of ice. While we are preparing our camp, the seals find their way to the cracks that form every year, crawl out of the water, and congregate in this place where they have been breeding and lying in the sun for who knows how long. As of today, we have counted 50 adult females, 14 with a newborn pup by their side. There are some adult males scattered among the nursing pairs, either resting from their battles or seeking refuge from a menacing rival. While the females birth and nurse their young on the ice, the males compete for the right to patrol the cracks and holes that females use once they re-enter the sea. Swimming guard below the ice, the males call.
Sitting in the lab hut, I hear the hypnotic call of the seal. The sound travels through 15 feet of ice and the solid floor of our hut to reach me in the calm and warmth of the cocoon we have made for ourselves. Reminding us that the true home of the seal is just below, in the ocean beneath our feet.
Smithsonian Ice Camp, Antarctica
Pahl, B. C., J. M. Terhune, et al. (1997). Repertoire and geographic variation in underwater vocalisations of Weddell seals (Leptonychotes weddellii, Pinnipedia: Phocidae) at Vestfold Hills, Antarctica. Australian Journal of Zoology 45: 171-187.