27 November, 2003
Our flights are scheduled to start at 2:40 PM today – the fourth day that we have been waiting to fly to our acclimatization camp on the Fang Glacier. We had waited all day yesterday only to be cancelled around 4 PM. With so much time to spare, I spent the last two days wandering around Crary Lab asking a flood of questions about other projects. As a result, word got out that I wanted to write some journal entries about other people’s work. Yesterday I was invited to go along with Dr. Art DeVries’s Antarctic Cod group as a diver tender (a person who helps transport dive gear and supports the divers from the surface). Sadly, I wasn’t able to go because Helo-ops hadn’t yet cancelled our flight for that day. I needed to be here in McMurdo, on standby, in the event that the weather cleared and we could fly out. But I was thrilled that they had invited me to go with them! Much to my delight, this morning I met Phil Forte, one of the divers the Cod Project. He heard that I was interested in learning about the fish projects and invited me to go out on the sea ice to pull up a plankton net.
We took one of the awesome McMurdo trucks, which have tracks instead of tires (Figure 1), out onto the sea ice. Several heated huts are built around the holes used for the fish projects and we were headed for Hut #6, which sits on 4.5 meters (15 feet) of sea ice above 400 m (1,300 ft) of water. The warm hut helps keep the hole open, but upon arrival we found that it needed a little maintenance. We spent about ten or fifteen minutes fishing ice cubes off of the surface (Figure 2) and dumping them into a box in the corner where they melt and the water is funneled back into the hole. Once we had cleared the bulk of the ice away from the hole, I could see exactly how thick the sea ice is. The top of the hole is well lit and you can see the walls extending down about 4.5 m (15 ft), but the open water below the ice appears to be a big, black void. Peering down the hole, my desire to dive here abated a little bit until Phil assured me that they actually do their diving in much shallower water where you can see the bottom. At 400 meters depth, you would have to be tethered to a safety line. I have a lot of respect for the divers here as the water is frigid and that big hole in the ice starts to look awful small when you consider the extent of the solid sea ice surrounding this one little hole. But the eternally curious side of me still would jump at the chance to dive here! Under the right conditions, the visibility can reach up to 243 m (800 ft)! And according to Phil, when there is less snow cover, sunlight filters down through the ice and lights the water up. Unbelievable!
After clearing the ice from the hole, Phil fired up the winch and proceeded to slowly pull up the plankton net (Figure 3), which was our objective in coming out today. Dr. DeVries’s projects focus on the Bathyberthella antarctica, or Ice Fish (Figure 4), and Antarctic Cod (see 11/25/03 Still Waiting), which feed on smaller organisms. Two days ago a long, cone shaped net with a little waterbottle sized sieve was dropped to the bottom. Trapped in the lower net and sieve are plankton and small shrimp and fish. We were pulling up the net and sieve to collect food for the Ice Fish that are back in the lab.
As I was peering down the ice hole, still contemplating how great it must be to dive under the ice, I noticed a dark shape spiraling up toward the surface (Figure 5). As I squinted a little harder in the dim light of the hut, the shape took on the distinct form of a Weddell Seal (Figures 6 and 7)! And just like that I suddenly found myself nose to nose with a seal, greeted by a big wet puff of seal-breath directly in my face (Figure 8)!
With the plankton stored away in a cooler, we had a few minutes to watch these graceful and comic giants (Figures 9-11). They happily utilize the dive holes as breathing holes and seems quite accustomed to the funny bipeds scuttling around the hole, snapping photos. In the meantime, the seals lounged about at the surface, just ducking out of sight each time I thought I had lined up the perfect photo. Occasionally one seal would blow at another, attempting to drive the competition away from the hole. Phil informed me that they had learned to cooperate fairly well by this point in the season as four seals were occupying this parcticular hole. Early in the season though, they would compete for the space. My question is “What happens to the diver who wants to come up through this hole?” The Weddell seal can grow to over three meters (10 feet) in length and weigh up to 400 - 450 kilograms. I imagine that one or two of these fellows present a formidable obstacle for a tired diver trying to surface.
The Weddell seals themselves are efficient divers, storing a large amount of oxygen in their blood and muscles enabling them to dive to depths of 300-400 meters for fifteen minutes. The record dives have been 82 minutes long and extended down to 700 meters. The Weddells establish breathing holes that allow them to fish under the ice and then haul out on the ice to rest and rear pups. Weddells maintain these breathing holes by scraping at the ice edge with their teeth, knocking loose any new ice. The net result of this activity is severe wear on their canines and incisors (Figure 12). But the Weddell seal skull is designed for this purpose, with forward facing incisors that become blunted with use. With a diet of fish (especially D. mawsoni; See 11/25/03 Still Waiting) and cephalopods (squid and octopus), krill, isopods, amphipods, and decapods, maintaining sharp canines is not as critical as it would be if they ate warm-blooded mammals like the Leopard Seals do.
The Leopard seal is sleeker than the Weddell seal and built for speed, as it is the only seal that regularly preys on warm- blooded animals. Leopard seals will eat penguin adults and chicks, birds, and Weddell seals in addition to cephalopods (squid and octopus), krill, fish, and crustaceans. Figure 13 illustrates how well adapted Leopard Seals are for such a diverse diet. Note the large canines and incisors, useful in snatching and holding a penguin while thrashing it about to remove the skin. Behind the large canines are smaller, interlocking teeth useful in straining the krill out of the water. Because Leopard Seal prefer the pack ice (broken up sea ice), they are found at the edge of the ice shelf until late summer when the ice breaks up in McMurdo Sound.
All good things must come to an end, and in my case, it was time to head back to the lab with the fish food. With one final look over its shoulder (Figure 14), the last remaining seal dove down the hole seeking a snack while I deliriously floated back to the truck, realizing as I left that I have never been so close to one of these awesome creatures before. As I stepped out the door, it dawned on me that my camera takes mpeg videos! I had completely forgotten this fact while entranced by my new pinneped friends. Maybe next time….
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