The walrus pulled himself along the ocean floor using his tusks as a sled. His long upper canine teeth appeared awkward but served the walrus well: as weapons for fighting, as “canes” for climbing and walking on land (giving rise to the animal’s scientific name, Odobenus rosmarus or toothwalkers), and as “axes” to chip the ice. As he skidded along the bottom, his tough whiskers (or vibrissae) twitched as they felt for clams, his preferred meal. Detecting his prey, he paused. He swished his head back and forth to dig it out but the soft sand hung on to the morsel. The young bull switched tactics. This time, he squirted water through his tongue to hydraulically “drill” the clam out. Success! Using his whiskers like “chopsticks,” he brought the meal to his mouth and inhaled it from its protective home. A second later, he spit out the empty shell and let it drop soundlessly beside the depression he’d just made.
The whole process took only about six seconds, so he had plenty of air to continue his feeding. Because his body had extra blood to carry oxygen, about 12 percent of his weight (compared to seven percent in humans), he could stay underwater for up to 30 minutes. This, along with the special tissue in his ears that equalized water pressure when he dove deep (up to 300 meters), let him scan the ocean floor for food.
The walrus paddled his flat hind flippers along the sea bottom and used his front ones as rudders to steer. Like the rest of his species, this Pacific walrus followed the edge of the melting ice pack north through t he Bering Strait for the veritable smorgasbord it supplied. The melting sea ice released both phytoplankton (or ice algae) and a layer of cold, relatively fresh water simultaneously, spurring an early and vigorous bloom. As the bloom decayed, it nourished the clams, crabs and other crustaceans he liked to eat.
The young bull satiated his appetite and surfaced. His big brownish white head rose just above the frigid water where he eyed his chances for joining the herd. Through the fog, he saw masses of pink and cinnamon-brown bodies huddled together on a large floe. He watched a big bull, almost 11 feet long and close to 2,500 pounds (about the weight of a pickup truck), lift his head above the crowd to search for potential danger. The young male dove. This time, he came up closer to the resting herd. He turned his head away from the large bull, in essence saying “I’m no threat.”
The newcomer regarded his competition. The younger, smaller walruses lay on the outer perimeter of the group while the more dominant ones rested in the middle, away from the surf and frigid temperatures of the Bering Sea. If he had to, he could wait. Like all walruses, he had an air sac under his throat, called a ‘pharyngeal pouch,’ that he could fill like a life vest to keep his head out of the water. He could even use it to sleep while bobbing in the sea!
The young male waited for the right moment and then, with a big heave, hauled himself awkwardly onto the ice. The old bull bellowed in rage and lifted his meter-long tusks aggressively. The young walrus changed course. He grunted as he scrambled over a smaller animal while, beneath him, the groggy lump snorted in protest and stabbed its tusks into the air. He ignored the din and continued clambering on top of the prostrate herd. When far e nough from the edge, he squeezed himself into the crush of bodies, squiggling and squirming until protected from the constant wind.
The sun peaked through the fog to dry him, albeit slowly. As he warmed up, he gradually changed color -- from muddy brown to pinkish cinnamon. Walruses’ circulatory systems help them adjust to the surrounding temperatures. When warmer, their expanding blood vessels move blood to their blubber and skin so that the air and water can cool them. This makes them pinker. When colder, the opposite happens. Their blood vessels constrict to reduce the flow to their skin and blubber. This saves body heat and turns them browner.
The young bull half-closed his eyes. In the background, he listened to a steady drone of snores, snorts, and whistles while, every now and then, an outburst of flatulence, roars or clacking teeth signaled a walrus renegotiating its basking position. At last, the continuous, slow, undulating motion of the ice floe rocked the tired walrus to sleep. Ahhhh!
Why is there a layer of relatively fresh water on the sea when ice melts? The water in this layer is less salty because when ice crystals form, salt is expelled. Because this fresher water is less dense than the salt water, it floats on top of the water column, thus forming a thin, relatively well-defined layer at the surface of the sea.
What is the temperature of the Bering Sea? Bering Sea surface temperatures average around 20-30 ° F in May and less than 40 ° F in June.
Why does an early bloom of phytoplankton occur on the edge of melting sea ice? The bloom occurs because the ice algae are “trapped” in the fresh water layer near the surface where there is plenty of light for photosynthesis. The result is rapid growth, a phytoplankton “bloom” which occurs much earlier than would be the case without the melting ice.