National Geographic - Explore Antarctica - (Page 31)

The Brinicle BY JEREMY BERLIN Adapted from "Ice Stalactites," by Jeremy Berlin, in National Geographic, May 2012 I n the frigid waters of Antarctica, briny tubes of ice can stretch down to the sea floor. Oddities abound at the world's poles. Now, thanks to time‑lapse cameras, we can see one coming to life. This salty ice stalactite, called a brinicle, was filmed as it formed by British cameramen Doug Anderson and Hugh Miller in Antarctica's McMurdo Sound. Ice stalactites were first described in detail in 1971 by American oceanographers Paul Dayton and Seelye Martin. Martin actually grew them in his Seattle laboratory. According to him, brinicles occur naturally in polar winters. Conditions are right there because air temperatures can dip well below 0°F, while the water may be a relatively balmy 28°F. The difference between the water and air temperatures is key. The phenomenon involves relatively warm sea water rising, cooling, and dropping again. The sea ice on the surface is filled with a network of channels. When the warmer seawater rises upward, it flows into these channels in the sea ice. The water cools. The dense brine in the sea BACKGROUND & VOCABULARY briny adj. (BRY-nee) containing a large amount of salt, or saturated with salt platelet ice n. (PLAYT-liht) the ice crystals typical of Antarctica that form in supercooled water under certain conditions water is too salty to become part of the ice pack. Instead, it drains out and sinks back into the ocean. As it descends, the brine freezes the water around it. This forms a plume that grows downward at about one foot an hour. If conditions are just right, a brinicle can reach the seabed. There it creeps along the bottom, pooling at low points. In the 1970s, Martin recalls with a laugh that "the Navy asked if they're dangerous to submarines." They're not. In fact, brinicles are too slow forming to freeze anything but bottom dwellers such as sea stars. And they're fragile enough to be broken apart by seals or currents. When that occurs, or when the brine stops seeping, a brinicle "dies." But it may get a second life. Anderson has seen fish making homes of dead brinicles covered in platelet ice. Platelet ice forms structures resembling "very beautiful chandeliers"-just another polar curiosity. T H I N K A B O U T I T! Make Inferences Why is the brinicle deadly to sea stars but not to fish? stalactite n. (stuh-LAHK-tyt) a mineral deposit shaped like an icicle, typically hanging from the roof of a cave 31

Table of Contents for the Digital Edition of National Geographic - Explore Antarctica

National Geographic - Explore Antarctica
Contents
Letter from the Editors
Discovering Antarctica
Antarctica’s Life
Escape Velocity
Amundsen: The Man Who Took the Prize
Explorer’s Journal with Jon Bowermaster
The Brinicle
Whales of the Antarctic
Frozen Under
Document-Based Question

National Geographic - Explore Antarctica

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