Swimming Beneath The Brinicles Finger of Death, In Antarctica
A diver examines a large brinicle. It’s rare these days to uncover a phenomenon completely new...
|A diver examines a large brinicle.|
They’re bizarre, otherworldly structures, spindly tentacles reaching down from the floating sea ice into frigid Antarctic waters.
Typically, a new observation fits within a previously established theory, which can then be applied and tweaked to accurately characterize the discovery. But because brinicles are relatively new to the scientific world, there’s no theoretical framework to start with. So which model is best applied to brinicles? What’s the most useful way to analogize these unusual icy structures?
|The open end of a brinicle, where cold, dense fluid emerges into the seawater.|
Chemical gardens are a staple of high school chemistry classes – a rapid, visually impressive experiment that has at least a fighting chance to keep a teenager’s attention. When a metal salt (use copper sulfate for blue gardens, nickel sulfate for green) is introduced to an aqueous solution of sodium silicate, the metals initially dissolve, but are quickly configured into solid silicate mineral shells. Inside, the solution is salty; outside, more pure, and the osmotic imbalance causes water to gush inward through tiny gaps in the mineral’s structure. The flux increases the interior volume, ultimately puncturing the shell and allowing the salt-rich solution to flow further into the water. At the chemical front, the “shell formation-osmotic rebalance-crystal burst” cycle repeats, leading to an advancing, dendritic solid structure.
Brinicles can be understood in a conceptually similar way. As winter descends on the Southern Ocean, ice begins to form. But ice is a solid matrix of water molecules, and the salts contained in seawater aren’t allowed; rather, they are concentrated in thin films that form briny, viscous pools. Intrepid water molecules can squeeze through the ice shell from the underlying seawater into the brine, encouraged by the osmotic differential. When the expanding brine pool pushes through the ice, it falls downward into the seawater; having been supercooled because of its high salinity (thanks to the same principle that governs our application of salt to icy roads), the briny liquid flash freezes the seawater it contacts. A tube of ice grows downward, driven by the salt differential and the freezing point differences that follow.
Dr. Andrew Thurber is one of the few scientists who has seen brinicle growth firsthand. As a Postdoctoral Fellow supported by the National Science Foundation’s Office of Polar Programs, he’s investigating the impact of animal predation on microbial communities and nutrient cycles in the oceans around Antarctica. While diving beneath the sea ice in pursuit of samples, Thurber describes a fantastical scene punctuated by downward creeping brinicles. “They look like upside-down cacti that are blown from glass,” he says, “like something from Dr. Suess’s imagination. They’re incredibly delicate and can break with on the slightest touch.”
But to nearby sea creatures, the fragile ice sheaths hide a deadly weapon: the frigid brine can kill animals caught in the wrong place at the wrong time. “In areas that used to have the brinicles or underneath very active ones, small pools of brine form that we refer to as black pools of death,” reports Thurber. “They can be quite clear but have the skeletons of many marine animals that have haphazardly wandered into them.”
The scientific study of brinicles is in its early stages, but these mysterious icy fingers are a remarkable addition to nature’s repertoire.
By Jeffrey Marlow, WIRED