There is no doubt that Antarctica is melting, as the surface area of the icy continent is easily measurable, and so is the volume of the seawater that is melting it. However, what researchers couldn’t understand precisely was how the warm water was coming into contact with Antarctica. Now, though, with the help of robotic gliders that look similar to dolphins, Caltech researchers have discovered that underwater eddies with similar characteristics to storms may be responsible for the continent melting. It appears these eddies are helping to move warm water and bring it into contact with the sheets of ice that make up Antarctica.
Andrew Thompson, the study’s lead author and a Caltech assistant professor of engineering and environmental sciences, explains that a slab of ice can either be melting from above due to an increase in the temperature of the atmosphere, or it can be melting from beneath due to the ocean warming up. He goes on to say that evidence has led researchers to conclude that the warming up of the ocean is likely the biggest variable impacting Antarctica’s ice shelves. This is why, he explains, the research was undertaken as they wished to gain insight into how the heat is transferred.
Traditionally, water temperature is measured with the help of ships that drop equipment into the water, but this is clearly problematic when one wants to measure water temperature underneath a continent as ships are unable to reach the source. And satellite imaging isn’t very helpful because it doesn’t show the whole picture since the problem isn’t at the surface.
The robotic gliders, however, are only approximately 5 feet long and very efficient in terms of energy consumption. This means they are able to stay out and explore for longer periods of time than a manned ship. After a few hours, a glider will come to the surface and contact the parent ship using a device embedded in its tail, thus allowing researchers to download and access all the information the unit has gathered in real time.
Researchers have been using the gliders since the beginning of 2012, and their name is quite descriptive of how they make their way through the water. They have no propellers; instead, the glider works by sucking in or jettisoning water to change how buoyant it is. The wings are shaped so that they convert vertical movement into horizontal motion when the glider floats or sinks, quite similar to an aircraft.
Surprisingly, it appears that the water with the highest temperature isn’t close to the surface, as principles of density would imply. In fact, it seems that the differences in saline content have led to the warmest water being found between the surface and the deeper waters, like the cheese in a sandwich. Due to the gliders’ stamina, they were able to spend a number of months underwater, which enabled them to find that the warm water from below is moved upwards towards the Antarctic ice sheets by eddies. These are similar to the storms of aboveground weather patterns.
Thompson explains that because of the variability of ocean currents, taking a measurement just once may not reflect what the current will look like the next day. It’s similar to the weather: summers are expected to be warm and winters are expected to be cold, but when you look closer, on a daily basis, you can have cold days in summer because of storms. He further states that eddies have the same effect in the ocean, so if researchers don’t understand how the temperature of the currents changes from one day to the next, they can’t possibly understand how heat is transported over the long-term. And this is information the gliders are able to collect.