The mightiest and fastest ocean current on Earth carries more than 100 times as much water as all the world’s rivers combined. It reaches from the ocean’s surface to its bottom, measures as much as 2,000km across, connects the Indian, Atlantic and Pacific oceans, and helps regulate the Earth’s climate. This is the Antarctic circumpolar current and with no land mass to get in its way, it races around the Antarctic. In recent decades the current has been speeding up, although what impact this may have is uncertain.
A new study looked at cores of sediment drilled out of the ocean sea bed and revealed details about climate over the past 5.3 million years. The sediments showed that past natural swings in the ocean current had matched the Earth’s temperature, slowing down over cold epochs and speeding up in warmer times. The periods of faster current also matched the times when large parts of the Antarctic ice melted, a warning that its recent speeding may have the same effect, leading to rising sea levels. The ocean waters circulating around Antarctica also absorb about 40 per cent of the excess CO₂ emissions from the atmosphere caused by humans, although it’s unclear whether the faster ocean current is affecting this.
Records of winds over the Southern Ocean show they have grown about 40 per cent stronger over the past 40 years, helping to speed up the current. As the current speeds up it has driven relatively warmer waters towards Antarctica’s ice shelves. These shelves float on the sea and act like brakes that help to hold back the giant glaciers in the interior of Antarctica, and in some parts the invasion of warmer waters is eating into the undersides of the ice shelves and weakening them. Most vulnerable is much of the West Antarctic Ice Sheet, which is frozen to land that lies below sea level, so is highly susceptible to invasion by warm ocean waters. Were it to melt entirely, it would raise global sea levels by about 190ft.
