Meet small shrimp-like amphipod Apherusa glacialis. This crustacean beauty is thought to live its entire lifespan directly underneath the Arctic sea ice – or some of it actually caught inside it. But now that more than half the Arctic Ocean is open water, it apparently has a trick up its sleeve to survive the summer heat. Photo credit: Geir Johnsen, Norwegian University of Science and Technology & The University Centre in Svalbard UNIS.

One reason why the Arctic sea ice is declining so rapidly under the current climate change is that the ever thinner ice breaks up more easily in summer – and that individual chunks of floating ice are then carried away by ocean currents, until they reach the big Arctic drain, which lies between Greenland and Spitsbergen: Fran Strait. Once the floating ice debris passes south through this strait it meets the much warmer water of the Atlantic Ocean, in which it melts.

This is not only problematic as it presents another positive feedback to ice melting, but also because it essentially flushes the ice-dependent fauna that live directly underneath the sea ice away from the Arctic Ocean where they belong, ecologists fear.

Now a group of hardy Norwegian polar researchers write in Biology Letters that they have found out [through winter field work – got to respect that!] that at least one abundant little crustacean, which is essential to the Arctic food chain, has a means of ensuring it stays within the right ocean: by dropping itself to a depth of 200 to 900 meters below the ocean surface, to reach slow-running ocean currents that carry it back towards the North Pole – and sea ice remnants.

This is by no means a quick process. The creatures will have to wait out their travel, which can last months, meaning they’ll be back at the ice front when a more favourable season starts.

“Based upon unique samples collected within the Arctic Ocean during the polar night, we provide a new conceptual understanding of an intimate connection between these under-ice crustaceans and the deep Arctic Ocean currents. We suggest that downwards vertical migrations, followed by polewards transport in deep ocean currents, are an adaptive trait of ice fauna that both increases survival during ice-free periods of the year and enables re-colonization of sea ice when they ascend within the Arctic Ocean.”

“From an evolutionary perspective, this may have been an adaptation allowing success in a seasonally ice-covered Arctic.”

Apparently these polar crustaceans have a strong will to live. Other researchers have recently uncovered that Antarctic krill sometimes choose to travel to a depth of several kilometers, to reach the ocean floor – collect some sediments, travel back up, fertilise the upper ocean and create a nice algal bloom to feed on. How about that for another one of nature’s wonders, obscured from the human eye…

© Rolf Schuttenhelm | www.bitsofscience.org