The clue? Scientists were looking at concentrations of aragonite, a mineral that can't form in highly acidic water. They noticed that parts of the western Arctic Ocean have lower than expected aragonite levels.

Climate change isn't the only factor -- the team notes that changes in ocean currents have seen a greater than usual influx of carbon-rich Pacific water, most likely due to changing ocean patterns that leaves the water 'stuck' in the Arctic. However it happens, though, things don't look good. Computer models suggest that the Arctic Ocean may be ice-free in summers by 2030, and that the entire surface of the Arctic Ocean could have a dearth of aragonite before long. If that happens, the larger Arctic ecosystem might be at risk.