At first glance, this new NASA image from space has striking similarities to the famous painting “The Great Wave off Kanagawa” by the Japanese painter Katsushika Hokusai. The picture was actually taken by a satellite near the Japanese coast in mid-March.
The picture is of drift ice in the Sea of Okhotsk – a marginal sea in the Pacific that lies north of Japan off the coast of Russia. The white stripes on the satellite image could be mistaken for spray, which is driven by the wind in waves.
But the white waves are thin sea ice that formed before Sakhalin – the largest island in Russia – and is then carried south by the so-called Sakhalin stream. North-west and west winds then pushed the ice to the southeast and east, as the strips show. Some streaks of ice are even carried by the current to the coast of Japan’s second largest island, Hokkaido.
Ice formation is caused by cold west winds that blow across from Eastern Siberia in winter. The fresh water from the Amur River also helps. Its delta lies opposite the northern part of the Sakhalin island. There the river water mixes with the salty sea water. As a result, the water there has a lower salt concentration and also freezes faster.
While in fresh water an ice layer already forms at zero degrees Celsius, the freezing point in saline water is up to 1.9 degrees lower.
The satellite images show that sea ice is not only found in the Arctic. Seasonally thin layers of ice in the sea can also form south of the Arctic Circle. The ice waves are the southernmost foothills of sea ice in the northern hemisphere. In lower latitudes, the temperatures are no longer sufficient for the salt water to freeze.