Drift Ice
Drift ice is more than just simple frozen seawater. It carries with it to Hokkaido an abundant amount of plankton, contributing to the continuation of rare wildlife species and the maintenance of Shiretoko ecosystems.
Sea of Okhotsk drift ice that reaches Hokkaido is said to originate in seawater originally from the Amur River, and thus containing less salt. It approaches Hokkaido from late January to February, covering some 80% of the sea surface by the middle of March, and when the drift ice moves away from the shore from March to April, a “clearing of the ice” is declared.
The ABC's of Drift Ice
Drift ice is 40 - 50 centimeters thick off the coast of Hokkaido, 150 centimeters in the northern Sea of Okhotsk and 2 meters thick in northern Alaska, one of the coldest regions on the globe. The ice moves at a speed of 1 - 2 kilometers per hour. The drift ice is not perfectly solid ice. When seawater freezes, it is only the fresh water that freezes; the remaining saline element is concentrated and confined in the ice, which is called a brine, or concentrated saline cell. Because of this high salt concentration however, the temperature at which the brine completely solidifies is -54℃. Such low temperatures are impossible in the natural world, so the seawater / drift ice always contains liquid brine to some extent.
Nutrient Rich Drift Ice
The Sea of Okhotsk is the southernmost ocean on earth where drift ice is observable, and is relatively shallow and suitable for the growth of marine animals. Soil containing a large volume of freshwater and nutrients flows out from the Amur River and enriches the seawater, making the Sea of Okhotsk an everlasting repository of fish and other marine animals. Certain species of seals living in the Sea of Okhotsk raise their offspring on the drift ice as it is relatively free from natural predators. White-tailed eagles and other birds, as well as northern red foxes, also come from Siberia to eastern Hokkaido on the drift ice. Phytoplankton attached to drift ice suddenly multiplies in spring. Although clione and other predators of animal plankton exist in large numbers under the drift ice, the plankton can increase their population by feeding on phytoplankton, and thereby enriching the fishing grounds of the Sea of Okhotsk.
Drift Ice Sightseeing
In Monbetsu, visitors can observe the drift ice aboard the Garinko-go, an ice-breaker used as a cruise ship. The Ryuhhyoh Norokkko-go train operates along JR Hokkaido's Senmo Line, enabling passengers to enjoy a leisurely journey while admiring the panoramic view of the drift ice covered Sea of Okhotsk from the train's windows. As well, the Town of Shari and other Hokkaido municipalities situated along the coast of the Sea of Okhotsk organize a number of events such as Drift Ice Walking and Drift Ice Diving.