File:The Icy Heart of the North Pacific (MODIS 2021-03-09).jpg

English: The Sea of Okhotsk, wedged between Russia’s Kamchatka Peninsula and the Siberian mainland, has been called the “heart of the North Pacific Ocean”, thanks to the powerful circulation driven by freeze-up of the waters each winter. As salty seawater freezes, the ice that forms on top contains very little salt, while the water underneath becomes increasingly saline. This is particularly true in the Sea of Okhotsk, where dense freezing is encouraged by the inflow of fresh water from Siberia’s Amur River. Each winter, a thick layer of sea ice forms over the Sea of Okhotsk, creating an extremely saline layer underneath. This saline water is very dense and cold—and it is also rich in minerals, oxygen, and other nutrients which are expelled as water freezes into its crystalline form (ice). Cold, dense (i.e., salty) water sinks and creates a powerful circulatory flow known as “thermohaline circulation”. Water flows from the Sea of Okhotsk, first to the east where it feeds to Sakhalin Current and then northward where it pumps into the Oyashio Current. On March 7, 2021, the Moderate Resolution Imaging Spectroradiometer (MODIS) on board NASA’s Aqua satellite acquired a true-color image of the ice-covered Sea of Okhotsk. Looking much like a frigid heart, the bright white frozen water is surrounded by the Russian mainland, Sakhalin Island (south) and the Kamchatka Peninsula (east). Dense clouds, pushed into long parallel rows that align with the prevailing wind, nearly obscure Sakhalin Island and the waters of the Pacific Ocean from view. This cloud pattern, called “cloud streets”, often forms when very cold, dry air is pushed over relatively warmer, moist air.