Sea ice is formed directly from seawater, and thus melting will not raise sea level. However, loss of sea ice will have major consequences on global climate, overall ocean health, and polar ecosystems.
Global Importance of Sea Ice
Sea ice is frozen seawater. It forms when air temperatures plummet in the autumn and winter at both poles. Sea ice floats on the ocean’s surface and rarely exceeds three meters in thickness. Sea ice forms both in the Arctic and the Antarctic, and while sea ice covers a small fraction of the ocean’s surface, its impact is global. Sea ice’s bright, white surface reflects sunlight back to space and impacts global temperatures. Sea ice formation also drops salt into the ocean water below it, helping drive global ocean currents that move heat, nutrients, and dissolved gases like O2 and CO2 around the planet.
Antarctic Sea Ice
The quantity of Antarctic sea ice changes dramatically over the seasons. In February, at the end of the Antarctic summer, sea ice covers only 2.5 million square kilometers. It then expands throughout the dark, cold winter months to cover about 18.5 million square kilometers by September – an area nearly twice the size of the United States. It starts to melt again as temperatures rise throughout the spring and summer.
Sea Ice and the Antarctic Ecosystem
Sea ice is a fundamental component of the Antarctic ecosystem. Melting sea ice releases nutrients to the ocean as well as allows sunlight to reach the ocean surface. As a result, huge blooms of microscopic plants — phytoplankton — grow in the Antarctic summer. Sea ice also provides habitat and shelter for krill and fish to hide from predators. Larger predators like seals and penguins rely on sea ice in numerous ways, such as resting platforms while foraging for food, and breeding habitat.
Changes in Sea Ice
As the planet warms, annual sea ice is decreasing at both poles. The Arctic has been experiencing dramatic year-over-year losses of sea ice for decades. The trend in the Antarctic is more complex.
Since 1979, when we first had satellite data, the winter sea ice area in Antarctica was actually increasing overall until 2016, though there were large differences in regional sea ice trends. Some areas, like the Ross Sea, gained sea ice during that time, while the Antarctic Peninsula started experiencing losses in the 1990s.
In 2016, Antarctic sea ice seems to have crossed a critical threshold, and since then we have seen losses of sea ice in nearly every region around the continent, leading to multiple record minimum extents. Recent research has led to a better understanding of what drives the sea ice system. It is crucial that we expand sea ice science, as it is so critically important to the entire globe.
