By reducing the uncertainty in the amount of ice, scientists can be more certain that changes over time are real.īeyond measuring ice coverage, satellites can also help scientists get a better handle on thickness. When scientists are analyzing satellite data, it is easier to say whether there is or isn’t at least 15 percent ice cover in a pixel than it is to say, for example, whether the ice cover is 70 percent or 75 percent. ![]() The threshold–based approach may seem less accurate, but it has the advantage of being more consistent. The Advanced Microwave Scanning Radiometer–for EOS (AMSR-E) on NASA’s Aqua satellite also contributed data (2002-2011), a record that was extended with the 2012 launch of the Advanced Microwave Scanning Radiometer 2 (AMSR2) on JAXA’s GCOM-W1 satellite. ![]() The continuous sea ice record began with the Scanning Multichannel Microwave Radiometer (SMMR) on the Nimbus-7 satellite (1978-1987) and continued with the Special Sensor Microwave/Imager (SSM/I) and the Special Sensor Microwave Imager Sounder (SSMIS) on Defense Meteorological Satellite Program (DMSP) satellites (1987 to present). This means it can be measured year-round, even through the long polar night. Unlike visible light, the microwave energy radiated by ice passes through clouds. ![]() Valuable data are collected by satellite sensors that observe the microwaves emitted by the ice surface. Since 1979, a collection of satellites has provided a continuous, nearly complete record of Earth’s sea ice cover. Currently, only the satellite record is considered sufficiently reliable for studying Antarctic sea ice trends. Since phytoplankton grow most abundantly along the edges of the ice, the concentration of sulfur-containing compounds has been proposed as an indicator of how far the ice edge extended from the continent. Because whales tend to congregate and feed near the sea ice edge, their locations could be a proxy for ice extent.Ī second proxy is the detection of phytoplankton-derived organic compounds in Antarctic ice cores. One reference is the records kept by Antarctic whalers since the 1930s, which document the location of all whales caught. To extend the historical record of Southern Hemisphere sea ice back in time, scientists have been investigating two types of proxies. In the Antarctic, data prior to the satellite era are even more sparse. These pancakes slide over each other to form smooth rafts, or they collide into each other, creating ridges on the surface and keels on the bottom. In rough seas, ice crystals converge into slushy pancakes. These wafer-thin sheets of ice slide over each other and form rafts of thicker ice. In calm seas, the crystals form thin sheets of ice, nilas, so smooth that they have an oily or greasy appearance. How the crystals coalesce into larger masses of ice depends on whether the seas are calm or rough. When seawater begins to freeze, it forms tiny crystals just millimeters wide called frazil. Melting sea ice won’t raise ocean levels any more than melting ice cubes will cause a glass of ice water to overflow. Because it is already floating in the ocean, sea ice is already displacing its own weight. Over several years, this positive feedback cycle (the ice-albedo feedback) can influence global climate.Ĭontrary to some public misconceptions, sea ice does not influence sea level. The sun-warmed water then melts more ice. As more ice melts and exposes more dark water, the water absorbs more sunlight. (In scientific terms, ice has a high albedo.) Once sea ice begins to melt, a self-reinforcing cycle often begins. The white surface reflects far more sunlight back to space than ocean water does. The influence of sea ice on the Earth is not just regional it’s global. The ice itself is habitat for animals such as seals, Arctic foxes, polar bears, and penguins. When ice freezes, the underlying water gets saltier and sinks, mixing the water column and bringing nutrients to the surface. As the ice melts, it exposes ocean water to sunlight, spurring photosynthesis in phytoplankton. When the ice melts in the summer, it releases nutrients into the water, stimulating the growth of phytoplankton, the center of the marine food web. ![]() Sea ice also plays a fundamental role in polar ecosystems. As a result, the weather over ice-covered areas tends to be colder and drier than it would be without ice. Sea ice also creates an insulating cap across the ocean surface, which reduces evaporation and heat loss to the atmosphere. The sea ice layer also restricts wind and wave action near coastlines, lessening coastal erosion and protecting ice shelves. This cold, salty water is dense and can sink to the ocean floor, where it flows back toward the equator. As ice crystals form at the ocean surface, they expel salt, which increases the salinity of the underlying waters.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |