Sea Ice
node · earth · Both polar oceans
Frozen seawater, which is a different substance from the glacial ice of an ice sheet: it forms at the ocean surface at about -1.8 degrees Celsius, expels most of its salt as it freezes, and floats because it is already part of the ocean, so its melting does not by itself raise sea level. It is not a lid but a habitat with structure - a brine-channel network inside the ice supports algae, the underside is a grazing surface, the top carries snow that animals dig into, and the leads and cracks are breathing and hunting geometry. The Arctic and Antarctic ice behave differently in kind: Arctic ice is confined by land and can survive several summers, so a substantial multi-year component once existed, while Antarctic ice is unbounded to the north, spreads freely each winter and almost entirely melts away each summer. Continuous satellite passive-microwave monitoring of both since the late 1970s is the reason the two hemispheres can be compared at all.
Read in · 1
Evidence · 1
Timeline
No dated observations are stored for this object. Atlas shows what was observed and when — it does not infer a history.
Connections · 0
Assembled narrative · 1
Assembled from 20 blocks · 1 evidence · 19 related
- Story
- Frozen seawater, which is a different substance from the glacial ice of an ice sheet: it forms at the ocean surface at about -1.8 degrees Celsius, expels most of its salt as it freezes, and floats because it is already part of the ocean, so its melting does not by itself raise sea level. It is not a lid but a habitat with structure - a brine-channel network inside the ice supports algae, the underside is a grazing surface, the top carries snow that animals dig into, and the leads and cracks are breathing and hunting geometry. The Arctic and Antarctic ice behave differently in kind: Arctic ice is confined by land and can survive several summers, so a substantial multi-year component once existed, while Antarctic ice is unbounded to the north, spreads freely each winter and almost entirely melts away each summer. Continuous satellite passive-microwave monitoring of both since the late 1970s is the reason the two hemispheres can be compared at all.
- Knowledge
- Sea Ice
- Connections
- Polynya
- Arctic Amplification
- Antarctic Krill (Euphausia superba)
- Polar Bear (Ursus maritimus)
- Emperor Penguin (Aptenodytes forsteri)
- Halley Bay Emperor Penguin Colony
- The continuous satellite sea-ice record begins
- A long-term decline in krill density is linked to winter sea ice
- The Arctic summer minimum drops far below anything previously observed
- The lowest Arctic sea-ice extent in the satellite record
- The Halley Bay emperor colony fails and does not recover
- The emperor penguin is listed as threatened under the US Endangered Species Act
- Antarctic sea ice reaches a record low, a year after the previous one
- Evidence
- A continuous, consistently processed record of sea-ice extent in both hemispheres exists from 1979, from which the Arctic September minima of 2007 (approximately 4.2 million km2) and 2012 (approximately 3.4 million km2) and the Antarctic February minima of 2022 and 2023 (the first below 2 million km2 in the record, and lower again the following year) are drawn. V55 VERIFICATION BASIS: nsidc.org was probed during production and refused by the network egress proxy, and the WebSearch budget was exhausted. EVERY NUMERIC VALUE IN THIS RECORD IS APPROXIMATE AND UNCHECKED, given to one or two significant figures for that reason. A curator must replace them with values read from the Sea Ice Index before publication.
Observed changes · 0
No public Signals are attached to this object. Signals show what changed and when it was observed — never a direction or a rank.
Actions
/atlas?object=PHENOMENON_SEA_ICE&experience=PHENOMENON_SEA_ICE