Short answer
Sea ice forms when ocean water freezes in place. An iceberg is a chunk of land ice that has broken from a glacier or ice shelf and now floats. Both may be seen in polar seas, but only the iceberg began as accumulated snowfall on land. 1 2
Both float in the sea, but their origins differ: frozen seawater versus calved land ice.
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At a glance
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| Question | Sea ice | Iceberg |
|---|---|---|
| Origin | Frozen seawater | Calved land ice |
| Typical form | Sheets and floes | Floating block or mass |
| Connection to glacier | None required | Direct land-ice origin |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Sea ice. Ice formed by freezing seawater at the ocean surface. 1
Iceberg. A floating piece of land-origin ice that broke from a glacier or ice shelf. 2
Key differences
Origin is a more reliable distinction than shape. Sea ice expands and contracts seasonally over ocean water. An iceberg may drift among sea-ice floes, but its glacier origin remains different. The two also differ in their role in sea-level accounting because land ice added to the ocean introduces new water. 1 2
How to tell them apart
If a floating patch formed from freezing seawater, call it sea ice. If it broke from a glacier or ice shelf, call it an iceberg. A photograph alone may be ambiguous; location, structure and observational context help establish origin. 1 2
Where they overlap
Both are frozen water floating in the ocean and can hinder navigation. Both can melt or drift and coexist in the same polar waters. 1 2
Edge cases
An ice shelf is floating but remains attached to a land ice mass; a piece that calves away can become an iceberg. Broken sea-ice floes may be thick and imposing without becoming icebergs. 1 2
Why the distinction exists
Scientists distinguish the two to track ocean-surface freezing separately from loss of land ice. Their causes and climate implications are different. 1 2
Common misconceptions
An iceberg is not simply a giant piece of sea ice, and sea ice is not a miniature glacier. 1 2
Examples
Winter freezing makes a sheet of Arctic sea ice. A block breaking from Greenland’s glacial margin and drifting offshore is an iceberg. 1 2
Sources
Sources checked October 3, 2026.
- National Snow and Ice Data Center — Quick Facts About Sea Ice. What is sea ice?.
- National Snow and Ice Data Center — Glacier Quick Facts. What is a glacier?; What is an iceberg?.