sea ice
Refers to frozen seawater, typically in polar regions. A technical and general term.
北極海の海氷が年々減少している。
The sea ice in the Arctic Ocean is decreasing year by year.
海氷の厚さを測る
A survey was conducted to measure the thickness of the sea ice.
Compound of 海 (sea) and 氷 (ice). The reading is on'yomi for both characters.