noun
surface water; upper layer water
Oceanographic term for water from the surface down to about 200 meters depth.
上層水の温度は季節によって大きく変わる。
The temperature of surface water changes greatly with the seasons.
深層水 refers to deep ocean water, typically below 200 meters, contrasting with 上層水.
Compound of 上層 (upper layer) + 水 (water). A straightforward technical term.