Nansen bottle

A Nansen bottle is a device for obtaining samples of seawater at a specific depth. It was designed in 1894 by the early 19th to 20th-century explorer and oceanographer Fridtjof Nansen and further developed by Shale Niskin in 1910.

The bottle, more precisely a metal or plastic cylinder, is lowered on a cable into the ocean, and when it has reached the required depth, a brass weight called a "messenger" is dropped down the cable. When the weight reaches the bottle, the impact tips the bottle upside down and trips a spring-loaded valve at the end, trapping the water sample inside. The bottle and sample are then retrieved by hauling in the cable.