Niskin

Niskin, or Niskin bottle, is a water sampling device used in oceanography to collect precise depth samples during CTD rosette deployments. Named for its inventor, the bottle is designed to trap seawater at a chosen depth without significant upwelling or mixing during retrieval.

Designed as a cylindrical container, typically stainless steel or plastic, with a pair of removable end caps sealed by O-rings. Each end cap is connected to a closing mechanism that is normally kept open and is triggered by a messenger line or by an electronic trigger. When the line passes, the end caps open to allow water to enter or exit. On retrieval, the caps close, sealing the sample.

In practice, the bottle is lowered to a target depth; a line or electronic signal triggers opening of the end caps; while the ship moves, the bottle fills with water from that depth. As the messenger passes, the caps close, preserving a discrete depth water sample for later analysis.

Niskin bottles are widely used on CTD rosettes and during hydrographic surveys to collect samples for salinity, dissolved oxygen, nutrients, carbon isotopes, and other chemical analyses. They may be deployed in arrays with multiple bottles to sample across depths, and variants exist, including Go-Flow versions that aim to minimize contamination and sample exchange during descent and ascent.