Nansen bottle

A heavily-weighted cable is lowered from a ship and multiple bottles are attached at calculated intervals in order to place them at specific depths.

[1] The sea temperature at the water sampling depth is recorded by means of a reversing thermometer fixed to the Nansen bottle.

A modern variation of the Niskin bottle uses actuated valves that may be either preset to trip at a specific depth detected by a pressure switch, or remotely controlled to do so via an electrical signal sent from the surface.

This arrangement conveniently allows for a large number of Niskin bottles to be mounted together in a circular frame termed a rosette.

Thermistor temperature sensors are more commonly employed on Niskin bottle as they are more accurate than mercury thermometers.