A Nansen bottle is a device for obtaining samples of seawater

Seawater

Seawater is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% . This means that every kilogram of seawater has approximately of dissolved salts . The average density of seawater at the ocean surface is 1.025 g/ml...

 at a specific depth. It was designed in 1910 by the early 20th-century explorer and oceanographer Fridtjof Nansen

Fridtjof Nansen

Fridtjof Wedel-Jarlsberg Nansen was a Norwegian explorer, scientist, diplomat, humanitarian and Nobel Peace Prize laureate. In his youth a champion skier and ice skater, he led the team that made the first crossing of the Greenland interior in 1888, and won international fame after reaching a...

 and further developed by Shale Niskin

Shale Niskin

Shale Niskin was the inventor of the Niskin bottle, a device used for collecting water samples. He also founded General Oceanics, Inc., in 1966 and served as the company's first president. General Oceanics, based in North Miami, Florida, manufactures oceanographic and environmental monitoring...

.

The bottle, more precisely a metal or plastic cylinder, is lowered on a cable into the ocean

Ocean

An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

, 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

Valve

A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

 at the end, trapping the water sample inside. The bottle and sample are then retrieved by hauling in the cable.

A second messenger can be arranged to be released by the inverting mechanism, and slide down the cable until it reaches another Nansen bottle. By fixing a sequence of bottles and messengers at intervals along the cable, a series of samples at increasing depth can be taken.

The sea temperature

Temperature

Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 at the water sampling depth is recorded by means of a reversing thermometer

Reversing thermometer

Unlike most conventional mercury thermometers, a reversing thermometer is able to record a given temperature to be viewed at a later time. If the thermometer is flipped upside down, the current temperature will be shown until it is turned upright again...

 fixed to the Nansen bottle. This is a mercury thermometer

Thermometer

Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...

 with a constriction in its capillary tube which, when the thermometer is inverted, causes the thread to break and trap the mercury, fixing the temperature reading. Since water pressure

Pressure

Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 at depth will compress the thermometer walls and affect the indicated temperature, the thermometer is protected by a rigid enclosure. A non-protected thermometer is paired with the protected one, and comparison of the two temperature readings allows both temperature and pressure at the sampling point to be determined.

The Nansen bottle has largely been superseded by the Niskin bottle and now is no longer under manufacture, though it still sees use.

Niskin bottle

The Niskin bottle is a development of the Nansen bottle patented by Shale Niskin

Shale Niskin

Shale Niskin was the inventor of the Niskin bottle, a device used for collecting water samples. He also founded General Oceanics, Inc., in 1966 and served as the company's first president. General Oceanics, based in North Miami, Florida, manufactures oceanographic and environmental monitoring...

 in March 1966. Instead of a metal bottle sealed at one end, the 'bottle' is a tube, usually plastic to minimize contamination of the sample, and open to the water at both ends. Each end is equipped with a cap which is either spring-loaded or tensioned by an elastic

Elastomer

An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...

 rope. The action of the messenger weight is to trip both caps shut and seal the tube.
A reversing thermometer may also be carried on a frame fixed to the Niskin bottle. Since there is no rotation of the bottle to fix the temperature measurement, the thermometer has a separate spring-loaded rotating mechanism of its own tripped by the messenger weight.

A modern variation of the Niskin bottle uses actuated

Actuator

An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...

 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

Rosette

-People:* Rosette , a French actress* Rosette Bir , a French sculptor* Clinton Rosette , a prominent citizen of DeKalb, Illinois...

. As many as 36 bottles may be mounted on a single rosette.

Thermistor

Thermistor

A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor...

temperature sensors are more commonly employed on Niskin bottle rosettes due to their higher accuracy compared to mercury thermometers.