Water Column
The water column extends from the top of the surface to the bottom of the floor, a distance that can be a great as 11km. Exploring it is achieved through a range of techniques, depending on the particular interests of scientists. Those studying marine life may be interested in the food chain and how food and chemicals move through the water layers. Others might investigate the differences in water composition, its temperature and movement. Understanding the water that makes up this environment can be done in many ways using a wide range of instruments.
Properties
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Layers of the water column
The water column is a way of describing the different features found in seawater at different depths. Scientists use these descriptions to classify how deep a section of the ocean is anywhere in the world. Read more about the water column's layers →
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What is in seawater?
To investigate the oceans and the water that forms it, a scientist first needs to understand what makes seawater the way it is. Salt is the obvious difference. Seawater has around 60 times more salt in it than freshwater, but adding salt to freshwater dose not make it seawater. So what else is there? Read more about what makes up seawater →
Profiling
Profiling of the water column is taking a suite of measurements and comparing them against the depth at which the measurement was taken. An instrument package is vertically lowered through the water and then returned to the surface. This gives one profile or vertical line of data through the water column of one point or ‘station’ on the oceans surface. Scientific cruises often take a series of profiles along a line on the ocean surface, which can be joined together to form what is called a section. A section is a two-dimensional plane of data or ‘picture’ through the water column. If a section across an ocean starts and ends close to the coast, then the section is bounded and additional information on the physics of the ocean can be inferred. With many international programmes in operation, there are a large number of sections available to researchers.
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Conductivity Temperature Depth
A large instrument package called a CTD is the standard workhorse of oceanographers for acquiring water column profiles. It is called a CTD because as a minimum it measures electrical Conductivity, Temperature, and Depth (pressure). Read more about the CTD →
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Stand-Alone Pumps
Some trace measurements require so much water that even the 240 litres of water that a trace-metal CTD can obtain is not enough. For large volume trace samples we use a device called a Stand-Alone Pump or SAP. Read more about Stand-Alone Pumps →
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Microstructure Profiling
One disadvantage of the CTD is the ship rolling motion in the waves causes the CTD package to move up and down continuously. As a CTD is quite large, its drag and entrainment of water creates a lot of mixing of fine-scale structure in the water around it and prevents making small scale measurements. To make this type of measurement we use an instrument called a free-fall microstructure or turbulence profiler. Read more about microstructure profiling →
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Towed Undulators
The main problem with CTDs and Turbulence profilers is the time taken to gain one profile thus the number of profiles (usually 50-100 per month), and hence resolution that can be obtained in one section. If high spatial resolution data is required, we can profile whilst the ship is underway using a Towed Undulator. Read more about towed undulators →
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BRIDGET
BRIDGET is a towed vehicle used for chemical and biochemical analysis of seawater down to depths of 5000m. Designed to be as flexible as possible, BRIDGET has a standard suite of instruments for sampling and measuring the plumes from underwater volcanic vents, “Black Smokers”. New sensors can be added, and their data stream incorporated into the BRIDGET record. Read more about BRIDGET →
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Acoustic Doppler Current Profilers
Acoustic Doppler Current Profilers (ADCPs) are type of sonar (SOund Navigation And Ranging) device. They can be fitted either to the hull of a vessel and look down through the water column, fitted to CTDs or other sensors that are lowered down through the water column, or fitted to landers or moorings that sit on the sea bed and look upwards. Read more about ADCP →
