Sorry for the delay its been manic!!
Today was another busy day. Everything is moving quickly and we are getting everything ready for our first dive. This has been rescheduled for tomorrow (10th January) along with a CTD dip. Now, I have talked a lot about ISIS our ROV. However, I have not said anything about CTD's, so the first part of the blog will look at CTD's. Our CTD will play an equally important role on this cruise.
If you get bored just keep scrolling down to the bottom of the page for the pictures.
My day started early. One of our systems encountered a minor issue during the night and I need to investigate why it stopped logging data. Then one of the ship's computers failed, then a scientists PC started experiencing problems
Ok, we started conducting science today. The ship is equipped with two systems for 3d mapping the seabed. We have been using our deep sea system to map the seabed on the way to South Georgia. The terrain has been very interesting and the data quality has been pretty good making the scientists excited. In addition to our deep sea mapping equipment we have also been running another system that allows us to see the structure of sediment on the seabed known as a Sub Bottom profiler (blush). I will discuss this in more detail in the next few days
We showed the scientist around the ROV container and deck space for a familiarization and safety talk. ROv operations are really interesting. But the majority of scientists have never worked with ROV's before and need to be made aware of the technology and safety precautions.
The next task was to undertake routine maintenance on our meteorological system during which I got thoroughly soaked!
In the evening it was time to relax and we had our units in the bar
 |
"It's been a busy day today and the guys from the ROV team have been getting ISIS ready for my first dive tomorrow. I'm a bit nervous but really looking forward to seeing what lives at the bottom of the sea. Will has been checking the lights on ISIS so that it will light up the seabed when we get to the bottom. The sea here is very deep - about 3000m and no light from the sun reaches the seabed. ISIS must carry some really big lights which we will use like torches to help us investigate what's down there!" |
CTD - Conductivity Temperature Depth
What is it and why do we use it?
A CTD — an acronym for Conductivity, Temperature, and Depth — is the primary tool for determining essential physical properties of sea water. It gives scientists a precise and comprehensive charting of the distribution and variation of water temperature, salinity, and density that helps to understand how the oceans affect life. A CTD has a large number of bottles attached to it which snap close to take water samples. These can be studied and the scientist will be able to see what chemicals the hydrothermal vents pump into the surrounding water. Other sensors will reveal how the heat from the hydrothermal vents disipate
Due to the massive array of equipment mounted on our CTD for JC042 you wouldn't get much change out of £250,000!!.
Above: One of the CTD's similar to the one we will be using,. The grey plastic cylinders are 20LNiskin bottles used to hold water samples. The metal frame is used to protect "the package" from damage. The bottom part of the frame contains the sensors for measuring Conductivity, Temperature and Depth. Our CTD also contains ADCP's (The yellow device at the bottom of the CTD - more about these again) that are used to measure the speed of currents. We also have a Transmissometer, Fluorometer, Altimeter, 10Khz pinger, Homer Beacon....Surround sound system (only joking)
Also visible in the above image are the white "taps" at the bottom of each bottle through which the scientists are able to extract the samples for analysis
Above: A conductivity sensor (top) and a temperature sensor (bottom) located on the CTD's "vain"
Above: Another conductivity and temperature sensor just visible inside the CTD Frame
Some information about Conductivity, Temperature and Depth
|
Conductivity
Uh-oh, is it too early for science?
Conductivity is a measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge). Organic compounds like oil, phenol, alcohol, and sugar do not conduct electrical current very well and therefore have a low conductivity when in water. Conductivity is also affected by temperature: the warmer the water, the higher the conductivity. |
Temperature
Well temperature is not constant throughout the depths of the sea - or water column as we call it. Most of the solar radiation (light and heat fromm the sun) that hits the ocean is absorbed in the first few tens of meters of water. Waves and turbulence mix this heat downward quickly.
The polar seas (high latitude) can be as cold as -2 degrees Celsius (28.4 degrees Fahrenheit) while the Persian Gulf (low latitude) can be as warm as 36 degrees Celsius (96.8 degrees Fahrenheit). The average temperature of the ocean surface waters is about 17 degrees Celsius (62.6 degrees Fahrenheit).
There is a boundary between surface waters of the ocean and deeper layers that are not mixed. The boundary usually begins around 100-400 meters and extends several hundred of meters downward from there.
This boundary region, where there is a rapid decrease of temperature, is called the thermocline. 90 % of the total volume of ocean is found below the thermocline in the deep ocean. Here, temperatures approach 0 degrees Celsius. So even though surface waters can be a comfortable 20 degrees Celsius (good for swimming in!), the majority of our ocean water has a temperature between 0-3 degrees Celsius (32-37.5 degrees Fahrenheit).
The density of ocean water continuously increases with decreasing temperature until the water freezes.
Ocean water, with an average salinity of 35 psu, freezes at -1.94 degrees Celsius (28.5 degrees Fahrenheit).At very high latitudes, ocean water can reach these low temperatures and freeze. Dissolved salts in the water tend to be rejected by the forming ice so that sea ice is only about 1 % salt. An interesting tidbit for those of you interested in survival tactics - because of the lessened amount of salt, melted sea ice would be fit to drink even if sea water is not! Sea ice formation at high latitudes ultimately drives circulation of the deep waters of the ocean.
At the surface of the ocean, temperature measurements are often taken by thermometers placed on buoys. Recently, the Argo program has taken on the task of monitoring the state of ocean surface waters across the globe. The Argo program involves over 3000 - floats that measure salinity and temperature throughout the surface layer of the ocean.
You can visit the argo website:
http://www.argo.ucsd.edu/
Each float is programmed to sink 2,000 meters down, drifting at that depth for about 10 days. The float then makes its way to the surface measuring temperature and salinity the whole time. Data is transmitted to a satellite once the float reaches the surface, so that scientists have access to the state of the ocean within hours of the data collection. Each float lasts 4-5 years.
However, for greater depths in situ measurements are often made with CTD's like ours!
|
Depth
We also measure depth using a pressure sensor. There's a lot more that goes into it..... But I wan't you to carry on reading the blog not fall asleep!! |
So how does our CTD work?
Our shipboard CTD is made up of a set of small probes attached to a large metal rosette wheel or carousel - on our CTD we have a whole suite of scientific sensors in addition to those mentioned for measuring conductivity, temperature and depth above we also have the following sensors:
Transmissometer
How to explain this :-s Ok, Our Transmissometer shines a thin beam of light through the water and a receiver measures how much light arrives at the other end of a set distance. This can be used to study how much suspended sediment is in the water
Above: The Transmissometer is just visible in this image below the grey plastic bottles.
|
Fluorometer
Now this one is a bit more difficult.
A fluorometer or fluorimeter is a device used to measure parameters of fluorescence: its intensity and wavelength distribution of emission spectrum after excitation by a certain spectrum of light.
These parameters are used to identify the presence and the amount of specific molecules in a medium. Modern fluorometers are capable of detecting fluorescent molecule concentrations as low as 1 part per trillion.
Above: Our Fluorometer |
Above: An image showing the sensors and electrical units located in the bottom section of the CTD package when some of the bottles are removed. The yellow device is the ADCP used for measuring currents. The silver device with the black "cap" is a homing beacon - this allows us to locate the CTD on the seabed with a ROV should (God forbid) the wire part. The large cylinder in the centre is a Seabird 911+ which contains the pressure sensor that is used for measuring depth.
The carousel also has a number of large plastic bottles attached to it - these are called Niskin bottles and there are 24 (20L) bottles on our CTD. These bottles are used to trap water samples that can then be analyzed to determine the properties of the water at different depths.
The carousel is lowered on a cable down to a position just above the seafloor, and scientists observe the water properties from the scientific sensors in real time via a conducting cable connecting the CTD to a computer on the ship.
However, the water in the bottles must be returned to the ship for analysis.
A remotely operated device allows the water bottles to be closed selectively as the instrument ascends. A standard CTD cast, depending on water depth, requires two to five hours to collect a complete set of data. Water sampling is often done at specific depths so scientists can learn the physical properties of the water column are at that particular place and time.
Above: Each bottle lid is connected via a strong line to a round mechanical "firing" device. This device is controlled by a computer on the ship via the CTD cable. When the CTD operator fires a bottle e.g. bottle 3 - the corresponding trigger for bottle three "lets go" of the wire. This release tension on the lids which are spring loaded - causing them to snap closed.
 
Above: These two images show the top and bottom lids/plugs used to seal the bottles. In the left image you can see the snug fit that each plug has. In the right image you can see the springs that cause the plugs to snap shut when tension is released from the "firing mechanism"
Above: A CTD ready for deployment. These bottles are cocked in the open position. You can see in this image that each bottle has a number printed on it. As a bottle is "Fired" from the control computer onboard the ship , the operator makes a note of the bottle number and the depth it was fired at. This allows the scientists to cross reference the sample with a positon in the water column - E.g. bottle 3 - 3200m.
Above: The CTD control computer in the main lab (RRS Discovery). The operator can "fire" the bottles from here and monitor the realtime data from the sensors,
Deploying the CTD
There a lots of ways to deploy CTD's. Most oceanographic institutes have different ways depending on the size of the CTD and the ship involved. Both RRS Discovery and RRS James Cook have a device called a Parallelogram that makes deploying CTD's a lot easier.
The RRS James Cook has a special adaptation to this system specifically for deploying CTD's called a Hydro Boom. The Hydro Boom allows the CTD to be moved from the CTD hangar to a position over the starboard side of the ship where it can be deployed. The system also acts in reverse - recovering the CTD and then placing it back inside the CTD lab where the scientists can extract samples from the Niskin bottles and data from the sensors can be downloaded.
Above: RRS James Cook's Parallelogram in the retracted position. The Hydro Boom is visible just in front of the shutter doors. The Hydro Boom serves as a common overboarding support structure for CTD cables. The Hydro Boom is located amidships on the starboard side, the area of least ship motion.
Above: The Hydro Boom being used to deploy the CTD
Above: The Hydro Boom on Maria S. Merian
Above: RRS Discovery deploying a CTD using the Parallelogram
|
Above: Albatross
