Let me introduce you to the Rosette, the apparatus that we use for sampling the ocean waters at different depths. The idea is pretty simple, the design is elegant.
Sam and Eric preparing the rosette for a deployment
The idea is to submerge an open plastic bottle to the desired depth, close it to trap a certain volume of water, and then bring it up to the boat where we can analyze its contents. The plastic bottles look more like pieces of tube than regular bottles. In fact, they are made out of standard PVC pipes at Scripps Institution of Oceanography. The good thing about the PVC is that it does not react with the water, so it does not add or remove chemicals that we would like to measure.
The pipe shape allows the water to freely flow through the bottles as they are lowered, making sure that they only contain water of the right depth when we close them. The bottles close on both ends with plastic caps that have a handle, which makes them look like a hat. We number the bottle so we know which one corresponds to which depth. The picture below shows the bottles open; it is easier to see the bottom caps than the upper ones.
Bottles made out of PVC pipe with 10 liter capacity
We are using a huge rosette on this trip; 36 bottles with 10 liters capacity each. The bottles are attached to a metal frame that has an inner circle and on outer one. The picture below shows a view of the top of the rosette when all the bottles are open.
View of the top of the rosette.
The question is, how do we close them? How are they kept open? The natural state of the bottles would be to stay closed because both caps are connected to each other with a spring.
A spring that connects both caps tries to close the bottle
They are kept open by fishing lines that are tied to little hooks at the center of the rosette (see picture). The white plastic beads are there to make it easier to place the lines in the hooks.
The center of the rosette, called the carousel, controls the closing of the bottles
Once the rosette has reached a desired depth, someone aboard presses a button on the computer. A signal is sent to the center of the rosette, one of the hooks moves releasing the corresponding line, and a bottle closes in a snap. Water has been trapped. The following picture is a view form below the rosette. You can see the nylon lines going from the cpas to the center of the rosette.
A view of the rosette from below. You can see the carrousel holding the nylon lines that keep the rosette open.
Part of the job of the scientists is to decide at which depth will each bottle be triggered. At the end, we have up to 36 bottles with water of different depths. Once the bottles reach the deck, samplers will empty them a little bit at a time. I will write about this process in another entry. Let's think what do we need the bottles to have in order to be sampled.
We find a spigot at the bottom of the bottle. It opens when you push it in. There is a valve at the top of each bottle to let the air in as the water goes out. If one forgets to open the valve, water stops flowing.
Spigot through from which water will be sampled
The valve allows air to go into the bottle as the water is drained
We also attach other instruments to the rosette. In the center we add an instrument that measure the salinity (by measuring the electrical conductivity of water), the temperature of the water, and the depth (by means of the pressure). This is the CTD (conductivity, temperature, depth). We also have an instrument that measure the currents above and below the rosette. The instrument works similar to a policemen's radar gun. We call it the ADCP (Acoustic Doppler Current Profiler).
The Acoustic Doppler Current Profiler (ADCP) orange on the left, and the Conductivity (salinity), Temperature and Depth (pressure) CTD on the right.
I will explain these instruments with more detail later. For the moment I will say that the CTD needs to have its sensors on fresh water when not in operation to avoid the formation of salt crystals in the sensors, so we put a syringe with fresh water on them, and the ADCP needs to be connected to power.
Syringes that keep fresh water on the CTD sensor to avoid salt crystals
We brought a spare rosette for the trip. Imagine we loose one, which has happened before, and we find ourselves in the middle of the ocean with nothing to do. A very large waste of money! Less expensive on the long run to bring a spare.
We brought a spare rosette in case we loose one to the depths of the Southern Seas.
We also have a smaller rosette that we use for measuring trace metals. This rosette does not have any metal part exposed to the water so we can measure accurately the metals that are dissolved on it. Here is our trace metal rosette before being deployed on a snowy day. We had to cover the top of the bottles with plastic so the snow would not contaminate our samples. The plastic was removed just before deployment.
A smaller rosette fro measuring trace metals. It has not metal surface that would be in contact with the water.
I did not follow JIm's advice while writing this entry. He said that readers like you ant to see people and not the equipment. My apologies to you. I will go over the deployment on the next entry.
By the way, if yo are keeping track of our position you might have realized we have not moved much. We have been inside a stubborn storm for the past two days that has stopped all sampling procedures. I have spent most of the day on bed avoiding getting sea sick. Most other people seem fine; I am not a good sailor...