Now for a change from looking at the mud, time to explore the cleanest places on board the Pelagia. The cruise is focusing on measuring iron within the water column and sediments. Iron concentration within sediments is very high (mille molar-to-1%). However, within the water column the range of concentration of iron is pico-to-nano molar concentration – similar to finding a needle in 1 billion pieces of hay. Because of the large differences between these two environments, we have to be extra careful when working with the water on the ship. One of the ways that we use to make clean measurements is by wearing special clothing to avoid contact with iron-plentiful materials. Our special clothes look at lot like we are working in a bakery including the hair nets. We are very fashionable!
Watching water drip in our special clothes with the CTD rosette bottles
On this cruise, we are using an ultra clean CTD rosette that was specially made by NIOZ technicians for low concentration sampling. An ultra clean setup is essential when measuring concentrations that are very low (which is the case for most metals in open ocean seawater). Within a traditional CTD rosette, copper wires along with some other metal parts will cause contamination of the waters that are being collected. For copper and those other metals, we cannot get accurate measurements of the concentration because the seawater is in contact with the metal.
On this cruise, we are using an ultra clean CTD rosette that was specially made by NIOZ technicians for low concentration sampling. An ultra clean setup is essential when measuring concentrations that are very low (which is the case for most metals in open ocean seawater). Within a traditional CTD rosette, copper wires along with some other metal parts will cause contamination of the waters that are being collected. For copper and those other metals, we cannot get accurate measurements of the concentration because the seawater is in contact with the metal.
Here is a traditional CTD, notice how dirty it looks compared to the other photo below of the ultra clean CTD.
A CTD measures Conductivity (salinity), Temperature, and Depth. Surrounding the sensors of the CTD is 24 large bottles. These bottles are used to collect water from specific depths and are made of Teflon (for the ultra clean). When it is deployed, it is hoisted with a Kevlar (plastic like substance; it is also used for bulletproof vests) cable and is monitored as it descends towards the bottom of the sea. When it nears the bottom (about 10m above), we start to collect samples. Based on the features we are trying to capture, we will fill up the bottles with certain depths of water. After a few hours (for a deep station) the CTD rosette arrives back on board the crew help move this very heavy instrument into a container where we will sample it.
A CTD measures Conductivity (salinity), Temperature, and Depth. Surrounding the sensors of the CTD is 24 large bottles. These bottles are used to collect water from specific depths and are made of Teflon (for the ultra clean). When it is deployed, it is hoisted with a Kevlar (plastic like substance; it is also used for bulletproof vests) cable and is monitored as it descends towards the bottom of the sea. When it nears the bottom (about 10m above), we start to collect samples. Based on the features we are trying to capture, we will fill up the bottles with certain depths of water. After a few hours (for a deep station) the CTD rosette arrives back on board the crew help move this very heavy instrument into a container where we will sample it.
The crew is very helpful in moving the CTD around on deck and also in getting it in and out of the water. Each bottle can hold 24L of water, thus it is a heavy instrument that needs many people to move it around.
Inside the container, we first enter into the little hallway that connects the clean area holding the CTD to the deck of the ship. In this hallway, we put on our suits, hats, and a pair of clean rubber shoes- it gets very wet inside. We then go into the clean area and wash down the floors, bench, and walls to remove any dirt from the space. We are now ready to sample!
Inside the container, we first enter into the little hallway that connects the clean area holding the CTD to the deck of the ship. In this hallway, we put on our suits, hats, and a pair of clean rubber shoes- it gets very wet inside. We then go into the clean area and wash down the floors, bench, and walls to remove any dirt from the space. We are now ready to sample!
Here is a view of the container that we keep the CTD in. There is a plexiglass door that helps to keep the inner area protected from contamination.