I have been visiting the trace metal lab and I am ready to report more about how they work on the ship. The way this team works is very different from the way people working on the main rosette do. If you read the journal of the 21st of March, you might remember the following about trace metals:
Trace metals are metals that are dissolved in water at en extremely low concentration (a billionth of a gram in a liter of water)
Phytoplankton, the marine plant-like organisms that float on the surface of the water and obtain their energy from the sun through photosynthesis, need those metals to survive like we need vitamins.
There are parts in the surface of the worlds oceans in which phytoplankton is not abundant even when there is enough sun and nutrients. This areas do not have enough trace metals, particularly iron, for sustaining large phytoplankton populations.
The trace metals team is creating an inventory of the trace metals in the world's surface waters.
The biggest difference between the trace metal rosette and the main rosette is that the trace metals measures properties that have nearby sources of those properties that could pollute the samples. Most everything around the ship is made of metals, at a time when we are trying to measure the same metals at very small concentrations.
The main rosette does not have nearby sources that could pollute the samples, so we do not need to be as careful about pollution in this case, even though we do measure some parameters at even lower concentrations than trace metals (CFC and SF6, for example).
The design of the trace metals rosette attempts to minimize the amount of metals that are exposed to the water. It has a plastic coating on the frame and on the heavy weights that make it sink. It uses a special oceanographic cable made out of kevlar, a plastic compound so strong that it is used in bullet proof vests, covered in nylon. It does have electrical cables buried in it, but no metal is exposed. The main rosette's cable is made of steel with the electrical wires inside. There are a few stainless steel clamps here and there, but it is metal free fro the most part.
The bottles in this rosette, based in the same principle, are slightly different from the main ones. The biggest difference I could see is that the caps (valves in this case) can be kept covered with plastic shower caps when not in the water. This is done to prevent dust and smog from the ship's exhaust from entering the bottle. The group also covers the spigots with disposable gloves.
The trace metal group uses a special rosette and cable to minimize exposing the water to metals
The rosette has less bottles than the main one because the CLIVAR program is mainly a physical oceanography program and not a chemical oceanography one. As a result, the trace metals group was funded to have an hour of ship time for every degree in the ocean (degree in latitude and longitude). They could have sent a rosette down at the bottom at around 4000 m, like the main rosette does at every station, only once every four stations. Instead, they decided to send it at 1000 every other station to get more spatial coverage, and also because trace elements change the most in the upper 200m. The four member team does not work in watches as a result of this schedule. They work whenever it is time for a trace metal cast, even at odd hours of the night.
Another big difference is that the main rosette is stopped at the target depth for collecting water for 30 seconds (or two ship rolls) before closing the bottle to allow the sensors in the rosette to equilibrate, and so the inside of the bottle gets 'washed' by the water. The trace metals team has a different approach. They slow down the winch as they approach to the target depth and then 'trip the bottle on the fly'. They do not stop the rosette to avoid sampling any water that comes in contact with the frame and sensors of the rosette.
Dr. Chris Measures, from the University of Hawaii, and Dr. Bill Landing, form Florida State University, pioneered this method for trace metal sampling. Most previous analysis where done by attaching single bottles at different parts of the cable and then sending by the cable a heavy plastic piece that would close them. Chris says they were not the first ones to use a rosette, but the first ones to show that the 'tripping on the fly' works well. This method reduces the amount of time required for sampling and increases the number of depths at which they can sample. A new very large program for measuring trace metals, called Geotraces, has already started based on the results that Chris and Bill have gotten on other CLIVAR cruises. The new program is designed to sample more trace metals all the way to the bottom (on this cruise they are only sampling for iron, aluminum, and manganese in every cast, and mercury in a few casts).
The differences do not stop there. The care that the trace metal teams takes so no water droplet gets into the bottles might seem paranoiac to a physical oceanographer. Once the rosette arrives from its journey through the deep water, the bottles are removed from the frame and placed on their lab, which is a container on deck instead of a lab inside the ship.
Rosette bottles carried into trace metal vans after sampling. Having a van on deck helps keep the lab space free of metal pollutants.
By having a van, as they call it, they are able to keep it extremely clean of dust. It has an air conditioner with a great filter that blows air in. The rosette valves and spigots are then washed with ultra clean water, and sampling begins. They first sample for salinity and nutrients to be used as reference with the main rosette's salinity and nutrients. Sometimes they sample for mercury in regular looking plastic bottles that are no regular bottles. They are designed to not react with mercury and cost $100 each.
Sampling for mercury form the trace metal rosette on what appear to be regular plastic bottles. They are special bottles so they do not react with mercury and each costs $100
After they are done with mercury sampling they connect an air compressor to the valve of each bottle, and a filter to each spigot. The filter traps the phytoplankton and large bacteria. They collect water samples from the filtered water. This are the samples that are used for measuring the amount of trace metals dissolved in the water.
Dr. Hugo Oliveira samples for trace metals from the rosette after the water is filtered on the blue cartridges
The filters will also be analyzed for measuring the trace metals in the phytoplankton and bacteria. They are removed from their filter cartridge (the blue plastic), and rinsed with distilled water and a little bit of ammonia. The ammonia is added to prevent the metals from dissolving back in the water by increasing the pH. The filters will be analyzed back on land.
I made a 25 minutes video on the whole process that I will place here once we get on land. Meanwhile, here is the four member trace metal team at the ice party. From right to left, Brian Kilgore and Dr. Bill Landing both from Florida State University; Max grand, Dr. Hugo Oliveira and Dr. Chris Measures from University of Hawaii. The hand sign some are making is a T and an M; it only works if you do it with the left hand.
Trace metal group on CLIVAR S4P. From right to left, Brian Kilgore and Dr. Bill Landing both from Florida State University; Max grand, Dr. Hugo Oliveira and Dr. Chris Measures from University of Hawaii