Hello my readers! I apologize for not posting yesterday, but, to be honest, I was exhausted and fell asleep before I had a chance to write anything. Yesterday was just an extremely busy day – a ton of samples were collected and the nutrient analyses run.
We did have an excellent surprise though – a group of pilot whales decided to hang out and swim alongside the ship for a while! They were beautiful.
Today was our third day at the Process Station. As I mentioned previously, we are spending time here because we want to study the biological processes occurring in this part of the ocean more thoroughly. One of the ways we do that is with McLane pumps.
These pumps allow for large volume filtration (around 300L) in situ, meaning that seawater gets pumped through while the pump is still in the ocean, concentrating lots of particles onto the filter for analysis. So, instead of collecting water then filtering (like I explained in the spotlight on Dr. Fawcett), she can collect much more suspended particles directly from the ocean.
The McLane pump is truly an interesting piece of electrical equipment. It’s controlled by a computer, and the researchers can program the McLane what time to start and stop and the flow rate at which to pump (how fast the water moves through the filters). The McLane also records data (flow rate, depth, etc.) that can be accessed when next connected to the computer. Timing is very important, as we need to ensure that the pump is at the right depth before it starts pumping. We usually deploy the pumps about an hour before they are scheduled to being their work.
At the upper left is a round black casing – this houses the filters and is where the water flows into the machine. The actual pump is the smaller silver cylinder in the center of the machine; this is what allows for the movement of water. The large, brownish-gray cylinder at the bottom contains the electronics and batteries that control the machine and transmit information to a computer. Water flows out of the pump at the bottom right – through a flow meter and out the white spigot. We have two pumps on board and they are both deployed simultaneously, but go to different depths. The housing for the pumps (the metal case surrounding the whole thing) has notches and a clamp that secure it to a very strong line so they can be safely and securely deployed to whatever depth we want to study.
The pump can hold up to three filters, depending on what is going to be studied and the filters’ various sizes (i.e. 100µm, 5µm, 0.4µm, etc.) allow us to collect different particles/organisms. Filter size refers to space between the pores – larger spaces capture larger particles (for example, phytoplankton) whereas smaller filters will collect smaller cells, like bacteria. Using multiple filters to collect particles of different sizes is called size fractionation – things on each filter are similar in size to each other. This is the first step in identifying the various particles that are present in the seawater.
Once the McLane pumps are recovered, the first step is to remove any excess water from the filters to ensure that particles are not lost when the filter is taken out of the pump. To do this, the filter and its casing are connected to a small vacuum pump that sucks out the water. Once this is complete, the filter is removed and then stored for further processing (often in the freezer until we return to Princeton).
There are numerous analyses that can be performed from the filters – measurements of carbon and nitrogen content, isotope ratios (13C/12C and 15N/14N), DNA, natural abundance, and flow cytometry.
Flow cytometry is very cool. First, the filters, and therefore the cells, are fixed in formalin (a solution of formaldehyde in water) to retain their shape and structure. When the filters are put into a flow cytometry machine, the cells are essentially lined up, then cut with lasers. Based on how the cells scatter the light, the machine is able to determine size, complexity, and pigmentation of the cells. What this does is allow researchers to look at different populations based on their morphology (size and shape) and pigmentation.
We have another day at the Process Station, then we continue our journey – there’s only a week left of the expedition!
Until next time,