BIOS Research: Trophic BATS: Post # 7 (Day 5)

At day 5, this is the half way point of Trophic BATS and at the minute we are steaming to our next and final station, outside of the eddy. While investigating the transfer of carbon through the complex food web processes, we are choosing our experimental sites based upon on certain physical features of the ocean current. These physical features are called eddies, which are rotating rings within large-scale ocean currents. Eddies are initially formed by instabilities in wind patterns and can range in size. In the North Atlantic, meso-scale eddies (rings of 100km diameter) generate in the east and progress along west until they meet the Gulf Stream. This transit usually takes between 6-8 months.

Now why is there such an interest in eddies? If an eddy circulates counter clockwise (anti-cyclonic) in the Northern Hemisphere, down welling events take place inside the core. If an eddy circulates clockwise (cyclonic) upwelling events occur. These upwelling events introduce deep, cold water enriched with nutrients that can help fuel phytoplankton blooms. Determining the variations of food web structure within and outside of these meso-scale eddies, both anti-cyclonic and cyclonic, may be very important in understanding the complexity of the biological carbon pump. On this cruise, we chose a local cyclonic eddy and have indeed seen relatively large amounts of biomass from collected water.

Phytoplankton collected from Matt Baumann and Brenden Mackinson (URI) in-situ pumps. Pumps will run for a predetermined programmable time. Matt sets the pumps to run between 2-4 hrs and set depths. Pumping for that duration can filter between 300-500L of water!

So far, we’ve talked about the majority of the research and experiments taking place on this cruise. However, I have still failed to introduce the 20ft container on the 01 deck (deck up from the main deck). Check back to Post #1 to see it being loaded onto the ship. Inside of the van contains an instrument called a flow cytometer and/or cell analyzer/sorter. The flow cytometer is a part of Dr. Mike Lomas’s Phytoplankton Ecology Lab on this cruise, along with myself, Stacey Goldberg (flow tech/superhero), and two POGOs (international graduate students), Priscilla Lange and Arvind Singh.

Hopefully I’ll do the instrument (and its owner and operator!) justice and correctly explain its functioning and applications. The first cell counters were originally designed in the 50’s-60’s to be used in hospitals for the enumeration of blood cells. In the 1970-80’s flow cytometers passed from strictly medical purpose to new fields, such as oceanography. In oceanography, its application was similar, but instead of blood cells, scientists were counting smaller phytoplankton cells. While years have passed, the instruments have evolved into incredibly powerful tools for oceanographic research.

Typically, these instruments stay in the lab. But as I mentioned previously, container vans (portable science labs) can be made for any designed purpose and Mike specifically had it in mind to design a van that could be equipped with cytometer to take out to sea. This is no easy endeavor as seen after watching the van being loaded onto the ship and then hearing that only a handful of ocean scientists have successfully brought their flow cytometers into the field. Its jump from lab to ship is beneficial for two reasons. First, samples can be processed at sea generating data in real-time. Second, with processing at sea, there is no use of fixatives (needed for long-term storage), which eliminates assumptions of chemical impact to sample integrity. Mike’s flow tech, Stacey Goldberg, is quite pleased and impressed with their found ability to successfully operate the instrument while working on a rocking and rolling platform. Weather has been incredibly cooperative which immensely alleviates the challenge of operating the cytometer.

Inside of the Cytometer van. Red light can be used allowing technicians to see while they work, while still making sure phytoplankton are not able to utilize any light source.

Mike explains that the challenges of operation are not dependent on vibrations of the ship, but the pitching and rolling of the ship. Thousands of water droplets are produced each second from the instrument and that droplet’s motion is dependent on gravity. For certain applications, each droplet needs to be collected, so when you consider a free-falling object with a moving target, the difficulties can be seen.

The Cytopeia flow cytometer. Note the straps.

Just like all the researchers on this cruise, the cytometer is incredibly hard working. It’s so hard working that it runs at a rate of 20,000 events per second. I can barely multi-task (limited to eating and shouting), so needless to say it is impressive. Each event starts out from the sample, where the sample stream meets a sheath fluid (perpendicular cross road). Based upon a specific hydrostatic pressure, the flow of sample now has individual cells aligned in single file. This pressure separates each cell for analysis, and a harmonic generator will disrupt the flow, eventually producing a free falling water droplet with an individual cell that can be collected.

Now before it’s water droplet period, each cell will meet a laser (as pictured below). The cell will absorb the light and emit the light at a longer wavelength and lower energy. The fluorescence produced along with the forward scatter of the light characterizes the cell into taxon specific groups and size, respectively. From this instant, the instrument generates population counts of several types of phytoplankton from the sample.

Blue - 488nm Laser equipped on the cytometer.

However, another application of the cytometer is its ability to sort, which is what Stacey has been doing for the majority of the cruise. Once the instrument identifies the cell type, it sends a message to produce an electric charge in the stream. This instrument is so clever that within 5 x 10^-5 of a second the charge is produced and given to each water droplet before the instant if forms. Once the droplets free-fall, they pass between charged plates that will direct the charged particles into a tube. Like and opposite charges of different strength are given to each specific taxa of phytoplankton, enabling all similar taxa, such as synechochus and prochlorococchus to be grouped together and kept for taxon-specfic analysis. Pretty nifty.

Analysis post sort include genomics, biogeochemistry, and cell physiology. The applications of sorting seem to be continuously evolving as well. The Phytoplankton Ecology Lab focuses on producing “sorts” for genomic analysis and biogeochemistry. On Trophic BATS, Bridget and Francesca are having their primary production and grazing samples analyzed by the cytometer to give them taxon specific rates. PEL filters water for taxon-specific carbon, nitrogen, and phosphorus quantities.

Well that's all for today. Unfortunately, I don't have any zooplankton pictures of the day, but I have organisms of the day and another sunset picture to make you all jealous.