Kerry is getting her PhD at URI in the laboratory of Dr. Tatiana Rynearson. Kerry studies diatoms, single celled algae that are photosynthetic and are a great food source for krill. Kerry uses genetic methods to follow populations of diatoms and these are similar methods that geneticists use to follow human populations and family relationships. On this cruise, Kerry is collecting samples so that we can determine what kind of organisms the krill might be eating. To determine where to obtain her samples, Kerry profiles the water at every sampling station from surface to the bottom using an instrument package called a CTD-that’s short for temperature, conductivity (salinity) and depth. There is also an instrument that measures autofluorescence from organisms containing chlorophyll and instrument that measures how light travels through the surface ocean.
These instruments are lowered into the water on the bottom of a large sampling frame that also hosts a rosette of bottles called Niskin bottles that are used to collect water at discreet depths. The rosette and instruments are deployed via a very large winch and are cabled to monitors on the ship that show data in real time as it is lowered. Scientists like Kerry watch the data as the instruments head down into the water toward the bottom and use this data to make decisions about where to capture water samples on the return trip on the way toward the surface. For example, for diatoms which make carbon molecules from sunlight and oxygen, it is useful to know the depth of light penetration and depths where there may be a maximal signature of chlorophyll fluorescence.
The water bottles on the rosette are held open with a spring loaded system that is also electronically wired to the cable on the winch that lowers it. On the descent, the water flushes through the bottles and on the ascent once depths for water sampling are selected, an electronic signal is sent to an individual bottle that releases the spring holding the bottle open. This snaps the bottle shut and traps water at a specific depth. Bottles are fired from the deepest depths to the shallowest depths.
Once aboard the ship, the water is collected via spigots at the ends of each bottle. Each scientist is assigned specific bottles for sample collection. Kerry filters water from each sampling depth onto filters that have specific pore sizes that select for different organisms. Since diatoms are small the filters have pores that pass water through no bigger than thousandths of a millimeter. Kerry uses a pressurized pump system to filter water and then she flash freezes the filters holding the diatoms (and other organisms that are trapped on the filters) in liquid nitrogen. This cryogenically preserves her samples so she can extract DNA from the organisms trapped on the filters back in her laboratory at URI.