Mike Stukel, a former CCE grad student, is now a professor at Florida State University.  He and his grad student Tom Kelly are on the cruise deploying sediment traps and filtering countless liters of water. I could explain what they are doing, but here it is in Stukel’s own words:


What you are researching:

I study the role of microscopic organisms (plankton) in the global carbon cycle. Phytoplankton (the tiny plants of the ocean) float in the surface layers and constantly take up carbon dioxide while doing photosynthesis. In fact, they are responsible for half of the world’s photosynthesis and as these tiny organisms remove carbon dioxide from the surface ocean, carbon dioxide is drawn out of the atmosphere. However, most of these phytoplankton will die in the surface layers of the ocean and the carbon that they have fixed will be respired by zooplankton (tiny animals like krill), bacteria, and fish and hence go back into the atmosphere. However, if the carbon taken up by these organisms sinks into the deep ocean, it will be removed from the atmosphere for periods of decades to millennia.


What instruments you are using:

I use two primary types of instruments. One is called a sediment trap, and it is an instrument that I deploy in the ocean. It will drift along with the water for a period of 3-4 days, while communicating its position back to me by satellite. While it drifts it will also collect particles that are sinking in the ocean, so that I can measure carbon flux. I also use a beta counter that allows me to measure low-level radioactivity in the ocean. The background radiation levels in the ocean are incredibly low (they are not at all harmful to you or me), but the information they provide allows us to learn about ocean processes.


What types of data you are collecting:

I collect samples related to the transport of carbon from the surface ocean into the deep ocean. This includes direct collection of sinking particles and also biogeochemical proxies that allow us to estimate carbon flux. One example of a biogeochemical proxy is the ratio of Uranium-238 to Thorium-234. Uranium-238 is found naturally in the ocean at very low concentrations and it has a very long half-life (meaning it decays very slowly). When it does decay, its first long-lived daughter particle is Thorium-234 with a half-life of approximately a month. If you were to take a sample of seawater and put it in a bucket for a few months, the uranium and thorium would reach what is known as secular equilibrium – the thorium would decay away at the same rate that it is produced from uranium. However, thorium and uranium behave differently in the ocean. Uranium acts like a salt and stays dissolved in the seawater. Thorium sticks to particles so when those particles sink they take thorium with them and we find less thorium in the surface ocean than we would expect. Thus if we measure the concentrations of thorium and uranium in the ocean, we can calculate the rate of export of sinking particles from the surface ocean (and the amount of carbon and thorium that they have taken with them).


Why normal people would care why you are doing what you’re doing out there:

Humans are releasing ~7-8 petagrams of carbon dioxide into the atmosphere every year by burning fossil fuels. The biological pump, meanwhile transports ~5-10 petagrams of carbon dioxide from the surface ocean into the deep ocean, thus removing carbon dioxide from the atmosphere. It is important to keep in mind that this is a natural process and it is balanced (in part) but carbon dioxide that gets released from the ocean after upwelling. However, we do not know how the biological pump will change in the future as the ocean adjusts to warmer temperatures, greater stratification, and ocean acidification. If the biological pump becomes stronger, we would expect climate change to happen more slowly. If the biological pump becomes weaker, we expect that climate change will speed up. My goal is to help predict which of these scenarios is more likely.


Tom Kelly stands in front of one of their filtering racks.