Science in the Southern Ocean

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SEM Image of Coccolithophores

Scientists participating in the Great Belt Research Cruise are spending 5 weeks in the Southern Ocean exploring the Great Southern Coccolithophore Belt, an area with an abundance of a type of phytoplankton called coccolithophores.  This fieldwork will help to determine the species of coccolithophores make up the Great Belt, which factors control the distribution of these coccolithophores, the effect of the Great Belt coccolithophores on the global carbon cycle, and how ocean acidification may affect coccolithophores.

Dr. Barney Balch of Bigelow Laboratory for Ocean Sciences first noticed the Great Belt on satellite images about ten years ago, when it appeared that there was a large band of phytoplankton running through the Southern Ocean each year during the austral summer.  Certain types of phytoplankton have shells made up of overlapping calcite plates, which reflect light and essentially act as mirrors, making it possible for large populations, or blooms, of these microscopic plants to change the color of the ocean and show up on satellite images.  After following the Great Belt on satellite images for ten years and hypothesizing that it was made up of coccolithophores, Dr. Balch and his colleagues wrote a proposal and received funding from the National Science Foundation to undertake the first systematic study of the Great Belt from sea.

Some of the questions these researchers hope to answer, as specified in their proposal to the National Science Foundation, include:

  • What coccolithophore species make up the Great Belt and how are they distributed around the world?
  • How abundant are these coccolithophores, and how much calcium carbonate do they add to the ocean?
  • What are the calcification rates in the Great Belt, and how much does the Great Belt contribute to global calcification?
  • What factors (temperature, stratification, etc) influence the range of the Great Belt?

In early 2011, a team of researchers led by Barney spent 5 weeks at sea in the portion of the Great Belt between South America and Africa, collecting data and water samples, and conducting shipboard experiments.  Now, many of the same scientists who participated in the first expedition are back at sea on this cruise, examining another portion of the Great Belt.  While work done on the 2011 cruise verified that what appears on the satellite images is indeed a phytoplankton feature, there is still much more to learn about the Great Belt: why it’s located where it is, which types of coccolithophores live in the Belt, the factors affecting the abundance of the coccolithophores and their distribution, and how changes in ocean health, such as ocean acidification, will affect calcifying phytoplankton.  The Great Belt covers about 20% of the world ocean, so these studies help researchers understand changes in the ocean not just in the Great Belt, but in the entire world ocean.  If the pH of seawater changes due to ocean acidification, the shells of certain ocean organisms may dissolve, or grow more slowly, resulting in small and large-scale environmental changes.  The impact on a place like coastal Maine, where Bigelow Laboratory for Ocean Sciences is located, may be that the commercial shellfish industry is affected; globally, a phytoplankton die-off would have implications for the carbon cycle and ocean’s food webs, as phytoplankton are food for many ocean inhabitants.

Filtering (Photo courtesy of Jeff Lawrence)

On the last expedition, more than 5000 samples were collected, many of which are still being processed, analyzed and interpreted by the various researchers.  At the end of this project, scientists will present their findings in the form of papers, like this one, The contribution of coccolithophores to the optical and inorganic carbon budgets during the Southern Ocean Gas Exchange Experiment, published by Barney and colleagues in early 2011.  While conducting research on a 2008 cruise off the coast of Argentina, after all those years of monitoring satellite images, Barney finally had the opportunity to collect samples within the Great Belt.  His paper explains what they found and the implications of these findings for future research.  Barney and his colleagues used this information to write a proposal to the National Science Foundation seeking funding to for a multi-year, multi-institution investigation of the Great Belt; this proposal was funded, which helped launch today’s Great Belt research project.