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Mitchell group, from left, Greg Mitchell, Mattias Cape, Bridget Seegers, Brian Seegers
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Week 6
12 August 2006

Searching for the Elusive Element Using Biological Oceanography

Part II


Part III
Karen Selph

 

1. What do you want to find out?

  • I am looking at the phytoplankton distribution in the water samples we are taking on this cruise. We want to know why the distributions aren’t even, the factors that make the phytoplankton grow and the factors that cause them to die.

 

2.  How do the levels of phytoplankton differ between summer and winter?

  • There are fewer phytoplankton in the winter due to a lack of light. In the summer, we might find 10,000 algal cells in 1 milliliter of water, whereas in the winter there might be 500 – 1,000.

 

3.  How do you count the number of algal cells?

  • I use a flow cytometer. The flow cytometer was originally developed for the medical field in order to count blood cells. Oceanographers take advantage of technological developments in other fields in order to help them do their work more quickly and efficiently. Formerly, cells were individually counted under a microscope.

 

Chief Scientist Greg Mitchell
Flow Cytometry is an advanced method of counting individual cells, including single-celled organisms. It can rapidly measure small differences in individual cells as they pass through a laser beam. These variations are enough to identify different species of plankton, including very small microbes quickly and accurately.
Link Link

 

4.  How does the flow cytometer work?

  • A flow cytometer is a machine with a laser. It aims a wavelength of blue light as an extremely small sample stream flows by. This blue light excites the pigments in the phytoplankton so that they fluoresce and give off a red light. As the red light is detected, a signal is sent to computer software that keeps a count of the phytoplankton. A sample that would take 5 minutes to process by flow cytometer would take 1 hour under a microscope.

 

Flow cytometric signatures of phytoplankton in a seawater sample
Flow cytometric signatures of phytoplankton in a seawater sample.
Link Link

 

5. How many samples did you process?

  • I processed 4-8 samples from each CTD cast. I sample only water from the surface to 150 meters below the surface. Below that level there is not enough light for the phytoplankton to grow.

 

Question: If Karen can process 8 samples in 40 minutes, how many samples can she process in 12 hours?

 

 

http://www.soest.hawaii.edu/sfcf/

Karen Selph  is Director of the SOEST Flow Cytometry Facility, an assistant specialist, and a graduate faculty member in the Department of Oceanography at the University of Hawaii.

 

 

 

Week 6
12 August 2006
Searching for the Elusive Element
Using Biological Oceanography
Part I

Part I Section I Part I

 The Mitchell Group
Part II Part I Section II Part II The Hewes Group
Part III Part II Part II Karen Selph
Part I – Section II Part I Section II Part IV Mi-ok Park



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NSF Office of Polar Programs, Antarctic Sciences Section
This special report was made possible by the NSF Office of Polar Programs, Antarctic Sciences Section, Award Nos. ANT04-44134 University of California-San Diego Scripps Institution of Oceanography (B. Gregory Mitchell, Farooq Azam, Katherine Barbeau, Sarah T. Gille, Osmund Holm-Hansen); ANT04-43403 University of Hawaii (Christopher I. Measures, Karen E. Selph); ANT04-44040 University of Massachusetts Boston (Meng Zhou); ANT04-43869 Woods Hole Oceanographic Institution (Matthew A. Charette),  for the study entitled "Collaborative Research: Plankton Community Structure and Iron Distribution in the Southern Drake Passage".