Week 6
12 August 2006

Searching for the Elusive Element Using Biological Oceanography

Part II
The Hewes Group

Introduction: You may have seen cartoons where someone gets a “light bulb” over his head, indicating he has suddenly found the answer to his question. Answers to science are rarely so simple. Even reaching the point of asking the right question is a process.  This article describes how the current focus on phytoplankton in the Southern Ocean developed.

Question: Who was Archimedes? What did he shout and why?

In the 13th century, monks reused a copy of Archimedes' work by writing prayer texts (horizontal lines) over the underlying mathematical text (vertical lines).in 2003, experts of Christie's were able to enhance several pages using ultraviolet light and digital scanning. © Christie's Images Inc. 2004 Link	Archimedes (Greek) (c. 287 BC – 212 BC) was an ancient Greek mathematician, physicist, engineer, astronomer, and philosopher born in the seaport colony of Syracuse, Sicily. Today, historians agree that Archimedes, Newton, and Gauss are the greatest mathematicians who have ever lived.

Project Background: Christopher Hewes, staff research associate at Scripps Institution of Oceanography, University of California, San Diego, has worked in the Antarctic region as a phytoplankton ecologist for many years. He works with Osmund Holm-Hansen who began studies in the Antarctic area in 1959, and who is considered one of the foremost authorities of phytoplankton ecology of Antarctica. For many years, Oz asked the question of why there was relatively little phytoplankton in the Southern Ocean when the waters are enriched with plant nutrients. Both Chris and Oz collaborate with the US Antarctic Marine Living Resources (AMLR) which is a program primarily concerned with the krill fishery in Antarctica. Every year, Oz (since 1989) and Chris (since 1997) come to the same place in Antarctica to study phytoplankton ecology with AMLR. Through the earlier AMLR expeditions, the idea that iron was the plant nutrient missing in the Southern Ocean was explored. However, ships used for the AMLR surveys were not “clean” enough to actually prove that low iron concentrations existed and were the cause of low phytoplankton concentration in Antarctic regions.    

Jennifer Ayers Biography

Conditions: From AMLR studies, it was known that a blue water zone (very low chlorophyll concentrations) exists west of the Transverse Shackleton Ridge, while the green water zone (high chlorophyll concentrations) lies to the east. The sharp change between high and low chlorophyll concentration as found in this area was an ideal natural laboratory to examine the response of phytoplankton to iron fertilization. In 2004, NSF sponsored our science group and provided a “clean”-facility onboard ship in order to show that iron was controlling the phytoplankton.  One question that arose from the 2004 study, among others, was ”Where does the iron come from?” This is one reason we are here this year during winter.

Other Research: For information on how Chris Measures determines the source of the iron, whether from the land or from the passage of the ocean water through the Shackleton Gap, see Science in the Spotlight, week 3.

Distribution and Size of plankton: One way to get information about chlorophyll distributions is through satellite imagery. The satellite image gives a colorful picture of the areas of high and low chlorophyll distribution for the ocean surface.  In most areas of the Blue Water Zone, the highest concentrations of chlorophyll are found at depths of 75 meters or more. To find levels of chlorophyll below the surface, it is necessary for scientists to take water samples at varying depths. 

Phytoplankton bloom in the Ross Sea - Satellite Image Image Courtesy NASA Earth Observatory Link

Question: For those of you who fish, (or eat fish) name some types of fish that live at different levels of the ocean (e.g. bottom dwellers, surface feeders etc.)

Another important variable that Chris Hewes studies is the size of phytoplankton in these areas. The smallest phytoplankton are the size of large bacteria. The larger phytoplankton can almost be seen with the eye. The size of the phytoplankton indicates how the phytoplankton responds in its environment, and determines what animals can graze them. To use an analogy, we could say the small phytoplankton is the size of a mouse. The large phytoplankton would be the size of an elephant. The mouse and the elephant are both animals, but behave very differently in response to their environment based on their size, as well as having different creatures that might want to eat them. Chris Hewes is looking at the size distribution of phytoplankton as it changes from the blue to the green water as an indicator of a changing environment and a different food supply.

Significance: Phytoplankton are  the primary base for the Antarctic food chain and therefore important in the carbon cycle. We need to study them to find conditions that facilitate their growth and help them maintain the balance of the ecological system that exists in the Southern Ocean.

Armand Barilotti Biography

The Hewes group: Christopher Hewes, Scripps Institution of Oceanography; Jennifer Ayers, staff research associate; Armand Barilotti, research experience undergraduate.