EarthLabs > Climate and the Carbon Cycle: Unit Overview > Lab 6: Oceans: Carbon Sink or Source? > 6B: Phytoplankton: Ocean's Green Machines

The Oceans: Carbon Sink or Source?

Part B: Phytoplankton: Ocean's Green Machines

In Part A, you learned that phytoplankton are responsible for bringing carbon dioxide from the atmosphere into the ocean's biological pump. Given enough sunlight, CO2and nutrients, populations of phytoplankton can reproduce explosively, doubling their numbers in just one day.The satellite image on the right shows a massive phytoplankton bloom Phytoplankton rapidly reproduce producing high concentrations of phytoplankton in the water. containing millions to billions of individual phytoplankton all drawing down atmospheric CO2 to use for photosynthesis.
Brilliant shades of blue and green explode across the Barents Sea in this natural-color image taken on August 14, 2011, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite. The color was created by a massive bloom of phytoplankton that are common in the area each August. In this image, the milky blue color strongly suggests that the bloom contains coccolithophores, microscopic plankton that are plated with white calcium carbonate. When viewed through ocean water, a coccolithophore bloom tends to be bright blue. The species is most likely Emiliana huxleyi (Emily for short)whose blooms tend to be triggered by high light levels during the 24-hour sunlight of Arctic summer. The variations in bloom brightness and color in satellite images is partly related to its depth: E. huxleyi can grow abundantly as much as 50 meters below the surface. Other colors in the scene may come from sediment or other species of phytoplankton, particularly diatoms. The Barents Sea usually witnesses two major bloom seasons each year, with diatoms peaking in May and June, then giving way to coccolithophores as certain nutrients run out and waters grow warmer and more layered (stratified). (NASA)
Large phytoplankton blooms impact climate in two important ways:

Environmental factors that limit the size, longevity and timing of phytoplankton blooms will also limit the efficiency of the oceanic biological pump. Sunlight and nutrients are the most important ingredients for a phytoplankton bloom to occur. When nutrients and sunlight are plentiful, microscopic phytoplankton reproduce quickly. Some blooms are so massive that they tint the water and can be seen from space. The phytoplankton bloom at the top of the page is a excellent example.

There are many biotic and abiotic environmental variables factors that influence the formation of phytoplankton blooms. The most important ones include:

Begin exploring the importance of phytoplankton blooms by watching a NASA video "The Ocean's Green Machines" here or here. When you finish watching, answer the two Checking In questions below.

What causes phytoplankton blooms?

Checking In

  1. What do phytoplankton need to produce large blooms? Check all that apply.
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  2. Why are phytoplankton important? Check all that apply.
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Using satellites and ocean color to study phytoplankton blooms and the oceanic biological pump

Because phytoplankton blooms and the oceanic biological pump are important to climate, scientists are interested in studying:

Scientists use both in situ sea water samples and Ocean Color measurements from satellites such as Terra to monitor changes in size, location and timing of phytoplankton blooms and the impact of these changes on the Earth's system. You can easily observe ocean colors in this image above of a phytoplankton bloom off the coast of France. Ocean color is created when sunlight reflects off chlorophyll pigment molecules in the cells of phytoplankton floating in the upper surface of the ocean. Light reflected from sediments and dissolved organic material also contribute to ocean color. Different shades of the phytoplankton bloom depend on the types of species and the density of the phytoplankton population inside the bloom.

Ocean color chlorophyll data is used to determine the net primary productivity (NPP) A measure of the amount of carbon dioxide taken in by phytoplankton via photosynthesis and converted into carbon compounds.] of the phytoplankton bloom. Net primary productivity tells scientists how much CO2 carbon is being drawn down from the atmosphere by phytoplankton and moved into the oceanic biological pump.

Visualizations of ocean color can come in two formats: true-color (natural) images and false-color images.

Consider the two different images of the same phytoplankton bloom in the Bering Sea taken by Seawifs on June 15th and 16th, 2000. Click to enlarge.

  1. The top image is a true-color image. The various ocean colors indicate the presence of different types and quantities of phytoplankton. For example, a milky white color indicates the presence of coccolithophores. Although the true color image gives a sense of how big the bloom is, it does not provide much information about the exact quantity of phytoplankton or how much carbon is being taken in through photosynthesis.
  2. The bottom image is a simulated, mathematically reconstructed "false-color" image using chlorophyll data measured by instruments on the SeaWiFS satellite. Note: Other data from shipboard in situ measurements may be incorporated into these types of false color images.

Discussion

With a partner or your class, compare and contrast the two images.

1. Where is the biological pump the strongest in this phytoplankton bloom? How do you know?

2. Which image type - true-color or false-color- is more useful to scientists in determining the amount of carbon moving from the atmosphere down into the biological pump? Explain why.

Using ocean color to monitor size, location, and timing of phytoplankton blooms

Because phytoplankton blooms and the oceanic biological pump are important to climate, scientists are interested in studying the following questions:

To find answers to some of the questions above, you will examine static ocean color images and a time series ocean color animation created from ocean chlorophyll data.

The ocean color false image on the right has been generated from chlorophyll data taken by one of NASA's newest satellite - the Suomi NPP satellite. This image allows you to compare phytoplankton blooms in the summer in the northern hemisphere to summer in the southern hemisphere. Click to enlarge the image and take a few minutes to carefully examine the images for where phytoplankton populations thrive and where they don't thrive.

Note: You can examine the blooms in greater detail by entering the NASA Suomi NPP satellite site. Once there, scroll down to the two links that allow you to view the Northern Hemisphere summer image and the Southern Hemisphere summer image in larger detail. You can also click on each of these images to see close-ups.

What does this chlorophyll data tell scientists about the location and size of phytoplankton blooms?

Next, watch a time series animation showing a decade of of phytoplankton blooms. Hint: You can identify seasons by looking at the land vegetation. For example, land vegetation appears in the northern hemisphere during summer.

Note: You can view this time series animation at:


Checking In

  1. Which of the following geographic area(s) are drawing down the largest amount of carbon into the oceanic biological pump? Check all that apply.
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  2. Phytoplankton need nutrients to grow and reproduce. Which geographic locations are nutrient-limited. Check all that apply.
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  3. Seasonal timing of phytoplankton blooms is most likely due to which of the following environmental variables?
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The oceanic carbon cycle and nitrogen cycle: An interdependent relationship

Like land plants, phytoplankton need nitrogen and other nutrients to make important carbon-compounds needed to grow and reproduce. For this reason, nitrogen and other nutrients have strong limiting effects on the growth, size, timing and longevity of phytoplankton blooms. When nutrients are plentiful, phytoplankton blooms appear. When the phytoplankton use up the nutrients, they die and sink and phytoplankton bloom disappears.

Nitrogen gas, in the form of N2, is very abundant in the atmosphere and dissolves in the sea surface water. However, marine organisms cannot use the N2 form. Click through the Wood's Hole Oceanographic Institute's (WHOI) nitrogen cycle interactive below to get a sense of the role of microbes in making N2and other nitrogen-compounds available to marine plants (phytoplankton) and food webs.

This content is available in flash format only


To view this interactive on an iPad, use this link to download/open the free TERC EarthLabs App.


Trichodesmium- A tiny organism with a BIG role!

When you studied soil in Lab 5, you learned that mycorrhizal fungi and tiny soil microbes have big roles in the terrestrial nitrogen and carbon cycle by making nitrogen and other nutrients available to trees and plants. Without fungi and soil microbes, trees and other plants could not grow and store large amounts of carbon. Tiny organisms also play a big role in the oceanic nitrogen cycle and carbon cycle. Use the WHOI interactive below to investigate the role of the tiny cyanobacterium Trichodesmium in the nitrogen and carbon cycle and then answer the discussion questions below:

This content is available in flash format only



To view this interactive on an iPad, use this link to download/open the free TERC EarthLabs App.


Discussion

With a partner or your group, think about and discuss the following:
  1. Describe Trichodesmium's role in the nitrogen cycle and the formation of phytoplankton blooms.
  2. Why is the nitrogen cycle critical to moving carbon from the atmosphere into the oceanic biological pump?
  3. How could a small organism such as Trichodesmium impact climate?

Optional Extensions

Use NOAA's View Data Exploration Tool to investigate variables such as chlorophyll and nitrate data from NOAA's vast archives of satellites, climate models and observation tools. For example, you could track changes in nitrates and chlorophyll in the North Atlantic Phytoplankton Bloom over time. When you open the tool, make sure you take the Video Tour.

Read articles about phytoplankton:



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