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

The Oceans: Carbon Sink or Source?

Part B: Phytoplankton: Nature's Green Machines


In Part A, you learned that the ability of the oceans to absorb and sequester a lot of carbon is dependent on phytoplanktontiny one-celled photosynthetic organisms that float in the upper surface of ocean. The satellite image above shows a massive phytoplankton bloom in the Barent's Sea, off the coast of Norway. This phytoplankton bloom contains billions - trillions of individual phytoplankton drawing down carbon dioxide from the atmosphere into the ocean's biological pump. Given appropriate conditions, populations of phytoplankton can reproduce explosively.

In Lab 6B, you will investigate answers to these questions and more.

Begin by watching a NASA video The Ocean's Green Machines. When you finish watching, answer the two Checking In questions below.

Checking In

  1. What are the basic needs of phytoplankton? Check all that apply.
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  2. Why are phytoplankton important? Check all that apply.
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Ocean Color: Measuring and visualizing phytoplankton blooms and primary productivity.

In the satellite image of phytoplankton blooms in the Barents Sea at the top of this page, you can see brilliant blue and green colors in the ocean. Scientists refers to these colors as Ocean Color. Scientists measure ocean color to determine ocean primary productivity - the amount of carbon phytoplankton are removing from the atmosphere via photosynthesis. Satellites can measure ocean primary productivity by measuring the amount of green chlorophyll in the water.

The basic premise behind measuring ocean color to determine ocean primary productivity is as follows:

Scientists use ocean color to track changes in the size, location and timing of phytoplankton blooms and primary production over different spatial and temporal scales. The data collected from these ocean color measurements help scientists to understand the impact of changes in the ocean carbon cycle on climate.

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

Discussion

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

1. What information or "story" does each image tell you about this phytoplankton bloom?

2. Which image type - true color or false color- gives more information about ocean primary productivity and the strength of the biological pump? Why?

The image on the right has been generated from chlorophyll data taken by one of NASA's newest satellite - the Suomi NPP satellite. It is the first of a new generation of satellites that will observe many facets of a changing Earth. With this type of chlorophyll visualization data, scientists can study many different types of research topics, including:

Enter 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 do these images tell you about where phytoplankton populations thrive and where they don't thrive during that time period? Take a few minutes to carefully examine the images and then answer the Checking In questions below. Note: These images may take a few minutes to fully load.

Checking In

  1. Where might you expect to see phytoplankton blooms during the early summer in either hemisphere? Check all that apply.
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  2. Phytoplankton need nutrients to grow. Based on the chlorophyll concentration data, where would you expect to find low levels of nutrients? Check all that apply.
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Next, look at a animation representing a time series of phytoplankton blooms derived from chlorophyll concentration data. What does this animation(s) tell you about seasonal changes in phytoplankton primary production? How do the phytoplankton blooms change from season to season? Note: You can view a time series animation of phytoplankton blooms at one of three places:

Stop and Think

  1. How do seasons affect the size and distribution of phytoplankton blooms?
  2. Where and when is primary production and the draw-down of carbon into the biological pump the strongest?


What causes phytoplankton blooms?

Sunlight and nutrients are the most important ingredients for a phytoplankton bloom to occur. When nutrients and sunlight are plentiful, microscopic phytoplankton reproduce quickly, developing huge population explosions. 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 factors that influence the formation of phytoplankton blooms. The most important ones include:



Next, read about a new and surprising large phytoplankton bloom that was recently discovered under the Arctic Ice. You can also read about this new discovery at Huge Phytoplankton Bloom Found Under the Arctic Ice and/or you can read and visualize this exciting discovery on the NASA Visualization App for IPad. Scroll down to "Secret Garden." When you get to the visualization, play the videos and read the accompanying text. Then, answer the discussion questions below.

Discussion

1. What would some immediate and some long term effects of a phytoplankton bloom on the ocean's biological pump and the carbon cycle?

2. Phytoplankton need light to photosynthesize. What changes are happening to Arctic sea ice that provided the necessary light for the surprising under-ice phytoplankton bloom to occur?



Why are nutrients important to the ocean's biological pump?

In Lab 1, you learned that nutrients such as nitrogen and phosphorus were critical for land plants to grow and reproduce. As plants of the ocean, phytoplankton also need nitrogen and phosphorus and other nutrients to grow. The two critical nutrients are nitrogen and phosphorus since they are needed in large amounts but are present in low concentrations in sea water. For every 106 molecules of CO2 phytoplankton take in for photosynthesis, they need 16 atoms of nitrogen and 1 atom of phosphorus to produce DNA, protein and other carbon compounds molecules. Like land plants, phytoplankton will keep growing until either the nitrogen or phosphorus runs out. For this reason, availability of nitrogen and phosphorus have strong limiting effects on phytoplankton population growth.


Stop and Think

Examine the image of chlorophyll and nitrogen(nitrate) concentration on the above right. Click to enlarge.

3. What evidence from these images tells you that nitrogen is a limiting factor on phytoplankton primary production? List all the evidence that you can. Note: Nitrogen measurements are made from oceanographic ships and ocean buoys. Chlorophyll measurements are derived mostly from satellite data.


Where do the nutrients essential for phytoplankton growth come from?

Nutrients come into the oceans from a variety of sources. For example, soil erosion and fertilizer used on farms bring nitrogen and phosphorus compounds to rivers where they wash down into the ocean. Much of the iron (Fe) that phytoplankton need is blown in from deserts far away.

A major source of nutrients for phytoplankton is a process called upwelling. When upwelling occurs, deep cold waters rise to the surface bringing along nutrients originally from dead bits of decomposed matter, feces and urine that sank down to the deep ocean and entered the deep ocean currents. These nutrients act like fertilizer, stimulating phytoplankton growth which in turn, stimulates food webs. Upwelling occurs in open ocean and along coastlines as the image above right indicates. Wind direction and speed, water temperature and topography all play a role in developing upwelling areas. Watch an animation of coastal upwelling animation of coastal upwelling and then answer the Stop and Think question below.

Stop and Think

4. Explain why areas of upwelling and river deltas contribute to a stronger biological pump.

Nutrients, microbes and the biological pump.

Revisit the image of the ocean's biological pump on the right. In this image, the complex relationships between nutrients (N, P, Fe), microbes (microbial loop), the carbon cycle and the ocean's biological pump are illustrated. Enlarge the image and take a few moments to re-familiarize yourself with the diagram. Then, answer the discussion questions with your partner and/or the class.

Discussion


1. Identify and describe all the ways that the nutrients(N, Fe and P) move into and around the ocean's biological pump.

2. Which processes carried out by microbes are the most important in moving N, P and Fe throughout the ocean's biological pump?

Trichodesmium- A tiny but important player in the ocean's nitrogen cycle.

Like land plants, phytoplankton cannot absorb and use nitrogen in the form of N2. Instead, phytoplankton rely on microbes to convert N2 into other types of nitrogen-based molecules that phytoplankton can take-up and use to biosynthesize their DNA, proteins and other important carbon compounds. Recent oceanographic research has identified that the tiny cyanobacterium Trichodesmium has a critical role in making nitrogen available to phytoplankton. To investigate Trichodesmium's role in the ocean's nitrogen cycle, you will use two interactives developed by the Wood's Hole Oceanographic Institute(WHOI). Then, you will answer the Checking in Questions and the Stop and Think questions that follow.

  1. First, go to the WHOI's interactive Trichodesmium:The little creatures that turn the wheels in the ocean. Click through the interactive to investigate the role of this tiny cyanobacteria in the oceanic nitrogen cycle.
  2. Next, enter The Nitrogen Cycle interactive. Click through the interactive to investigate the oceanic nitrogen cycle in greater detail.
  3. When you have finished, answer the Discussion questions below:

Discussion

With a partner or your group, think about and discuss the following:
  1. What is Trichodesmium's role in the nitrogen cycle? How is Trichodesmium's role in the oceanic nitrogen cycle similar or different from the terrestrial nitrogen cycle?
  2. Which of the carbon cycle processes (photosynthesis, respiration, decomposition, biosynthesis and combustion) are critical processes in the nitrogen cycle?
  3. Why is the nitrogen cycle critical to moving carbon from the atmosphere down to long term storage in deep sea currents and sediments.

Stop and Think

Overall, the world's oceans are warmer now than at any point in the last 50 years. The change is most obvious in the top layer of the ocean, which has grown much warmer since the late 1800s. This top layer is now getting warmer at a rate of 0.2°F per decade. Oceans are expected to continue getting warmer—both in the top layer and in deeper waters.(EPA). When surface waters get warmer and sit on top of the water column, the mixing of nutrients from below slows down.
  1. In what ways could warmer ocean surface water change the ocean's biological pump?
  2. In turn, how would these changes affect the global carbon cycle?

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