Ross Sea Connection

A teacher noted: I made some changes to the previous diatom worksheet. In trial run I left the light on for 48 hours. The diatoms had notable growth in the N+P+Fe media. For the run with students we’ll run the lamp 12 hrs. on 12 hrs. off. We’ll start tomorrow and finish up next week. It allows me to develop the photosynthesis piece that students last studied in grade 6.

This is following an introduction to cell parts and cell chemistry. We tested foods for carbohydrates, proteins, and lipids, compared results to nutrition fact labels for the foods, watch Bill Nye “Nutrition,” and are observing transport across potato membranes and egg membranes. For photosynthesis, I’ll be demoing geranium leaf sugar and starch and we’ll capture gas from an Elodea leaf. That will bring up to the diatoms and the Ross Sea.

Background Information

From mid-January to mid-February, 2011, scientists aboard the research vessel Nathaniel B. Palmer will assess carbon dioxide capture in the Ross Sea off the coast of Antarctica. They will be using a variety of technologies to conduct experiments and collect data to answer the question: “Can increased phytoplankton production reduce atmospheric carbon dioxide?”
Why must the Ross Sea research be done in January-February?
To learn more use the Google Earth datasets at COSEE NOW Ross Sea Connection.
Energy Transfers
Antarctic Food Web
Source: http://www.coolantarctica.com/Antarctica%20fact%20file/wildlife/whales/
food%20web.htm / Analyze the food web.
A producer makes food for itself and others through photosynthesis. What group of organisms is the producer?
A primary consumer depends directly on the producers for nutrition. What organisms are primary consumers?
Explain the difference between phytoplankton and zooplankton.
Explain the difference between a carnivorous zooplankton and an herbivorous zooplankton.
Evaluate the role of krill in the food web. Are krill herbivores, omnivores, or carnivores? What depends on krill?

Trophic is Greek for feeding. Place the organisms of the food web into trophic levels.

If a producer is autotrophic, what does heterotrophic mean?

Matter Transformations

As autotrophs, phytoplankton make food through the process of photosynthesis. Using energy from the sun, phytoplankton convert carbon dioxide into biomass.
The biomass of phytoplankton is digested by primary consumers into chemical building blocks. As heterotrophs, primary consumers rearrange the building blocks into their own biomass for growth and repair. Their biomass is processed by higher-level consumers. / Source: http://www.gma.org/onlocation/globecactiv.html

Biomass includes carbohydrates, proteins, lipids, and nucleic acids. The main product of photosynthesis, glucose, is needed for cellular respiration so that cells can have energy to carry out life processes. The carbon in glucose and other carbohydrates provide the carbon backbone needed for proteins, lipids, and nucleic acids.

Nutrient Cycling

Nitrogen and carbon dioxide are gases that dissolve in the ocean. The gases will move into the ocean until the pressures of the gases in the water are equal to the pressures of the gases above the water. Iron, phosphorous, and silicon are solids that wash into the ocean from soil and rocks on land.

Photosynthetic organisms need carbon dioxide to build carbohydrates – sugars and starches. Nitrogen is needed for proteins including enzymes that control biochemical reactions. Phosphorous compounds are found in proteins and phospholipids that form cell and nuclear membranes. Iron is an example of a micronutrient, something that living organisms need in small amounts in order to conduct life processes.

What nutrients would phytoplankton need for growth?

Trapping Carbon Dioxide

When phytoplankton are alive they take-up carbon dioxide dissolved in ocean water. When consumers eat and digest the phytoplankton, carbon dioxide is released through cellular respiration. Some of the carbon dioxide will return to the atmosphere. Some of the carbon dioxide will remain in the ocean. Organisms that die and sink to the deep ocean floor trap carbon dioxide, as they become part of the ocean floor sediments. Carbon trapped in sediments is sequestered.

What micronutrients do diatoms need for growth?

Diatoms

Diatoms are a type of common phytoplankton found in freshwater and marine environments. Like most algae and other photosynthetic organisms, diatoms have a nucleus, cytoplasm, vacuoles, and chromatoplasts.

Chromatoplasts (colored plastid) are the site of photosynthesis in a diatom. The chromatoplasts are yellow-brown instead of green like the chloroplasts of plants.

Diatoms are unique in that they have a cell wall made of silica, the main mineral found in sand. The pores in the cell wall allow gases and nutrients to enter and leave the cytoplasm. Because of their silicate shells, diatoms tend to sink and trap carbon more than other phytoplankton. Diatomaceous earth is used in swimming pool filters.

Test It

Step 1:

Observe and describe the four flasks of diatom growth media. Each flask contains a different ratio of nitrogen, phosphorous, and iron.

Use the nitrate, phosphate, and iron test kits to determine the ratio of micronutrients that were added to each flask. Record you test results.

Step 2:

Add a similar amount of diatoms to each flask. Carbon dioxide enters water in the flask from the air above the water. Light energy will be provided by a compact fluorescent light bulb. You will observe the flasks again in 5-8 days. (The diatoms are the white-brown sediment at the bottom of the flask.)

Describe and sketch what you observe after 5-8 days of growth.

Test the liquid in the flask and compare the results with the initial micronutrient tests.

What do diatoms need for growth? Explain any changes in nutrient ratios.

Support your claim with evidence and reasoning.

Which flask was the control? Explain why.

What was the variable? Explain why.

Step 3:

Oceanographer Alfred Redfield used data to mathematically model the ratio of carbon, nitrogen, phosphorous, and iron needed for biomass production by phytoplankton. Count the beads on the biomass string. Black is carbon, blue is nitrogen, purple is phosphate, and the orange is iron. Write the numbers as a ratio. (Note: Each black, blue, and purple bead represents one unit of the nutrient. The orange bead represents 0.25 units.)

Compare the ratio to your growth media data. Explain what you observe.
Growth Experiment Observations

Use color pencils to shade the flasks.

Starting Growth Media

1A / 1B / 1C / 1D

Observations

Concentration of Nutrients in Each Flask

Flask / Nitrogen / Phosphorous / Iron
1A
1B
1C
1D

Growth Media with Diatoms After _____ Days

2A / 2B / 2C / 2D

Observations

Concentration of Nutrients in Each Flask

Flask / Nitrogen / Phosphorous / Iron
2A
2B
2C
2D


Micronutrients and Phytoplankton Growth

Scientist John Martin was interested in the role of phytoplankton in controlling global climate because phytoplankton can process millions of tons of carbon dioxide.

Could increased phytoplankton production reduce atmospheric carbon dioxide? Explain why.

In the ocean, there are large areas that have high-nutrient concentrations, but low phytoplankton production. Phytoplankton production is measured by the chlorophyll color they emit. The high nutrient, low-chlorophyll (HNLC) zones are in the sub-arctic North Pacific, equatorial Pacific, and Antarctic Ocean. There was speculation that this was the result of overgrazing by zooplankton.

Analyze the food web. Is overgrazing a reasonable explanation? Explain why. What evidence would be needed to support this argument?

John Martin suspected that the problem was related to concentrations of nutrients that phytoplankton need for growth. An earlier oceanographer, Alfred Redfield discovered that phytoplankton need 106 carbon units to 16 nitrogen units to 1 phosphate unit to 0.25 iron units in order to make biomass.

Could a micronutrient be a limiting factor in the HNLC zones? Explain why. What nutrient would likely be the limiting factor in the HNLC zones?

Check Your Understanding

John Martin’s research team collected clean water from Antarctica. They added iron to some samples and left others untreated. The graph shows the amount of phytoplankton in two flasks of ocean water, one seeded with iron, the other untreated.

(Graph courtesy U.S. Joint Global Ocean Flux Study, based on data from K. Johnson and K. Coale.)

Source: http://earthobservatory.nasa.gov/Features/Martin/martin_4.php

Interpret the data. How does the experiment compare to your experimental results?

Evaluate the Claim

John Martin claimed that iron levels could be partly responsible for past ice ages. During an ice age, large quantities of continental freshwater are locked up in ice caps. This disrupts the water cycle causing exposed land surfaces to become drier. Iron blowing from the drier surfaces into the ocean’s high nutrient, low-chlorophyll zones may have caused a burst in phytoplankton growth. More phytoplankton would trap carbon dioxide from the atmosphere deep in the ocean. The lower atmospheric carbon dioxide levels would keep temperatures cooler, prolonging the ice age.

Does the evidence support the claim? Explain.

Make your own claim and support it with reasoning and evidence.

Could adding iron to HNLC zones increase phytoplankton growth?

Could increased phytoplankton growth reduce current atmospheric carbon dioxide levels?

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