In this lab, students learn how to use actual observational (chemical) data to investigate the role of ocean biology in redistributing nutrients between the surface and deep ocean (the Biologic Pump) as well as its role in affecting the vertical distribution of oxygen. Students also see that scientists can use the phosphate concentration in deep waters to observe the effect of deep ocean circulation in "sweeping" deep ocean nutrients from one basin to another. The second part of this lab allows students to examine upwelling and downwelling through the concentration of chemical elements, as well other physical processes. Observing vertical profiles of the ocean, you will be able to determine from what depths upwelled water originates, as well as the relationship existing between surface and deepwater circulation and the occurrence of upwelling and downwelling.
Students will learn the following:
• To use actual observational (chemical) data to investigate the role of ocean biology in redistributing nutrients between the surface and deep ocean (the Biologic Pump) as well as its role in affecting the vertical distribution of oxygen.
• To examine upwelling and downwelling through the concentration of chemical elements, as well other physical processes.
• To observe vertical profiles of the ocean to understand the relationship between surface and deepwater circulation and the occurrence of upwelling and downwelling in the ocean.
CONTEXT FOR USE
The format suggested for this lesson is a lab. Since it requires no laboratory equipment, the class size can range from a small student seminar to a medium sized lecture hall. The only mitigating factor related to class size is the necessity for each student (or perhaps pairs if the instructor elects to make the lab report a paired activity) to have a computer terminal or to bring a laptop to class. The class does not need to have a SmartBoard or LCD projector, since the lab work will be conducted at individual computers, but access to multimedia equipment is preferred. See “Description and Teaching Materials” below for link to the source lab.
ACTIVITY DESCRIPTION AND TEACHING MATERIALS
The structure and primary components of this lab lesson is sourced from Columbia University’s Earth Environmental Systems Climate (EESC) course.
Below are the links for source material and resources:
· EESC course page Spring 2011, Ocean Nutrients: https://courseworks.columbia.edu/cms/
Nutrients are elements or compounds that organisms need to live and grow. “Major” nutrients are nitrogen (N) and phosphorus (P), which are essential to photosynthesis. “Minor” nutrients include iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), cobalt (Co), and molybdenum (Mo), which are used for various purposes such as enzyme and protein production. In the ocean, many processes control the distribution of nutrients, such as surface and deep circulation, continental weathering, and biologic uptake. In turn, nutrient abundances influence primary productivity (production of organic matter by autotrophs).
Photosynthesis occurs in the euphotic zone, which extends from the ocean surface down to approximately 80 – 100 meters depth. Below this depth, there is generally not enough light for photosynthesis to occur. In most of the surface ocean, low nutrient concentrations are the main limiting factor to growth, but light can also be limiting, especially near the poles. Water temperature plays a role as well because some organic reactions happen more quickly or easily under higher-temperature conditions. The response of the whole planktic community to changes in nutrient concentrations, light, and temperature is complicated because different species have different needs and optimal conditions. In general, higher nutrients, temperature, and light lead to greater productivity (though under very bright conditions sometimes “photoinhibition” can occur – it is possible to have too much of a good thing!).
The general reaction describing photosynthesis (from left to right) and respiration (from right to left) is:
106 CO2 + 78 H2O + 16 HNO3 + H3PO4 Û C106H175O42N16P + 150 O2
This reaction is an important link between nutrients and oxygen; keep it in mind when comparing your maps and cross-sections later. It is also important to think about:
1) where photosynthesis occurs, and
2) where organic matter is respired.
Refer back to lecture slides on recycling and transport, especially with respect to ocean circulation (deep water migration, upwelling/downwelling).
During this lab, students will use a program called Ocean Data View (ODV) to explore the distribution of nutrients and oxygen in three dimensions. The dataset – World Ocean Atlas 2005 – was compiled by the National Oceanographic Data Center, and represents average annual conditions measured from ships in 2005.
II. Lab Goals:
1. Learn how to use ODV: investigate seawater properties in map & cross-section view.
2. Create figures that illustrate nutrient distributions, and explain these observations in the context of different processes (biologic productivity, ocean circulation).
3. Investigate the relationship between nutrients and oxygen. Discuss how/why/where they covary or don’t covary.
4. Explore relationships between large-scale circulation patterns, “age” of deep water masses (time since sinking from the surface), and your observed nutrient/oxygen concentrations.
III. Pre-Lab Exercise: (do this on a personal laptop, preferred; or an accessible desktop)
1. Go here to register for ODV, and download the software (ODV4).
2. Go here to download the World Ocean Atlas 2005 dataset (Annual).
3. Un-zip the file, and open ODV4.
4. In ODV’s top menu, go to File > Open > WOA05_Annual.var
5. You should see a global map (blue ocean, gray land) and a “property” map next to it. Right-click on the property map, and select a Z-variable (Temperature, Salinity, etc). If there is no property map, go to View > Layout Templates (or right-click on blank part of display and choose “Layout Templates”) and select “1 SURFACE Window” (or as many as you want).
6. Play with the settings – you can do this by right-clicking on the plot and selecting “Properties.”
7. If you have trouble or questions, check out the ODV help files here.
TASK 1. Create a global surface map for nitrate (draw contours).
Results: Briefly describe general patterns (a couple sentences).
Discussion: Find a location where nitrate is unusually high (> 5 µmol/l). What could explain the high concentration at this location? (there are multiple correct answers)
TASK 2. Create the following global maps for phosphate (PO42-) and oxygen saturation (% O2):
a. surface (0 meters)
b. mid-depth (choose somewhere 50 – 150 meters)
c. deep (choose somewhere > 1000 meters) (total of 6 maps)
Results: In a few sentences, describe the surface distributions, and how they change with depth.
Discussion: What processes control phosphate and oxygen concentrations in the ocean? Based on your maps, discuss how and where these processes occur, and predict where you would expect to find high concentrations of dissolved carbon.
TASK 3. Define a section (along the conveyor, N-S Atlantic, or N-S Pacific) and plot PO42- and % O2 (as z-variables) against depth (y-variable) and section length (x-variable). This should give you a view of a vertical slice of ocean. (2 separate plots)
Results: How do PO42- and % O2 vary with depth, and along your transect length?
Discussion: Keeping in mind what you know about deep ocean circulation patterns, what process(es) may help explain the trends you see? What is the relationship between water “age” (the time since it sank) and its PO42- and % O2 content?
TASK 4. Using maps and/or cross-sections, investigate a region of upwelling or downwelling. Results: How are nutrients and O2 behaving?
TASK 5. Free exercise. Pose a question that interests you and use ODV to explore the answer. Write a short paragraph explaining your thoughts.
Handouts and Directions:
· Lab instructions (data)
· Computer lab or moveable laptops with Internet access and Excel.
· LCD projector or SmartBoar
Ocean Productivity and Nutrients (LAB)
Word version of the module described here.
Ocean Data Tips
A document describing tips for using the data and program associated with this lab.
Instructors/TAs may find it useful to refer to following lectures:
· EESC Spring 2011 Ocean Productivity and Nutrients as well as Ocean Chemistry and Cycling (accessible only to Columbia University faculty and students): https://courseworks.columbia.edu/cms/
· EESC Fall 2007 lab and lecture materials are available on a publicly accessible site (will be updated with 2011 materials and data this summer): http://eesc.columbia.edu/courses/ees/climate/syllabus.html
Students summarize their findings in a lab report.
REFERENCES AND RESOURCES
See websites noted above in "Teacher Notes."
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