History of the Gulf of Mexico "Dead" Zone
Summary
Student analysis of the last 1000 years of the Gulf of Mexico hypoxia zone (informally "dead" zone) by using relative abundance of low-oxygen tolerant benthic foraminifera. In this example of environmental micropaleontology, students evaluate whether the "dead" zone has existed in its current form for many centuries or has become more intense in the time of increased anthropogenic input of organics (i.e., fertilizer).
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Context
Audience
Upper-level undergraduate course
Skills and concepts that students must have mastered
Basic knowledge of forams (i.e., what they are, benthic vs. planktonic, very basic foram ecology). Since this activity uses abundance data (already determined), students don't need foram identification skills, however.
Making scatterplots in Excel or other graphing software
How the activity is situated in the course
An exercise in the last portion of the course that deals with how paleontology addresses broader scientific questions.
Goals
Content/concepts goals for this activity
How geologic or paleontologic methods developed for deep time can be used to investigate shallow time, that is, the use of environmental micropaleontology.
Use of fossils to infer paleoenvironmental conditions
Higher order thinking skills goals for this activity
Interpret pattern of hypoxia of several cores individually from graphs of foram abundance through time
Synthesize the pattern across all locations through time and connect these patterns to location (where cores are relative to modern hypoxia zone)
Evaluate how the historical record supports, modifies, or refutes the hypothesis that modern hypoxia is driven by anthropogenic effects.
Other skills goals for this activity
Build graphing skills with moderately large datasets (too large to graph by hand)
Develop appropriate skepticism about interpolation of numerical ages between broadly spaced tiepoints.
Description and Teaching Materials
In this exercise, students have background on the "dead" zone and download the data spreadsheet and location figure. The data (from USGS research) consist of abundances of benthic forams versus depth for 3 shallow gravity cores (approx. 1.6-2.5 m long) and 1 box core (approx. 40 cm long) from the the Gulf of Mexico. Forams have been identified at 1 cm intervals throughout each of these cores. Two of the gravity cores have C14 dates at their bottom; the box core has Pb210 chronology. Students calculate the relative abundance of three taxa of low-oxygen tolerant benthic forams, graph this abundance against depth for the cores, and print the graphs. Then they evaluate the pattern in each core, relate the patterns to locations relative to the modern hypoxia zone, and make interpretations. They also attempt to identify the effect of the 1927 Mississippi River flood (floods increase hypoxia). This requires adjusting the interpolated numerical ages from Pb210. I have arbitrarily labeled this a "lab activity" but it could be a "classroom activity" and since my Paleontology course has no separate lab, technically that is what is is for me.
Dead zone student exercise (Microsoft Word 42kB May22 14)
Dead zone student data (Excel 2007 (.xlsx) 145kB May22 14)
Hypoxia map--no cores marked (Acrobat (PDF) 146kB May22 14)
Dead zone data with graphs (Excel 2007 (.xlsx) 144kB May22 14)
Hypoxia map with core locations (Acrobat (PDF) 150kB May22 14)
Graphmaking hints (Microsoft Word 23kB May22 14)
Teaching Notes and Tips
See GOM Dead Zone Instructor advice (Microsoft Word 2007 (.docx) 28kB Jun12 14) for detailed information.
Community Contributions
- A modified student-facing spreadsheet with the data. I placed all of the data (core locations, age data, foram data, map) that Farley made available into a single spreadsheet to have everything in one place. In the spreadsheet I also placed instructions for working the data. Part of this involved highlighting parts of the data in different colors, again to aid navigation and ease of use.
- The text and images that introduced the assignment to students through the course Learning Management System (LMS).
I had no emails from students with questions on how to perform the activity or requests for clarification. The responses to the prompts indicated a robust data analysis and interpretation had taken place. There was a noticeable difference in performance between sophomores and juniors+seniors, with the latter submitting more sophisticated discussions/responses. That said, the sample size is quite small.
Assessment
I assess the quality and accuracy of student graphs using the graphs I've made (in Dead Zone data with graphs).
I also assess their written analysis of each core, the overall spatial pattern, and their interpretation of implications for the interpretation of effects of anthropogenic input. The Instructor Notes gives rough "official" interpretations, but I'm more interested for assessment in student detail and how they support their argument.
References and Resources
Handy summary about the Dead Zone:
Osterman, L.E., Poore, R.Z., Swarzenski, P.W., 2008, Gulf of Mexico Dead Zone–1000 year record: U.S. Geological Survey, Open-File Report 2008-1099, 2 p. http://pubs.usgs.gov/of/2008/1099/
There is an activity on the modern dead zone and policy implications for the upstream Mississippi River at
http://serc.carleton.edu/quantskills/activities/13946.html