STUDENT INVESTIGATION OF THE HISTORY OF THE GULF OF MEXICO “DEAD ZONE”

A micropaleontologic dataset on the history of the Gulf of Mexico “dead zone” provides for data-driven student investigation into historical context for a modern environmental phenomenon. Hypoxia occurs in the Gulf of Mexico west of the Mississippi River mouth, resulting from eutrophication of organics from the River and varies in size correlated with river discharge. Its cause is interpreted as driven by anthropogenic runoff of fertilizer and other organics.

Goals for student learning include making/interpreting graphs, synthesizing multiple locations in geographic context, and learning about the discipline of environmental micropaleontology.

Historical investigation uses benthic forams including those tolerant of low-oxygen conditions as a proxy over the last 1000 years. High abundances of Protononion, Epistominella, and Buliminella as a proportion of all benthics (PEB index) imply hypoxia. The data, from Osterman, et al. (USGS), are foram abundances from box and gravity cores that sample in the modern hypoxia zone, on its edge, and well outside. Peaks in the PEB index indicate greater organic input and possibly large floods. Density of samples requires computer graphing; my students find making useful graphs a challenge.

Students can recognize the following from their graphs and core locations: The core outside modern hypoxia has low PEB values throughout. The core on the edge of modern hypoxia has spikes in PEB implying intermittent hypoxia from floods and increase in the shallowest core. The cores within modern hypoxia show low PEB index at the base, periodic spikes upward, and a striking increase in the shallowest part. These data are consistent with an increase in hypoxia in the youngest record when anthropogenic input of organics increased in Mississippi River runoff.

In my experience with this exercise, a challenge is balancing telling students too closely what to do versus encouraging their own critical thinking. Making it too open-ended has resulted in terse student responses that don’t fully engage the material, but I want to avoid making it too cookbook. In my paleontology course, this exercise fits with other data-driven exercises that show students how fossils are used to address key paleobiologic, stratigraphic, and paleoclimatic questions.