GULF OF MEXICO DEAD ZONE—STUDENT MICROPALEONTOLOGY ACTIVITY ABOUT HISTORY OF A MODERN SOCIETAL ISSUE

Geosciences can provide historical context for important societal issues. One example is the “dead zone” in the Gulf of Mexico. Organic matter from the Mississippi River leads to eutrophication, depleting oxygen in the water column. This causes hypoxia and eliminates aquatic life. The size of the zone is correlated with Mississippi River discharge. The interpretation is that the dead zone is caused by introduction of anthropogenic fertilizers (broadly) running off the drainage basin of the river and this increased in the past century. From a historical perspective, we can wonder if the dead zone has just developed or how it existed earlier than the current anthropogenic input.

I have created an activity for students to learn how micropaleontologic data shed light on this question and provide historical context. Some benthic foraminifera tolerate low-oxygen conditions. Cores from outside the modern hypoxia zone, on its edge, and within it provide samples of benthic forams over the last 1000 years (data from the USGS). Relative abundance increase of low-oxygen forams indicate hypoxia and possibly floods. When correctly graphed, students can recognize how the record of low-oxygen conditions has changed at these locations. For this presentation, participants will receive the graphs and latitude/longitude positions of the cores so they can judge the historical changes in space. The dataset shows that hypoxic conditions have formed in the past in the Gulf of Mexico, but primarily during brief events (presumably floods) until recently. Lead-210 chronology in one core gives precise timing that major increase in hypoxia occurred in the last 60 years. Students can infer that organic matter input to the Gulf to cause eutrophication increased consistent with increased anthropogenic input of the last century. In practice, I have experienced two hurdles to effectiveness. Students have difficulty making the graphs. They also have trouble making a full interpretation of each core/synthesizing across all the cores if I avoid making the exercise cookbook. In this activity, students gain experience in creating graphs, interpreting them, recognizing spatial variation, and seeing how micropaleontology provides historical context to an important phenomenon.