A BIG LESSON FROM TINY FORAMS: A SIMPLE HANDS-ON ACTIVITY FOR HOW SCIENTISTS INFER CLIMATE OF THE PAST

Our primary goal is to help students and the public understand how scientists infer the climate of the distant past, long before thermometers. The MSI-REaCH professional development workshop facilitates use of climate proxies in undergraduate exercises and models hands-on, inquiry-based pedagogy. Participation in MSI-REaCH was integral in creating an activity that conveys one way climate scientists know about past climate change. Marine sediments are an important means of inferring climate change over the past 100 Myr. Precise modern methods involve isotopic chemical processes, analysis, and interpretation that can be challenging for many to understand. Instead, we created a simple, engaging, hands-on example of a paleoclimate proxy temperature record showcasing a technique that is still used in research and corroboration of isotopic analysis. We rely on temperature sensitivity of indicator species, G. menardii, a well-established proxy for paleo-sea surface temperatures and climatic change. This planktic foraminfer needs relatively warm surface water and its abundance is highly sensitive to surface ocean layer temperatures in key regions of the tropics and subtropics. Downcore presence/absence of G. menardii has been used for decades to help establish timing of the glacial-interglacial cycles.

In this activity, which is appropriate for introductory lower-division courses and outreach events for K-12 students and the community, students are tasked with constructing a temperature record with age by examining a set of reusable cavity slides containing forams. Each cavity slide was created by washing and screening marine sediments from key depths of a single marine sediment core corresponding to known glacial and interglacial stages. Students first learn to identify G. menardii and then examine the slides to detect its presence or absence with core depth. The simple conclusion revealed is that sea surface water has alternated between warm and cold periods over time at this site. Students compare their proxy record to different proxy records (e.g. Antarctic ice core) to see a global signature of glacial-interglacial cycles driven by Milankovitch cycles. More advanced discussions focus on proxy records as pieces in a puzzle revealing changes in global ocean circulation and climate.