Rebecca Teed

Multiproxy Lake Sediment Records at the Northern and Southern Boundaries of the Aspen Parkland Region of Manitoba, Canada

Aspen parkland in central Canada may change substantially with increased warming and aridity as prairies replace forests, fire return intervals decrease and lake levels decline. We examined the relationships among vegetation, climate, fire and lake-ecosystem properties using lake sediment cores from the current northern and southern boundaries of the aspen parkland in southwestern Manitoba. We analyzed pollen, charcoal, sediment magnetics, biogenic silica, phosphorus, grain size and LOI, and dated the cores using 210Pb and 14C (AMS, calibrated). The Jones Lake record, from the southern edge of the parkland, began considerably earlier (~11 000 cal. BP) than the Mallard Pond record at the northern edge (~8600 cal. BP). These sites were characterized as prairie communities with low fire severity and relatively low lake productivity during the warm, dry period from 9000 to 6000 cal. BP. Beginning around 6500 cal. BP at Jones Lake and 3400 cal. BP at Mallard Pond, conditions appeared to get wetter as indicated by arboreal pollen percentage increases from ~30% to 40— 60%, concurrent with a rise in charcoal and proxies for lake productivity (biogenic silica and percent organic phosphorus). Similar to previous studies along the prairie—forest border, we found that charcoal increased during warmer, wetter periods with increased forest cover and fuel loading rather than during warmer, drier periods of prairie dominance. Our results underscore the importance of regional changes in moisture, and its effects on lake levels and forest biomass, as a dominant control of the aspen parkland dynamics.

A Student-Centered Project for Earth System History

This project is intended to replace some of the lectures that would ordinarily be necessary in a survey of Earth history over geologic time. The students will be taking the lecturers place in front of the class, presenting some of the material to their colleagues. Students will work in groups on a single era or period. Each student role-plays an expert (such as an oceanographer) and works with teammates playing other sorts of experts (a biologist, a geologist, an atmospheric scientist). Their presentation will require them to do research. They will be constructing resource lists to keep track of how they learned what they are presenting and beginning a critical analysis of resources found on the World Wide Web. They will also write brief individual summaries of the findings within their area of expertise. While the students are researching and preparing their presentations, the instructor will start giving lectures on the earliest time units, modeling the kind of presentation that the students will be doing. Eventually, students will take the stage, presenting their time units in order. Rubrics for assessing the presentation and the resource list are included.