Analyzing pollen in lake sediments to understand climate change

Dan Maxbauer
Carleton College, Geology Department
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Initial Publication Date: May 15, 2019

Summary

This activity is aimed at analyzing a stratigraphic sequence of pollen samples from local lake sediments in order to reconstruct past climate and environmental conditions. The main activity fits into a larger course project (described below) but could likely be adapted and taught as a stand alone unit. For this activity, students work to become familiar with pollen types by looking at reference slides with microscopes. Each student draws a sketch for the different reference pollen types to create a key for pollen identification based on their own observations. Once all reference pollen has been studied, students begin pollen counts on samples from a lake sediment record. Individual students count 1-3 slides worth of pollen and the class pools data together to create a full pollen record. This dataset is integrated into a larger project using multiple proxies to reconstruct past climates from a local lake - but the data could independently be analyzed and discussed if this activity was part of a stand alone unit. Student ultimately work to understand and make connections between plant communities and climate variables (temperature, precipitation) and use these relationships to interpret changes to those variables in the past.

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Learning Goals

Students should aim to learn 1) connections between plants and climate, 2) controls on biome distribution, 3) importance of careful observation and quality control on data collection, and 4) how to integrate and draw inferences from a dataset. Skills required for this activity are the ability (or willingness to learn) to work with a spreadsheet to gather and manipulate data, to plot results to create figures, and to synthesize a conclusion from a multiple types of data.

Context for Use

The educational level for this activity is designed for introductory college students, but could easily be applied to upper level college courses or adapted for high school students. Work for this activity occurs primarily during one 4 hour lab, but often work extends beyond that time. Technical skills require experience or ability to work with microscopes and spreadsheet skills to organize and manage pollen data as it is collected. No prior knowledge is required.

Description and Teaching Materials

The workflow for this activity typically involves:
  1. An introductory lecture introducing pollen, covering the relationships between different biomes and climate, and describing some of the main pollen types present in the samples.
  2. Work with reference pollen slides to develop identification key unique to each student.
  3. Pollen counts on pollen slides from lake sediment cores.
  4. Integration of data from all students in one spreadsheet for students to organize and being analyzing dataset.
  5. Final product for this activity typically is integrated into a larger project on lake sediments which requires integration of pollen data with other proxy datasets. However, activity could be modulated to create final interpretation based solely on pollen data.

Assessment

Assessment for this activity is based primarily on the consistency with how students are able to interpret the pollen data, particularly in light of data from other proxies. Students present results in a formal scientific presentation at the end of the term and are graded in groups.