Paleoclimate and Ocean Biogeochemistry

Allison W. Jacobel, Middlebury College and Brown University

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Summary

This module guides students through an examination of how surface ocean productivity relates to global climate on glacial-interglacial timescales and how the availability of ocean nutrients can be correlated with changes in productivity. In Part A, students reflect on how nitrogen and phosphorous are distributed globally, and how patterns of primary productivity compare with those nutrient patterns. In Part B, students use statistical analysis to examine the influence of dust-borne iron on carbon export in two ocean regions. In Part C, students choose a data set to investigate the relationship between ocean carbon export and climate, formulate a hypothesis to test using that data set, and share their findings with peers.

The overarching question the module helps students answer is:

How does primary productivity influence global climate?

Strengths of Module

This activity has been designed using the Project EDDIE (Environmental Data-Driven Inquiry and Exploration) module framework. Thus, the module is focused on giving students an opportunity to use large, real-world data sets to improve their quantitative reasoning through self-directed inquiry.

This module uses published data sets that are fundamental to our understanding of Earth's biogeochemical and climate history. The module guides students through a descriptive and statistical analysis of these data sets that includes both spatial and temporal dimensions. Students also have the opportunity to develop a hypothesis about variables that have significance for global climate and test that hypothesis with data. The module structure requires students to work both independently and collaboratively, and provides clear opportunities for both self-assessment and instructor evaluation throughout.

What does success look like

By the end of the module students should be able to:

  1. Describe patterns of nitrogen (N), phosphorous (P) and primary productivity in the global oceans. Discuss regions where productivity aligns with expectations based on macronutrient availability and identify one region where they do not.
  2. Quantify the magnitude of glacial-interglacial changes in iron (Fe) delivery to the oceans via dust.
  3. Describe and evaluate the statistical evidence they obtained for relationships between dust and increased ocean productivity at two sites, and provide a hypothesis for why those relationships might be different.
  4. Describe the relationships between Southern Ocean carbon export and three paleoclimate data sets that reflect different dimensions of Earth's climate system.

Context for Use

This module was designed for use as part of an introductory undergraduate course on Earth's climate history. The module is also appropriate for use in introductory courses in oceanography, marine biology, and paleoclimatology. The module should take approximately 90 minutes to complete, including the presentation and discussion of the module PowerPoint. The activity requires that students have experience plotting quantitative data sets - both time series and scatter plots - and students need to know how to perform and interpret a linear regression. Module Activities A and B are designed to be completed individually; Activity C should be completed in collaborative teams.

Description and Teaching Materials

Why this Matters:

The deep ocean is the second largest reservoir of carbon, after carbonate rocks. The partitioning of carbon between the ocean and the atmosphere significantly impacts global climate on both modern and geologic timescales. Understanding the mechanisms of ocean carbon storage and release is therefore critical for understanding global climate past and present.

Marine primary productivity is one of the crucial mechanisms that influences the partitioning of carbon between the ocean and the atmosphere. The balance between surface export productivity (carbon removal from the ocean's surface) and the upwelling of respired carbon determines the net flux of CO2 into (or out of) the atmosphere. Surface export productivity is in turn largely controlled by the distribution of macro- and micro- nutrients. These nutrient patterns are also fundamental to our understanding of ocean ecosystems as photosynthetic organisms form the basis of the food web.

Quick outline/overview of the activities in this module

  • Activity A: Examine and describe spatial patterns of nitrogen and phosphorus concentrations, N:P ratios, and primary productivity in the global oceans.
  • Activity B: Investigate how the input of iron-bearing dust to the oceans varied during glacial and interglacial climates of the past and how that input affected primary productivity.
  • Activity C: Students choose a climate data set (options below), formulate a hypothesis, and examine the relationship between Southern Ocean carbon export and that data set to test their prediction. They then connect with a group who chose a different climate data set and present their results.

A complete student handout containing the module components and guiding questions is available under Teaching Materials

Teaching Materials:

Data sets:

Teaching Notes and Tips

Please see the instructor's manual for details about prerequisite knowledge/skills, potential module sticking points, suggestions about potential variations to the module, and additional information that may enhance student learning and understanding. Plan for the module to take students ~90 minutes depending on their level of familiarity with their plotting software of choice.

Workflow of this module:

  1. Have students download excel and install the data analysis toolkit.
  2. Have students download the student handout.
  3. Instructor begins class by giving a brief presentation to introduce the module and the proxies used in Part C.
  4. Students download the data sets.
  5. Students work through module activities.
  6. Students turn in their completed handout with answers to the questions and the graphs they made.

Measures of Student Success

Students will self-assess throughout the exercise by answering the module questions. Additional opportunities for reflection are built into Part C, in which students develop testable hypotheses, discuss their results with their peers and integrate their peers' work into their own understanding of the climate system.

Instructors can assess student's progress towards the learning goals by evaluating their answers to the module questions.

Final Data Plots and Answer Key:

  • Excel answer key (plots) -
  • Student handout answer key -

References and Resources

Papers presenting the original data sets*, and reference articles/links

*Note that these data sets are as presented by their original authors and do not contain the interpolated data sets as do the data sets attached directly to this module document.