Paleoclimate and Ocean Biogeochemistry

Allison W. Jacobel, Brown University
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This module guides students in 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 who chose a different data set.

The overarching question the module helps students answer is:

How does primary productivity influence global climate?

Strengths of Module

This activity has been designed around the Project EDDIE (Environmental Data-Driven Inquiry and Exploration) module goals. 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, and includes both spatial and temporal dimensions. The last activity of the module gives students 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 self-assessment and instructor evaluation through the activity questions.

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 with emphasis on where the concentrations of all three variables are relatively high and where their concentrations show disparate variability.
  2. Quantitatively characterize the magnitude of glacial-interglacial changes in iron (Fe) delivery to the oceans via dust.
  3. Describe 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 which reflect different dimensions of Earth's climate system.

Context for Use

This module was designed for use as part of an undergraduate course on Earth's Climate System. The module might also be appropriate for use in courses that have a focus on oceanography, marine biogeochemistry, paleoclimatology or paleoceanography. 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 cross plots- (in any software environment), and students need to know how to perform a linear regression and interpret it. 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 can thus (and has) significantly impact(ed) global climate on 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 ecosystem 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 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 (make a prediction), and examine the relationship between Southern Ocean carbon export and that data set. 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:

  • Instructor's Manual -
  • Module Powerpoint - Module.pptx (PowerPoint 2007 (.pptx) 104.7MB Mar20 20)
  • Student Handout - Student Handout.docx (Microsoft Word 2007 (.docx) 23kB Apr17 20)

Data sets:

Part A

Part B

Part C

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 from 3-4 hours depending on their level of familiarity with their plotting software of choice.

Workflow of this module:

  1. Have students download the student handout.
  2. Instructor begins class by giving a brief presentation to motivate the module and introduce the proxies used in Part C.
  3. Students download the data sets.
  4. Students work through module activities.
  5. 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 identify 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:

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.