Sediments and the Global Carbon Cycle
North Carolina State University
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This is a series of exercises designed to introduce undergraduate students to the role of sediments and sedimentary rocks in the global carbon cycle and the use of stable carbon isotopes to reconstruct ancient sedimentary environments. Students will make some simple calculations, think about the implications of their results, and see an optional demonstration of the density separation of a sediment sample into a light, organic fraction and a heavier mineral fraction.
These exercises would be appropriate to an undergraduate course in sedimentary geology.
Skills and concepts that students must have mastered
Students should be familiar with the classification of siliciclastic sediments by grain size and should have a general knowledge of depositional environments (e.g., the definition of an estuary)
How the activity is situated in the course
In my courses on Sedimentology/Stratigraphy and Marine Sediment Transport, I generally devote several class meetings toward the end of the course to discussion of the implications of sedimentary geology for understanding Earth systems as a whole or current environmental topics. Discussion of the role of sediments in the carbon cycle fits well into those general themes.
Content/concepts goals for this activity
The objectives of these exercises are to:
1) Make students aware that sedimentary rocks are the primary long-term repository for carbon on Earth, although over the short term only a small amount of terrestrial and marine productivity is preserved.
2) Demonstrate the relevance of sedimentary geology to current issues (global warming).
3) Introduce students to the the importance of the relationship between organic carbon and mineral surfaces, and get them to think about its implications.
4) Introduce students to the use of organic geochemistry (stable carbon isotopes) for paleoenvironmental interpretations.
Higher order thinking skills goals for this activity
The exercises include the analysis of data (including making some simple calculations) and formulation of hypotheses.
Other skills goals for this activity
The exercises may optionally be done in small groups. Depending on time and facilities, collection and analyses of some sediment (or soil) samples for OC content, stable carbon isotopes, and or mineral surface area could be included.
Description of the activity/assignment
This set of exercises focuses on exploring the role of marine sediments in organic carbon burial and on using the composition of organic carbon preserved in sediments and sedimentary rocks to reconstruct ancient environments.
Determining whether students have met the goals
The exercises are completed by individual students or small groups and can be collected for grading.
More information about assessment tools and techniques.
Teaching materials and tips
Hedges, J.I., and Keil, R.G., 1995, Sedimentary organic carbon preservation: an assessment and speculative synthesis
: Marine Chemistry, v. 49, p.81-115.
Lamb, A.L., Wilson, G.P., and Leng, M.J., 2006, A review of coastal paleoclimate and relative sea-level reconstructions using 13C and C/N ratios in organic material: Earth Science Reviews, v. 75, p.29-57.
Meyers, P.A., 1997, Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes: Organic Geochemistry, v. 27, p.213-250.
Ransom, B., Kim, D., Kastner, M., and Wainwright, S., 1998, Organic matter preservation on continental slopes: Importance of mineralogy and surface area: Geochimica et Cosmochimica Acta, v. 62, p.1329-1345.
Zong, Y., Lloyd, J.M., Leng, M.J., Yim, W.W.-S., and Huang, G., 2006, Reconstruction of Holocene monsoon history from the Pearl River Estuary, southern China, using diatoms and carbon isotope ratios
: The Holocene, v. 16, p.251-263.