Holocene Optimum: A time of massively increased sediment discharge for Asian Rivers

Steve Kuehl, Lonnie Leithold, Kathleen Surpless, Adam Hoffman

Summary

This is one component of the Source to Sink Mini Lesson Set

This module is part of a larger set of mini-lessons that explores the variations in water and particulate mass flux from rivers that result from changing climate patterns and human activity in the Holocene. Long-period variations in runoff will be explored in this module on the Holocene Climatic Optimum, when intensification of the Southwest monsoon affected massively increased river discharge in South Asia. The exercise will detail the operation of the Asian monsoon and interpret stratigraphic evidence for increased sediment discharge during the Holocene Climatic Optimum using the Ganges-Brahmaputra as an example.

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Learning Goals

After completing this module, students will have an understanding of the physical controls on the Asian Monsoon system, including basic orographic rainfall patterns and its seasonality in South Asia. Students will also be introduced to the concept of isotopic distillation of rainfall along the monsoonal flow pathways. Students will learn to manipulate stratigraphic data to produce linear sedimentation rates from core data and volume estimates from isopach maps in order to understand longer-term (beyond historical gauging records) changes in riverine mass fluxes.

Context for Use

This module is appropriate for mid- and upper-level undergraduate courses in oceanography, environmental science, sedimentology and stratigraphy, and geography. Students should have a basic understanding of river hydrology and the role of river sediments in constructing the continental margin. The students will need computers connected to the internet, in order to access online databases and visualization freeware such as GeoMapApp, and Google Earth. The entire module is suitable for a multi-day activity.

Description and Teaching Materials

This lesson consists of two parts which address 1) the Asian monsoon system and 2) the Ganges-Brahmaputra river system. Each part includes an introductory powerpoint lecture and student exercise.

The complete exercise materials (Parts 1 and 2) can be obtained here: Holocene Climatic Optimum (Microsoft Word 2007 (.docx) 489kB Nov18 13)

Part 1. Asian Monsoon and Climate (PowerPoint 2007 (.pptx) 2.6MB Sep1 15) a powerpoint presentation introducing the fundamental concepts related to Monsoon conditions in Asia.

  • Short (in class) GeoMapApp exercise to help illustrate Orographic Effect
    • Use distance profiling tool to see depth-elevation transect from Bay of Bengal to Himalayan Plateau.
    • Use Data Sets "Atmosphere and Precipitation" to compare annual rainfall totals at stations in the lowlands and plateau.
    • Optional exercise to compare del18O values in rainfall from

Part 2. Introduction to the Ganges-Brahmaputra Delta-Fan system (PowerPoint 7.4MB Sep1 15)

  • Exercise (introduced in class take home) on use of stratigraphic data to calculate sediment budgets for the Ganges-Brahmaputra system.
    • Use bore-hole data from three wells to estimate and compare linear accumulation rates for two periods (7-11ka and 0-7 ka).
    • Examine two transects across Bengal Basin from multiple boreholes to explore "real world" challenges of constructing a sediment budget from a limited data set.
    • Take isopach estimates of sediment volume during the two time periods, and convert these to annual river fluxes based on measured bulk density. Discuss how do the values compare to the modern gauged river discharge and to each other? What are some of the limitations of such estimates?


Assessment

Assessment is through written reports, group and/or individual presentations, homework assignments, and exam questions.

References and Resources

GeoMapApp - an exploration and visualization application to be used with the exercise in Part 1 above.

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