Texas A&M University Student Spotlight: Tracking Monsoons with Thorium

Understanding ocean processes often requires a little detective work, identifying clues left in the marine environment for scientists to find. The Niger River’s flow and discharge are controlled by the amount of regional precipitation in West Africa. West Africa’s regional precipitation is controlled by the west African monsoon, when winds shift seasonally causing both a wet and dry season. Changes in monsoon intensity can affect the stability of regional infrastructure, as well as financial and food security.

Changes in west African monsoon intensity as a response to climate events can be studied by looking at the sediments deposited in the Niger River Delta. An isotope is an element with a specific number of neutrons in its nucleus; some isotopes in marine environments can be used as tracers, informing scientists about chemical or physical processes. Uranium and thorium-230 isotope ratios in sediment can be used to estimate rates of sediment accumulation, and if the sediment has been transported to or from the surrounding area.  If the amount of thorium-230 found in the sediment is higher than the theoretically-estimated amount, new sediment has been transported to the area and if it is lower, sediment has been removed.

Shifting of the Intertropical Convergence Zone is responsible for monsoons.
Shifting of the Intertropical Convergence Zone is responsible for monsoons.

 

Another form of thorium, thorium-232, can be used to study sediment sources. Thorium 232 is virtually entirely derived from continents.  Previously, thorium-232 was only used to study the amount of windblown sediment to the open ocean.  However, current research in the department of oceanography at Texas A&M is hoping to expand the use of both thorium 230 and 232 to study changes in the delivery of sediment and other material to the ocean by rivers. Since the Niger River’s flow and discharge is controlled by the amount of regional precipitation, and West Africa’s regional precipitation is controlled by the west African monsoon, the amount of sediment delivered by the Niger river should reflect the intensity of the monsoon.

This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click On the Ocean.

Script Author: Ruby Schaufler

Editor: James M. Fiorendino

Contributing Professor: Dr. Kathryn Shamberger