Caves in Central China Reveal 500 Year Storm Cycle

Credit: Becky Strauss (University of Minnesota Ph.D. 2016).

The research used stalagmites collected from Heshang Cave in central China within the Yangtze River drainage. Researchers measured the magnetic properties of layered stalagmites, or columnar mineral deposits formed in caves by the growth of carbonate minerals from dripping groundwater. As they form over time, stalagmites develop annual layers of the mineral calcite, which are broadly similar to the rings of a tree.

They also collect iron-rich magnetic materials within these layers, which originated in overlying soil and are transported into the cave during precipitation and flooding events. These iron-rich minerals are far less than the width of human hair in size, but produce a strong magnetic signal that can be easily measured by modern magnetometers.

Feinberg and his team analyzed the magnetic properties of the layered stalagmites and discovered more than 8,000 years of data within the materials. The magnetic data varied in such a way as to trace out a 500-year cycle of storm variation, where wetter intervals showed an increased concentration of magnetic minerals. This correlates well with the cycles of El Niño Southern Oscillation pattern and measured changes in the amount of the energy from the sun. The cycle can be used to anticipate broad precipitation patterns in the future, and provide insight on climate change in the region over time. Feinberg and his team hope to expand this work wherever possible around the globe.

With the help of the Institute for Rock Magnetism (IRM), based at the University of Minnesota, the group was able to measure the magnetic materials within the speleothems to at a higher resolution and sensitivity than previously possible. Many rocks record the direction and strength of the Earth’s magnetic field at the time of their formation. By measuring these magnetizations, researchers are able to show how tectonic plates have moved around the globe through time, as well as how the Earth’s magnetic field has varies over timescales ranging from millions of years to decades. The short-term behavior of the Earth’s magnetic field has important ramifications for satellites and satellite communication.

Postdoctoral research associates Zongmin Zhu and Mark Bourne, IRM and Department of Earth Sciences; research scientist Hai Cheng, Xi’an Jiatong University; and Shucheng Xie, Chunju Huang and Chaoyong Hu, researchers from the China University of Geosciences are co-authors of the study.

The research was financially supported by the National Natural Science Foundation of China, State Key R&D program of China, and the 111 program (National Bureau for Foreign Experts and the Ministry of Education of China). The Institute for Rock Magnetism is funded by the U.S. National Science Foundation (NSF) Division of Earth Sciences Instruments and Facilities Program and the University of Minnesota. Feinberg’s research is funded by NSF-EAR1316385.

Contacts and sources:
 University of Minnesota College of Science and Engineering

To read the complete study entitled “Holocene ENSO-related cyclic storms recorded by magnetic minerals in speleothems of central China,” visit the PNAS website.

For more information about the Institute for Rock Magnetism, visit www.irm.umn.edu.