The self-organized and rhythmical shapes of sand waves/dunes and the related physical mechanisms are always attractive to scientists. Till now, massive studies have been deployed on the formation, dynamics, evolution of individual dunes on the seafloor. However, we still do not know much about the behaviors of a dune field. The interactions between different dune fields are still elusive.

Recently, a new research published in Geomorphology on Mar. 18 conducted by the team of Prof. YAN Jun from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS) opened up a door on this topic.

Researchers analyzed comprehensive field data collected in 2014 and 2016 in the Beibu Gulf, northwestern South China Sea and used simulation to present a vivid case of head-to-head encounter of mobile dune fields in a typical bidirectional flow system for the first time.

Researchers found the dune fields on the seafloor encountered with each other, end-by-end or side-by-side, and exhibited different patterns. The morphology and mobility of dunes across the encountering fields showed great variability, which were determined by regional net sand transport regime.

"The interactions between the encountering dune fields over the field boundaries look like the battle fronts in a war between troops, and the shifts of field boundaries are like advances and retreats of battle fronts. These boundaries and the behaviors between dune fields have never been described as clearly and visually as this research does. As commented by the reviewers, we presented new terminology on submarine dune studies," said Dr. MA Xiaochuan, the first and corresponding author.

Researchers also found that the field boundary was shifting from 2014 to 2016. The field boundary shifts reflected location inconsistency between the long-term accumulative transport balance (symmetrical shape) and the recent transport balance (non-migration) on dunes near field boundary, which was ascribed to the modulation of residual sand transports associated with the systematic changes in the regional flow conditions. These results suggest that the behavior of dunes near the field boundary can sensitively reflect the field-field interplay and reveal the relevant minor environmental changes.

 "This is quite important for the understanding of the past evolutions of shelf tidal environment. Usually, to extract the effects of tiny changes in the regional tide condition from geological or sediment records is extremely difficult. Now this result indicate that dune field interaction may give us a hand," said Dr. MA. "These results bring new insights into the surface processes under a bidirectional flow system on a planet, either in eolian or subaqueous environments."

The research was supported by the National Natural Science Foundation of China.

The study area (Upper left panel), the mechanisms of boundary shifts (lower left panel), and the constructed bedload transport pathways (right panel).

Ma, X., Li, J., Yan, J., Feng, X., Song, Y., Xu, T., Zhuang, L., Luan, Z., Zhang J. (2022). The encountering dune fields in a bidirectional flow system in the northwestern South China Sea: Pattern, morphology, and recent dynamics. Geomorphology, 2022, Volume 406, 108210.

MA Xiaochuan

Institute of Oceanology

Email: mxch@qdio.ac.cn

(Editor: ZHANG Yiyi)