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Multimillennial climate-freshwater legacy beneath a large-river delta-front estuary
Chong Sheng1,2, Liuting Yuan3, Jiu Jimmy Jiao1,4,5
1Guangdong-Hong Kong Joint Laboratory for Soil and Groundwater Pollution Control, Department of Earth and Planetary Sciences, The University of Hong Kong, Hong Kong, China.
Science Advances
|April 1, 2026
Summary
Vast offshore freshwater reservoirs, remnants of ancient rainfall, have been discovered beneath the Pearl River estuary. This ancient groundwater offers a resilient, long-term resource for coastal water security.
Area of Science:
- Geology and Hydrology
- Marine Science
- Environmental Science
Background:
- Offshore relatively fresh groundwater (ORFG) is an understudied resource for addressing global freshwater scarcity.
- The origin, persistence, and vulnerability of ORFG are not well understood.
- Understanding these reservoirs is crucial for coastal water security.
Purpose of the Study:
- To investigate the origin and characteristics of a large ORFG reservoir.
- To determine the age and preservation mechanisms of this ancient groundwater.
- To assess the potential of ORFG as a strategic freshwater reserve.
Main Methods:
- Hydrochemical profiling and isotopic tracing to analyze groundwater composition.
- Groundwater dating using 14C and 226Ra/230Th activity ratios.
- Numerical modeling to constrain degradation timescales and assess resilience.
Main Results:
- A vast reservoir of ancient meteoric groundwater was identified beneath the Pearl River estuary and adjacent shelf.
- Groundwater ages range from tens of millennia, indicating preservation from the Late Pleistocene.
- Evidence confirms the fossil nature of the groundwater, distinct from modern circulating systems.
- Numerical modeling suggests significant resilience to natural degradation.
Conclusions:
- ORFG beneath the Pearl River estuary is a relic of ancient recharge, preserved for millennia.
- This ancient groundwater represents a stable and potentially strategic freshwater resource.
- Findings have significant implications for coastal water security in the context of climate change.
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