Deglacial water-table decline in Southern California recorded by noble gas isotopes

Alan M. Seltzer; Jessica Ng; Wesley R. Danskin; Justin T. Kulongoski; Riley Gannon; Martin Stute; Jeffery P. Severinghaus

doi:10.1038/s41467-019-13693-2

Home/Archive/USGS

USGS · 70225713

Deglacial water-table decline in Southern California recorded by noble gas isotopes

Alan M. Seltzer·Jessica Ng·Wesley R. Danskin·Justin T. Kulongoski·Riley Gannon·Martin Stute·Jeffery P. Severinghaus

View original source ↗Export metadata ↓

Abstract

Constraining the magnitude of past hydrological change may improve understanding and predictions of future shifts in water availability. Here we demonstrate that water-table depth, a sensitive indicator of hydroclimate, can be quantitatively reconstructed using Kr and Xe isotopes in groundwater. We present the first-ever measurements of these dissolved noble gas isotopes in groundwater at high precision (≤0.005‰ amu −1 ; 1σ), which reveal depth-proportional signals set by gravitational settling in soil air at the time of recharge. Analyses of California groundwater successfully reproduce modern groundwater levels and indicate a 17.9 ± 1.3 m (±1 SE) decline in water-table depth in Southern California during the last deglaciation. This hydroclimatic transition from the wetter glacial period to more arid Holocene accompanies a surface warming of 6.2 ± 0.6 °C (±1 SE). This new hydroclimate proxy builds upon an existing paleo-temperature application of noble gases and may identify regions prone to future hydrological change.

Explore related subjects

Nature Communications Article

Source-reported bounding extent: 32.56996256044998° to 32.99484290420988° latitude; -117.44384765625° to -116.663818359375° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Alan M. Seltzer, Jessica Ng, Wesley R. Danskin, Justin T. Kulongoski, Riley Gannon, Martin Stute, Jeffery P. Severinghaus. 2019-12-16. Deglacial water-table decline in Southern California recorded by noble gas isotopes. https://doi.org/10.1038/s41467-019-13693-2

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Barrier island geomorphic complexity drives storm and post-storm response

Barrier islands are at the forefront of climate-driven changes, with their resiliency threatened by rapid fluctuations in the physical drivers that shape them. Quantifying magnitudes and directions of storm-driven sediment fluxes and rates and modes of sediment recovery is essential for predicting barrier island trajectories. Yet scarce shoreface observations have limited such efforts. Here, shoreface-inclusive measurements of barrier sediment fluxes over five years following an extreme storm reveal distinct sediment redistribution patterns that vary with island geomorphology. Overwash fluxes were low compared with seaward fluxes, inlet-related landward transport, and previously modeled estimates. Without these observations, models may overestimate island elevation-building capacity that is key to sea-level adaptability. Post-storm recovery was incomplete despite human intervention, altering barrier sediment distribution from pre-storm conditions. This may increase vulnerability to future storms and rising water levels and suggests management approaches tailored to island geometry may better compete with climate change effects.

New York↗

USGS2026

The saline groundwater legacy of a large buried coastal paleo-estuary

Elevated groundwater salinity in coastal regions threatens the beneficial use of fresh groundwater. Coastal groundwater management typically focuses on preventing intrusion from modern sources of seawater; however, past geological processes can also leave a legacy of saline groundwater now hidden in the subsurface. Here, multiple extensive airborne electromagnetic surveys provide detailed evidence of residual salinity from a paleo-estuary filling a late Pleistocene incised valley impacting more than 10,000 km 2 that is now hidden beneath coastal Louisiana’s deltaic plain. Our results show that the three-dimensional pattern of saline groundwater beneath Louisiana mimics that of near-surface aquifers surrounding the modern Delaware Bay estuary, fingerprinting the signature of the past drowning of a large, incised valley of the Mississippi River following post-glacial sea-level rise. These findings demonstrate a new framework for understanding legacy sources of saltwater critical for managing stressed water resources along global coastlines.

Louisiana↗

USGS2026

Sharp structural variability of the Gorda slab imaged by a fiber array

Structural variability at the subduction interface imposes stress and strength heterogeneity that affects the behavior of megathrust earthquakes. Characterizing this variability can be challenging because the slab interface is often deep and seismically quiet. Seismic wavefields from intraslab earthquakes can contain high-frequency phase conversions from the megathrust fault that are delayed and distorted by interface topography and velocity heterogeneity. Distributed acoustic sensing (DAS) allows for long-term deployments of dense seismic arrays that can yield many observations of these converted phases at high spatial resolution over large areas. Here, we develop a technique to identify and enhance slab-converted phases in DAS data, and we pick the differential arrival times and relative polarities between the direct and converted phases at short wavelength along the fiber optic cable. We apply this framework to earthquake wavefields measured by a DAS array at the southern end of the Cascadia Subduction Zone, above the locked zone, which suggests kilometer-scale interface roughness and variations in crustal thickness and absolute depth of the Gorda slab. Converted phase wavefields also suggest sharp variability in the presence and position of fluids in the slab and forearc crust.

California↗