Orbitally paced groundwater in the Ice Age Southwest
Devils Hole cave calcite shows Nevada’s water table rose and fell with glacial cycles for 750,000 years, with a slow long-term drop.
Source
Moisture availability and groundwater recharge paced by orbital forcing over the past 750,000 years in the southwestern USA
What they did
The authors dated mammillary calcite from 350–820 ka with paired 230Th–U and 234U–U methods (92 samples) and mapped deposition elevations to reconstruct Ash Meadows/Devils Hole water-table history.
What they found
The continuous record starts after 746 ± 16 ka. Pre-350 ka oscillations reached 15 m amplitude with ~20 kyr beats. Mean long-term decline is 3.4 m per 100 kyr from +19.5 m at 719 ka to +9.9 m at 438 ka, then little secular drop. A major lowstand occurred at 550 ± 15 ka. Glacial highstands can imply up to +240% recharge in models.
The limits
What it doesn't show
234U–U ages beyond 650 ka carry percent-level systematic uncertainty in initial δ234U. One aquifer system may not represent the whole Great Basin. Recharge percentages come from a groundwater model, not direct flux measurements.
Key terms
- Mammillary calcite
- Cave calcite that grows underwater; its highest elevation marks past water-table highstands.
- 234U–U dating
- An age method for calcite older than ~650 ka that uses uranium-isotope disequilibrium when initial δ234U can be constrained.
- Orbital pacing
- Hydroclimate variations aligned with ~20 kyr precession and glacial–interglacial ice-volume cycles.
Flashcards
Research intelligence for this paper
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Quiz yourself
Devils Hole calcite can be dated back to about:
Common questions
Why Devils Hole?
It preserves an absolute-dated terrestrial water-table record through eight glacial cycles, near Yucca Mountain.
Is the water table only falling?
A slow 3.4 m/100 kyr decline is superimposed on large glacial–interglacial oscillations; after 438 ka the secular trend fades.
What drives moisture in moderate warm states?
The authors link recharge to insolation-induced North American ice-volume changes rather than local summer monsoon (<10% of modern recharge).
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