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Hydrology controls lithium isotopes in rivers and seawater
High-resolution river water δ7Li, 87Sr/86Sr, and hydrometeorological data from the NE Tibetan Plateau. Weekly variations of δ7Li and 87Sr/86Sr in the carbonate-dominated BH (a) and silicate-dominated SL (b) catchments (Supplementary Fig. 2) along with daily Qw and precipitation, showing inverse trends between δ7Li and Qw in each river. When plotting up weekly data from the two rivers together (c), there is still an overall negative relationship, highlighting a strong hydrology control on riverine δ7Li. (d) 87Sr/86Sr versus Qw, showing large differences between the two rivers, reflecting their distinct lithology (Supplementary Fig. 3). The dashed lines in a and b represent ice-melting times. Errors for δ7Li are <0.9‰. The shaded regions in c show 95% confidence intervals. Symbols with black borders in c and d represent wet seasons, and others are dry seasons. Credit: Nature Communications (2022). DOI: 10.1038/s41467-022-31076-y
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High-resolution river water δ7Li, 87Sr/86Sr, and hydrometeorological data from the NE Tibetan Plateau. Weekly variations of δ7Li and 87Sr/86Sr in the carbonate-dominated BH (a) and silicate-dominated SL (b) catchments (Supplementary Fig. 2) along with daily Qw and precipitation, showing inverse trends between δ7Li and Qw in each river. When plotting up weekly data from the two rivers together (c), there is still an overall negative relationship, highlighting a strong hydrology control on riverine δ7Li. (d) 87Sr/86Sr versus Qw, showing large differences between the two rivers, reflecting their distinct lithology (Supplementary Fig. 3). The dashed lines in a and b represent ice-melting times. Errors for δ7Li are <0.9‰. The shaded regions in c show 95% confidence intervals. Symbols with black borders in c and d represent wet seasons, and others are dry seasons. Credit: Nature Communications (2022). DOI: 10.1038/s41467-022-31076-y
Seawater lithium isotopes (δ7Li) record changes over Earth history, including a ~9‰ increase during the Cenozoic, which is interpreted as the reflection of either a change in continental silicate weathering rate or weathering feedback strength, associated with tectonic uplift. However, mechanisms controlling the dissolved δ7Li remain debated.
Researchers from the Institute of Earth Environment of the Chinese Academy of Sciences and their collaborators from the U.K, France and Australia have found a clear link between δ7Li and hydrology based on data from river samples collected across seasonal changes in river flow.
The findings were published in Nature Communications on June 10.
When adding these new data to a global compilation of rivers (across latitudes and basin sizes), they found a consistent story: when the climate is dry, river δ7Li values are high, and when the climate is wet, river δ7Li values are low. They interpreted this result in emerging theme regarding continental weathering: that water residence time controlled river δ7Li values.
Then they re-examined geological records of shifts in δ7Li (from the last glacial to >106 years) and found that the dataset can be explained by a similar mechanism—shifts in the fluid residence time linked to changes in continental hydrology and the water cycle.
The researchers showed, for the first time, that a hydrological control mechanism can explain all δ7Li records across various climatic transitions during the last ~445 million years, and led to a provocative conclusion: the Cenozoic seawater δ7Li record reflected overall drying of the continental climate over millions of years, rather than control by tectonic uplift.
More information:
Fei Zhang et al, Hydrological control of river and seawater lithium isotopes, Nature Communications (2022). DOI: 10.1038/s41467-022-31076-y