The authors infer relative changes in precipitation seasonality using the difference in clay and carbonate δ18O (Δδ18Oclay−carbonate). More negative Δδ18Oclay−carbonate values in the west compared to the east are consistent with the winter-wet to summer-wet gradient spanning west-central North America today. The increase in Δδ18Oclay−carbonate in all three domains across the open habitat transition suggests winters became drier as grassy, open habitats expanded across the region. Credit: Kukla et al., 2022, Figure 3c
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Source: AGU Advances

The open habitat transition (OHT) in west-central North America has been explained as the result of climate change, but until now evidence has mostly relied on the vegetation record itself. Kukla et al. [2022] compiled phytolith and δ18O data of clays and pedogenic carbonates to analyze shifts in precipitation and vegetation over the Cenozoic in Western North America. They interpret a shift in the difference between clay and carbonate δ18O that corresponds with the timing of the open habitat transition to reflect a change in precipitation seasonality. Specifically, they suggest a decrease in the amount of wintertime precipitation and increased aridity best fits the available data, and further speculate that uplift of the Cascades could have triggered these precipitation changes. These hypotheses will spur further investigation into this important ecological change.

Citation: Kukla, T., Rugenstein, J. K. C., Ibarra, D. E., Winnick, M. J., Strömberg, C. A. E., & Chamberlain, C. P. [2022]. Drier winters drove Cenozoic open habitat expansion in North America. AGU Advances, 3, e2021AV000566.  

—Susan Trumbore, Editor in Chief, AGU Advances

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