Results of a water isotope-enabled model that simulates Pliocene conditions and isotope records summarized in Bhattacharya et al. [2022]. The model imposes a pattern of increased warming of surface waters off the southern California margin relative to the tropical Pacific shown in (a). Model predicted anomalies in δD of (b) water vapor and (c) precipitation, as well as (d) precipitation amount, all consistent with the westward extension of the North American monsoon. (e) Detail showing vertical profile of lower-atmospheric changes in δD of vapor and θe in the dashed box shown in panel d. Credit: Bhattacharya et al., 2022, Figure 2
Source: AGU Advances
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.

Climate models predict future drying in areas like subtropical southwestern North America, including Arizona and Baja/southern California. However, paleoclimate proxies suggest that this region was in fact wetter than today at the end of the Pliocene warm period, a time often proposed as a potential analogue for a near-future climate.  Bhattacharya et al. [2022] present a 3.5 million-year record of leaf wax δD indicating an increase in summer monsoon rains caused by a westward expansion of the North American Monsoon (NAM). Applying an isotope-enabled climate model, they link the stronger monsoon with a diminished east Pacific subtropical-tropical temperature gradient. As similar patterns occur during recent episodes of high NAM rainfall associated with marine “heat waves”, they infer that this mechanism can help explain current monsoon variability and underscore the potential relevance of the Pliocene as an analog for future hydroclimate in this and other regions.

Citation: Bhattacharya, T., Feng, R., Tierney, J. E., Rubbelke, C., Burls, N., Knapp, S., & Fu, M. [2022]. Expansion and intensification of the North American Monsoon during the Pliocene. AGU Advances, 3, e2022AV000757.

—Susan Trumbore, Editor in Chief, AGU Advances

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