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Abstract During the last ice age, the western United States was covered by large lakes, sustained partly by higher levels of precipitation. Increased rainfall was driven by the atmospheric circulation associated with the presence of large North American ice sheets, yet Pleistocene lakes generally reached their highstands not at glacial maximum but during deglaciation. Prior modeling studies, however, showed nearly monotonic drying since the last glacial maximum. Here I show that iTraCE, a new transient climate simulation of the last deglaciation, reproduces a robust peak in winter rainfall over the Great Basin near 16 ka. The simulated peak is driven by a transient strengthening and southward shift of the midlatitude jet. While meltwater forcing is an important driver of changes to the North Pacific Jet, changing orbital conditions and rising atmospheric CO2also shift the jet south and contribute to wetter conditions over the western US during deglaciation.
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Wind‐Driven Evolution of the North Pacific Subpolar Gyre Over the Last Deglaciation
Abstract North Pacific atmospheric and oceanic circulations are key missing pieces in our understanding of the reorganization of the global climate system since the Last Glacial Maximum. Here, using a basin‐wide compilation of planktic foraminiferal δ18O, we show that the North Pacific subpolar gyre extended ~3° further south during the Last Glacial Maximum, consistent with sea surface temperature and productivity proxy data. Climate models indicate that the expansion of the subpolar gyre was associated with a substantial gyre strengthening, and that these gyre circulation changes were driven by a southward shift of the midlatitude westerlies and increased wind stress from the polar easterlies. Using single‐forcing model runs, we show that these atmospheric circulation changes are a nonlinear response to ice sheet topography/albedo and CO2. Our reconstruction indicates that the gyre boundary (and thus westerly winds) began to migrate northward at ~16.5 ka, driving changes in ocean heat transport, biogeochemistry, and North American hydroclimate.
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- Award ID(s):
- 1929775
- PAR ID:
- 10375397
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 47
- Issue:
- 6
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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