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Paleorainfall proxy records from the Middle East have revealed remarkable patterns of variability since the penultimate glacial period (140 ka), but the seasonality of this signal has been unresolvable. Here, seasonal-resolution oxygen isotope data from Soreq Cave speleothems suggest that summer monsoon rainfall periodically reaches as far north as Israel—well removed from the modern monsoon—at times (∼125, 105 ka) that overlap with evidence for some of the earliest modern human migrations out of Africa. These seasonal proxy data are corroborated by seasonal-resolution model output of the amount and oxygen-isotope ratio of rainfall from an isotope-enabled climate model. In contrast to the modern regional climate where rainfall is delivered predominantly in winter months along westerly storm tracks, the model suggests that during extreme peaks of summer insolation—as occurs during the last interglacial (e.g., 125, 105 ka)—regional rainfall increases due to both wetter winters and the incursion of summer monsoons. This interpretation brings clarity to regional paleoproxy records and provides important environmental context along one potential pathway of early modern human migration.
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Late Oligocene Precipitation Seasonality in East Asia Based on δ 13 C Profiles in Fossil Wood
Abstract The onset, characteristics, and drivers of paleo‐monsoon conditions in East Asia remain a topic of heated debate. Records from the Eocene suggest pronounced rainfall seasonality consistent with monsoon rainfall across China, likely driven by migrations of the Inter‐Tropical Convergence Zone. Model simulations indicate that modern‐like monsoon circulation of China was established by the early Miocene at the latest, but uncertainty remains due to a paucity of proxy records from the Oligocene. Here, we provide the first annually resolved, quantitative estimates of seasonal precipitation from East Asia during the Oligocene, based upon intra‐annual variation in carbon isotopes across growth rings of exquisitely preserved fossil wood from southern China. We find a clear pattern of consistent, summer‐dominated precipitation with ∼4.5 times more precipitation in summer (Ps) than winter (Pw). Seasonal precipitation estimates were calculated using Monte Carlo resampling, resulting in medianPs = 1,042 (95% C.I. = 628–1,517) andPw = 235 (95% C.I. = 50–578), which are indistinguishable from the instrument record at a nearby weather station, wherePs = 977 (95% C.I. = 662–1,434) andPw = 292 (95% C.I. = 165–515), and from proxy application on two modern trees near the fossil site, wherePs = 1,058 (95% C.I. = 617–1,558) andPw = 188 (95% C.I. = 31–583). These data demonstrate that by the late Oligocene, precipitation patterns in East Asia had similar strength and seasonality to modern conditions, which suggests the presence of an East Asian Monsoon‐style system prior to the Neogene.
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- Award ID(s):
- 1903601
- PAR ID:
- 10449946
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Paleoceanography and Paleoclimatology
- Volume:
- 36
- Issue:
- 4
- ISSN:
- 2572-4517
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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