Hydroclimate variability in tropical South America is strongly regulated by the South American Summer Monsoon (SASM). However, past precipitation changes are poorly constrained due to limited observations and high‐resolution paleoproxies. We found that summer precipitation and the El Niño‐Southern Oscillation (ENSO) variability are well registered in tree‐ring stable oxygen isotopes (
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In eastern Canada, Black spruce (
- Award ID(s):
- 1743738
- PAR ID:
- 10555928
- Publisher / Repository:
- Communications Earth & Environment
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Tropical South American climate is influenced by the South American Summer Monsoon and the El Niño Southern Oscillation. However, assessing natural hydroclimate variability in the region is hindered by the scarcity of long-term instrumental records. Here we present a tree-ring
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Abstract We evaluate the efficacy of the stable isotope composition of precipitation and plant waxes as proxies for paleoaltimetry and paleohydrology in the northern tropical Andes. We report monthly hydrogen (δ2Hp) and oxygen (δ18Op) isotope values of precipitation for an annual cycle, and hydrogen isotope values of plant waxes (δ2Hwax) obtained from modern soils along the eastern and western flanks of the Eastern Cordillera of Colombia. δ2Hp, δ18Op, as well as the unweighted mean δ2Hwaxvalues of
n ‐C29,n ‐C31, andn ‐C33n ‐alkanes in the eastern flank show a dependence on elevation (R 2 = 0.90, 0.82, and 0.65, respectively). In stark contrast, the stable isotope compositions of neither precipitation nor plant waxes from the western flank correlate with elevation (R 2 < 0.23), on top of a negligible (p ‐value >0.05) correlation between δ2Hwaxand δ2Hp. In general, δ2Hwaxvalues along the eastern flank of the Eastern Cordillera seem to follow the trend of a simple Rayleigh distillation process that is consistent with studies elsewhere on the eastern side of the Andes in South America. Neither δ2Hpnor δ18Op, and therefore δ2Hwax, offer reliable estimates of past elevations in the western flank, due perhaps to water vapor source mixing, evaporation overprint, contrasting plant communities, and/or differences in evapotranspiration. Thus, δ2Hwaxis only reliable for paleohydrology and paleoaltimetry reconstructions on the eastern flank of the Andes, whereas interpretations based on δ2Hpand/or δ18Opwest of the highest point of the Eastern Cordillera need to consider mixing of moisture sources in addition to precipitation amount. -
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Abstract Understanding the hydroclimate representations of precipitation
δ 18O (δ 18Op ) in tropical South America (TSA) is crucial for climate reconstruction from available speleothem caves. Our preceding study (Part I) highlights a heterogeneous response in millennial hydroclimate over the TSA during the last deglaciation (20–11 ka before present), characterized by a northwest–southeast (NW–SE) dipole in both rainfall andδ 18Op , with opposite signs between central-western Amazon and eastern Brazil. Mechanisms of suchδ 18Op dipole response are further investigated in this study with the aid of moisture tagging simulations. In response to increased meltwater discharge, the intertropical convergence zone (ITCZ) migrates southward, causing a moisture source location shift and depleting the isotopic value of the vapor transported into eastern Brazil, which almost entirely contributes to theδ 18Op depletion in eastern Brazil (SE pole). In contrast, the moisture source location change and local condensation change (due to the lowering convergence level and increased rain reevaporation in unsaturated subcloud layers) contribute nearly equally to theδ 18Op enrichment in the central-western Amazon (NW pole). Therefore, although a clear inverse relationship betweenδ 18Op and rainfall in both dipole regions seems to support the “amount effect,” we argue that the local rainfall amount only partially interprets the millennialδ 18Op change in the central-western Amazon, whileδ 18Op does not document local rainfall change in eastern Brazil. Thus, the paleoclimate community should be cautious when usingδ 18Op as a proxy for past local precipitation in the TSA region. Finally, we discuss the discrepancy between the model and speleothem proxies on capturing the millennialδ 18Op dipole response and pose a challenge in reconciling the discrepancy.Significance Statement We want to comprehensively understand the hydroclimate footprints of
δ 18Op and the mechanisms of the millennial variability ofδ 18Op over tropical South America with the help of water tagging experiments performed by the isotope-enabled Community Earth System Model (iCESM). We argue that the millennialδ 18Op change in eastern Brazil mainly documents the moisture source location change associated with ITCZ migration and the change of the isotopic value of the incoming water vapor, instead of the local rainfall amount. In contrast, the central-western Amazon partially documents the moisture source location shift and local precipitation change. Our study cautions that one should not simply resort to the isotopic “amount effect” to reconstruct past precipitation in tropical regions without studying the mechanisms behind it.
