End of Green Sahara amplified mid- to late Holocene megadroughts in mainland Southeast Asia

Griffiths, Michael L.; Johnson, Kathleen R.; Pausata, Francesco S. R.; White, Joyce C.; Henderson, Gideon M.; Wood, C.; Yang, Hezhen; Ersek, Vasile; Conrad, Cyler; Sekhon, Natasha

doi:10.1038/s41467-020-17927-6

Cited by 56 publications

(56 citation statements)

References 78 publications

(122 reference statements)

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“…4d). This record also shows a rapid SST cooling concomitant with an abrupt retreat of the SAM as suggested by a recently published paleoclimate archives from western Yunnan Plateau in southwestern China (Wang et al, 2020) and northern Laos (Griffiths et al, 2020).…”

supporting

confidence: 71%

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Pausata¹,

Messori²,

Yun³

et al. 2020

Preprint

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Abstract. Previous studies based on multiple paleoclimate archives suggested a prominent intensification of the South Asian Monsoon (SAM) during the mid-Holocene (MH, ~ 6000 years before present day). The main forcing that contributed to this intensification is related to changes in the Earth’s orbital parameters. However, other key factors likely played important roles, including remote changes in vegetation cover and airborne dust emission. In particular, northern Africa also experienced much wetter conditions and a more mesic landscape than today during the MH (the so-called African Humid Period), leading to a large decrease in airborne dust globally. However, most modelling studies investigating the SAM changes during the Holocene overlooked the potential impacts of the vegetation and dust emission changes that took place over northern Africa. Here, we use a set of simulations for the MH climate, in which vegetation over the Sahara and reduced dust concentrations are considered. Our results show that SAM rainfall is strongly affected by Saharan vegetation and dust concentrations, with a large increase in particular over northwestern India and a lengthening of the monsoon season. We propose that this remote influence is mediated by anomalies in Indian Ocean sea-surface temperatures and may have shaped the evolution of the SAM during the termination of the African Humid Period.

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supporting

confidence: 71%

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Pausata¹,

Messori²,

Yun³

et al. 2020

Preprint

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“…During this period, lakes existed in, for example, the central Sahara (Gasse, 2002) and the Rub al Khali (Awafi Lake), where falling lake levels indicate the onset of climatic aridity ∼5900 cal yr BP (Preston et al, 2012). Griffiths et al (2020) investigated the relationship between the end of the AHP and an aridification of mainland Southeast Asia. They refer to a correlation of orbital forcing factors, less vegetation, and increased dust-load that influenced atmospheric circulation patterns and cooled the Indian Ocean during this time.…”

Section: Holocene Climate Variabilitymentioning

confidence: 99%

“…Singh et al (1990) investigated sediments of a mid-Holocene deep, permanent freshwater lake and revealed a significant lowering of the lake level ∼6000 cal yr BP. In addition to the reduced precipitation, a cooling of the Indian Ocean due to vegetation-dust climate feedbacks from the Sahara (Griffiths et al, 2020) worsened the living conditions for the temperature-sensitive mangroves. Cooler SSTs can explain the final decline of Rhizophoraceae and the persistence of the more robust A. marina that inhabits Oman's coastline today.…”

Section: Forcing Factor Climate Changementioning

confidence: 99%

Collapse of Holocene mangrove ecosystems along the coastline of Oman

et al. 2020

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Sedimentological, geochemical, and paleontological investigations of the coastline of northeastern Oman have provided the authors with an in-depth insight into Holocene sea levels and climate conditions. The spatial distribution and species assemblage of mangrove ecosystems are analyzed. These ecosystems are sensitive to changes in sea level and precipitation and thus reflect ecological conditions. The close proximity to archaeological sites allows us to draw conclusions regarding human interaction with the mangrove ecosystems. Our interdisciplinary inquiry reveals that the mangrove ecosystems along the east coast of Oman collapsed ~6000 cal yr BP on a decadal scale. There is no sedimentological evidence for a mid-Holocene sea-level highstand. The ecosystem collapse was not caused by sea-level variation or anthropogenic interferences; rather, it was the consequence of reduced precipitation values related to a southward shift of the Intertropical Convergence Zone. This resulted in a decrease of freshwater input and an increase in soil salinity. Further, the aridification of the area caused increased deflation and silting up of the lagoons.

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“…Hence, we show that δ 18 O p in central Vietnam is sensitive to small-scale variations in the position of the ITCZ. This offers the opportunity for palaeoclimate archives, such as speleothems and tree ring cellulose, to use changes in δ 18 O as indicators of ITCZ dynamics, especially for periods where large changes have been inferred [74][75][76][77] . Further, variability in the ITCZ position is tightly linked to broader tropical ocean dynamics including ENSO and the IOD 78 .…”

Section: Spatial Variability Of δ 18mentioning

confidence: 99%

Rainwater isotopes in central Vietnam controlled by two oceanic moisture sources and rainout effects

Wolf

Roberts

Ersek

et al. 2021

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Oxygen isotopes are commonly used proxies in paleoclimate research, however, a correct interpretation requires a detailed understanding of processes controlling isotope variability for a specific site.&#160; A common interpretation for oxygen isotopes in precipitation across the Asian monsoon region, links the seasonal and interannual variability to changes in the summer monsoon strength.However, some locations within tropical Asia do not receive rainfall during the summer monsoon season. In central Vietnam most of the annual rainfall falls during autumn instead of summer, making central Vietnam ideal to investigate processes controlling rainwater isotope variability, independent from the summer monsoon. By using rainwater isotopes, collected over five years, and moisture uptake simulations for these time periods, we investigate the seasonal cycle and interannual variability of hydrological processes in central Vietnam.Our results show that the seasonal variability is dominated by a shift in moisture source from the Indian Ocean in summer to the South China Sea (western Pacific) from autumn to spring. The different source locations are reflected by an increase in &#948;18O values from around &#8722; 8 to &#8722; 10&#8240; during summer to values between 0 and &#8722; 3&#8240; during winter/spring. Further, we show that the amount effect and the occurrence of tropical cyclones, which are typical for the region, have no effect on a seasonal to interannual scale. Instead, we find that the timing of the seasonal ITCZ migration is a driving component of variability on these time scales.

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End of Green Sahara amplified mid- to late Holocene megadroughts in mainland Southeast Asia

Cited by 56 publications

References 78 publications

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

The remote response of the South Asian Monsoon to reduced dust emissions and Sahara greening during the middle Holocene

Collapse of Holocene mangrove ecosystems along the coastline of Oman

Rainwater isotopes in central Vietnam controlled by two oceanic moisture sources and rainout effects

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