Stalagmite evidence for Early Holocene multidecadal hydroclimate variability in Ethiopia

Asfawossen Asrat; Andy Baker; Wuhui Duan; Melanie J. Leng; Ian Boomer; Rabeya Akter; Gregoire Mariethoz; Lewis Adler; Catherine N. Jex; Meklit Yadeta; Lisheng Wang

doi:10.1017/qua.2022.29

Stalagmite evidence for Early Holocene multidecadal hydroclimate variability in Ethiopia

Asfawossen Asrat^*, Andy Baker, Wuhui Duan, Melanie J. Leng, Ian Boomer, Rabeya Akter, Gregoire Mariethoz, Lewis Adler, Catherine N. Jex, Meklit Yadeta, Lisheng Wang

^*Corresponding author for this work

Earth and Environmental Sciences

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Abstract

A multiproxy oxygen and carbon isotope (δ¹³C and δ¹⁸O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ∼9.25 ka. Statistically significant and coherent spectral frequencies in δ¹³C and δ¹⁸O are observed at 15-25 and 19-23 years, respectively. The observed ∼1‰ amplitude variability in stalagmite δ¹⁸O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO₂ from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ¹⁸O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ¹⁸O, these processes can generate multidecadal δ¹⁸O variability.

Original language	English
Pages (from-to)	67-81
Number of pages	15
Journal	Quaternary Research (United States)
Volume	110
Early online date	29 Jun 2022
DOIs	https://doi.org/10.1017/qua.2022.29
Publication status	Published - Nov 2022

Bibliographical note

Funding Information:
Stable isotope analyses were funded by NERC National Environmental Isotope Facility grant (IP-1099-0509) and Australian Research Council LIEF funding. U-Th dating was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB26020000). Fieldwork to the Mechara caves and subsequent sample preparation (lamina counting, drilling) was supported by START-PACOM, the UK Royal Society, and the Leverhulme Trust. The School of Earth Sciences of the Addis Ababa University supported and facilitated fieldwork. Hilary Sloane undertook the stable isotope measurements at the National Environmental Isotope Facility. We thank John Gunn, Henry Lamb, and the late Mohammed Umer, who have been very helpful during the successive field trips to the Mechara caves. The editors and two anonymous reviewers are acknowledged for their valuable comments, which helped improve the original paper.

Publisher Copyright:
© 2022 University of Washington. Published by Cambridge University Press.

Keywords

Early Holocene
Eastern Africa
Multidecadal variability
Oxygen isotopes
Paleoclimate

ASJC Scopus subject areas

Arts and Humanities (miscellaneous)
Earth-Surface Processes
General Earth and Planetary Sciences

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AsratA2022StalagmiteFinal published version, 1.25 MBLicence: Creative Commons: Attribution (CC BY)

Cite this

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title = "Stalagmite evidence for Early Holocene multidecadal hydroclimate variability in Ethiopia",

abstract = "A multiproxy oxygen and carbon isotope (δ13C and δ18O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ∼9.25 ka. Statistically significant and coherent spectral frequencies in δ13C and δ18O are observed at 15-25 and 19-23 years, respectively. The observed ∼1‰ amplitude variability in stalagmite δ18O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO2 from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ18O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ18O, these processes can generate multidecadal δ18O variability.",

keywords = "Early Holocene, Eastern Africa, Multidecadal variability, Oxygen isotopes, Paleoclimate",

author = "Asfawossen Asrat and Andy Baker and Wuhui Duan and Leng, {Melanie J.} and Ian Boomer and Rabeya Akter and Gregoire Mariethoz and Lewis Adler and Jex, {Catherine N.} and Meklit Yadeta and Lisheng Wang",

note = "Funding Information: Stable isotope analyses were funded by NERC National Environmental Isotope Facility grant (IP-1099-0509) and Australian Research Council LIEF funding. U-Th dating was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB26020000). Fieldwork to the Mechara caves and subsequent sample preparation (lamina counting, drilling) was supported by START-PACOM, the UK Royal Society, and the Leverhulme Trust. The School of Earth Sciences of the Addis Ababa University supported and facilitated fieldwork. Hilary Sloane undertook the stable isotope measurements at the National Environmental Isotope Facility. We thank John Gunn, Henry Lamb, and the late Mohammed Umer, who have been very helpful during the successive field trips to the Mechara caves. The editors and two anonymous reviewers are acknowledged for their valuable comments, which helped improve the original paper. Publisher Copyright: {\textcopyright} 2022 University of Washington. Published by Cambridge University Press.",

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AU - Baker, Andy

AU - Duan, Wuhui

AU - Leng, Melanie J.

AU - Boomer, Ian

AU - Akter, Rabeya

AU - Mariethoz, Gregoire

AU - Adler, Lewis

AU - Jex, Catherine N.

AU - Yadeta, Meklit

AU - Wang, Lisheng

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PY - 2022/11

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N2 - A multiproxy oxygen and carbon isotope (δ13C and δ18O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ∼9.25 ka. Statistically significant and coherent spectral frequencies in δ13C and δ18O are observed at 15-25 and 19-23 years, respectively. The observed ∼1‰ amplitude variability in stalagmite δ18O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO2 from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ18O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ18O, these processes can generate multidecadal δ18O variability.

AB - A multiproxy oxygen and carbon isotope (δ13C and δ18O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ∼9.25 ka. Statistically significant and coherent spectral frequencies in δ13C and δ18O are observed at 15-25 and 19-23 years, respectively. The observed ∼1‰ amplitude variability in stalagmite δ18O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO2 from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ18O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ18O, these processes can generate multidecadal δ18O variability.

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KW - Eastern Africa

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KW - Paleoclimate

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ER -

Stalagmite evidence for Early Holocene multidecadal hydroclimate variability in Ethiopia

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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