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A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.).

Woodborne S, Hall G, Robertson I, Patrut A, Rouault M, Loader NJ, Hofmeyr M - PLoS ONE (2015)

Bottom Line: Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean.The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static.The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

View Article: PubMed Central - PubMed

Affiliation: iThemba LABS, Private Bag 11, Wits 2050, South Africa; Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.

ABSTRACT
A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

No MeSH data available.


Related in: MedlinePlus

Sampling depth, dates and isotopic analysis of baobabs.The isotopic analysis of 2 baobab ring sequences and two additional baobabs yielding three core samples provides coherent variability over the last 1000 years. Each colour represents a different tree or core. The sampling depth is presented on the right axis. Red crosses indicate the age of AMS radiocarbon dates used to establish the chronology.
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pone.0124202.g002: Sampling depth, dates and isotopic analysis of baobabs.The isotopic analysis of 2 baobab ring sequences and two additional baobabs yielding three core samples provides coherent variability over the last 1000 years. Each colour represents a different tree or core. The sampling depth is presented on the right axis. Red crosses indicate the age of AMS radiocarbon dates used to establish the chronology.

Mentions: The uncertainty in the age model differs for each of the cores in the study. When the δ13C values of the individual cores and ring sequences (Fig 2) were annualized to produce the isotope chronology (Fig 3) the value assigned to any particular year is the average of several samples each with a different time integral period as well as chronological errors associated with intrinsic radiocarbon errors and with the linear age interpolation. The age model is anchored on the annually resolved data from the Pafuri and Pafuri Outpost trees and has an age error of ±5 years, but for any individual δ13C data point from the core samples it is expected that the greatest source of error will result from differential growth rates. Since the core data points may be time averaged up to 3.3 years per point (which is assigned a single average date for the amalgamation) it is not reasonable to use this dataset to address precipitation changes at less than decadal scales.


A 1000-Year Carbon Isotope Rainfall Proxy Record from South African Baobab Trees (Adansonia digitata L.).

Woodborne S, Hall G, Robertson I, Patrut A, Rouault M, Loader NJ, Hofmeyr M - PLoS ONE (2015)

Sampling depth, dates and isotopic analysis of baobabs.The isotopic analysis of 2 baobab ring sequences and two additional baobabs yielding three core samples provides coherent variability over the last 1000 years. Each colour represents a different tree or core. The sampling depth is presented on the right axis. Red crosses indicate the age of AMS radiocarbon dates used to establish the chronology.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4430471&req=5

pone.0124202.g002: Sampling depth, dates and isotopic analysis of baobabs.The isotopic analysis of 2 baobab ring sequences and two additional baobabs yielding three core samples provides coherent variability over the last 1000 years. Each colour represents a different tree or core. The sampling depth is presented on the right axis. Red crosses indicate the age of AMS radiocarbon dates used to establish the chronology.
Mentions: The uncertainty in the age model differs for each of the cores in the study. When the δ13C values of the individual cores and ring sequences (Fig 2) were annualized to produce the isotope chronology (Fig 3) the value assigned to any particular year is the average of several samples each with a different time integral period as well as chronological errors associated with intrinsic radiocarbon errors and with the linear age interpolation. The age model is anchored on the annually resolved data from the Pafuri and Pafuri Outpost trees and has an age error of ±5 years, but for any individual δ13C data point from the core samples it is expected that the greatest source of error will result from differential growth rates. Since the core data points may be time averaged up to 3.3 years per point (which is assigned a single average date for the amalgamation) it is not reasonable to use this dataset to address precipitation changes at less than decadal scales.

Bottom Line: Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean.The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static.The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

View Article: PubMed Central - PubMed

Affiliation: iThemba LABS, Private Bag 11, Wits 2050, South Africa; Mammal Research Institute, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.

ABSTRACT
A proxy rainfall record for northeastern South Africa based on carbon isotope analysis of four baobab (Adansonia digitata L.) trees shows centennial and decadal scale variability over the last 1,000 years. The record is in good agreement with a 200-year tree ring record from Zimbabwe, and it indicates the existence of a rainfall dipole between the summer and winter rainfall areas of South Africa. The wettest period was c. AD 1075 in the Medieval Warm Period, and the driest periods were c. AD 1635, c. AD 1695 and c. AD1805 during the Little Ice Age. Decadal-scale variability suggests that the rainfall forcing mechanisms are a complex interaction between proximal and distal factors. Periods of higher rainfall are significantly associated with lower sea-surface temperatures in the Agulhas Current core region and a negative Dipole Moment Index in the Indian Ocean. The correlation between rainfall and the El Niño/Southern Oscillation Index is non-static. Wetter conditions are associated with predominantly El Niño conditions over most of the record, but since about AD 1970 this relationship inverted and wet conditions are currently associated with la Nina conditions. The effect of both proximal and distal oceanic influences are insufficient to explain the rainfall regime shift between the Medieval Warm Period and the Little Ice Age, and the evidence suggests that this was the result of a northward shift of the subtropical westerlies rather than a southward shift of the Intertropical Convergence Zone.

No MeSH data available.


Related in: MedlinePlus