A high-resolution record of Holocene Monsoon intensity from Central Asia

Lead Research Organisation: Imperial College London
Department Name: Earth Science and Engineering

Abstract

The Asian monsoon system is an important component of the climate system. Moreover, it exerts a major impact on the regional population, due to associated strong summer rainfall. In a world of changing climate, the Asian monsoon system is one of the major systems we must gain a better understanding on to accurately predict the future. A powerful way to increase our mechanistic understanding of the climate system is to look into the past. For example, chemical analyses of cave deposits constitute an effective way to learn about the history of rainfall in Asia. From such records we know that the intensity of the East Asian summer monsoon gradually weakened over the last ~9000 years. A similar evolution has been documented for the Indian summer monsoon. When comparing both monsoon histories with changes in the orbit of the Earth around the sun, so called orbital forcing, a general linkage can be found, suggesting that changes in the Asian monsoon system may also be linked to changes in other parts of the climate system (i.e., oceans, ice sheets). However, when looking in more detail, this neat correlation seems to fall apart: proxy records for precipitation from various lakes in Central Asia indicate an out-of-phase relationship of the two Asian summer monsoon systems and a high degree of variability throught the time interval of our current 'stable' interglacial, the Holocene (i.e., last 10,000 years). One way to explain this apparent controversy is to not only think about the actual amount of rainfall recorded, but to also think about where this rain was originating from. The Indian Summer monsoon is associated with southwesterly winds, while the East Asian summer monsoon is associated with southeasterly winds. Such different source regions could play an important role when trying to understand the monsoon records of the past. Hence a prime target for ongoing climate research is to find a way to reconstruct directions of winds in the past. In this project we will reconstruct such wind directions by analysing the dust extracted from a 9,600 year old core from a peat bog from the Eastern Qinghai-Tibetan Plateau. The continuous peat material contains inorganic dust, and this dust in turn carries a chemical fingerprint from the area where it was picked up. If we reconstruct this dust fingerprint for the last 9,600 years, we can infer a detailed history of wind directions and strengths in central Asia, allowing us to identify the prevailing monsoon sub-system at any given time. The result will be a local monsoon record, which can then be compared to other regional and global climate records. Agreement (or disagreement) between record is what tells us about common driving forces (or decouplings) in the climate system. It is this information which is vital for feeding climate models to accurately reconstruct the past and ultimately to predict the future. We work in close collaboration with modellers in Hamburg, who have developed a regional climate model for China and who look forward to including our new data. Previous collaboration with Hamburg already developed the dust code for the model to be used. Specific outcomes of the project will be: (1) the first ever high-resolution record of changes in the atmospheric circulation systems and of the weakening and strengthening of the East Asian and Indian Monsoon systems over Tibet during last 10,000 years, (2) the first record of any movement of the present day boundary between the two subsystems, and (3) contributing to the development of a regional climate model for China to predict future climate change.
 
Description Key discoveries are

(i) we find no evidence of signifiant impact of the Indian monsoon over Central Asia since the last glaciation.
(ii) we confirm that peat records record truthfully long range transport of dust in Central Asia
(iii) we determine periods of changing intensity of the westerly jet over Central Asia. this has direct implications on the presence of teleconnection between North Atlantic and
(iv) we determine for the first time the periods when the East Asian and the Summer Monsoon were active during the Holocene
Exploitation Route The change point modeling developed during this project is now widely used in the community studying mineral dust deposition
The peat archive is now widely used in the paleo climate community to study the dynamics of past atmospheric dust fluxes and circulation
Sectors Environment
 
Description The work has led to the development of a computer program that enables the determination of change points in dust records from geological archives (program has been written by Prof Gallagher at the University of Rennes, and is maintained at the following web page (https://geosciences.univ-rennes1.fr/spip.php?rubrique332?=fr) We also used the work to start collaborations with the South Atlantic Environmental Research Institute under the direction of Dr Bickle and we were invited to write an article in the general science journal PAGES
First Year Of Impact 2013
Sector Digital/Communication/Information Technologies (including Software),Environment
Impact Types Cultural
 
Description CLIM AMAZON
Amount £90,000 (GBP)
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 11/2012 
End 10/2015
 
Description Ocean micronutrient cycles: UK GEOTRACES
Amount £259,027 (GBP)
Funding ID NE/H005390/1 
Organisation Natural Environment Research Council (NERC) 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 09/2010 
End 09/2014
 
Description Revisiting the Neodymium Paradox
Amount £365,608 (GBP)
Funding ID NE/J021636/1 
Organisation Natural Environment Research Council (NERC) 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 09/2012 
End 03/2017
 
Description SOUTHERNCHANGE
Amount £180,000 (GBP)
Organisation European Research Council (ERC) 
Sector Public
Country European Union (EU)
Start 10/2016 
End 09/2018
 
Description University of Hamburg 
Organisation University of Hamburg
Country Germany, Federal Republic of 
Sector Academic/University 
PI Contribution experimental record of dust deposition
Collaborator Contribution calibration of the REMOTE model
Impact REMOTE model calibrated for Central Asia
 
Description University of Rennes 
Organisation University of Rennes 1 (Université de Rennes 1)
Country France, French Republic 
Sector Academic/University 
PI Contribution dust deposition data set from peat archive
Collaborator Contribution CPM
Impact Change point model
 
Title Basin Change point Model 
Description application for change point modeling in geological data sets 
Type Of Technology Software 
Year Produced 2011 
Open Source License? Yes  
Impact change point modeling is now widely used in the peat archive community 
URL http://www.iearth.org.au/codes/
 
Description Public Talk at the Natural History Museum 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Gave a talk at the Nature Talk series of the Natural History Museum
Year(s) Of Engagement Activity 2011