Dust storms and Chinese loess sources over the last 22 million years

Lead Research Organisation: Royal Holloway, University of London
Department Name: Geography

Abstract

The dust cycle is a fundamental component of climate, but remains one of the least understood aspects of the Earth-system. Dust in the atmosphere affects oceanic productivity and atmospheric carbon dioxide levels, cloud formation and the amount of radiation absorbed or reflected by the atmosphere, all driving climatic change. However, how dust production and emission is controlled by environmental change in the past is poorly understood, preventing quantification of its effects on climate, fact acknowledged in the recent IPCC 2007 report. This project addresses this gap by attempting to pinpoint the precise sources of the world's largest and longest active dust sink, the Chinese Loess Plateau. The Chinese Loess Plateau contains a 22 million year archive of loess (deposited dust) deposition, covering one of the most significant time periods for understanding the Earth's history. Chinese loess has made crucial contributions to understanding past changes in the Asian monsoon and dust storms and is one of the most valuable climate archives available. However, its interpretation relies on detailed constraint of the precise sources of this dust, and the pathways by which it reaches the Loess Plateau. Unfortunately, despite investigation using the geochemical properties of bulk samples there are multiple competing hypotheses over 1) the precise loess source regions, 2) the environmental controls on dust production, 3) whether sources shift through time, 4) the atmospheric mechanisms are for dust transport and indeed 5) whether the oldest part of the record (8-22 Ma) is indeed wind-blown at all. These disagreements severely limit our understanding of the very origin of these deposits, preventing us from constraining the past atmospheric, tectonic and oceanographic conditions responsible for the emission and transport of dust and undermining the use of certain climate proxies in loess. In turn this restricts our understanding of the dominant environmental processes operating in China in the past, and the origin of the current atmospheric circulation systems. Key to overcoming this gap is to properly constrain the sources of loess. Our pilot work has demonstrated that widely applied bulk sediment geochemical analysis of sediment from loess and source regions will mask the detail of the multiple sources of loess dust. Only individual grains of certain heavy minerals (> 2.8 specific gravity) can be source diagnostic as each grain will have one source and certain of its geochemical and geochronological characteristics may be diagnostic of this. Thus analysis of multiple single grains of zircons and other heavy minerals isolated from loess and adjacent desert deposits will be undertaken using a multi-proxy single-grain geochemical approach to maximise the likelihood of success. Until our pilot work this has not been conducted on Chinese loess previously. Samples for these analyses will be taken from multiple, typical loess sequences in China, allowing determination of source variance through time and space. Sampling will concentrate on key intervals, such as the uplift of Tibet, the onset of Ice Age glaciation and the enhanced intensity of glaciation in more recent times. The results will allow us to test between conflicting hypotheses of loess dust source and transport, enabling constraint of the fundamental controls on dust emission and the atmospheric mechanisms involved in their transport. In turn and through comparison with independent records, this will allow us to assess the effect of global and regional climatic, tectonic and oceanographic changes on dust. This is currently a poorly understood yet critical component of the Earth-system. Finally, the results will test the validity of widely used sedimentary proxies such as mass accumulation rates and grain size in reconstructing past environmental changes from loess.

Publications


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Bird A (2015) Quaternary dust source variation across the Chinese Loess Plateau in Palaeogeography, Palaeoclimatology, Palaeoecology
Nie J (2013) Controlling factors on heavy mineral assemblages in Chinese loess and Red Clay in Palaeogeography, Palaeoclimatology, Palaeoecology
Rittner M (2016) The provenance of Taklamakan desert sand in Earth and Planetary Science Letters
 
Title MDS 
Description Newly redveloped method of analysis of multi-dimensional data, first applied and tested with geologic samples using our data. Tool is now becoming widely used among geoscientists, particularly where there are large datasets to work with, based on our results. 
Type Of Material Data analysis technique 
Year Produced 2012 
Provided To Others? Yes  
Impact Significant take up in the community 
URL http://www.ucl.ac.uk/~ucfbpve/mudisc/
 
Description Collaboration with Laboratory for Provenance analysis, University of Milan, Italy 
Organisation University of Milan-Bicocca
Country Italy, Italian Republic 
Sector Academic/University 
PI Contribution Joint research on Yellow River and loess system. Sharing of our U-Pb dating results with lab in Milan
Collaborator Contribution Use of their Raman facilities for mineral analysis leading to research output, published and in preparation. Also training in kind of project post doc.
Impact Stevens et al., 2013, 'genetic linkage' paper. A number of in submission and in prep articles.
Start Year 2011
 
Description Press coverage for Stevens et al., 2013 genetic linkage 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Press release from Royal Holloway triggered online coverage from various popular science websites including Sciencedaily.com

Increased interest in project and project website. Public awareness
Year(s) Of Engagement Activity 2013
URL https://www.royalholloway.ac.uk/aboutus/newsandevents/news/newsarticles/firstevidencethatdustandsand...