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Testing commonly used XRF core scanning based proxies for organic rich lake sediments and peat
Stockholm University, Faculty of Science, Department of Geological Sciences.
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2016 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 45, no 1, p. 180-189Article in journal (Refereed) Published
Abstract [en]

X-ray fluorescence (XRF) core scanning has become widely available for geological studies during the last decade. The data obtained from XRF core scanning, however, may be strongly influenced by the amount of organic matter, water content, density and porosity of the sediment matrix. In this study we discuss the usefulness of XRF core scanning to distinguish different kinds of organic-rich sediments and peat based on examples from tropical Lakes Kumphawapi and Nong Leng Sai in Thailand. We examined how sedimentary factors influence XRF core scanning analyses by comparing elemental and scattering ratios to lithological changes and quantitative LOI, TOC, biogenic silica (BSi) and grain-size values. Our comparison suggests that the (inc/coh) scattering ratio is of limited use as an indicator for variations in LOI and TOC in peaty gyttja or peat. In Lake Kumphawapi's sediments, Si/Ti ratios reflect clastic input associated with grain-size variations rather than BSi contents. The Ti-normalized ratios of Si, Zr, Sr, K and Rb are linked to mineral input and associated grain-size variations. We conclude that XRF core scanning of organic-rich tropical lake sediments and peat is useful to infer palaeoenvironmental conditions. However, XRF core scanning data does not stand-alone and needs to be underpinned by additional proxies.

Place, publisher, year, edition, pages
2016. Vol. 45, no 1, p. 180-189
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geology
Identifiers
URN: urn:nbn:se:su:diva-126154DOI: 10.1111/bor.12145ISI: 000373014700011OAI: oai:DiVA.org:su-126154DiVA, id: diva2:897452
Available from: 2016-01-25 Created: 2016-01-25 Last updated: 2018-02-01Bibliographically approved
In thesis
1. Paleoenvironmental and paleoclimatic changes in northeast Thailand during the Holocene
Open this publication in new window or tab >>Paleoenvironmental and paleoclimatic changes in northeast Thailand during the Holocene
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The long-term climatic and environmental history of Southeast Asia is still fragmentary. This thesis therefore aims at studying lake sediment/peat sequences using a multi-proxy approach to reconstruct the environmental history and the impact of past changes in monsoon variability and intensity on lake ecosystems in Thailand. The study focuses on two lakes located in northeast Thailand: the larger Lake Kumphawapi and the smaller Lake Pa Kho.

The comparison of multiple sediment sequences and their proxies from Kumphawapi suggests a strengthening of the summer monsoon between c. 10,000 and 7000 cal yr BP. Parts of the lake had been transformed into a wetland/peatland by c. 7000 cal yr BP, while the deeper part of the basin still contained areas of shallow water until c. 6600 cal yr BP. This gradual lowering of the lake level can point to a weakening of the summer monsoon. Paleoenvironmental information for the time interval between 6200 and 1800 cal yr BP is limited due to a several thousand-year long hiatus. This new investigation demonstrates that arguments using the phytolith and pollen record of Lake Kumphawapi to support claims of early rice agriculture in the region or an early start of the Bronze Age are not valid, because these were based upon the assumption of continuous deposition. The lithostratigraphy and multi-proxy reconstructions for Pa Kho support a strengthened summer monsoon between 2120-1580 cal yr BP, 1150-980 cal yr BP, and after 500 cal yr BP; and a weakening of the summer monsoon between 1580-1150 cal yr BP and between 650-500 cal yr BP. The increase in run-off and higher nutrient supply after AD 1700 can be linked to agricultural intensification in the region. Conclusively, the Holocene records from northeast Thailand add important paleoclimatic information for Southeast Asia and allow discussing past monsoon variability and movements of the Intertropical Convergence Zone in greater detail.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm Univeristy, 2014. p. 46
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper ; 354
Keywords
Paleoenvironment, paleoclimatic, sediment, peat, multi-proxy, Asian monsoon, the Holocene
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geology
Identifiers
urn:nbn:se:su:diva-107185 (URN)978-91-7447-961-4 (ISBN)
Public defence
2014-10-17, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Accepted. Paper 5: Manuscript.

Available from: 2014-09-25 Created: 2014-09-05 Last updated: 2018-02-01Bibliographically approved

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