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Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho
Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
Stockholm University, Faculty of Science, Department of Geological Sciences. Chulalongkorn University, Thailand.
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Number of Authors: 10
2015 (English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 111, 62-71 p.Article, review/survey (Refereed) Published
Abstract [en]

The Southeast Asian mainland is located in the central path of the Asian summer monsoon, a region where paleoclimatic data are still sparse. Here we present a multi-proxy (TOC, C/N, delta C-13, biogenic silica, and XRF elemental data) study of a 1.5 m sediment/peat sequence from Lake Pa Kho, northeast Thailand, which is supported by 20 AMS C-14 ages. Hydroclimatic reconstructions for Pa Kho suggest a strengthened summer monsoon between BC 170-AD 370, AD 800-960, and after AD 1450; and a weakening of the summer monsoon between AD 370-800, and AD 1300-1450. Increased run-off and a higher nutrient supply after AD 1700 can be linked to agricultural intensification and land-use changes in the region. This study fills an important gap in data coverage with respect to summer monsoon variability over Southeast Asia during the past 2000 years and enables the mean position of the Intertropical Convergence Zone (ITCZ) to be inferred based on comparisons with other regional studies. Intervals of strengthened/weaker summer monsoon rainfall suggest that the mean position of the ITCZ was located as far north as 35 degrees N between BC 170-AD 370 and AD 800-960, whereas it likely did not reach above 17 degrees N during the drought intervals of AD 370-800 and AD 1300-1450. The spatial pattern of rainfall variation seems to have changed after AD 1450, when the inferred moisture history for Pa Kho indicates a more southerly location of the mean position of the summer ITCZ.

Place, publisher, year, edition, pages
2015. Vol. 111, 62-71 p.
Keyword [en]
Wetland/peatland, Geochemistry, Paleoclimate, Last two millennia, Asian monsoon
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience; Marine Geology
Identifiers
URN: urn:nbn:se:su:diva-117744DOI: 10.1016/j.quascirev.2015.01.007ISI: 000353431100005OAI: oai:DiVA.org:su-117744DiVA: diva2:817468
Available from: 2015-06-05 Created: 2015-06-01 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Asian monsoon over mainland Southeast Asia in the past 25 000 years
Open this publication in new window or tab >>Asian monsoon over mainland Southeast Asia in the past 25 000 years
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of this research is to interpret high-resolution palaeo-proxy data sets to understand the Asian summer monsoon variability in the past. This was done by synthesizing published palaeo-records from the Asian monsoon region, model simulation comparisons, and analysing new lake sedimentary records from northeast Thailand.

Palaeo-records and climate modeling indicate a strengthened summer monsoon over Mainland Southeast Asia during the Last Glacial Maximum (LGM), compared to dry conditions in other parts of the Asian monsoon region. This can be explained by the LGM sea level low stand, which exposed Sundaland and created a large land-sea thermal contrast. Sea level rise ~19 600 years before present (BP), reorganized the atmospheric circulation in the Pacific Ocean and weakened the summer monsoon between 20 000 and 19 000 years BP.

Both the Mainland Southeast Asia and the East Asian monsoon hydroclimatic records point to an earlier Holocene onset of strengthened summer monsoon, compared to the Indian Ocean monsoon. The asynchronous evolution of the summer monsoon and a time lag of 1500 years between the East Asian and the Indian Ocean monsoon can be explained by the palaeogeography of Mainland Southeast Asia, which acted as a land bridge for the movement of the Intertropical Convergence Zone.

The palaeo-proxy records from Lake Kumphawapi compare well to the other data sets and suggest a strengthened summer monsoon between 10 000 and 7000 years BP and a weakening of the summer monsoon thereafter. The data from Lake Pa Kho provides a picture of summer monsoon variability over 2000 years. A strengthened summer monsoon prevailed between BC 170-AD 370, AD 800-960 and since AD 1450, and was weaker about AD 370-800 and AD 1300-1450. The movement of the mean position of the Intertropical Convergence Zone explains shifts in summer monsoon intensity, but weakening of the summer monsoon between 960 and 1450 AD could be affected by changes in the Walker circulation.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2014. 61 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 353
Keyword
Asian monsoon, ITCZ, palaeo-vegetation, palaeoclimate, lake sediment, Last Glacial Maximum, Holocene
National Category
Climate Research
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-107136 (URN)978-91-7447-969-0 (ISBN)
Public defence
2014-10-10, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2008-2855Swedish Research Council, 348-2008-6071Swedish Research Council, 621-2011-4684
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript..

Available from: 2014-09-18 Created: 2014-09-03 Last updated: 2016-01-27Bibliographically approved
2. 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. 46 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 354
Keyword
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)
Opponent
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: 2016-01-27Bibliographically approved

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