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Paleoenvironmental and paleoclimatic changes in northeast Thailand during the Holocene
Stockholm University, Faculty of Science, Department of Geological Sciences.
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 [en]
Paleoenvironment, paleoclimatic, sediment, peat, multi-proxy, Asian monsoon, the Holocene
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geology
Identifiers
URN: urn:nbn:se:su:diva-107185ISBN: 978-91-7447-961-4 (print)OAI: oai:DiVA.org:su-107185DiVA: diva2:745661
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
List of papers
1. Holocene environmental changes in Northeast Thailand as reconstructed from a tropical wetland
Open this publication in new window or tab >>Holocene environmental changes in Northeast Thailand as reconstructed from a tropical wetland
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2012 (English)In: Global and Planetary Change, ISSN 0921-8181, E-ISSN 1872-6364, Vol. 92-93, 148-161 p.Article in journal (Refereed) Published
Abstract [en]

Geochemical variables (TOC, C/N, TS, delta C-13) and diatom assemblages were analyzed in a lake sediment sequence from Nong (Lake) Han Kumphawapi in northeast Thailand to reconstruct regional climatic and environmental history during the Holocene. By around c. 10,000-9400 cal yr BP, a large shallow freshwater lake had formed in the Kumphawapi basin. Oxygenated bottom waters and a well-mixed water column were characteristic of this early lake stage, which was probably initiated by higher effective moisture and a stronger summer monsoon. Decreased run-off after c. 6700 cal yr BP favored increased aquatic productivity in the shallow lake. Multiple proxies indicate a marked lowering of the lake level around 5900 cal yr BP, the development of an extensive wetland around 5400 cal yr BP, and the subsequent transition to a peatland. The shift from shallow lake to wetland and later to a peatland is interpreted as a response to lower effective moisture. A hiatus at the transition from wetland to peatland suggests very low accumulation rates, which may result from very dry climatic conditions. A rise in groundwater and lake level around 3200 cal yr BP allowed the re-establishment of a wetland in the Kumphawapi basin. However, the sediments deposited between c. 3200 and 1600 cal yr BP provide evidence for at least two hiatuses at c. 2700-2500 cal yr BP, and at c. 1900-1600 cal yr BP, which would suggest surface dryness and consequently periods of low effective moisture. Around 1600 cal yr BP a new shallow lake became re-established in the basin. Although the underlying causes for this new lake phase remain unclear, we hypothesize that higher effective moisture was the main driving force. This shallow lake phase continued up to the present but was interrupted by higher nutrient fluxes to the lake around 1000-600 cal yr BP. Whether this was caused by intensified human impact in the catchment or, whether this signals a lowering of the lake level due to reduced effective moisture, needs to be corroborated by further studies in the region. The multi-proxy study of Kumphawapi's sediment core CP3A clearly shows that Kumphawapi is a sensitive archive for recording past shifts in effective moisture, and as such in the intensity of the Asian summer monsoon. Many more continental paleorecords, however, will be needed to fully understand the spatial and temporal patterns of past changes in Asian monsoon intensity and its ecosystem impacts.

Keyword
Northeast Thailand, lake sediments, geochemistry, Asian monsoon, environmental reconstruction, moisture availability
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-81300 (URN)10.1016/j.gloplacha.2012.05.008 (DOI)000307031000015 ()
Note

AuthorCount:9;

Available from: 2012-10-25 Created: 2012-10-15 Last updated: 2017-12-07Bibliographically approved
2. Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand
Open this publication in new window or tab >>Lake Kumphawapi - an archive of Holocene palaeoenvironmental and palaeoclimatic changes in northeast Thailand
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2013 (English)In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, 59-75 p.Article in journal (Refereed) Published
Abstract [en]

The long-term climatic and environmental history of Southeast Asia, and of Thailand in particular, is still fragmentary. Here we present a new C-14-dated, multi-proxy sediment record (TOC, C/N, CNS isotopes, Si, Zr, K, Ti, Rb, Ca elemental data, biogenic silica) for Lake Kumphawapi, the second largest natural lake in northeast Thailand. The data set provides a reconstruction of changes in lake status, groundwater fluctuations, and catchment run-off during the Holocene. A comparison of multiple sediment sequences and their proxies suggests that the summer monsoon was stronger between c. 9800 and 7000 cal yr BP. Lake status and water level changes around 7000 cal yr BP signify a shift to lower effective moisture. By c. 6500 cal yr BP parts of the lake had been transformed into a peatland, while areas of shallow water still occupied the deeper part of the basin until c. 5400-5200 cal yr BP. The driest interval in Kumphawapi's history occurred between c. 5200 and 3200 cal yr BP, when peat extended over large parts of the basin. After 3200 cal yr BP, the deepest part of the lake again turned into a wetland, which existed until c. 1600 cal yr BP. The observed lake-level rise after 1600 cal yr BP could have been caused by higher moisture availability, although increased human influence in the catchment cannot be ruled out. The present study highlights the use of multiple sediment sequences and proxies to study large lakes, such as Lake Kumphawapi in order to correctly assess the time transgressive response to past changes in hydroclimate conditions. Our new data set from northeast Thailand adds important palaeoclimatic information for a region in Southeast Asia and allows discussing Holocene monsoon variability and ITCZ movement in greater detail.

Keyword
Thailand, Asian monsoon, Lake sediment, Multi-proxy geochemistry, Holocene, Palaeoenvironment, Palaeoclimate, ITCZ, Palaeomonsoon
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:su:diva-91193 (URN)10.1016/j.quascirev.2013.01.030 (DOI)000318383900004 ()
Note

AuthorCount:10;

Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2017-12-06Bibliographically approved
3. Multi-proxy based reconstruction of Holocene environmental history around Lake Kumphawapi, NE Thailand
Open this publication in new window or tab >>Multi-proxy based reconstruction of Holocene environmental history around Lake Kumphawapi, NE Thailand
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(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-107141 (URN)
Available from: 2014-09-05 Created: 2014-09-03 Last updated: 2014-09-11
4. Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho
Open this publication in new window or tab >>Hydroclimatic shifts in northeast Thailand during the last two millennia - the record of Lake Pa Kho
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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.

Keyword
Wetland/peatland, Geochemistry, Paleoclimate, Last two millennia, Asian monsoon
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience; Marine Geology
Identifiers
urn:nbn:se:su:diva-117744 (URN)10.1016/j.quascirev.2015.01.007 (DOI)000353431100005 ()
Available from: 2015-06-05 Created: 2015-06-01 Last updated: 2017-12-04Bibliographically approved
5. An example of commonly used XRF core scanning based proxies for organic rich lake sediments and peat
Open this publication in new window or tab >>An example of commonly used XRF core scanning based proxies for organic rich lake sediments and peat
(English)Manuscript (preprint) (Other academic)
National Category
Earth and Related Environmental Sciences
Research subject
Marine Geoscience
Identifiers
urn:nbn:se:su:diva-107184 (URN)
Available from: 2014-09-05 Created: 2014-09-05 Last updated: 2014-09-11

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