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Asian monsoon climate during the Last Glacial Maximum: palaeo-data–model comparisons
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.
2013 (English)In: Boreas, ISSN 0300-9483, E-ISSN 1502-3885, Vol. 43, no 1, 220-242 p.Article in journal (Refereed) Published
Abstract [en]

The Last Glacial Maximum (LGM) (23-19ka BP) in the Asian monsoon region is generally described as cool and dry, due to a strong winter monsoon. More recently, however, palaeo-data and climate model simulations have argued for a more variable LGM Asian monsoon climate with distinct regional differences. We compiled, evaluated, and partly re-assessed proxy records for the Asian monsoon region in terms of wet/dry climatic conditions based on precipitation and effective moisture, and of sea surface temperatures. The comparison of the palaeo-data set to LGM simulations by the Climate Community System Model version 3 (CCSM3) shows fairly good agreement: a dry LGM climate in the western and northern part due to a strengthened winter monsoon and/or strengthened westerly winds and wetter conditions in equatorial areas, due to a stronger summer monsoon. Data-model discrepancies are seen in some areas and are ascribed to the fairly coarse resolution of CCSM3 and/or to uncertainties in the reconstructions. Differences are also observed between the reconstructed and simulated northern boundaries of the Intertropical Convergence Zone (ITCZ). The reconstructions estimate a more southern position over southern India and the Bay of Bengal, whereas CCSM3 simulates a more northern position. In Indochina, the opposite is the case. The palaeo-data indicate that climatic conditions changed around 20-19ka BP, with some regions receiving higher precipitation and some experiencing drier conditions, which would imply a distinct shift in summer monsoon intensity. This shift was probably triggered by the late LGM sea-level rise, which led to changes in atmosphere-ocean interactions in the Indian Ocean. The overall good correspondence between reconstructions and CCSM3 suggests that CCSM3 simulates LGM climate conditions over subtropical and tropical areas fairly well. The few high-resolution qualitative and quantitative palaeo-records available for the large Asian monsoon region make reconstructions however still uncertain

Place, publisher, year, edition, pages
2013. Vol. 43, no 1, 220-242 p.
National Category
Climate Research
Research subject
Marine Geoscience
Identifiers
URN: urn:nbn:se:su:diva-98041DOI: 10.1111/bor.12032ISI: 000328619600013OAI: oai:DiVA.org:su-98041DiVA: diva2:682228
Funder
Swedish Research Council, 621-2008-2855Swedish Research Council, 348-2008-6071Swedish Research Council, 621-2011-4684
Available from: 2013-12-25 Created: 2013-12-25 Last updated: 2017-12-06Bibliographically 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

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