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. 2016 May 13:6:25791.
doi: 10.1038/srep25791.

A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene

Arne Ramisch  1 , Gregori Lockot  2 , Torsten Haberzettl  3 , Kai Hartmann  2 , Gerhard Kuhn  4 , Frank Lehmkuhl  5 , Stefan Schimpf  1 , Philipp Schulte  5 , Georg Stauch  5 , Rong Wang  1 , Bernd Wünnemann  2   6 , Dada Yan  6 , Yongzhan Zhang  7 , Bernhard Diekmann  1   8
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A persistent northern boundary of Indian Summer Monsoon precipitation over Central Asia during the Holocene

Arne Ramisch et al. Sci Rep. .

Abstract

Extra-tropical circulation systems impede poleward moisture advection by the Indian Summer Monsoon. In this context, the Himalayan range is believed to insulate the south Asian circulation from extra-tropical influences and to delineate the northern extent of the Indian Summer Monsoon in central Asia. Paleoclimatic evidence, however, suggests increased moisture availability in the Early Holocene north of the Himalayan range which is attributed to an intensification of the Indian Summer Monsoon. Nevertheless, mechanisms leading to a surpassing of the Himalayan range and the northern maximum extent of summer monsoonal influence remain unknown. Here we show that the Kunlun barrier on the northern Tibetan Plateau [~36°N] delimits Indian Summer Monsoon precipitation during the Holocene. The presence of the barrier relocates the insulation effect 1,000 km further north, allowing a continental low intensity branch of the Indian Summer Monsoon which is persistent throughout the Holocene. Precipitation intensities at its northern extent seem to be driven by differentiated solar heating of the Northern Hemisphere indicating dependency on energy-gradients rather than absolute radiation intensities. The identified spatial constraints of monsoonal precipitation will facilitate the prediction of future monsoonal precipitation patterns in Central Asia under varying climatic conditions.

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Figures

Figure 1
Figure 1. Conceptual model of circulation patterns over central Asia during boreal summer.
Dashed arrows depict idealized boreal summer circulation over central Asia. MSE+ and MSE− refer to the advection of high and low moist static energy respectively. For detailed studies of present day moisture transport over the Tibetan Plateau during the monsoon season the reader is referred to and. Maps were created using ArcGIS 10.1 (www.esri.com) with the World Terrain Basemap (Esri, USGS, NOAA) and Adobe Illustrator CS 4 (www.adobe.com).
Figure 2
Figure 2. Sediment sources in the central Kunlun fault system.
(a) Regional overview and the North Tibetan precipitation barrier. Areas with similar or higher orographic forcing on southerly air masses (as compared to the study area) are indicated by colours as factor of higher forcing (supplementary information). (b) Topographic map of the study area. (c) Results of cluster analysis for reference samples on alluvial fans in the study area. Circles indicate sample location. Colours indicate dominant membership (μ > 0.5) of samples to mineralogical cluster C1 to C4 (supplementary information). Maps were created using ArcGIS 10.1 (www.esri.com) and Adobe Illustrator CS 4 (www.adobe.com).
Figure 3
Figure 3. Mineralogical similarity of lacustrine sediments to sediment sources.
Surface and core sample locations are shown in the center of the figure. (a) Membership degrees of lake surface samples to mineralogical cluster C1 to C4. Lake sketch indicates the position (circle) and membership degree (circle size) of individual samples to cluster center C1 to C4. Histograms indicate the total number (n) of lake surface samples in membership classes (μ with 0.2 bin) to a respective cluster center. (b) Membership degrees of core samples to mineralogical cluster C1 to C4. Sample memberships are plotted against depth in a sediment core. Maps were created using ArcGIS 10.1 (www.esri.com) and Adobe Illustrator CS 4 (www.adobe.com).
Figure 4
Figure 4. Radiative forcing and ISM intensity variations.
(a) Boreal summer insolation intensities (summer solstice) between 30° and 44°N. (b) Proxy for ISM precipitation variation in its northernmost location as determined in this study. Black dashed line indicates the Holocene evolution of the Latitudinal Insolation Gradient (LIG) between 30°N and 44°N. (c) Proxy for ISM precipitation intensity variation as recorded by speleothems in Oman. (d) Proxy for ISM wind strength over the Arabian Sea. (e) Moisture evolution in paleoenvironmental archives throughout monsoonal Asia (MA) and its out-of-phase relationship to the moisture evolution in arid central Asia (ACA).
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