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Influence of the intertropical convergence Zone on the East Asian monsoon Gergana Yancheva Ting-Ju Tsai Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan. Foreword The Asian–Australian monsoon is an important component
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Influence of the intertropical convergence Zone on the East Asian monsoon Gergana Yancheva Ting-Ju Tsai Institute of Applied Geosciences National Taiwan Ocean University, Keelung ,Taiwan
Foreword The Asian–Australian monsoon is an important component of the Earth’s climate system that influences the societal and economic activity of roughly half the world’s population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits, but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds.
ITCZ 1. What? The Intertropical Convergence Zone (ITCZ) is the area encircling the earth near the Equator where winds originating in the northern and southern hemispheres come together.
2. ITCZ & Monsoon Where the ITCZ is drawn into and merges with a monsoonal circulation, it is sometimes referred to as a monsoon trough, a usage more common in Australia and parts of Asia.
Diagram of Winter Monsoon Winds Gergana Yancheva 2007
January and July and the location of the LHM George H. Taylor 2007
＊Lake Huguang Maar﹕ 21。9 ' N ,110 。17 ' E ＊The sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years. ＊Lake Huguang Maar today lies 23m above sea level and has a water depth of 20m. The surface area of the lake is 2.25km2 , and it drains an extremely small catchment of 3.2km2. Gergana Yancheva 2007
Maar A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Palatinate German dialect of Daun, where it is in turn derived from Latin mare (sea). Maars are shallow, flat-floored craters that scientists interpret as having formed above diatremes as a result of a violent expansion of magmatic gas or steam; deep erosion of a maar presumably would expose a diatreme.
The Huguang Maar sediments recond the strength of the winter monsoon in four Independent ways： ＞The accumulation of wind-blown material. (The Ti content of sediment is used to reconstruct the aeolian input into the lake.) ＞The redox-sensitive characteristics and total organic carbon (TOC) content of the sediment as a result of changes in wind stress and winter column mixing.
＞S-ratio is a estimate of the abundance of magnetite compared to that of antiferromagnetic minerals, mainly haematite. ＞Magnetic susceptibility is sensitive to both lake redox condition and the aeolian input, both of which are affected by wind stength.
Palaeoclimate time series of record in Lake Huguang Maar During cold climates, for instance, before 14.8kyr ago and during the Younger Dryas (Y.D.), Ti content, magnetic susceptibility and S-ratio are high while TOC content is low. In contrast, during the B/A and early-Holocene, Ti content and rock magnetic amplitudes drop, and TOC increases.
TOC is a representatives of the winter monsoon :＞in winter: Amount of oxygen dissolved into the lake , caused oxidation environment, and TOC is low.＞in summer:Less of oxygen dissolved into the lake , caused restoration environment, and TOC is high.
Comparison the monsoon sensitive sedimentary records from Lake Huguang Maar with other climate records： When the ITCZ is displaced northward, the summer monsoon should strengthen, while the winter monsoon will weaken. A northward shift in the ITCZ would be expected during times of Northern Hemisphere warming, such as the B/A and the early Holocene, times when, indeed, the East Asian summer monsoon was strong and the winter monsoon was weak.
The Lake Huguang Maar palaeoclimate records during the past 4,500yr in context of major events in the Cultural history of China
Conclusion The sediments record from Lake Hugaung Maar︰ ＞During the B/A warming and early Holocene, the climate of Lake Hugaung Maar is show the condition of weak winter monsoon. ＞Before the B/A warming, during the Y.D. episode and the middle and late Holocene, the climate of Lake Hugaung Maar is show the condition of strength winter monsoon; when cave stalagmites suggest weaker summer monsoon.
＞Migration of the annual mean position of the ITCZ provides a single coherent explanation for the observed trends in both winter and summer monsoons over the 16kyr, as well as for the strong anti-correlation between them. ＞We suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and Classic Maya in Central America.
