The Climate Change Over Past 1000a Recorded By Major Ions Of An East Rongbuk Ice Core From Qomolangma

Climate change has significant influence on the survival and development of human beings. Studying the climate change in the past and analysing its mechanism are helpful to understand the process and the trend of modern climate. The Tibetan Plateau, due to its high altitude and low temperature, has many mountain glaciers and ice caps comprise the largest glaciated area outside the polar regions. Accompanying by the global warming, the climate change in Tibetan Plateau (TP) gradually attracts more attentions from the world. Ice core records with high resolution, good fidelity, abundant information and long time scale, are good material for the study of climate change. Ice cores from glaciers of TP recorded the climate information of the plateau and even the northern hemisphere. In 2002, an 108.8m ice core was drilled from the col of East Rongbuk glacier (28.01 N,86.58E; 6518m a.s.l.) on the northeast slope of Qomolangma (Mount Everest), central Himalaya. After years of effort, ion record and some other index were reconstructed. Using the major ions and 8D as the main index, with the mothed of EOF, M-K test and wavelet analysis, we studied the relationship between the ice core record and atmospheric circulation, and discussed the climate change over the past 1000 years recorded by this ice core. The results are as follows.1. Empirical orthogonal function (EOF) analysis shows that crustal major ions (Mg2+, Ca2+, SO42- and NO3-) are highly loaded on EOF1, whereas marine major ions (Cl- and Na+) are highly loaded on EOF2. Higher EOF1 is associated with high Asia surface pressure (the highly correlated region is Mongolia and the surround region), and higher EOF2 is associated with low Asia surface pressure. Further test shows that, when the high pressure and low temperature appearing over Asia (especially Mongolia), the continental air mass was strengthened and South Asia monsoon was weakened over southern TP, associated with increased crustal ion and the decreased marine ion in the ice core (high EOF1 and low EOF2); When the low pressure and high temperature appearing over Asia, the strengthened low pressure attracts South Asia monsoon shifted more northward over southern TP, this circulation mode increases the marine ion and decreases the crustal ion of the ice core (high EOF2 and low EOF1). Therefore, crustal and marine ions could represent the continental air masses and South Asia Monsoon over southern TP.2.The comparison on EOF1 and EOF2 over past 1000 years indicated that, before-1380 AD, EOF1 positively correlated to EOF2, after ?1380 AD, EOF1 negatively correlated to EOF2. M-K test shows that EOF1 is rising during last 1000 years while EOF2 is declining; the abrupt change point of both EOF1 and EOF2 are ?1382 AD and ?1358 AD respectively. Here, Ca2+ and Clm- were used to represent Mongolia high and South Asian monsoon for learning the changes of two circulations. Over past 1000a, by changes of Ca2+, Mongolia high were weaker before-1382 and stronger after-1382, during-1382-1900, Mongolia high had 4 weaken periods. The southern Asia Monsoon over southern TP, by changes of Clm-, is stronger before-1358 and weaker after-1358, during ? 1600-1700 it have an strengthened stage, and over the rest part of little ice age, it is always weak.Which suggest that the atmospheric circulation pattern over southern TP transited around 1358-1382 AD. This is consistent with the climate transition of Medieval Warm Period to the Little Ice Age. The major ion of East Rongbuk Glacier was recorded transition of Medieval Warm Period to the Little Ice Age.We speculated that, during Medieval Warm Period, the climate is warm, the South Asian Monsoon shifted to northward and contribute to more precipitation over southern TP. During this period, the ice core ion concentration mainly affected by the precipitation amounts, crustal ions and marine ions show similar fluctuations; Since the Little Ice Age, the climate become colder, the South Asian Monsoon Center shifted southward, the precipitation over Himalaya decreased, ice core ion concentration is mainly inpacted by the strength of continental air mass and monsoon air mass, due to the mutual interaction between two air masses, the crustal ions and marine ions reversely correlated. These further suggest that the circulation over southern TP was transited during ?1358-1382, and associated with the climate shift of Medieval Warm Period to Little Ice Age.Although the South Asia Monsoon over southern TP was weakened, but in low latitude of southern Himalayan, the South Asia Monsoon was strengthened. This may be attributed to the southward shift of South Asia Monsoon trough. Since the Little Ice Age, the South Asia monsoon trough was moving southward, the impact of monsoon air mass on the southern Tibetan Plateau was weakened, this circulation pattern continued to present.3. The correlation analysis indicated that the Asia-Pacific Oscillation (APO) index is negatively correlated to EOF1 and positively correlated to EOF2, whereas the Pacific Decadal Oscillation (PDO) index is positively correlated to EOF1 and negatively correlated to EOF2. Further analysis showed that, when APO strengthened (at the same time PDO weakened), the low the surface pressure and high tropospheric temperature appearing over the land of Asia (centered Mongolia), meanwhile, the continental air mass over southern Tibetan Plateau weakened, and monsoon air masses strengthened, hence the transport of crustal ions decreased and marine ion increased, and vice versa. APO and PDO impact the ions transport by the atmospheric circulation.The comparison on ion record and the Southern Oscillation index (SOI) show that the highest crustal ion concentrations and lowest marine ion concentrations are corresponded with a low SOI, and vice versa. Cross wavelet and wavelet coherence analysis between major ion time series and the SOI indicated that, there were significant sections with high common power between the major ion time series and the SOI, suggesting a correlation between the ion records of the Qomolangma ice core and ENSO. Further investigation indicated that the higher SOI years corresponded with weaker continental air masses and stronger South Asian Monsoon over the southern TP, leading to increased marine ions and decreased crustal ions. The in-phase surface pressure anomalies of the southern TP and Darwin of Australia, is associated with ENSO and ion transport over the southern TP, and thus suggested a link between aerosol transport over the southern TP and ENSO.APO, PDO and ENSO are large scale atmospheric circulation anomalies, which are closely related to the circulation over Tibetan Plateau. And in which the climate modes are also associated with each other. Climate modes impact the atmospheric circulation, then influence the ion transport over southern TP, therefore, the ice core ion recorded this information.