| The Lake Nuoertu, located at the South-Eastern margin of the Badain Jaran Desert where the northern fringe of modern East Asian Summer Monsoon, can be sensitive to the changes in regional climate, which in tern, is a suitable site for recovering the changes in the past climate and hydrological variation as well as the history of sand emission in dust source areas. In October 2013, a 92 cm drill core was retrieved at the central part of Lake Nuoertu and was sliced at 1cm intervals in the laboratory. Combined with the age-depth model, multi-proxy indices such as Grain-size、total organic carbon(TOC)、total nitrogen(TN)、 C/N、element relative content of Si、 S、Cl、K、Ca、Sr Zr/Rb and χlf were developed for the reconstruction of paleoclimate、 paleoenvironment and eolian sand activity. And we also make a comparison between our result and other record of paleoclimatic, and as well as the history of aeolian activity, the preliminary conclusion are outlined as follows:(1) The environmentally sensitive grain-size components (C3+C4) can be considered as the indicator of changes in lake areas and lake-level fluctuations; PC1 and TOC could be regarded as the indicator of changes in effective moisture; TN can be used as the indicator of the primary productivity of the lake; at the same time, the environmentally sensitive grain-size components C2、PC2 and χlf are inferred to reflect the strength of the winds.(2) The environmental changes of this region can be divided into 3 stages based on the multi-proxy analysis over the last 700 years as follows:Stage I (1333-1600A.D.,92-49cm) was characterized by high content of the environmentally sensitive grain-size components (C3+C4)、 TOC and TN, while the PCl in a negative phase.. and the environmentally sensitive grain-size components C2、the PC2 and χlf show the lower values, all above those indicating the climate was cold and humid with a high lake level and the decreasing intensity of the aeolian sand activity; Stage Ⅱ(1600-1834A.D.,49-11cm), the contents of the grain-size components (C3+C4)、TOC and TN reached the lowest levels, with the PC1 in a positive phase and the grain-size components C2、 the PC2 and χlf in their high value, which indicating the low stand of lake level and the increasing intensity of the aeolian sand activity with a colder and drier climate; Stage Ⅲ (1834-2013A.D.,11-0cm) was characterized by a more slightly increasing trend of the grain-size components (C3+C4)、TOC and TN, the PC1 fluctuating around the zero value, the remarkable decreasing in the grain-size components C2、PC2 and χlf compared with the previous stage, suggesting there was an increasing trend of the effective moisture(but not as high as Stage Ⅰ) and the decreasing intensity of the aeolian sand activity, especially after the mid 20th century, there exists a trend toward a drying climate of this region.(3) A comparison between our results and other paleoclimatic records that documented by the multiple groundwater profiles (such as the B1、SW1 and SWDA profile) nearby in SE Badain Jaran Desert over the last 700 years indicate that the paleoenvironmental variations of this region could correspond well with each other, but there also exists some discrepancies during some stages such as the 18th century. Within a more large regional scale, on a multi-decadal to multi-centennial time-scale, the paleoclimatic record reconstructed from Nuoertu region is similar to those on the NE Tibetan Plateau, suggesting that there is a good coupled relationship between them, while it is in contrasting pattern to those in arid central Asia in the whole, and also differs from those in the north-central China.The comparisons between history of sand emission of this study and the other dust records indicate that the strongest aeolian sand activity interval occurred in 18th century as well as recorded in the Dunde Ice core, but it differs from those in other sites indicating that the peak interval of sand emission was mainly in 17th century. |
PDF Full Text Request