Vegetation variations and associated environmental changes during marine isotope stage 3 in the western part of the Chinese Loess Plateau

摘要

This study further investigates the reported "uniqueness" of MIS 3 climatic changes in northwestern China by focusing on the MIS 3 lacustrine-wetland sequences in the western part of the Chinese Loess Plateau. The lacustrine-wetland sequence at the Suancigou section documented four major environmental changes. Stratigraphic unit (i) was formed under lake-dominated environments (48,420-35,730 C-14 yr 13P), unit (ii) under wetland-dominated environments (35,730-20,480 C-14 yr BP), and unit (iii) under eolian-dominated environments (20,480-13,090 C-14 yr P-13). Unit (iv) is a fluvially-reworked eolian (loess) unit (13,090-11,450 C-14 yr BP). Pollen zone A (47,210-33,370 C-14 yr BP), representing a coniferous forest, corresponds to stratigrapbic unit (i). Zone B (33,370-28,280 C-14 yr P-13), representing a coniferous woodland landscape, and zone C (28,28022,480 14C yr 13P), representing a landscape in which coniferous woodlands alternated with steppes; correspond to unit (ii). Zone D (22,480-11,450 C-14 yr BP), representing a steppe landscape, corresponds to unit (iii) and unit (iv). We propose that the extremely wet MIS 3 was a combined result of mildly high summer insolation and constantly higher-than-normal winter insolation. That is, mildly high MIS 3 summer insolation was probably able to maintain the warmth of the ocean surface to the extent so that the Tibetan Plateau and northwestern China received an adequate supply of water-vapour. A constantly higher-than-normal MIS 3 winter insolation might have shortened the duration of the winter monsoon, so lengthening the rainy season. In addition, the soil-vegetation-air coupled feedback mechanisms under extensively well-vegetated wet conditions might have further enhanced the MIS 3 wet conditions. (c) 2006 Elsevier B.V. All rights reserved.