Reconstruction of the 30–40 ka bp enhanced Indian monsoon climate based on geological records from the Tibetan Plateau

Multi-proxy records from ice caps, lakes and pollen records from the Tibetan Plateau are used to reconstruct the palaeoclimate during the period 30–40 ka bp. Lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and/or freshwater lakes occurred in large areas of western China at this time, including over the Tibetan Plateau where the area contains mostly shallow water and saline–hypersaline water lakes under extremely dry conditions of today. Pollen-based reconstruction of Tibetan vegetation shows systematic differences from the present: alpine steppe-forests were shifted ca. 400 km further north and the alpine conifer forest extended ca. 400–800 km beyond their present western limits. Variations in δ18O curves from ice cores from the Plateau suggest that the temperature was 2–4°C higher and precipitation was 40% to over 100% higher than today. All of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the Plateau. The vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture-rich southwest monsoon over the Tibetan Plateau. These climate patterns with strong summer monsoon circulation during the period 30–40 ka bp reflect the 20 ka earth orbital precessional cycle, when the Tibetan Plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the Plateau and the mid-south portion of the Indian Ocean.