Late Quaternary Climate and Precipitation δ18o Variations over the Tibetan Plateau from Paleoclimate Modeling

Abstract:

The Himalaya-Tibet orogen hosts some of the largest modern climate gradients on Earth. Quaternary climate change between glacial and interglacial cycles is an important driver for landscape and ecological change in the region. A common observational approach for documenting climate change is the measurement of modern precipitation, and terrestrial archives of, δ¹⁸O. In this study, we investigate variations in Mid Holocene (MH) and Last Glacial Maximum (LGM) climate and precipitation δ¹⁸O (δ¹⁸O_p). Paleoclimate model results for 3 time slices are considered including: Pre-industrial, MH and LGM conditions. These experiments bridge spatial and temporal timescales of environmental change over the plateau and provide a means for interpreting observational data sets.

Climate and precipitation δ¹⁸O (δ¹⁸O_p) variations over the Plateau are investigated using an atmospheric general circulation model equipped with isotope tracking capabilities (ECHAM5-wiso). Simulations are conducted at a resolution of 1.1°´1.1°, with 31 vertical levels (T106 L31). Pre-industrial boundary conditions come from AMIP2. MH and LGM boundary conditions come from a coupled atmosphere-ocean model ECHO-G, with vegetation cover from PMIP (http://pmip2.lsce.ipsl.fr).

Results are presented in comparison to pre-industrial conditions. More specifically, during the MH surface temperatures were ~0.5 C higher on the central and western plateau and ~0.5 C cooler across the Himalaya. Mean annual MH precipitation was <100 mm/yr higher on the plateau and 300-500 mm/yr higher across the Himalaya. MH δ¹⁸O_p is 1 per mil depleted on the plateau and 1 per mil enriched across the Himalaya. In contrast, during the LGM surface temperatures were ~2-4 C lower across the Himalaya and Tibet. Mean annual LGM precipitation was 200-600 mm/yr lower over the same region, and δ¹⁸O_p was 2-4 per mil enriched relative to pre-industrial predictions. The causes for the previous δ¹⁸O_p changes are discussed in the context of variable vapour source, temperature, precipitation amount, and evaporative recycling. Taken together, these results suggest muted climate change across the plateau during the MH with larger changes occurring during the LGM, possibly due to a weaker monsoon and shorted monsoon period than pre-industrial conditions.