Spatiotemporal relationship between temperature and precipitation in inland China from meteorological data and paleoclimatic implications for lacustrine oxygen records

The factors controlling climate in China's western interior are numerous and quite complex. These vary on seasonal to multi-millennial time scales as a result of changing dominance of influence from the Westerlies and the Asian and Indian Monsoon systems. These in turn respond to additional factors such as the dynamics of the Walker and Hadley circulation in the Pacific and Indian Ocean basins, the strength of the Siberian and Northwest Pacific Highs, and on long timescales to changes in the distribution of solar insolation resulting from orbital forcing. Here, we use the Empirical Orthogonal Function (EOF) analysis to investigate the spatiotemporal patterns of climate in China's western interior during the last 15 ka as revealed from a suite of 17 lacustrine carbonate delta O-18 records. Based on similarities to the EOF analysis of the modern data, we interpret the first two leading eigenmodes of the paleodata sets as P and T, respectively. Other climatic proxy data from this region appear to agree well with this interpretation. Our analysis reveals a discrete change in the spatial EOF patterns occurring at circa 7.5-6 ka BP with respect to the patterns observed prior to this. These patterns suggest that the arid NW region of the study area became significantly wetter following this juncture, but that the Asian Monsoon influenced (SE) region of the study area along the eastern flank of the Tibetan Plateau became drier. A more complex pattern of change is revealed by the second rank EOF, interpreted as temperature. This shows a discrete change at similar to 7.5-6 ka BP from cooler to hotter temperatures on the central Tibetan Plateau, but slightly cooler temperatures in the lowland Monsoon affected area (SE) after 6 ka BP. We interpret both these sets of changes to result from more persistent high pressure over the Tibetan Plateau during Boreal summer, with a resultant enhancement of moisture transport by the westerlies and diminished monsoonal flow following similar to 6 ka BP.