AN INVESTIGATION INTO THE CAUSES OF δ18O VARIATIONS IN THE DASUOPU ICE CORE, CENTRAL HIMALAYAS, USING INSTRUMENTAL DATA

The interpretation of variations in oxygen isotopes (δ¹⁸O) within tropical ice core records have been a subject of much debate. In this study the ice core record from Dasuopu (28° 23ʹ N, 85° 43ʹ E) in the central Himalayas was compared with precipitation data from the Global Precipitation Climatology Center (GPCC) v6 and Indian monsoon subdivisions, the Niño 3.4 index, sea surface temperature (ERSST v3b), and air temperature data (NCEP 20^th century reanalysis) to examine its relationship over interannual, 2-8 year, and multi-decadal timescales. The results from these analyses indicate that the Dasuopu record can be best understood in a hierarchical manner. Over interannual and 2-8 year timescales, the variability of the Dasuopu oxygen isotopic record is dominated by local and regional rainfall variability which are both strongly associated with the variations in the strength of El Niño-Southern Oscillation (ENSO). However, over decadal and especially multi-decadal timescales, the variation in its isotopic record is strongly driven by long-term trends in air and sea surface temperature in regions upwind of the ice core location. A multi-regression model constructed using the summer monsoon rainfall from the East Uttar Pradesh monsoon subdivision, the summer mean Niño 3.4 index and air temperature anomalies in a region bound by 20-28°N, 80-88°E described 27% of the variance in the Dasuopu δ¹⁸O record between 1886 and 1996, with temperature being the single most important parameter. This strongly suggests that these three parameters control a large degree of the variability observed in the Dasuopu δ¹⁸O record over this time frame.