FOR 1380: Himalaya: Modern and Past Climates (HIMPAC)
Final Report Abstract
The principal objectives of the HIMPAC proposal were to (i) to unravel the characteristics of modern- and palaeo-monsoons during the Holocene, and reconstruct the seasonality of precipitation on seasonal to decadal timescales, with special emphasis on extreme hydro-meteorological events (floods and droughts) in the climatically sensitive regions of India; (ii) quantify and characterise palaeoclimate variability within the framework of large-scale climate processes [e.g. El Niño-Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), tropical mid-latitude interactions] using an interarchive, interproxy approach; (iii) undertake palaeoclimate simulations using data from selected time slices to understand the causal mechanisms triggering extreme climate conditions. Ultimately, the overarching objective was to assess changes in the frequency of such phenomena with respect to their magnitude in a global warming scenario. Our analyses of dated modern sediments demonstrated (i) the site specific sensitivity of commonly used palaeoclimate indicators. The organic proxies (i.e., Lonar lake) were sensitive to subtle changes in lacustrine productivity that could be linked to large-scale teleconnections; the same proxy in high-altitude regions analysed by HIMPAC revealed that this data was “contaminated” by a terrestrial signal that could potentially have led to an erroneous interpretation; (ii) regional variability. In contrast to stalagmites from northern India, which did not show significant Indian Summer Monsoon (ISM) variability, the evaporite mineralogy and isotope data from the Lonar lake in Central India clearly indicated the occurrence of prolonged droughts; (iii) that the non-stationary link between the ENSO and the ISM is linked to the strength and position of the Indo Pacific Warm Pool (IPWP) and breakdowns already occurred during the mid- to late Holocene and not only in the recent decades as suspected earlier; (iv) the late Holocene orbitally induced weakening of the summer insolation appears to have led to an unstable climate, with a change in source of monsoonal precipitation (Bay of Bengal versus Arabian Sea) and pathways for the ISM; (v) there appears to be a coincidence between climate change and cultural evolution in NW (i.e. Indus Valley Civilisation) and central India; the onset of settlements in central India was later than in NW India and also appears to have been forced by monsoonal droughts; (vi) the results of pollen analysis and nalkane stable carbon isotope measurements in the Holocene sediment sequence from Lonar lake shed a new light on the Holocene evolution of vegetation cover in central India; (vii) the biome-reconstruction method was applied to the Tso Moriri fossil pollen record approximately covering the last 12 years to quantitatively reconstruct changes in major regional vegetation types and thus quantify past changes in mean annual precipitation; (viii) the changing precipitation seasonality during the early Holocene in the High Himalaya region resulted in an abrupt increase in lake levels (a rise of 65m between 16.4-12.2 cal ka and a second rise of 37m between 11.2-8.5 cal ka). Moreover, (ix) we developed a freely available software framework for the construction of age-depth models with uncertainties (COPRA). Finally, (x) palaeoclimate modelling using a model-proxy approach revealed a high consistency between simulated and reconstructed moisture signals and revealed a prominent dipole moisture pattern between the Himalaya and Central India.
