Executive Summary : | Based on the chronometric data, glacier advances in the Himalayan region are suggested to be driven by a relative contribution of the ISM and mid-latitude westerlies which varied across the spatial and temporal scales. For instance, the glaciers in the Ladakh and Karakoram Himalaya, which are westerlies dominated in the modern times are suggested to be driven by the strengthened ISM during the Quaternary (Brown et al., 2002; Owen et al., 2006; Dortch et al., 2010). It is also argued that the microclimatic variations introduce enough variability within the individual mountain ranges/valleys and make the response of the glaciers more complex (Bohner, 2006; Dortch et al., 2011; Owen and Dortch, 2014); hence leading to asynchronous advances in Himalaya (Benn and Owen, 1998; Owen and Dortch, 2014). Alternatively, it is seen that there is lack of suitable exposures, accessibility, datable material from the landform archives (e.g. moraine) leading to a coarser resolution record (Owen and Dortch, 2014 and references therein) that might have led us to assign an advance to two different climatic events (Sharma and Owen, 1996; Barnard et al., 2004; Owen etal., 1998; Eugster et al., 2016) and thus, erroneously suggesting asynchronous advances in adjacent valleys. Besides it also hampers our understanding of glaciers geomorphic response at a shorter time scale and to the interplay of temperature and precipitation thresholds. With recent studies presenting a contradictory evidence to suggest the role of enhanced mid-latitude westerlies in last ~70 ka from the valleys erstwhile suggested to be influenced by ISM; the alternative explanation is tempting and requires further probing (Nagar et al., 2013; Sharma et al., 2016; Sharma and Shukla, 2018, Ganju et al., 2018).
The inferences are not only important to improve our understanding of the impact that regional/synoptic scale climate dynamics have on the Himalayan glaciers but also have tremendous societal significance. It is feared that under the anticipated warm earth scenario, the hydrological characteristics of the rivers which largely depends on snowmelt and/or ice are likely to suffer hydrologic disruptions (Barnett et al., 2005). Therefore, the study of past glacier dynamics (millennial and multi-millennial time scale) becomes important as it provides important background information for our understanding of natural trends of, and human impacts on, climate change to assess the causes and possible future of the contemporary shrinking of glaciers (Solomina et al., 2008). |