Himalaya, Uttarakhand, India: We have initiated a new project, funded by the NSF, in northern India that centers on documenting long-term and abrupt fluctuations in the intensity of the Indian Summer Monsoon (ISM) during the Holocene. This project will employ non-destructive imaging and multi-proxy analyses of lake sediment cores to develop quantitative records capturing the timing, duration and nature of high frequency (multi-decadal scale) variability in the ISM and assess the correspondence between fluctuations in summer temperature and the strength of the ISM in northern India during the Holocene. Emily Niederman (M.S. student, UGA), together with Dr. Alex Cherkinsky at the Center for Applied Isotope Studies, UGA and Professor Bahadur Kotlia (Kumaun University, India) has undertaken analysis of a series of lake sediment cores using XRF, X-Ray and CT scans to better characterize the full range of variability in the ISM and in doing so, gain a deeper understanding of the processes driving the long-term and abrupt fluctuations in the ISM and its modes of variability. Intermountain West of the United States: Our research in the western United States has documented that the warming experienced by sub-alpine lakes in the Sierra Nevada, Snake Range, Ruby and East Humboldt Mountains and the Uinta Mountains, during the late 20th and early 21st centuries is unprecedented in the context of the last ~ 150 years (Porinchu et al. 2007; Porinchu et al. 2010; Reinemann et al. 2011; Reinemann et al. 2014a). We are extending these records further into the past, i.e. the middle to late Holocene, to develop high resolution (multi-decadal-scale) reconstructions of Great Basin paleoclimate over a longer time-scale, put contemporaneous changes into context, and increase our understanding of the linkage between these localized changes and regional climate dynamics. Together with Stephen Cooper (M.S. student, UGA) and colleagues at Ohio University and The Ohio State University we have also recently begun a project to use pollen, charcoal and geochemical signals extracted from meadow and lake sediment cores to develop lengthy, high-resolution (multi-decadal to sub-centennial scale) fire and vegetation histories for Great Basin National Park. Front Range, Colorado Rockies: We have increasingly become interested in using stable isotopes of carbon and nitrogen in bulk lake sediment and stable isotopes of oxygen extracted from sub-fossil chironomid remains to address how high elevation aquatic ecosystems are responding to elevated air temperature and hydroclimate variability in recent decades. I am particularly interested in characterizing how the retreat of small alpine glaciers, in response to altered temperature and precipitation regimes, will impact thermally sensitive aquatic invertebrates and aquatic communities. Cordillera de Talamanca, Costa Rica: This project is designed to address questions related to the temporal variability in thermal conditions characterizing Costa Rica during the Holocene. Using surface sediment collected by our collaborator, Dr. Sally Horn (University of Tennessee), Jiaying Wu (Ph.D. 2018, UGA) documented the modern distribution of sub-fossil midges in this region; developed a midge-based surface water temperature inference model (Wu et al. 2015); and reconstructed late Holocene thermal conditions for the region (Wu et al. 2017; 2019). Following her dissertation Dr. Wu has continued to work on: 1) identifying whether elevated temperatures played a role in exacerbating wide-spread, regional droughts and wildfires in Costa Rica during the Medieval Climate Anomaly (~ 700-1250 CE); and 2) determining if these climate events coincided with structural changes in ancient civilizations (e.g. the Maya) or landscape change in the tropical highlands of Central America.
