Recent research in the Great Basin has demonstrated the need for quantitative, high-resolution temperature reconstructions that extend understanding of past thermal regimes further into the last 10,000 years. This doctoral dissertation research will assess recent environmental change and human-related influences on a suite of lakes in the central Great Basin, and it will develop high-resolution temperature reconstructions spanning the past 8,000 years, with an emphasis on the two most recent warm intervals, the Medieval Climate Anomaly and the Holocene Thermal Maximum. The doctoral student will gather data from a network of sites will be collected in the central Great Basin and analyze these materials in search of signals of past climatic changes. Lake sediments collected from this network will be measured for a variety of physical and biological indicators to include sub-fossil chironomids, sediment organic content, biogenic silica, mercury concentration, spheroidal carbonaceous particles, grain size, and macroscopic charcoal. These indicators will be used to characterize the recent temperature changes and pollution loadings along with long-term changes to productivity, temperatures, and fire histories in the region. Accurate chronological control will be ensured through lead-210 dating the recent sediment and accelerator mass spectrometer radiocarbon dates on sedimentary charcoal and identifiable plant remains. The results from the research will be compared with other paleoclimate reconstructions to gain a better understanding of the spatial and temporal climatic changes in the Great Basin.

The results of this project will facilitate a more thorough examination of the influence of temperature on effective moisture and aridity in the Great Basin over the past 8,000 years. This will further contribute to basic understanding of the response of aquatic ecosystems to past and possibly future environmental change. Project results also should help identify how various human-related factors have influenced the structure and composition of these lakes during the most recent centuries. An ever-increasing supply of freshwater is required for the urban areas in the Great Basin, which have experienced dramatic population growth in recent decades. This research will help understand the long-term natural variability of thermal and moisture regimes for this region. The project also should help enhance decision making with regard to water policy and assist in adaptations to future climate variability and change. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.

Project Report

(Porinchu and Reinemann - BCS-1130340) The main objectives of the study were to: 1) develop a multi-proxy assessment of the 20th and 21st century environmental change and anthropogenic influence on sub-alpine and alpine lakes; and 2) develop a network of quantitative reconstructions of mid- to late Holocene thermal conditions in the central Great Basin of Nevada. During August of 2011 and 2012 two successful field campaigns were undertake, which resulted in the collection of four sediment cores from Teresa, Stella, Cold and Soldier lakes located in the central Great Basin. The cores recovered from Teresa, Cold and Stella span the interval from present to ~125 years Before Present (BP), while the Soldier Lake core spans the internal from present to ~10,000 years BP. The Great Basin is located in the Inter-Mountain West, a region that has experienced dramatic population growth in recent decades. The growth in population has lead directly to an increasing need for freshwater resources. It is critical that we understand the long-term natural variability of thermal and moisture regimes for this region to improve decision-making capacity and assist in adaptation to future climate variability and change. Our research documented the timing of anthropogenic influences and environmental change on a suite of sub-alpine and alpine lake ecosystems in the Great Basin. It suggests that the remote aquatic ecosystems in the central Great Basin have been affected by local, regional, and global anthropogenic pollutant loadings over the 20th century. Our research has further reinforced earlier research linking climate change and community response in aquatic ecosystems in the western United States. Documenting the timing and magnitude of anthropogenic pollutant loading to these sensitive ecosystems will improve our ability manage, protect and/or remediate freshwater resources in this region. This research has also facilitated the development of a high-resolution network of mid- to late Holocene temperature reconstructions in the central Great Basin. A sudden change to an equilibrium state similar to the conditions that existed during the Holocene Thermal Maximum (HTM; ~ 6,000 yrs BP) and/or the Medieval Climate Anomaly (MCA; 800-1200 yr BP) would have significant consequences for this region, which is increasingly stressed for freshwater. This component of the study, which is ongoing, will improve our understanding of how regional and extra-regional factors contribute to the sustained aridity and spatial variability in hydroclimatological conditions in the Great Basin. Results-to-date however, highlight the unmistakable need for careful site selection to minimize the influences of factors other than temperature (the environmental variable of interest) that could have an influence on the insect community assemblages. One important outcome of this research is it has provided a set of criteria for site selection in long-term temperature reconstructions. The results from this doctoral dissertation research improvement grant will be beneficial to a wide variety of researchers, such as paleoclimatologists, hydrologists, ecologists, and climate modelers, who are seeking to understand the spatial and temporal variability of past climate conditions in the Great Basin and identify the forcing factors responsible for these changes.

National Science Foundation (NSF)
Division of Behavioral and Cognitive Sciences (BCS)
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Thomas J. Baerwald
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Ohio State University
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