Projects

Testing Climatic Controls on Speleothem Radiocarbon

Reconstructing past atmospheric radiocarbon (¹⁴C) concentration is essential for improving the calibration of the radiocarbon timescale, investigating past variations in solar activity and Earth’s paleomagnetic field, and investigating the redistribution of carbon between terrestrial, atmospheric, and marine reservoirs that occurred over the past 50,000 years. Uncertainty in the radiocarbon calibration curve during the deglaciation and last glacial period, however, limits our understanding of these key issues. Previous work suggests that U-Th dated speleothems hold great potential for improving the record of atmospheric ¹⁴C, but may be complicated by changes in dead carbon fraction (DCF) derived from bedrock. To fully realize the potential of speleothems for ¹⁴C calibration, therefore, there is a need for detailed process-based cave studies to determine the modern controls on speleothem DCF and the potential impact of past climate variability on DCF. Towards this end, we are conducting a detailed study of C cycling at Heshang Cave, Hubei Province, China (30º27’N, 110º25’E; 294 m), the site of ongoing, extensive modern calibration and paleoclimate reconstruction efforts, through collection and analysis of the radiocarbon content of soil CO₂, dripwater DIC, modern calcite, and fossil speleothem samples to investigate the controls on speleothem radiocarbon and to determine how these might change with climate. This project is supported by NSF grant 0903101.

Timing and mechanisms of past hydrologic variability from Sierra Nevada speleothems

Precipitation in the southwestern United States is highly seasonal and exhibits inter-annual to inter-decadal variability which is linked to naturally recurring large scale atmospheric circulation patterns associated with sea surface temperature (SST) anomalies such as the Pacific Decadal Oscillation (PDO) and the El Nino-Southern Oscillation (ENSO). Proxy data from tree rings and lake sediments from the region indicate there were episodes of significantly decreased precipitation (~900-1250 AD) that were of greater magnitude and longer duration than any episode seen in the 20th century, yet the mechanisms behind these "mega-droughts" are still not well understood. Cave calcite deposits (speleothems) represent one of the best terrestrial archives of past climate variability and hold great potential to improve our understanding of past hydrologic variability magnitude and mechanisms, but to this date have been widely underutilized in the western US. In collaboration with the National Park Service, we are developing well-calibrated speleothem records of past hydrologic variability from Crystal Cave in Sequoia National Park. We have been conducting a detailed modern calibration study since 2007 and are currently completing a ~1,000 year, annual resolution speleothem record from this site. This project has been supported by a Newkirk Center for Science and Society faculty seed grant.

History and mechanisms of rainfall variability from Asian and tropical Indo-Pacific speleothems

Climate of the tropical Indian and Pacific Ocean regions is governed by a complex interplay of dynamical mechanisms which are highly sensitive to climate change, including migration of the Intertropical Convergence Zone (ITCZ), the Australasian monsoon system, the El Niño Southern Oscillation (ENSO), and the Indian Ocean Dipole (IOD). The seasonal migration of the ITCZ and the associated monsoon systems deliver life-giving moisture to billions of people, and any slight variations in the strength and/or timing of this can have catastrophic effects on the agricultural practices and industries within these vulnerable communities. While significant progress has been made in our understanding of orbital and millennial scale climate variability in this region, there still remains a large gap in knowledge about the timing and mechanisms of natural rainfall variability over centennial to interannual timescales that are likely to influence survival over a single human generation. This work will provide some of the first high-resolution, well-calibrated, and replicated, terrestrial records of past climate variability over the last ~50 kyr from the Tropical Indo-Pacific region. Such records are urgently needed to improve our understanding of background climate variability in the region and relationships with regional climate forcings and feedbacks and internal climate modes, such as ENSO. Gaining a clearer understanding of how tropical Indo-Pacific climate has varied through time is critical to improved rainfall predictions and timely adaptation measures, especially given the uncertainties still evident in climate model projections under enhanced greenhouse-gas forcing. In addition, through our collaboration with archaeologists from the Middle Mekong Archaeology Project (MMAP), we aim to investigate the relationship between past climatic and cultural changes in the region. This project has three main components: (1) Development of new annual resolution speleothem records from Indonesia, Laos, and Sri Lanka, (2) Calibration of 20^th century speleothem data with instrumental climate data and isotope-enabled GCM results, and (3) Compilation of existing Last Millennium speleothem records from South and East Asia and the Tropical-Indo-Pacific region for comparison with other records (paleoclimate, historical, and archaeological) and with the Last Millennium results from the Paleoclimate Modeling Intercomparison Project 3 (PMIP3).

American Indian Summer Institute in Earth System Science (AISESS): A residential summer institute for American Indian high school students

Despite a critical need for earth and environmental science professionals within Tribal communities, American Indians remain severely underrepresented in the geosciences. To address this problem, the University of California, Irvine will organize a two-week residential American Indian Summer Institute in Earth System Science (AISESS) for high-school students (grades 9-12) from throughout the nation. The specific objectives of the AISESS program are: 1) to encourage and empower American Indian high school students to pursue higher education; 2) to increase the number of American Indian students who pursue degrees in or related to the geosciences; 3) to increase retention and graduation rates of American Indian college students in the geosciences; 4) to encourage American Indian college graduates to pursue geoscience careers, in particular those available in Tribal communities; and 5) to enhance public literacy of Earth System Science, especially within American Indian Tribal communities. The first week of the AISESS program will be spent camping and conducting field projects on the reservation of the La Jolla Band of Luiseño Indians and the second week will be spent on the University of California, Irvine campus learning about Earth System Science through lectures, discussions, and laboratory activities. The scientific curriculum will be designed by faculty members from the UCI Department of Earth System Science in partnership with the Institute for Tribal Environmental Professionals at Northern Arizona University, the La Jolla Band of Luiseño Indians, and the Acjachemen Nation. The science curriculum will be closely woven together with appropriate cultural activities, native studies, and communication skills coordinated through the UCI American Indian Resource Program. The program will culminate with a closing ceremony in which students present poster projects on earth and environmental science issues that are particularly relevant to Tribal communities. Through key partnerships with the Louis Stokes California Alliance for Minority Participation, the UCI Center for Educational Partnerships, and Santa Ana College, we will conduct extensive follow-up and mentorship activities that will increase the likelihood of recruitment and retention of native students to the geosciences. This project is funded by NSF OEDG grant #.....