Our ability to understand the full complexity of climate change and forecast future regional trends requires that we extend the available instrumental records into the geologic past. Over the past several decades paleoclimatologists have developed myriad proxy indicators of past regional climate that are recorded in natural archives such as ice cores, cave deposits, and lake sediment, among many other archives. Proxy paleoclimate records from the tropics are particularly important because this region is the ?heat engine? of Earth. Long- and short-term changes in ocean-atmosphere circulation that are manifested in such phenomenon as the El Nino Southern Oscillation (ENSO), the mean position of the Intertropical Convergence Zone, and the response of the tropics to high latitude climatic ?events? are critical to understand because these phenomena can have a profound impact on regional water balance, which directly affects potable water supplies, hydroelectricity generation, and agricultural productivity. The longest continuous records of climate change in the tropics are limited to those derived from the relatively few old lake basins in the region. Lake Junin, the largest lake located entirely within Peru, is among the oldest lake basins in South America. It contains a sediment record that is at least 200 m long that may extend more than 250,000 years. Lake Junin is exceptional in the length of record that it contains, but also in the climate signals that it records. Considerable prior research has documented that Lake Junin records the waxing and waning of nearby alpine glaciers and changes in regional water balance through the isotope geochemistry of calcium carbonate deposited on the lake bottom at a rate of approximately 0.2 to 1.0 mm/yr. This research will develop these and other proxy climate records for the full length of recovered core; the records generated will comprise one of the longest continuous records of climate and environmental change from the inner tropics. The Lake Junin Drilling Project has several broader impacts. These include the joint renovation of an abandoned lodge for future shared use as the first shoreline outpost for officials of the Junin National Reserve, as a visitor center, and as a lake access point for ecotourism. Capacity building activities in the Junin Project include collaboration with Peruvian universities, training of geoscientists, as well as Peruvian and American student training. A specific team will be responsible for the organization of lectures at villages in the region to inform citizens about the significance of the drilling, and will work closely with the national park service to instruct the rangers on how to use the science to promote conservation efforts around the lake. During the drilling, a team will facilitate interactions with local and international media. The team expect to involve U.S. and Peruvian students in all aspects of Junin drilling, and much of the paleoecological research related to the Junin cores will be conducted by graduate students. Training opportunities during the drilling phase of operations are also planned for geoscientists from Peruvian universities. Numerous U.S. undergraduate and graduate students, and one postdoctoral fellow will be involved in all phases of the proposed research. The material collected during this project will set the stage for significant future research. LacCore, the National Lacustrine Core Facility at the University of Minnesota, will facilitate this by overseeing the long-term storage, curation, and access to data and samples obtained in this project.
Lake Junin, located at 4000 m asl in the inner-tropics of the Southern Hemisphere, is a prime target for drilling because it contains a thick (>200 m) sediment package deposited at a high rate (0.2 to 1.0 mm/yr). Abundant research conducted on and around Lake Junin provides a compelling rationale for deep drilling. Moraine mapping coupled with cosmogenic radionuclide dating indicate that paleoglaciers reached the lake edge, but have not overridden the lake in as much as one million years. Lake Junin is one of the few lakes in the tropical Andes that predates the maximum extent of glaciation and is in a geomorphic position to record the waxing and waning of glaciers in nearby cordillera. Sediment coring of Lake Junin began in the 1970s; two cores spanning the past 50,000 years reveal that sedimentation has alternated between clastic sediments deposited during peak glacial periods and authigenic calcite (marl) precipitated from the water column during interglacial times. The lake also contains ideal sediments for multiproxy analysis that can be reliably dated using both the radiocarbon and U/Th methods. The oxygen isotopic composition of marl and ostracod carapaces demonstrate that authigenic calcite in Lake Junin primarily records the isotopic composition of precipitation and secondarily the degree of evaporative enrichment of lake water. Lake Junin contains a continuous record of tropical hydroclimate over interglacial and interstadial intervals for much of the past several hundred thousand years that is both comparable to, and an extension of stable isotope records from regional ice cores and speleothems. New organic geochemical proxies compliment the marl isotope record and offer the potential for a truly continuous isotope paleoclimate record through glacial and interglacial intervals alike. Lake Junin is ideally situated, both from logistical and scientific standpoints, to provide continuous high-resolution, independently-dated, long-term records of glaciation, and the variability of phenomena such as ENSO, the South America Summer Monsoon, and the Intertropical Convergence Zone. Because of the strong, demonstrated U/Th dating potential of Junin marl, we will be able to address critical issues regarding the synchrony of climate change in the tropics with that in high latitude regions of both hemispheres, the rate and timing of ecosystem response to climatic perturbations, and the dynamics of the geomagnetic field from a tropical perspective. Lake Junin is a scientifically mature site that will yield critical scientific insights that only drilling coupled with analysis can unlock. The primary objective of the proposed research is to develop the first continuous, high-resolution, absolute-dated late Quaternary record of climate change, water balance (P/E), glaciation, vegetation, and paleomagnetic secular variation for the tropical Andes. The well-dated Junin record will allow the team to develop proxy records spanning >200,000yr, which will document the timing of wet/dry cycles, glacial advances/retreats, and the impacts of climatic phenomena such as the changing strength and variability of ENSO, the South America Summer Monsoon, and shifts in the location and range of the Intertropical Convergence Zone. In addition, this study will provide an opportunity to date (via U-Th) the >40ka sections of both the Titicaca and Sabana de Bogota records through correlation of pollen, stable isotope, and paleomagnetic time series. This study will also enable important insights into the response of tropical vegetation to climate change in the upper Amazon Basin, and will provide a rare southern equatorial perspective on the evolution of Earth?s geomagnetic field.
