David A. Hodell - US grants

This project is an investigation into the paleoclimatic variations of The Southern Ocean since the late Miocene (the most recent 10 million years) through the examination of climatically sensitive parameters from undisturbed piston cores obtained in the northeastern Weddell Sea on Leg 114 of the Ocean Drilling Program. Core recovery at this site was nearly continuous, and has already yielded a detailed magnetic stratigraphy to 6.5 million years before present, so that accurate dating of observed events can be expected. Identifying the climatic changes that have occurred, and understanding the responses of the antarctic current system to these changes is one of the major objectives of marine paleoenvironmental research. Such understanding is based on the detailed study of the sedimentation history of the region, which includes the location of modern surface and bottom current pathways, the examination of closely spaced samples from high quality sediment cores, and the regional correlation of environmental events. The climate related parameters to be measured include stable isotopes, percent carbonate and organic matter, silicoflagellates, and radiolarian census data. Paleotemperature estimates will be made from diatom assemblages, N. pachyderma coiling ratios, and silicoflagellate species ratios. These have been quite successful when applied to a somewhat later time frame in the subantarctic region.

The study will involve the use of oxygen and carbon isotopes of foraminifera to reconstruct the history of climates, polar ice sheets, and oceanic conditions during the last few million years of Earth's history. The research will focus on the role of Antarctic climates in causing oceanographic changes that have resulted in evolutionary changes in the microfauna and microflora. The research will have an impact on the understanding of past and future carbon dioxide changes in the Earth's atmosphere.

This award provides one-half the funding required to adapt an existing gas-source mass spectrometer so that it can be used for hydrogen/deuterium isotopic analysis. The instrument is housed in the Department of Geology at the University of Florida, and the University of Florida is committed to providing the remaining half of the funds required. The new capabilities of the instrument are needed in the research projects of eight faculty and their students. These include research in geohydrology, ecosystems, limnology, paleoclimatology, and archeology.

This 3-year study will elucidate the historical response of the lower Great Lakes to nutrient enrichment and abatement, and provide a basis for monitoring changes in trophic state variables in other large, deep-water lakes. Data collected will calibrate existing proxy indicators to modern conditions and develop new techniques for estimating past, present and future changes in the trophic state of the Great Lakes. The field program will include data collection from the water column, sediment traps and cores from Lake Ontario and Erie. Laboratory experiments will determine the effects of nutrient enrichment on the carbon and nitrogen isotopic signature of organic matter produced by phytoplankton.

Abstract ATM-9305750 Brenner, Mark Title: Paleoclimate of Southwest China: Development of the Asian Monsoon This award suports a study of sediment cores from four Yunnan lakes which will be used to reconstruct the paleoclimate of southwest China from late Pleistocene to present . Long, 14C-dated sections (>10kyr BP) have been obtained. Contrary to "predictions" from general circulation models, pollen, diatom and geochemical data indicate a shift from wet late Pleistocene to drier early Holocene conditions. The sediment record also suggests lake-level shifts during the Holocene. Chronologic resolution of paleoclimatic records will be enhanced by close-interval sampling and AMS dating. Stable isotope and trace metal ratios in sedimented ostracod shells will be used to test previous paleoclimatic inferences and establish whether late-Pleistocene, high lake levels were a consequences of glacial meltwater input. Paleoenvironmental reconstruction will also be based on stable isotope signals in carbonates and organic matter. Proxy paleoclimatic data from southwest China will shed light on the development of the Asian monsoon system and can be used to test moisture simulations from general circulation models.

9503817 Hodell This collaborative field program in the sub-Antarctic ocean involves researchers from University of Florida, Georgia Tech, Scripps Institution of the University of California at San Diego and Lamont-Doherty Earth Observatory of Columbia University. The objectives of the research cruise planned for early 1996 are to sample sediments deposited within various water masses of the Antarctic ocean for studies of climatic and oceanographic variations over the past few hundred thousand years. The Antarctic region has a major influence on global oceanography, for it is here that many of the intermediate and bottom waters of the world ocean are formed, and thus the heat and chemical budgets of the ocean are dependent in a number of ways on changes in climate and oceanography here. The record of these variations is recorded in microfossils preserved in the sediments, and this group of investigators will sample sediments from all of the major intermediate and deep water masses of the region. Their research will include faunal, chemical and pore water analysis of the sediments recovered to construct chronologies of change in a large number of parameters throughout the last two or three glacial cycles (as far as their piston cores will reach). In addition, the data they collect will be used to define suitable sites for drilling by JOIDES Resolution in 1997 or 1998 at sites which have been highly ranked as part of the Ocean Drilling Program, the international program for scientific ocean drilling of which NSF is a major sponsor. Though presently considered a high drilling priority, these Antarctic sites do not presently have sufficient site survey information to allow precise hole locations, and this project will provide those necessary geophysical and sedimentological data. ***

9709314 Hodell The Department of Peten in northern Guatemala represents the central area where ancient Maya civilization arose more than 3000 years ago, flourished during the so-called Classic Period, and mysteriously collapsed around 800 - 900 AD. The cause of the Collapse has been debated by archaeologists for over a century. Climate change has been suggested as a contributing factor, but this hypothesis has not been tested rigorously. Our previous work, funded by NOAA-Paleoclimatology, sought to understand the role that climate change may have played in the collapse of Maya civilization. We discovered compelling paleoclimatic evidence from two lakes in central and northern Yucatan for a protracted drought between ~800 and 1000 AD that coincided with the Classic Maya Collapse (Hodell et al., 1995; Curtis et al., 1996). Correlation of arid events in paleoclimate records between Yucatan lakes and the Peruvian Quelccaya ice core suggests that aridity was widespread in Central and South America over the last 1500 years, and may have been related to large-scale departures in atmospheric and oceanic fields. Here we propose to test if the droughts documented in Yucatan affected the southern Maya lowlands of Peten, Guatemala, where Maya population densities were highest and the Collapse was most profound. We propose to collect geochemical, palynological, and sedimentologic data from sediment cores taken in the Peten Lake District to reconstruct climatic and ecologic changes in sufficient detail to reveal decadal to centennial fluctuations over the past 5,000 years. Specifically, we will measure oxygen isotopic ratios in microfossil shells (ostracods and gastropods) from cores taken in close-basin lakes and reconstruct changes in the ratio of evaporation to precipitation (E/P) over the catchment. We will also document stratigraphic changes in pollen spectra from the same cores to reconstruct regional vegetation changes that may have been influenced by climatic factors and/or human impact. The proposed study will elucidate the spatial and temporal pattern of changes in E/P and vegetation in the Maya lowlands during the late Holocene. Paleoenvironmental records from Peten will contribute to our understanding of: 1.) the full range of natural hydrometeorologic variability during the Holocene in the lowland Neotropics; 2.) teleconnective linkages with climatic records (marine, lacustrine, and ice core records) from other regions; and 3.) the response of Classic Maya social and economic systems to climate and ecologic change.

This award will support the generation of planktic and benthic foraminiferal stable isotope data, and concentration of ice-rafted detritus, at multi-century-scale resolution for sediment cores from the Southern Ocean spanning the last half million years. The data will be used to determine how millenial-scale variability has evolved during the late Pleistocene and its relation to orbital forcing.

This research will examine a suite of cores from the Peten Lakes District in Guatemala to examine the pre-Holocene record of climate change in tropical lakes that did not dry out in the last glacial. The sediments of these lakes contain the potential for preserving a unique and full record of rapid climate change from an area of the world with few continuous climate records.

Abstract

Under this award the PIs will study ice-rafted detritus (IRD) in high-sedimentation-rate cores from the high-latitude South Atlantic (SA). Previos studies have identified six to seven discrete episodes of IRD deposition between 12 and 60 kyr during the last glaciation that have been suggested to be regionally correlative. If these events can be shown to be widely distributed and synchronous, they may indicate instability in Antarctic ice sheets. The PIs will examine the origin of these South Atlantic IRD (SA-IRD) events, their significance for Antarctic ice-sheet dynamics, and their exact relationship to millennial-scale climate events recorded in polar ice cores. This project will 1.) map the aerial distribution of IRD events in the South Atlantic basin; 2.) date SA-IRD events using AMS-14C and estimating particle flux and sediment redistribution using the Th-normalization method; 3.) trace the origin of IRD events to their Antarctic source area(s) using mineralogy and geochemistry; and 4.) correlate South Atlantic IRD events to Antarctic and Greenland ice cores, other marine sediment cores (e.g., North Atlantic), and global sea level records.

EAR-0418905
Mueller

This proposal seeks support for the appointment of a Ph.D. scientist to act as laboratory manager for a new ICP-based analytical facility at the University of Florida for an initial 3-year period. The University of Florida will assume 100% financial responsibility for this position on a permanent basis subsequent to this initial period. The construction of the ICP laboratory and the acquisition of two new ICP mass spectrometers (Finnegan-MAT Element-2 and Nu Plasma multicollector) are part of the recent relocation into >10,000 sq. ft. of new geochemical laboratories as part of an overall relocation of our Department into greatly expanded and renovated facilities (Williamson Hall). These instruments have been interfaced with newly acquired Excimer (193 nm) and Nd-YAG (213 nm) lasers, as well as a desolvating nebulizer and autosamplers. Financial support for both laboratory renovation and instrument acquisition involved cost sharing between the University of Florida and the NSF. The primary responsibilities of this person will include: 1) contribute to method development and participate in collaborative and independent research, 2) maintain quality control of the facility, which will be a challenge in light of the large number of users; 3) oversee and administer day-to-day activities such as maintenance and scheduling, in order for the facility to efficiently produce the highest quality data; and 4) make the instruments capabilities known to and accessible to a wide range of users inside and outside of the department, including students. In addition, the laboratory manager will be the primary instructor for students exposed to elemental and isotopic methods both in courses and via individual research projects at the graduate and undergraduate levels. Without an experienced laboratory manager, access to this facility for these students and other users will be very limited.
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The researchers in this collaborative project seek to use GLAD800 (the Global Lake Drilling 800) system to retrieve sediment cores from Lake Peten-Itza in northern Guatemala to study climate variability in lowland Central America during the late Pleistocene and Holocene on time scales ranging from decades to millennia.

The researchers hypothesize that changes in the mean meridional position of the Atlantic inter-tropical convergence zone (ITCZ) are responsible for rainfall variations in the northern lowland Neotropics on interannual to multi-millennial time scales. The ITCZ is a region within 5 degrees of the equator where the trade winds converge to form low atmospheric pressure, enhancing precipitation and influencing global circulation. Coupled general circulation models indicate high sensitivity to climate and circulation changes in the high-latitude North Atlantic.

Specifically, the researchers will establish marine-terrestrial linkages by correlating rainfall and runoff proxies in sediment cores from Lake Peten-Itza with those from the Cariaco Basin, northern Venezuela, to determine regional precipitation changes. In turn, the Peten-Itza and Cariaco records will be compared with proxy signals from the high latitudes of the North Atlantic to assess linkages with that region. It is believed that terrestrial-marine-ice correlations of paleoclimate archives at sub-millennial time scales can be used to decipher the history of the northern Neotropic hydrologic cycle, its relation to the Atlantic ITCZ, and linkages to climate in the high-latitude North Atlantic. To accomplish this, six primary drilling sites have been identified in Lake Peten-Itza on the basis of detailed seismic surveys.

The Peten-Itza Scientific Drilling Project will have a strong education and outreach component through ongoing, close, and active collaboration with colleagues at Guatemalan universities (UVG and UNSC) in the research agenda. Both U.S. and Guatemalan undergraduate and graduate students will be directly and significantly involved in the research.