- Email: [email protected]
Particle properties and paleoceanographic proxies
Goldschmidt Conference Abstracts 2006
A155
Timing and nature of late Quaternary climate change from cave deposits
Particle properties and paleoceanographic proxies
R.L. EDWARDS1, D.X. YUAN2, Z.S. AN3, Y.J. WANG4, A.S. AULER5, H. CHENG1, H. ROWE6, X.F. WANG1, M.J. KELLY1, C.A. DYKOSKI1
T.I. EGLINTON1, J. HWANG1, N. OHKOUCHI2, R. FRANCOIS3, D. MONTLUCON1, S. MANGANINI4 1
1
University of Minnesota, MN 55455, USA (edwar001@ umn.edu) 2 Karst Dynamic Laboratory, Guilin 541004, China (dxyuan@ karst.edu.cn) 3 Institute of Earth Environment, CAS, Xi’an, China (anzs@loess. llqg.ac.cn) 4 Nanjing Normal University, Nanjing, China (yjwang@ njnu.edu.cn) 5 Instituto de Geociencias, Universidade Federal de Minas Gerais, Brazil ([email protected]) 6 University of Kentucky, KY 40506, USA ([email protected]) Well-chosen cave calcite sub-samples can be dated accurately and precisely by uranium–thorium methods, using mass spectrometric techniques. The current limit is 700,000 years, although further technical improvements may well expand the range. In a number of caves around the world, it has been established that calcite oxygen isotopic composition represents, in essence, the history of the oxygen isotopic composition of meteoric precipitation. Using these approaches, we are establishing high resolution, absolute-dated oxygen isotope stratigraphics for meteoric precipitation over the last several glacial cycles. The foci of our work are multiple cave sites in China and Brazil. So far, we have established a 300,000-year record of Asian Monsoon precipitation, with resolutions ranging from 2 years to several decades, and a similar record of southern Brazil precipitation covering the last 90,000 years. We correlate our records to benchmark records of climate and environmental change. The cave records are correlated to (1) each other through precise dating, (2) Greenland and Antarctic ice core records through atmospheric methane (which responds to changes in the Asian Monsoon), and (3) North Atlantic marine oxygen isotope records (by linking Heinrich events and intervals of unusually high oxygen isotopic composition recorded in Chinese caves). Our data and the correlations to other records improve our knowledge of the absolute timing and spatial pattern of late Quaternary climate change. Highlights include: (1) The discovery of last glacial period Dansgaard-Oeschger (DO) events in China and Brazil. Chinese and Greenland events are in phase, whereas Brazilian events are anti-phased, suggesting a N. Hemisphere–S. Hemisphere low-latitude precipitation seesaw, caused by feedbacks between high and low latitude climate. (2) The discovery and characterization of DO events in the penultimate and antepenultimate glacial periods in China. These have approximately the same pacing and amplitude as the last glacial DO events. (3) Determination of the timing and sequence of events during termination II. These observations have led to new ideas about the triggers for glacial terminations. doi:10.1016/j.gca.2006.06.1376
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA ([email protected]) 2 Institute for Research on Earth Evolution, Japan-Agency for Marine-Earth Science and Technology, Yokosuka, Japan ([email protected]) 3 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada ([email protected]) 4 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA (smanganini@ whoi.edu) Our understanding of past variations in the ocean–climate system is largely based on information gleaned from proxy signals embedded in marine sediment records. In seeking to develop high temporal resolution records of past ocean and climate variability, paleoceanographers frequently target high deposition-rate sedimentary environments. While these archives can yield records of exquisite detail, interpretations of geochemical proxies are not always straightforward. For example, coupled radiocarbon measurements on molecular markers (alkenones) and calcareous microfossils (planktonic forams) from Bermuda Rise (subtropical N. Atlantic Ocean) sediments reveal that corresponding proxy signals are temporally decoupled Such age offsets arise from sedimentological processes that act differently upon proxies residing in different grain-size fractions. In particular, organic and other components associated with fine-grained minerals and low density aggregates are prone of resuspension and lateral transport. Studies of this and other high-deposition-rate settings indicate that redistribution of particulate matter may play an important role in shaping sedimentary records. With respect to the Bermuda Rise, it is hypothesized that export and long-range transport of particles from the NW Atlantic margin may occur in association with the Deep Western Boundary Current (DWBC). In order to evaluate the NW Atlantic margin as a source of particulate matter, and the DWBC as a potential conduit for its redistribution, we are characterizing geochemical signals (e.g., molecular markers, carbon isotopes, uranium series) in sinking and suspended particulate matter over the continental slope off New England. Preliminary results indicate significant advective transport of detrital minerals and pre-aged carbon associated with nepheloid layers, and highlight the need to better understand particle dynamics in this region. Results will be discussed in the context of the relevance of these processes to the interpretation of marine sedimentary records from a range of depositional settings. doi:10.1016/j.gca.2006.06.1377
A155
Timing and nature of late Quaternary climate change from cave deposits
Particle properties and paleoceanographic proxies
R.L. EDWARDS1, D.X. YUAN2, Z.S. AN3, Y.J. WANG4, A.S. AULER5, H. CHENG1, H. ROWE6, X.F. WANG1, M.J. KELLY1, C.A. DYKOSKI1
T.I. EGLINTON1, J. HWANG1, N. OHKOUCHI2, R. FRANCOIS3, D. MONTLUCON1, S. MANGANINI4 1
1
University of Minnesota, MN 55455, USA (edwar001@ umn.edu) 2 Karst Dynamic Laboratory, Guilin 541004, China (dxyuan@ karst.edu.cn) 3 Institute of Earth Environment, CAS, Xi’an, China (anzs@loess. llqg.ac.cn) 4 Nanjing Normal University, Nanjing, China (yjwang@ njnu.edu.cn) 5 Instituto de Geociencias, Universidade Federal de Minas Gerais, Brazil ([email protected]) 6 University of Kentucky, KY 40506, USA ([email protected]) Well-chosen cave calcite sub-samples can be dated accurately and precisely by uranium–thorium methods, using mass spectrometric techniques. The current limit is 700,000 years, although further technical improvements may well expand the range. In a number of caves around the world, it has been established that calcite oxygen isotopic composition represents, in essence, the history of the oxygen isotopic composition of meteoric precipitation. Using these approaches, we are establishing high resolution, absolute-dated oxygen isotope stratigraphics for meteoric precipitation over the last several glacial cycles. The foci of our work are multiple cave sites in China and Brazil. So far, we have established a 300,000-year record of Asian Monsoon precipitation, with resolutions ranging from 2 years to several decades, and a similar record of southern Brazil precipitation covering the last 90,000 years. We correlate our records to benchmark records of climate and environmental change. The cave records are correlated to (1) each other through precise dating, (2) Greenland and Antarctic ice core records through atmospheric methane (which responds to changes in the Asian Monsoon), and (3) North Atlantic marine oxygen isotope records (by linking Heinrich events and intervals of unusually high oxygen isotopic composition recorded in Chinese caves). Our data and the correlations to other records improve our knowledge of the absolute timing and spatial pattern of late Quaternary climate change. Highlights include: (1) The discovery of last glacial period Dansgaard-Oeschger (DO) events in China and Brazil. Chinese and Greenland events are in phase, whereas Brazilian events are anti-phased, suggesting a N. Hemisphere–S. Hemisphere low-latitude precipitation seesaw, caused by feedbacks between high and low latitude climate. (2) The discovery and characterization of DO events in the penultimate and antepenultimate glacial periods in China. These have approximately the same pacing and amplitude as the last glacial DO events. (3) Determination of the timing and sequence of events during termination II. These observations have led to new ideas about the triggers for glacial terminations. doi:10.1016/j.gca.2006.06.1376
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA ([email protected]) 2 Institute for Research on Earth Evolution, Japan-Agency for Marine-Earth Science and Technology, Yokosuka, Japan ([email protected]) 3 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada ([email protected]) 4 Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, USA (smanganini@ whoi.edu) Our understanding of past variations in the ocean–climate system is largely based on information gleaned from proxy signals embedded in marine sediment records. In seeking to develop high temporal resolution records of past ocean and climate variability, paleoceanographers frequently target high deposition-rate sedimentary environments. While these archives can yield records of exquisite detail, interpretations of geochemical proxies are not always straightforward. For example, coupled radiocarbon measurements on molecular markers (alkenones) and calcareous microfossils (planktonic forams) from Bermuda Rise (subtropical N. Atlantic Ocean) sediments reveal that corresponding proxy signals are temporally decoupled Such age offsets arise from sedimentological processes that act differently upon proxies residing in different grain-size fractions. In particular, organic and other components associated with fine-grained minerals and low density aggregates are prone of resuspension and lateral transport. Studies of this and other high-deposition-rate settings indicate that redistribution of particulate matter may play an important role in shaping sedimentary records. With respect to the Bermuda Rise, it is hypothesized that export and long-range transport of particles from the NW Atlantic margin may occur in association with the Deep Western Boundary Current (DWBC). In order to evaluate the NW Atlantic margin as a source of particulate matter, and the DWBC as a potential conduit for its redistribution, we are characterizing geochemical signals (e.g., molecular markers, carbon isotopes, uranium series) in sinking and suspended particulate matter over the continental slope off New England. Preliminary results indicate significant advective transport of detrital minerals and pre-aged carbon associated with nepheloid layers, and highlight the need to better understand particle dynamics in this region. Results will be discussed in the context of the relevance of these processes to the interpretation of marine sedimentary records from a range of depositional settings. doi:10.1016/j.gca.2006.06.1377