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42418-AC2
Understanding Holocene Climate Variability in the Northeast: Insights from Multiple Sedimentary Proxy Records
We continue to analyze the sediment cores from two lakes (Silver and Grinnell) in northern New Jersey for oxygen and carbon isotopes of inorganic calcites and mollusk shells, fossil pollen, and lithology. These analyses will be part of Mr. Cheng Zhao's PhD dissertation research and Ms. Paula Zelanko's MSc thesis, both at Lehigh University. Our data from White Lake have resulted in 2 published papers (Y.-X. Li et al. 2006. EPSL; Li et al., 2007, The Holocene), 1 paper in review, and 2 Ph.D. dissertations (Y.-X. Li 2005, and L. Li, 2006). The results from all these three lakes have produced 6 presentations at national and international meetings.
We report the following new scientific findings from Silver Lake. The lithologic and isotopic evidence from Silver Lake shows multiple climate oscillations between 9.5 and 8 ka, indicating the highly unstable nature of early Holocene climate. A large negative excursion of >2‰ is observed between 9.5 and 8 ka (1 ka = 1000 years before the present). The low d18O values of the carbonate likely reflect a decrease in regional air temperature. Superimposed on this negative excursion are multiple oscillations at a magnitude of up to >1‰. These oscillations correspond to decreases of 20-80% in carbonate content and simultaneous increases in organic matter. On the basis of present sediment distribution at the lake, organic-rich peaty sediments were likely deposited during low lake levels; whereas carbonate-rich sediments were likely deposited in more open and deep water environments. The decreases in lake level at Silver Lake could reflect periods of dry conditions in the region during the early Holocene. We also observed a trend of increasing variability, especially in lithologic oscillations from 9.5 to 8 ka. This suggests an increase in the environmental instability in the region, which correlates with the increase in magnitude of the outburst floods. Our sediment records from this lake suggest that six cool-dry events occurred between 9.5 and 8 ka, including the largest 8.2 ka event. The apparent correlation of our sedimentary records with the documented outburst floods suggests a possible causal relationship. This implies that the climate in the Mid-Atlantic region was extremely sensitive to perturbations of ocean circulation.
Also, high resolution oxygen and carbon isotope records from Lake Grinnell show strong insolation control of Holocene temperature (O isotopes), while moisture change (inferred from C isotopes) appears to respond to ocean temperatures. The analysis has been done on this lake, and the results are being written up for publication. The multiple isotope and pollen analysis of the top 60-cm sediments spanning the last 700 years from White Lake show complex interactions of human activities (forest clearance, and industrial pollution), landscape stability and aquatic productivity. Our results demonstrate the usefulness of multiple isotope proxies (from calcite and organic matter) in strengthening the interpretations of environmental changes. A manuscript reporting the results has been submitted for publication.
The project has contributed to two completed Ph.D. dissertations at Lehigh University. These two Ph.D. students have advanced their scientific careers as postdoctoral research scientists at Tulane University (New Orleans, LA) and at the Institut de Physique du Globe de Paris in France. Also, the two graduate students (C. Zhao, and P. Zelanko) now work on the project for their dissertation and thesis research. A visiting research scientist (Y. Zhao) visited Lehigh early this year to carry out pollen analysis at Grinnell Lake, which strengthened the international collaboration. The project has benefited my career in recruiting qualified graduate students and in securing additional funding from NSF on other paleoclimate projects.
