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Late Holocene hydrologic changes in northern New Zealand inferred from stable isotope values of aquatic cellulose in sediments from Lake Pupuke |
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| Authors: | Alexander M Heyng Christoph Mayr Andreas Lücke Holger Wissel Bernd Striewski |
| Institution: | 1. Department of Earth and Environmental Sciences, GeoBio-Center, Ludwig-Maximilian-University, Richard-Wagner-Str. 10, 80333, Munich, Germany 2. Institute of Geography, Friedrich-Alexander University, Kochstr. 4/4, 91054, Erlangen, Germany 3. Institute of Bio-and Geosciences, IBG-3: Agrosphere, Research Center Jülich, 52425, Jülich, Germany 4. Department of Mines and Petroleum, Geological Survey of Western Australia, 100 Plain Street, East Perth, WA, 6004, Australia |
| Abstract: | Isotopic records of aquatic cellulose are becoming increasingly important for palaeohydrological reconstructions, but widespread application of this climate proxy is hampered by minerogenic contamination that affects oxygen isotope measures in cellulose. Few records of isotopes in aquatic cellulose are available from palaeoclimate archives in the Southern Hemisphere. In this study, we used a new bulk cellulose extraction method and determined the oxygen (δ18O) and carbon (δ13C) isotope values in cellulose from a Holocene lake sediment core segment (7.2–1.1 cal ka BP) from Lake Pupuke, Auckland, New Zealand. Isotope values from modern, potential sources of sedimentary cellulose revealed the aquatic origin of the cellulose extracted from the core, and hence enabled inference of past lake water δ18O values from the δ18O of measured cellulose in the core. A shift to a more positive water balance in the lake was identified around 2.8 cal ka BP by a decrease in inferred lake water δ18O values. At that time, greater epilimnetic primary productivity is indicated by the higher δ13C values of sedimentary cellulose. Greater divergence between the δ13C values of cellulose and bulk organic matter suggests stronger stratification of the lake, likely caused by greater freshwater input. We discuss a possible link to a solar minimum that occurred at that time. |
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