Regional climate signal vs. local noise: A two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land

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Abstract

In low-accumulation regions, the reliability of &delta;<sup>18</sup>O-derived temperature signals from ice cores within the Holocene is unclear, primarily due to small Holocene climate changes relative to the intrinsic noise of the isotopic signal. In order to learn about the representativity of single ice cores and to optimise future ice-core-based climate reconstructions, we studied the stable-water isotope composition of firn at Kohnen station, Dronning Maud Land, Antarctica. Analysing &delta;<sup>18</sup>O in two 50 m long snow trenches allowed us to create an unprecedented, two-dimensional image characterising the isotopic variations from the centimetre to the hundred-metre scale. Our results show a clear seasonal layering of the isotopic composition, consistent with the accumulation rate, as well as high lateral isotopic variability caused by local stratigraphic noise. Based on the horizontal and vertical structure of the isotopic variations, we derive a statistical model for the stratigraphic noise. Our model successfully explains the trench data and allows to determine an upper bound of the reliability of climate reconstructions from seasonal to inter-annual time scales, depending on the number and the spacing of the cores taken. Implications for our study region include that reliably detecting a warming trend (0.1 °C decade<sup>−1</sup>) in 50 years of data would require &sim;10–50 replicate cores with a horizontal spacing of at least 10 m. More generally, our results suggest that in order to obtain high-resolution records of Holocene temperature change, fast measurements, thus allowing multiple cores, are more important than to minimise analytic uncertainty as the latter only plays a minor role in the total uncertainty.

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Münch, T., Kipfstuhl, S., Freitag, J., Meyer, H., & Laepple, T. (2016). Regional climate signal vs. local noise: A two-dimensional view of water isotopes in Antarctic firn at Kohnen Station, Dronning Maud Land. Climate of the Past, 12(7), 1565–1581. https://doi.org/10.5194/cp-12-1565-2016

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