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. Ice-core-based records of isotopic composition are a proxy for pasttemperatures and can thus provide information on polar climate variabilityover a large range of timescales. However, individual isotope records areaffected by a multitude of processes that may mask the true temperaturevariability. The relative magnitude of climate and non-climate contributionsis expected to vary as a function of timescale, and thus it is crucial todetermine those temporal scales on which the actual signal dominates thenoise. At present, there are no reliable estimates of this timescaledependence of the signal-to-noise ratio (SNR). Here, we present a simplemethod that applies spectral analyses to stable-isotope data from multiplecores to estimate the SNR, and the signal and noise variability, as afunction of timescale. The method builds on separating the contributions froma common signal and from local variations and includes a correction for theeffects of diffusion and time uncertainty. We apply our approach to firn-corearrays from Dronning Maud Land (DML) in East Antarctica and from the WestAntarctic Ice Sheet (WAIS). For DML and decadal to multi-centennialtimescales, we find an increase in the SNR by nearly 1 order of magnitude( ∼0.2 at decadal and ∼1.0 at multi-centennial scales). The estimatedspectrum of climate variability also shows increasing variability towardslonger timescales, contrary to what is traditionally inferred from singlerecords in this region. In contrast, the inferred variability spectrum forWAIS stays close to constant over decadal to centennial timescales, and theresults even suggest a decrease in SNR over this range of timescales. Wespeculate that these differences between DML and WAIS are related todifferences in the spatial and temporal scales of the isotope signal,highlighting the potentially more homogeneous atmospheric conditions on theAntarctic Plateau in contrast to the marine-influenced conditions on WAIS. Ingeneral, our approach provides a methodological basis for separating localproxy variability from coherent climate variations, which is applicable to alarge set of palaeoclimate records.

What climate signal is contained in decadal- to centennial-scale isotope variations from Antarctic ice cores?