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

Abstract

Abstract. Ice-core-based records of isotopic composition are a proxy for past temperatures and can thus provide information on polar climate variability over a large range of timescales. However, individual isotope records are affected by a multitude of processes that may mask the true temperature variability. The relative magnitude of climate and non-climate contributions is expected to vary as a function of timescale, and thus it is crucial to determine those temporal scales on which the actual signal dominates the noise. At present, there are no reliable estimates of this timescale dependence of the signal-to-noise ratio (SNR). Here, we present a simple method that applies spectral analyses to stable-isotope data from multiple cores to estimate the SNR, and the signal and noise variability, as a function of timescale. The method builds on separating the contributions from a common signal and from local variations and includes a correction for the effects of diffusion and time uncertainty. We apply our approach to firn-core arrays from Dronning Maud Land (DML) in East Antarctica and from the West Antarctic Ice Sheet (WAIS). For DML and decadal to multi-centennial timescales, 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 estimated spectrum of climate variability also shows increasing variability towards longer timescales, contrary to what is traditionally inferred from single records in this region. In contrast, the inferred variability spectrum for WAIS stays close to constant over decadal to centennial timescales, and the results even suggest a decrease in SNR over this range of timescales. We speculate that these differences between DML and WAIS are related to differences in the spatial and temporal scales of the isotope signal, highlighting the potentially more homogeneous atmospheric conditions on the Antarctic Plateau in contrast to the marine-influenced conditions on WAIS. In general, our approach provides a methodological basis for separating local proxy variability from coherent climate variations, which is applicable to a large set of palaeoclimate records.

Stable water isotopes and accumulation rates in the Union Glacier region, Ellsworth Mountains, West Antarctica, over the last 35 years

“…In summary, the signal-to-noise ratios of accumulation rates at UG are consistent with those determined by Schlosser et al (2014) and Altnau et al (2015) for firn cores from Fimbul Ice Shelf, DML, and much higher than those found in low-accumulation areas of the Amundsenisen mountain range, DML Altnau et al, 2015). Generally, the higher the accumulation rates at a specific site are, the higher the signal-to-noise ratios for stable water isotopes and accumulation rates are (Hoshina et al, 2014;Münch et al, 2016). Hence, the UG region with higher accumulation rates as compared to low-accumulation sites on the EAIS (e.g.…”

Microstructure of Snow and Its Link to Trace Elements and Isotopic Composition at Kohnen Station, Dronning Maud Land, Antarctica

“…Retrieving these climate proxies from ice cores allows to reconstruct past changes in earth's climate history from annual to glacial-interglacial time scales (e.g. Brook and Buizert, 2018;Münch and Laepple, 2018). More specifically, stable water isotopes are a well-established proxy for past air temperature variations in Greenland (e.g.…”

Resonant Forcing of the Climate System in Subharmonic Modes

“…It must be emphasized, however, that during the last glacial maximum and the Holocene the decrease in temperature variations as the mean temperature increased while exhibiting a zonal pattern may explain some discrepancies between the hemispheres [33,34].…”