Abstract
Abstract. A high-resolution, well-dated foraminiferal δ18O record from a shallow-water core drilled from the Gallipoli Terrace in the Gulf of Taranto (Ionian Sea), previously measured over the last two millennia, has been extended to cover 707 BC–AD 1979. Spectral analysis of this series, performed using singular-spectrum analysis (SSA) and other classical and advanced methods, strengthens the results obtained analysing the shorter δ18O profile, detecting the same highly significant oscillations of about 600, 380, 170, 130 and 11 years, respectively explaining about 12, 7, 5, 2 and 2% of the time series total variance, plus a millennial trend (18% of the variance). The comparison with the results of multi-channel singular-spectrum analysis (MSSA) applied to a data set of 26 Northern Hemisphere (NH) temperature-proxy records shows that NH temperature anomalies share with our local record a~long-term trend and a bicentennial (170-year period) cycle. These two variability modes, previously identified as temperature-driven, are the most powerful modes in the NH temperature data set. Both the long-term trends and the bicentennial oscillations, when reconstructed locally and hemispherically, show coherent phases. Furthermore, the corresponding local and hemispheric amplitudes are comparable if changes in the precipitation–evaporation balance of the Ionian sea, presumably associated with temperature changes, are taken into account.
Highlights
IntroductionThe key to gaining information on climate analogues and periodicities, on decadal to multi-centennial and millennial timescales, is the measurement of proxy records over recent millennia, with multi-annual resolution and matching accuracy in dating.Among the different timescales of natural climatic variability, the centennial scale is interesting, being comparable to the scale of human life and to the modern variation related to anthropogenic forcing (Jones and Briffa, 1996; Jones et al, 1999, 2012).The instrumental observations, covering only a couple of centuries (Ghil and Vautard, 1991; Martinson et al, 1995; Plaut et al, 1995; Jones et al, 1999, 2012, 2013; Folland and Karl, 2001; National Research Council of the National Academies, 1996), are influenced by human activity (Barnett et al, 1999) and are too short to study centennial variability
Several classical and advanced spectral methods were applied to the δ18O time series, such as classical Fourier analysis, the maximum entropy method (MEM), singularspectrum analysis (SSA) and the multi-taper method (MTM)
We focus on the Singular-spectrum analysis (SSA) results that were obtained using an embedding dimension M = 150, equivalent to a time window M t ≈ 600 years, but we will show that these results are stable to varying M over a wide range of values
Summary
The key to gaining information on climate analogues and periodicities, on decadal to multi-centennial and millennial timescales, is the measurement of proxy records over recent millennia, with multi-annual resolution and matching accuracy in dating.Among the different timescales of natural climatic variability, the centennial scale is interesting, being comparable to the scale of human life and to the modern variation related to anthropogenic forcing (Jones and Briffa, 1996; Jones et al, 1999, 2012).The instrumental observations, covering only a couple of centuries (Ghil and Vautard, 1991; Martinson et al, 1995; Plaut et al, 1995; Jones et al, 1999, 2012, 2013; Folland and Karl, 2001; National Research Council of the National Academies, 1996), are influenced by human activity (Barnett et al, 1999) and are too short to study centennial variability. The key to gaining information on climate analogues and periodicities, on decadal to multi-centennial and millennial timescales, is the measurement of proxy records over recent millennia, with multi-annual resolution and matching accuracy in dating. Among the different timescales of natural climatic variability, the centennial scale is interesting, being comparable to the scale of human life and to the modern variation related to anthropogenic forcing (Jones and Briffa, 1996; Jones et al, 1999, 2012). C. Taricco et al.: A high-resolution δ18O record proxy weighting and proxy calibration. Taricco et al.: A high-resolution δ18O record proxy weighting and proxy calibration These factors may lead to non-robust reconstructions (Lehner et al, 2012)
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