Abstract
Abstract. This experimental work addresses the need for high-resolution, long and homogeneous climatic time series that facilitate the study of climate variability over time scales of decades to millennia. We present a high-resolution record of foraminiferal δ18O from a Central-Mediterranean sediment core that covers the last two millennia. The record was analyzed using advanced spectral methods and shows highly significant oscillatory components with periods of roughly 600, 350, 200, 125 and 11 years. Over the last millennium, our data show several features related to known climatic periods, such as the Medieval Optimum, the Little Ice Age and a recent steep variation since the beginning of the Industrial Era. During the preceding millennium, the δ18O series also reveals a surprising maximum at about 0 AD, suggesting low temperatures at that time. This feature contradicts widely held ideas about the Roman Classical Period; it is, therefore, discussed at some length, by reviewing the somewhat contradictory evidence about this period. We compare the δ18O record with an alkenone-derived sea surface temperature time series, obtained from cores extracted in the same Central-Mediterranean area (Gallipoli Terrace, Ionian Sea), as well as with Italian and other European temperature reconstructions over the last centuries. Based on this comparison, we show that the long-term trend and the 200-y oscillation in the records are temperature driven and have a dominant role in describing temperature variations over the last two millennia.
Highlights
Knowledge of long-term natural variability is required to assess anthropogenic effects on climate (Martinson et al, 1995; National Research Council of the National Academies, 2006)
Several features clearly correspond to distinct climatic periods: the low δ18O values near 1000 AD are associated with the Medieval Optimum (MO), while the modern steep decrease since 1800 AD leads to even lower values; relatively high values correspond to the Little Ice Age (LIA, 1600–1800 AD) and we find high values at the beginning of the Christian Era
The eigenvalues that lie outside the 99% error bars are only those associated with empirical orthogonal functions (EOFs) 1–12, which have been included in the null hypothesis; this confirms that the model AR(1)+EOFs 1–12 captures the variability of our δ18O time series, at the 99% confidence level
Summary
Knowledge of long-term natural variability is required to assess anthropogenic effects on climate (Martinson et al, 1995; National Research Council of the National Academies, 2006). Multi-proxy records extend the spatial coverage of climate reconstructions, typically using ice cores (Jones, 1996) for high latitudes, tree rings (Luckman et al, 1997; Esper et al, 2002) for mid-latitudes, and corals (Boiseau et al, 1999; Crowley, 2000) for low latitudes. We have measured the oxygen isotope composition δ18O of planktonic foraminifera in a high-resolution, well-dated Central Mediterranean core These measurements yield a homogeneous, 2200-year-long record, which captures climatic.
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