Articles | Volume 8, issue 2
Clim. Past, 8, 831–839, 2012
Clim. Past, 8, 831–839, 2012

Research article 20 Apr 2012

Research article | 20 Apr 2012

Natural variability and anthropogenic effects in a Central Mediterranean core

S. Alessio1, G. Vivaldo1, C. Taricco1, and M. Ghil2,3 S. Alessio et al.
  • 1Dipartimento di Fisica Generale dell'Università, and Istituto di Fisica dello Spazio Interplanetario (IFSI–INAF), Turin, Italy
  • 2Geosciences Department & Laboratoire de Météorologie Dynamique (CNRS and IPSL), Ecole Normale Supérieure, Paris, France
  • 3Department of Atmospheric and Oceanic Sciences & Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095-1565, USA

Abstract. We evaluate the contribution of natural variability to the modern decrease in foraminiferal δ18O by relying on a 2200-yr-long, high-resolution record of oxygen isotopic ratio from a Central Mediterranean sediment core. Pre-industrial values are used to train and test two sets of algorithms that are able to forecast the natural variability in δ18O over the last 150 yr. These algorithms are based on autoregressive models and neural networks, respectively; they are applied separately to each of the δ18O series' significant variability components, rather than to the complete series. The separate components are extracted by singular-spectrum analysis and have narrow-band spectral content, which reduces the forecast error. By comparing the sum of the predicted low-frequency components to its actual values during the Industrial Era, we deduce that the natural contribution to these components of the modern δ18O variation decreased gradually, until it reached roughly 40%, as early as the end of the 1970s.