Anthropogenic and solar forcing in δ¹³C time pattern of coralline sponges

Abstract

We present the results of a re-analysis of a previously published carbon isotope data-set related to coralline sponges in the Caribbean Sea. The original interpretation led to the discrimination between a pre-industrial period, with a signal controlled by solar-induced climatic variations, followed by the industrial era, characterized by a progressive δ(13)C negative shift due to the massive anthropogenic carbon emissions. Our re-analysis allowed to extract from the raw isotopic data evidence of a solar forcing still visible during the industrial era, with a particular reference to the 88-year Gleissberg periods. These signals are related to slope changes in both the δ(13)C versus time and the δ(13)C versus carbon emission curves.

Decoupling of coral skeletal δ13C and solar irradiance over the past millennium caused by the oceanic Suess effect

“…As the anthropogenic influence on climatic and environmental changes was relatively weak before the Industrial Revolution, anthropogenic CO 2 should have played a limited role in the long‐term change of preindustrial coral δ 13 C levels. The time series of δ 13 C records from coralline sponge skeletons can be subdivided into two parts: a preindustrial period, during which the isotopic composition is controlled by climatic forcings, followed by the Industrial Era, characterized by a progressive enrichment in 12 C caused by massive carbon emissions of anthropogenic origin [ Böhm et al, ; Madonia and Reitner , ]. The Medieval Warm Period (MWP, A.D. 900–1300) [ Lamb , ; Crowley and Lowery , ; Bradley et al, ] and the Little Ice Age (LIA, A.D. 1550–1850) [ Robock , ; Bradley and Jones , ; Matthews and Briffa , ] were climatic and environmental anomalies caused by natural forcing (e.g., solar variability and volcanic emissions).…”