Potential imprint of Spörer and Maunder solar minima on coral skeleton carbon isotopes

Abstract. Despite being routinely measured with δ¹⁸O in corals, records of δ¹³C are seldom presented in paleoceanographic studies. Numerous factors influence the biologically-mediated fractionation of carbon isotopes during skeletogenesis, resulting in a complex behaviour of this tracer. Here we present a long coral δ¹³C series, dating back to 1475, and showing the potential impact of solar activity. We note a significant decrease of δ¹³C during the Spörer and Maunder minima. We argue for a change in metabolical processes, from an autotrophical pattern to a more heterotrophical mode of feeding guided by change in sun irradiation. In addition, nearby volcanic eruptions might also have an impact and cause δ¹³C shifts, depending on the dust load associated with the eruption. Following previous work, we advocate the systematic presentation of δ¹³C vs. δ¹⁸O plots in coral studies to identify whether isotopic fractionation might have been affected by change in mode of feeding.