Carbon stable isotope record in the coral species Siderastrea stellata: A link to the Suess Effect in the tropical South Atlantic Ocean

摘要

Coral skeletons are natural archives whose geochemical signatures provide insights into the tropical ocean history beyond the instrumental record. Carbon stable isotopes from coral skeletons (delta C-13(coral)) have been used as a proxy for multiple variables on a seasonal basis. Long-term changes in coral delta C-13 could be related to the changing isotopic composition of the dissolved inorganic carbon (delta C-13(DIC)). delta C-13(DIC) in turn reflects changes in the delta C-13 of atmospheric CO2, which in the modern Earth system is governed primarily by anthropogenic injection of CO2 into the atmosphere - a process known as the Suess Effect. Here we report three delta C-13 coral-based records of Siderastrea stellata from the tropical South Atlantic. U-series dating for the colonies 12SFB-1, 13SS-1 and 13SS-2 suggests these corals lived 13, 57 and 65 years, respectively. Short-term delta C-13 variations in their skeletal aragonite are dominated by interannual variation. All three delta C-13 records additionally exhibit an overall decreasing trend, with a depletion of about -0.0243 +/- 0.0057 parts per thousand.yr(-1) (12SFB-1), -0.0208 +/- 0.0007 parts per thousand.yr(-1) (13SS-1) and -0.0214 +/- 0.0013 parts per thousand.yr(-1) (13SS-2). These rates of the coral records from Rocas Atoll are similar to the reported trend for the delta C-13 of atmospheric CO2 over the years 1960-1990 (-0.023 to -0.029 parts per thousand.yr(-1)), and to the decreasing rates of global delta C-13(DIC). Our findings suggest that multiple delta C-13 coral-based records are required for confidently identifying local changes in the delta C-13(DIC) of the ocean. This information, in turn, can be used to infer changes in the delta C-13 of the atmospheric CO2 composition and provide valuable information about recent changes on the carbon biogeochemical cycle during the Anthropocene epoch.