A 200-Year Record of Interannual SST and pH Variability from the Lesser Antilles (Caribbean Sea, North Atlantic) Inferred from a Siderastrea Siderea Reef Coral

Abstract:

Global warming and ocean acidification caused by the rising levels of anthropogenic CO₂ in the atmosphere need to be better constrained by long-term studies of high resolution natural archives, especially at inter-annual and decadal scales. In the framework of the French INSU program LEFE/CYBER ACID-Antilles, here we developed a 200-year long interannual time series of sea surface temperature and pH based on the geochemical composition of tropical reef forming coral. The selected tropical coral called CHANCEL-1 is a colony of genus Siderastrea Siderea which was collected in 2008 from a living micro–atoll off Martinique in the Lesser Antilles, facing the eastern side of the Caribbean Sea. The colony of 1-meter extension presents a mean growth rate of 4 – 5 mm/yr. Along the growth axis, we measured the boron isotopic composition (delta¹¹B) and trace element ratios (Li/Mg, Sr/Ca), which reveal a progressive decrease of the surface water pH and increase of temperature during the past 200 years. These observations cooperate the anthropogenic forcing, i.e. rising atmospheric CO₂ and rising sea surface temperatures due to global warming. However, other processes apparently affect the geochemical records, as indicated by sub-decadal variations of pH and temperature reconstruction overprinting the long term global trend. Possible drivers of such most likely regional variability might be decadal changes of oceanographic conditions (upwelling, freshwater runoff, seawater masse changes, etc.) as well as species dependent biological controls.