An assessment of reef coral calcification over the late Cenozoic

• Published in: Earth-Science Reviews
• Main Authors: BRACHERT, Thomas, CORREGE, Thierry, REUTER, Markus, WROZYNA, Claudia, LONDEIX, Laurent, SPRETER, Philipp, PERRIN, Christine
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Reef coral; calcification rate; ocean acidification; geological past; Neogene; Quaternary; Planète et Univers [physics]/Sciences de la Terre; Planète et Univers [physics]/Sciences de la Terre/Océanographie; Planète et Univers [physics]/Sciences de la Terre/Paléontologie; Pacific; Ocean acidification
• Online Access: https://oskar-bordeaux.fr/handle/20.500.12278/187399; https://hdl.handle.net/20.500.12278/187399; https://doi.org/10.1016/j.earscirev.2020.103154

Shallow-water reef-building corals have an extensive geological record and many aspects of their evolution, biodiversity, and biogeography are known in great details. In contrast, the adaptive potential and risk of extinction of coral reefs in response to excessive warming and ocean acidification remains largely undocumented. It is well established that anthropogenic CO2 emissions cause global warming and ocean acidification (lowering of pH), which increasingly impede the biomineralization process in many marine calcareous biota. The “light-enhanced” calcification machinery of the shallow-water reef corals is particularly threatened by this development through the combined effect of a lowering of the supersaturation of seawater with CaCO3 (aragonite) and an expulsion of the symbiotic zooxanthellae (bleaching). The bleaching is of prime importance, because it interrupts the supply of DIC and metabolites required for pH upregulation within the calcification fluid. The degree of calcification in scleractinian reef corals may therefore represent a suitable tracer to assess the state of the ocean carbonate system and the photosynthetic performance of the zooxanthellae during past episodes of natural environmental change. This study presents the first comprehensive set of calcification data from corals covering the early Miocene to early Pleistocene interval (20.8 to 1.2 million years, Ma). Various screening procedures ensured that the studied coral skeletons are pristine and suited to yield meaningful stable isotope data (δ¹⁸O, δ¹³C) and calcification records. δ¹⁸O and δ¹³C values document growth environments consistent with current tropical and subtropical settings. To assess fossil calcification rates, we use a reference dataset of recent corals from the Indo-Pacific (Porites) and an independent validation dataset from the Western Atlantic-Caribbean (Orbicella). Almost all fossil corals document very low annual rates of upward growth (“extension rate”) relative to present, and lower skeletal bulk density than ...