Latitudinal differences in the amplitude of the OAE-2 carbon isotopic excursion: p CO 2 and paleo productivity

• Published in: Biogeosciences
• Main Authors: J. S. Sinninghe Damsté, A. Forster, E. C. van Bentum, G.-J. Reichart
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2012
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; North Atlantic
• Online Access: https://doi.org/10.5194/bg-9-717-2012; https://doaj.org/article/f6f4733ebefe4894b53b58bfac86eac4

A complete, well-preserved record of the Cenomanian/Turonian (C/T) Oceanic Anoxic Event 2 (OAE-2) was recovered from Demerara Rise in the southern North Atlantic Ocean (ODP site 1260). Across this interval, we determined changes in the stable carbon isotopic composition of sulfur-bound phytane (δ 13 C phytane ), a biomarker for photosynthetic algae. The δ 13 C phytane record shows a positive excursion at the onset of the OAE-2 interval, with an unusually large amplitude (~7‰) compared to existing C/T proto-North Atlantic δ 13 C phytane records (3–6‰). Overall, the amplitude of the excursion of δ 13 C phytane decreases with latitude. Using reconstructed sea surface temperature (SST) gradients for the proto-North Atlantic, we investigated environmental factors influencing the latitudinal δ 13 C phytane gradient. The observed gradient is best explained by high productivity at DSDP Site 367 and Tarfaya basin before OAE-2, which changed in overall high productivity throughout the proto-North Atlantic during OAE-2. During OAE-2, productivity at site 1260 and 603B was thus more comparable to the mid-latitude sites. Using these constraints as well as the SST and δ 13 C phytane -records from Site 1260, we subsequently reconstructed p CO 2 levels across the OAE-2 interval. Accordingly, p CO 2 decreased from ca. 1750 to 900 ppm during OAE-2, consistent with enhanced organic matter burial resulting in lowering p CO 2 . Whereas the onset of OAE-2 coincided with increased p CO 2 , in line with a volcanic trigger for this event, the observed cooling within OAE-2 probably resulted from CO 2 sequestration in black shales outcompeting CO 2 input into the atmosphere. Together these results show that the ice-free Cretaceous world was sensitive to changes in p CO 2 related to perturbations of the global carbon cycle.