Productivité récifale durant le Neogene tardif

National audienceDuring the glacial-interglacials cycles that prevailed duringPlio-Pleistocence times, the pace of sea level oscillations exertsa major control on coral reef growth and expansion. We designeda numerical model to quantify reef productivity and carbonatepreservation that accounts for sea level oscillations, reef growth,erosion and subsequent geomorphological carving. We carried outa parametric study of a variety of processes (reef growth, erosion,local slope, uplift and subsidence, relative sea level, etc) towardsa probabilistic analysis of reef productivity and carbonate production.We further test the effect of the frequency and amplitudeof sea level oscillations using sea level curves derived from boththe 18O isotope record of past sea level change and synthetic sinusoidalsea level curves. Over a typical climate cycle, our modelsimulations confirm that the rate of sea level change is the primarycontrolling factor of reef production, as it modifies the productivityby several orders of magnitude. Most importantly, reef productivityincreases during periods of sea level rise, and decreasesduring sea level stands, while conversely, the morphology recordsthe opposite in a misleading fashion: Reef terraces expand duringsea level stands due to the joint effects of erosion and patient reefgrowth at a stationary level until the accommodation space is filledup. On the long-term, over the Plio-Pleistocene period, verticalground motion also significantly alters the production: moderateuplift or subsidence can boost reef productivity up to tenfold withrespect to a stationary coastline. Last, the amplitude and frequencyof the sea level oscillations (typically 40 kyrs vs. 100 kyrsperiods) moderately impact reef productivity. These results can beultimately converted into estimates of carbonate production andcarbon sequestration during the Late Neogene, provided relativesea level is documented in the tectonically agitated intertropicalzone