Evaluation of coral reef carbonate production models at a global scale

[摘要] Calcification by coral reef communities is estimated to account for half ofall carbonate produced in shallow water environments and more than 25%of the total carbonate buried in marine sediments globally. Production ofcalcium carbonate by coral reefs is therefore an important component of theglobal carbon cycle; it is also threatened by future global warming andother global change pressures. Numerical models of reefal carbonateproduction are needed for understanding how carbonate deposition responds toenvironmental conditions including atmospheric CO₂ concentrations inthe past and into the future. However, before any projections can be made,the basic test is to establish model skill in recreating present-daycalcification rates. Here we evaluate four published model descriptions ofreef carbonate production in terms of their predictive power, at both localand global scales. We also compile available global data on reefcalcification to produce an independent observation-based data set for themodel evaluation of carbonate budget outputs. The four calcification modelsare based on functions sensitive to combinations of light availability,aragonite saturation (Ω_a) and temperature and were implementedwithin a specifically developed global framework, the Global Reef AccretionModel (GRAM). No model was able to reproduce independent rate estimates ofwhole-reef calcification, and the output from the temperature-only basedapproach was the only model to significantly correlate withcoral-calcification rate observations. The absence of any predictive powerfor whole reef systems, even when consistent at the scale of individualcorals, points to the overriding importance of coral cover estimates in thecalculations. Our work highlights the need for an ecosystem modellingapproach, accounting for population dynamics in terms of mortality andrecruitment and hence calcifier abundance, in estimating global reefcarbonate budgets. In addition, validation of reef carbonate budgets isseverely hampered by limited and inconsistent methodology in reef-scaleobservations.

[学科分类] 地球化学与岩石