Exploring coral reef responses to millennial-scale climatic forcings: insights from the 1-D numerical tool pyReef-Core v1.0

Abstract

Abstract. Assemblages of corals characterise specific reef biozones and the environmental conditions that change spatially across a reef and with depth. Drill cores through fossil reefs record the time and depth distribution of assemblages, which captures a partial history of the vertical growth response of reefs to changing palaeoenvironmental conditions. The effects of environmental factors on reef growth are well understood on ecological timescales but are poorly constrained at centennial to geological timescales. pyReefCore is a stratigraphic forward model designed to solve the problem of unobservable environmental processes controlling vertical reef development by simulating the physical, biological and sedimentological processes that determine vertical assemblage changes in drill cores. It models the stratigraphic development of coral reefs at centennial to millennial timescales under environmental forcing conditions including accommodation (relative sea-level upward growth), oceanic variability (flow speed, nutrients, pH and temperature), sediment input and tectonics. It also simulates competitive coral assemblage interactions using the generalised Lotka-Volterra system of equations (GLVEs) and can be used to infer the influence of environmental conditions on the zonation and vertical accretion and stratigraphic succession of coral assemblages over decadal timescales and greater. The tool can quantitatively test carbonate platform development under the influence of ecological and environmental processes and efficiently interpret vertical growth and karstification patterns observed in drill cores. We provide two realistic case studies illustrating the basic capabilities of the model and use it to reconstruct (1) the Holocene history (from 8500 years to present) of coral community responses to environmental changes and (2) the evolution of an idealised coral reef core since the last interglacial (from 140 000 years to present) under the influence of sea-level change, subsidence and karstification. We find that the model reproduces the details of the formation of existing coral reef stratigraphic sequences both in terms of assemblages succession, accretion rates and depositional thicknesses. It can be applied to estimate the impact of changing environmental conditions on growth rates and patterns under many different settings and initial conditions.

Bayesreef: A Bayesian inference framework for modelling reef growth in response to environmental change and biological dynamics

“…We employ a carbonate stratigraphic forward model of vertical reef growth called pyReef-Core, which simulates vertical sequences of coralgal assemblage changes like those found in actual fossil reef drill cores 2. PyReef-Core represents one of the first attempts to incorporate coral ecological dynamics into carbonate system modelling [1]. The tool simulates the interaction of the main biological and physical reef-building processes including hydrodynamic energy, sediment input and the ecological interactions between different coralgal assemblages ( Figure 1).…”

“…In PyReef-Core, four values define each exposure threshold, where the outer two values indicate the absolute minimum and maximum values of the environmental stressor which are known to be tolerable to an assemblage and beyond which, the effects of exposure are lethal [21]. The remaining two values within the minimum and maximum bounds indicate where flow velocity or sediment input begin to restrict growth [1]. During each time step, flow velocity and sediment input will intersect different points of the threshold curves for each assemblage.…”

“…As a result, limited work has been done in modelling reef evolution. While some software and models of long-term interactions of organisms in a marine ecosystem exist [3], only recently has a specific software for coral reef modelling has been created [1,4].…”

“…PyReef-Core [1] is a forward model that captures a number of important ecological dynamics in coral reef systems and is the first model to constrain hydrodynamic energy and sediment input exposure thresholds for coralgal assemblages on a geological timescale. It is a deterministic, one-dimensional (1-D) carbonate stratigraphic forward model (SFM) that simulates the vertical (and not lateral, hence 1-D) coralgal growth patterns observed in a drill core.…”

“…At the end of the time step, boundary conditions are updated and the process is repeated. Figure adapted from Salles et al [1].…”