Modelling Environmental Impacts on Marine Ecosystems and Coral Reefs

Abstract

Coral reefs are the iconic ecosystem of tropical seas and yet they are under increasing pressure as a result of multiple climatic stressors. This thesis uses observations and models to further understanding of environmental impacts on coral reefs. In particular it examines the impact of rising Sea Surface Temperature (SST) and ocean acidification on coral growth and the frequency of coral bleaching events. UK ocean biogeochemical models are assessed for implementation in the next UK Earth System Model. This analysis finds little evidence that more complex ocean biogeochemical models provide better simulations of large scale biogeochemical features. An established wavelet-based spatial comparison technique is used to analyse the spatial scales that Earth System Models can skillfully simulate patterns of SSTs. It is shown that in coral regions, current models cannot skilfully simulate patterns of historical SST anomalies at sub-regional (<32◦) scales. These findings are used in combination with SST and aragonite saturation state outputs from Earth System Models to show that historical Caribbean coral growth has been influenced by anthropogenic aerosol emissions over the 20th Century. Earth System Model outputs are also used to make projections of global coral bleaching throughout the 21st Century. It is shown that under even the most extreme conventional mitigation scenarios the majority of the world’s coral reefs are projected to experience levels of thermal stress induced bleaching that cause reef degradation throughout the 21st Century. Geoengeering scenarios involving the injection of SO2 into the stratosphere can reduce the projected thermal stress on coral reefs relative to conventional mitigation scenarios but such benefits are shown to be highly dependent on the sensitivity of coral bleaching thresholds to ocean acidification.