The biogeomorphology of Shark Bay's microbialite coasts

Abstract The World Heritage microbialites, coquinas, and microbialitic-sediments of Hamelin Pool, Shark Bay, Western Australia, form through complex community and environmental interactions resulting in surficial CO2 sequestration. Predicted climate-change impacts threaten the stability of this setting and the balance of biogeomorphologicalprocesses that generate them. In this setting, long-term surficial CO2 sequestration occurs through the combination of biomineralisation, organomineralisation and lithification, which locks atmospheric CO2 into CaCO3 rocks and sediments. Biogeomorphlogical processes that control the distribution and effectiveness of these mechanisms including biostabilisation, bioconstruction, bioerosionand bioturbationhave not been addressed in this setting to date. A 3-dimensional biogemorphological mapping unit framework is defined at three locations in Hamelin Pool within the shallow-subtidal to supratidal zones based on historical and recent multiscale datasets. This framework is used to review the complex distribution of geomorphological and biogeomorphologicalprocesses. The distribution of lithificationwithin a biogeomorphologicalprocess context is examined, and current geological analogue modelsof microbialite and coquinadevelopment are expanded to include biogeomorphologicalprocesses. The framework is used to understand the impacts of increased water elevation in response to intensification of the Leeuwin Current during the 2010–2012 Ningaloo Nino event. Potential climate change impacts are identified including reduced intertidal bioconstruction, and a shift from microbialitic structure generation to increased grain generation reducing stromatolitedevelopment. Review of the uncertainty of impacts of ocean acidificationand temperature shifts on biomineralisation, organomineralisation and lithificationprocesses, crucial to the maintenance of the outstanding universal valuesin this World Heritage setting, suggests urgent research is required.