The influence of turbidity on ancient and modern coral reefs

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The role that turbid water has played in coral and coral reef survival through two Cenozoic hyperthermal events (temporal intervals of global warming) is investigated. Diverse coral reef systems were long considered to be phenomena limited to clear water settings. Areas of high clastic sediment input were considered to be harmful to corals due to reduced water transparency (reducing photosynthesis by coral symbionts), fine-grained sediment clogging the feeding / respiration apparatus of sessile benthic faunas and increased nutrients and particulate organics in the water column (which causes extensive algal colonization and smothering of coral taxa). Unfortunately, clear water settings provide no respite from increased water temperatures and prolonged, cloudless exposure to intense solar radiation that result from a warming climate and thus, in recent years extensive bleachings have resulted in the widespread demise of tropical corals and coral reefs. Recent studies have suggested that, rather than smothering reefs, moderate levels of turbidity (cloudiness) may lower reef stress by shielding coral taxa from high solar radiation. Several recent studies have identified turbid-system (murky water) coral reefs as refugia wherein reef biota may retreat and survive environmental crises. Despite the importance of turbid water coral reefs, they are poorly understood relative to their clear-water equivalents. The goal of this research program is to investigate the role that turbid water coral reefs play and have played in maintaining regional coral reef health and reef fauna diversity during hyperthermal events. Two hyperthermal intervals are investigated. The older interval is the Paleocene-Eocene Thermal Maximum (PETM) - Early Eocene Climate Optimum (EECO) interval (~56 to 49 million years ago), which includes the warmest interval on the earth up until the present day. Latest Paleocene to early Eocene reefs in the neoTethys region (modern southern Europe) are my focus for this research program as this area was the centre of reef diversity during the Paleogene and thick vertically continuous, reef-prone outcrop is available through both pure carbonate and mixed siliciclastic-carbonate successions. The younger interval considered is the Middle Pleistocene to Modern. Here my focus is on the northeastern coast of Sumba, Indonesia. Sumba occurs in the Coral Triangle, the most diverse marine ecosystem on the planet, hosting 76% of the world's coral species and 37% of coral fish species. extensive bleaching has resulted in the widespread demise of these tropical corals and coral reefs. The island of Sumba was chosen as it includes an one-million year record of uplifted coral reefs, includes ancient and modern turbid-water and clear-water coral reefs in close proximity and occurs on an island in the Wallacea straits (an island-rich region that occurs between the Sahul and Sunda shelves, which were subaerially exposed during the Pleistocene).