Dynamics of flow on a wide reef flat at Dongsha Atoll

Thermal and chemical environments on coral reefs are shaped by the circulation processes acting on the system. Dynamical scales on coral reefs can range from millimeters to kilometers, and the geometry of coral reefs leads to complex flows. Hydrodynamic processes which drive flow in coastal regions, and specifically on coral reefs, include tidal, wave and wind driven flow. Dongsha Atoll is encompassed by a circular barrier reef that is 28 km in diameter and 3 km wide. A recent study has shown that exceptionally large internal waves bring cold, nutrient-rich water to the shallow east reef flat. This study will focus on the dynamics of tide, wave and wind driven flows across the barrier reef and the effectiveness of those flows at fluxing the cold nutrient-rich ocean water across the barrier reef. Different transport time scales will be explored, including flushing time, residence time and water age. These will be compared to various physical properties of the water on the reef flat, including 3-km of high resolution (~1 meter spacing, sampled every 2 minutes) temperature data from a distributed temperature sensing system. Understanding the flow dynamics on coral reefs can inform what is driving changes in residence time of water and variability of environmental properties and can explain why some corals may thrive under different conditions.