Spatial Heterogeneity of Air–Sea Energy Fluxes over a Coral Reef—Heron Reef, Australia

Abstract

AbstractThe thermal environment of a coral reef is moderated by complex interactions of air–sea heat and moisture fluxes, local to synoptic-scale weather and reef hydrodynamics. Measurements of air–sea energy fluxes over coral reefs are essential to understanding the reef–atmosphere processes that underpin coral reef environmental conditions such as water temperature, cloud, precipitation, and local winds (such as during coral bleaching events). Such measurements over coral reefs have been rare, however, and the spatial heterogeneity of surface–atmosphere energy exchanges due to the different geomorphic and biological zones on coral reefs has not been captured. Accordingly, the heterogeneity of coral reefs with regard to substrate, benthic communities, and hydrodynamic processes has not been considered in the characterization of the surface radiation budget and energy balance of coral reefs. Here, the first concurrent in situ eddy covariance measurements of the surface energy balance and radiation transfers over different geomorphic zones of a coral reef are presented. Results showed differences in radiation transfers and sensible and latent heat fluxes over the reef, with higher Bowen ratios over the shallow reef flat zone. The energy flux divergence between sites increased with wind speed and during unstable, southeasterly trade winds with the net flux of heat being positive and negative over different geomorphic zones. The surface drag coefficient at measurement height ranged from 1 × 10−3 to 2.5 × 10−3, with no significant difference between sites. Results confirm that spatial variation in radiation and air–reef–water surface heat and moisture fluxes occurs across a lagoonal platform reef in response to local meteorological conditions, hydrodynamics, and benthic–substrate cover.