Measuring Environmental ThreatsA Study of Coral Reefs in the Red Sea
Last summer, an international group of scientists warned that one-third of reef-building corals worldwide are threatened with extinction.
Now a year later, an Ohio State engineer is studying the meteorological conditions in a coral-reef lagoon in the Red Sea to develop parameters scientists can use for better prediction of reef response to climate change.
The International Union for Conservation of Nature and Conservation International in 2008 reported that climate change and local stresses, such as destructive fishing, declining water quality and the degradation of coastal habitats are the main threats to coral reefs, important for environmental monitoring because of their high sensitivity to these changes.
Gil Bohrer, assistant professor of ecological engineering, is measuring parameters that relate wind turbulence, waves, evaporation and heat exchange between the air and water above coral reefs in Eilat, Israel, on the Red Sea. His direct observations of wind, turbulence, solar radiation, heat flux, evaporation and wave fluctuations at high frequency will enable him to evaluate the parameters used in analytical models of evaporation, which causes the heavier, more saline water near the ocean surface to sink down and also drives vertical circulation of water. In the Red Sea, this circulation increases nutrient levels in the water, leading to algal blooms and coral destruction.
Typically, evaporation and heat flux are determined from long-term low-frequency (minutes to hours) averages of air humidity and temperature at meteorological stations near the shore. These data are processed by analytical models, which rely on different empirical parameters, to infer heat flux and evaporation from humidity, water and air temperature, wind speed and radiation.
Bohrer, on the other hand, is using direct observations of fluxes to obtain additional data to increase the accuracy of the oceanographic and ecological models. He collects the data from a system of two eddy-flux towers equipped with ultrasonic wind anemometers to measure high-frequency fluctuations of temperature and wind speed at three dimensions; open-path laser gas analyzers to measure the fluctuations of water vapor and CO2 ; and two probes that measure the temperature and relative humidity at low frequency.
Combined, the two-tower system directly measures evaporation and heat flux from the water surface, the horizontal advection of heat, water vapor and CO2 toward land, and the correlation coefficients and frequencies at which turbulence and frictional velocity are related to sea wave frequencies and aerodynamic roughness length. Bohrer’s research is funded in part by the PADI Foundation, a California nonprofit organization that encourages and supports underwater science, environmental projects and education.
“These meteorological conditions will be used to improve the parameterization of equations and models that calculate a prediction for evaporation,”Bohrer says.“The calculations are needed by ocean and large-scale atmosphere models to predict the water temperature and vertical mixing in the Red Sea, where future changes to meteorological forcing can increase evaporation. This results in an increase in the vertical mixing and nutrient levels in the water and lead to the extinction of corals in the region.”
