Nadav G. Lensky

Coral bleaching events are more frequent and severe as global temperatures rise. However, analysis of the surface energy fluxes that substantially affect the thermoregulation of shallow reef environments is rare. Previous work on evaporative cooling in a humid reef environment led to the hypothesis that in proximity to desert regions, drier air enhances evaporative cooling of water overlying coral reefs, reducing the risk of extreme high‐water temperatures. Eddy Covariance measurements made over a shallow desert fringing coral reef in the Gulf of Eilat (Israel) during summer measured evaporation of 10.3 mm d −1 which is maintaining water temperature much lower than the overlying air temperature. In addition, measurements of the most severe marine heatwave that was ever documented in the region are presented as a case study for future reference to the processes that lead to and proceed a marine heatwave, which is induced by synoptic scale events that cause a ∼50% reduction in evaporation rate. Results are compared to similar measurements from a tropical coral reef, where a lower evaporation rate suppressed by higher humidity is unable to offset the heating of water overlying the reef. We conclude that evaporative cooling is a key mechanism protecting coral reefs located in deserts from extreme high‐water temperatures, thereby representing possible thermal refugium for corals against background global warming.

Understanding the role of coral reefs on air‐sea CO 2 exchange is essential to accurately estimate carbon budgets throughout the tropical and subtropical oceans. Results from research conducted in humid marine environments show coral reefs are mainly net sources of CO 2 to the atmosphere due to calcification being dominant over respiration and dissolution. However, coral reefs are also found bordering deserts in the subtropical high‐pressure belt. Here, we present results from concurrent direct measurements of air‐sea CO 2 exchange over fringing coral reefs and open sea bordered by hyper‐arid deserts in the Gulf of Eilat (Aqaba). The fringing coral reefs were found to be a net sink of CO 2 at −1.62 ± 4 μmol m −2 s −1 sequestering 1.96 times more CO 2 than adjacent open sea. The CO 2 fluxes showed a negative correlation with some local meteorological parameters such as humidity, wind speed, and net radiation but were positively correlated to air temperature. The air‐sea CO 2 fluxes were also found to be correlated with dust, which is believed to trigger metabolic processes in bacteria and phytoplankton in the low‐nutrient, low‐chlorophyll sea of the study site. Results are compared to measurements from the humid marine setting of the Great Barrier Reef, Australia.