Dust fertilization: Measurements of CO2 sequestration by coral reefs in the Gulf of Eilat, Israel after atmospheric dust loading.

Coral reefs are complex biophysical, geochemical and hydrodynamic marine environments impacted by meteorological processes. In continental coastal and oceanic locations bordering or downwind of dust source areas, coral reefs are affected by the deposition of dust. Dust may supply nanomolar amounts of nitrate and essential bio-elements including iron, manganese, zinc and copper from natural, industrial and agricultural processes to coral reefs; in turn these are absorbed by the coral algae symbionts, thereby enhancing chlorophyll concentrations. This fertilization of coral reefs by dust increases photosynthesis which lowers the aqueous CO₂ partial pressure relative to the overlying air. If this causes a reversal of the coral reef water to air CO₂ gradient, then a coral reef will switch from a source to sink of CO₂.

Here we present the first direct measurements of air-sea CO₂ exchange measured by an eddy covariance tower exclusively over the fringing coral reefs in the Gulf of Eilat, Israel. These show a strong relationship to atmospheric dust load entrained from the surrounding hyper-arid deserts in Israel, Saudi Arabia and North Africa. The coral reefs became CO₂ sinks most notably during episodes of moderate to high atmospheric dust load. We conclude that the coral reefs in the Gulf of Eilat are net sinks of atmospheric CO₂ due to the deposition of dust and suggest that direct measurements of air – sea CO₂ exchange are required over coral reefs in other locations impacted by dust to increase accuracy of marine and global carbon budgets.