Science Source

Mass coral mortality under local amplification of 2 °C ocean warming

States that sea surface temperature in June 2015 in the South China Sea (SCS) increased by 2°C (in response to El Niño); reports that this amount was unlikely to cause widespread damage to coral reefs
Adds that on the Dongsha Atoll, in the northern South China Sea, unusually weak winds created low-flow conditions that amplified the 2°C basin-scale anomaly
States that water temperatures on the reef flat, normally indistinguishable from open-ocean SST, exceeded 6 °C above normal summertime levels and that mass coral bleaching quickly ensued, killing 40% of the resident coral community in an event unprecedented in at least the past 40 years
Findings highlight the risks of 2 °C ocean warming to coral reef ecosystems when global and local processes align to drive intense heating, with devastating consequences
Concludes that the extreme temperature (36 °C) reached in June 2015 was a result of global (El Niño warming superposed upon a global warming trend), regional (high pressure system and reduced winds), and local hydrodynamic (shallow reef, neap tide and unusually slow currents) factors aligning – at the right time – to drive intense heating