Role of a cyclonic Eddy in the 7000-year-old Mentawai coral reef death during the 1997 Indian Ocean dipole event

Abstract

A major discovery on the coral fronts was the death of the 7000-year-old coral reefs along the Mentawai Islands located offshore of southwest Sumatra, Indonesia, in the equatorial eastern Indian Ocean due to the Indian Ocean Dipole event of 1997. Using two ocean general circulation models, the NASA Ocean Biogeochemistry Model and Estimating the Circulation and Climate of the Ocean Model, we investigate the variability in nitrate influx, mixed layer depth (MLD), and surface currents over the region 0??-8?? S; 90??-106?? E. An enhanced nitrate influx by 6.5 micromoles (3150% higher than the mean), a lower MLD by 5 m (300% lower than the mean), and a massive cyclonic eddy (400 km meridonally and 500 km zonally) are observed over the region 4??-8?? S; 94??-100?? E (along the region of coral mortality) for three months (November and December 1997 and January 1998). Cyclonic eddies enhance phytoplankton and primary productivity, but when in the proximity of a coral reef, they can destroy the coral colony through asphyxiation caused by massive phytoplankton blooms. The results bring to the fore the importance of mesoscale processes that significantly impact the health of coral reefs.