Geological faulting a possible trigger for brine-induced reef mortality at East Flower Garden Bank, NW Gulf of Mexico

Abstract

Localized mortality within reef crest depressions in the Flower Garden Banks National Marine Sanctuary in 2016 may have resulted from inundation by brine that erupted when reef rock collapsed into a solution cavern in the salt dome below the bank. This mechanism offers an alternative explanation of mortality that has previously been attributed to hypoxia caused by either offshore movement of brackish, organically rich flood waters, upwelling, or both. Faults at the mortality site, discovered previously, and field observations of water conditions and mortality patterns during the event suggest that salt dissolution, undermining, and collapse may have driven a brine eruption. Elsewhere on the bank, anoxic, sulfurous brine flows have been found adjacent to areas of seafloor collapse, producing localized, brine-induced stress and mortality, but evidence of acute, lethal brine eruptions caused by active faulting would be novel for this system.