Chemical aspects of a brine pool at the East Flower Garden bank, northwestern Gulf of Mexico1

A small pool on the flank of the East Flower Garden bank at a depth of 72 m in the Gulf of Mexico contains anoxic, hypersaline (∼200 g·kg−1) water. The flux of brine into and out of the pool contributes to erosional processes on the bank. The bulk ionic composition of the brine is similar to that of the Orca Basin brine, but differences between the two in gaseous hydrocarbon and carbon isotope content indicate different modes of origin. High levels of bacterial activity in the brine are indicated by ATP (>80 ng·liter−1), hydrogen sulfide (>2,000 µmol·liter−1), isotopically light ∑CO2 (δ13C = −23%), and the apparent generation of elemental sulfur.