CONTROL OF PORE-WATER CHEMISTRY AT THE BASE OF THE FLORIDA ESCARPMENT BY PROCESSES WITHIN THE PLATFORM

PORE waters collected from seep sediments hosting active chemosynthetic communities1,2 tend to be rich in sulphide, chloride and ammonium and depleted in sulphate relative to the concentrations in sea water. To investigate the source of the energy-rich compounds and the processes causing low sulphate concentrations in seep-sediment pore waters, we have measured the sulphur isotope composition, delta-34S, of pore waters from seep sediments at the base of the West Florida escarpment. The isotopic composition of pore-water sulphate remains approximately constant as its concentration is depleted, indicating that processes within the Florida platform, rather than microbial processes at seep sites, control pore-water chemistry in these sediments. The composition of the seep brines, deduced from a linear mixing model, provides information on processes deep within the platform.