Submarine groundwater discharge (SGD) patterns through a fractured rock: a case study in the Ubatuba coastal area, Brazil

The flow of groundwater out across the sea floor has the potential to influence sedimentary processes, sea floor morphology, pore water chemistry and benthic habitats. Relatively few observations of the process of submarine groundwater discharge (SGD) have been made. Measurements along the South American coast and over fractured rock aquifers are especially rare. The rate and distribution of SGD was measured using vented, benthic chambers on the floor of Flamengo Bay located at the southeast coast of Brazil. Discharge rates were found exceeding 200 cm3 s-1 of pore water per cm2 of sea floor per day (200 cm day-1). Large variations in SGD rates were seen over distances of a few meters. We attribute the variation to the geomorphologic features of the fracture rock aquifer underlying a thin blanket of coastal sediments. Clustering of fractures and the topography of the rock-sediment interface might be focusing or dispersing the discharge of groundwater.