Geoacoustic investigations of cold vents and sedimentary processes at the active continental margin offshore Nicaragua
Discharge of cold fluids from the seafloor into the ocean is known from many continental margins. The amount and mechanism of this fluid and volatile recycling are important factors for global mass balances. This work investigates cold vents and seeps in the forearc region of the active continental margin offshore Nicaragua with geoacoustic methods (multibeam bathymetry, deep-towed sidescan sonar, subbottom profiler). Ground truthing is available from camera system surveys and coring on several of the structures. The area is characterized by a high number of so-called mound structures visible in the multibeam bathymetry, and various intensity anomalies without a significant topographic expression but showing high backscatter in the sidescan sonar image. The increased backscatter on mounds and intensity anomalies is mainly related to an increased seafloor roughness, and attributed to hardgrounds like authigenic carbonate formations. A significant influence of the seafloor topography on the sidescan sonar signal is largely excluded. This is shown by a new processing algorithm, developed in this work. The detailed analysis of the seep sites suggests a classification into three end members and explains their formation through the interaction of several processes: Episodic fluid venting and associated authigenic carbonate formation, background sedimentation with subsidence, and erosion.