Fresh submarine groundwater discharge offshore Wellington (New Zealand): hydroacoustic characteristics and its influence on seafloor geomorphology

Fresh submarine groundwater discharge (FSGD) influences the biogeochemistry of coastal areas and can be a proxy for potential untapped resources offshore freshened (OFG). In most however, onshore-offshore connection recharge characteristics aquifers are poorly constrained, making exploitation this resource challenging. Offshore Wellington (New Zealand), well-defined onshore aquifer system extends beneath harbour, where substantial amounts freshwater seep out from ocean floor. The has been studied in detail recently first attempts worldwide have made here to use as future source drinking water. However, locations extent FSGD well its influence on seafloor morphology still understood. Exact localisation sites is essential sample quantify discharging waters but remains challenging due lack robust appropriate measurement procedures. Novel sensing strategies, such seeping hydroacoustic water column reflectivity could greatly improve identification worldwide. Therefore, we multidisciplinary dataset evaluate different methodologies map spatial determine their geomorphologic expressions Harbour. study, single multibeam hydroacoustics towfish (temperature, salinity turbidity) transects were combined with remotely operated vehicle (ROV) dives sediment cores better characterise sites. We observed several hundred depressions (pockmarks) that attribute continuous seepage gas seafloor. Different pockmark morphologies indicate fluid flow regimes persistent allows even small pockmarks remain unchanged over time, while anchor scours diminish same region. Enhanced reflections within above suspended particles, which likely kept suspension by density boundaries.