Voyage report RV Tangaroa voyage TAN1703, 5 April-1 May 2017

Abstract

Meteoric recharge and topographically-driven flow are the most important sources of groundwater recharge in terrestrial settings. In passive continental margins, topographically driven meteoric (TDM) groundwater is only one of a range of drivers of offshore groundwater flow. Other drivers include seawater recirculation, sediment loading, geothermal convection, and diagenesis. Sea level has been much lower than today for 80% of the Quaternary, resulting in the emergence of extensive sections of continental shelf, a reduction of pressure exerted by the sea water column, as well as steepening of the hydraulic gradient and an increase in hydraulic head. The potential of TDM recharge to establish extensive water tables, create massive groundwater fluxes, and generate pore overpressures and discharges across the continental shelf and upper continental slope must have been significantly higher during the majority of the last 2.6 Ma than it is today. Considering that geothermal convection is strongest beneath the continental slope and tends to be dominated by TDM flow during sea level lowstands, whereas sediment loading is most important during rapid deglaciations in high sedimentation zones, TDM recharge is a likely very important driver of offshore groundwater systems in continental shelves and upper slopes globally.