Submarine groundwater discharge and associated nutrient and carbon inputs into Sydney Harbour (Australia)

•Radium isotopes revealed SGD-derived nutrient fluxes (N, P and C) into Sydney Harbour, Australia.•SGD fluxes (42121 × 104 m3 d−1) were ~60 times higher than the mean annual river discharge.•Urbanization and ocean forces seemed to explain spatial variation in SGD.•SGD rates were similar to the global average of radium-derived-SGD in urban estuaries.•SGD delivers significant amounts of DOC, DIP and DIN to the Sydney Harbour.