Submarine groundwater discharge from oceanic islands standing in oligotrophic oceans: Implications for global biological production and organic carbon fluxes

Abstract

We investigated submarine groundwater discharge (SGD)–associated nutrient fluxes and budgets in two coastal embayments, Hwasun Bay and Bangdu Bay, off the volcanic island of Jeju, Korea. SGD in Hwasun Bay is a composite of marine and meteoric groundwater, while that in Bangdu Bay mainly includes marine groundwater. The submarine inputs of groundwater into Hwasun and Bangdu Bays were approximately 0.12 and 0.27 m3 m−2 d−1, respectively, on the basis of the 222Rn mass balance models. The nitrogen:phosphorus ratios in coastal groundwater (85 ± 96) were considerably larger than those in the seawater (3.8 ± 1.6) of both bays. Fluxes of dissolved inorganic nitrogen (DIN) through SGD were more than 90% of the net DIN input into both bays; approximately 93% and 39% of SGD‐driven DIN was consumed inside Hwasun and Bangdu Bays, respectively. The discharge of DIN through SGD from the entire island was approximately 2.1 × 109 mol yr−1, which is equivalent to that of some large rivers, potentially supporting approximately 1.6 × 1011 g carbon yr−1 of new primary production. Because Jeju accounts for less than 1% of the total land mass of the volcanic islands, SGD‐driven nutrient fluxes from highly permeable islands standing in oligotrophic oceans could be very important for global nutrient budgets.