The Influence of Fresh Submarine Groundwater Discharge on Seawater Acidification Along the Northern Mediterranean Coast of Israel

Abstract In the oligotrophic Southeastern Mediterranean Sea ( SEMS ), it has been shown that dissolved inorganic nutrient ( DIN ) from fresh submarine groundwater discharge ( FSGD ) enhance primary production in coastal waters. In this study pH , Total Alkalinity ( TA) and DIN of seawater and fresh water in a sea‐cave in the northern part of the Israeli Mediterranean coast and a nearby contact spring, respectively, were measured during October 2018–March 2020. The results show gradients of measured salinity, TA , pH and DIN along the cave axis year‐round, suggesting that they are influenced by FSGD . The seawater near the back of the cave was supersaturated with respect to atmospheric CO 2 nearly year‐round and there is a strong positive divergence from its regional open‐water thermal dependence, which suggests that FSGD is also a source of atmospheric CO 2 in this region. Comparison of TA , salinity and pCO 2 from the back of the sea cave to their corresponding values from an abrasion platform monitoring site, ca. 3 km south of the cave, suggests that FSGD is occurring along the entire shoreline in this region. Thus, despite the increased productivity due to FSGD mediated nutrient enrichment of adjacent coastal waters of the oligotrophic SEMS , they are still a source of atmospheric CO 2 nearly year‐round. Finally, the apparent trends of seawater acidification ( ΔpH/Δt = −0.006 yrs −1 ) and pCO 2 increase (+8 ppmV yr −1 ) observed at the nearby monitoring site since 2013 are explained by increased groundwater recharge and resulting FSGD total alkalinity compared to dissolved inorganic carbon inputs ( ΔTA/ΔDIC = 1:1.2).