Atmospheric Groundwater Forcing of a Subterranean Estuary: A Seasonal Seawater Recirculation Process.

Here we isolate groundwater responses to atmospheric forcing of surface water levels by relating anomalies in coastal aquifer hydraulic head time‐series to weather events. Our results demonstrate that atmospheric forcing has a greater effect on groundwater exchange and extended residence time over astronomical tidal pumping at times. During winter, atmospheric groundwater forcing was associated with winter storm passage and had a recurrence interval of approximately 7 days. During summer, atmospheric groundwater forcing was limited to weak diurnal atmospheric convection and infrequent tropical cyclone activity. Because winter storms and tropical cyclones commonly produce precipitation, atmospheric groundwater forcing can synergize with the timing of meteoric recharge producing periods of intense submarine groundwater discharge. Plain Language Summary: Groundwater discharges from the seafloor into coastal waters through a process known as submarine groundwater discharge. Submarine groundwater discharge is composed of fresh water from the land and recirculated seawater drawn into the seafloor by ocean processes. In this manuscript, we document the effect of shifting winds brought about by winter storms, tropical cyclones, and land/sea breezes on seawater recirculation through seafloor sediments. Strong onshore winds cause regional mounding of seawater against the shoreline and infiltration into coastal aquifers while offshore winds allow groundwater to drain from the seafloor back into coastal waters. This effect we term, atmospheric groundwater forcing, leads to periods of intense submarine groundwater discharge following tropical cyclones and winter storms. Key Points: Atmospheric groundwater forcing is a seawater recirculation process driven by wind forcing of coastal surface water levelsAtmospheric groundwater forcing is seasonally associated with winter storms, tropical cyclones, and atmospheric convection cyclesThe timing of atmospheric groundwater forcing can synergize with meteoric recharge leading to subterranean estuary flushing [ABSTRACT FROM AUTHOR]