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Temporal Variability in Chemical Cycling of the Subterranean Estuary and Associated Chemical Loading to the Coastal Ocean

Meagan Gonneea, Ph.D., 2014
Matthew Charette, Advisor

At the land-ocean interface, terrestrial groundwater interacts with seawater to form a subterranean estuary, which can play host to dynamic biogeochemical cycling of nutrients, trace metals and radionuclides. This chemically altered groundwater enters the ocean through submarine groundwater discharge (SGD), a process that is driven by a number of physical processes acting on aquifers and the coastal ocean. In this thesis, seasonal variability in chemical cycling and associated loading to the coastal ocean was observed in a monthly time series within a subterranean estuary. At this location, seasonal variability in sea level, not groundwater level, was the dominant variable driving the hydraulic gradient and therefore SGD. Sea level rise enhanced chemical export, while variable nitrogen attenuation and SGD nutrient loading were associated with seasonal changes in mixing. Interannual climate fluctuations that control sea level and precipitation may ultimately control the timing and magnitude of chemical and water flux via SGD. The potential for the chemical signature of SGD to be recorded in the coral record was tested through coral culture experiments and field and modeling studies in the Yucatan Peninsula, where coral barium correlated with precipitation. This proxy offers the potential to extend SGD records into the past.