H3: Downscaling (process oriented localization) of larger scale simulations of sea water currents to assess interactions between sea and groundwater bodies
supervised by Burchard, Janssen, Lennartz
The aim of this topic is to quantitatively investigate the exchange of water, solutes and particulate matter mediated by submarine groundwater discharge (SGD) and its impact on the coastal ocean. It will be the challenge to combine physical forcing with biogeochemical transformations, dynamics of suspended particulate matter and the exchange processes between sea floor and water column. Interactions with morphological changes of the seafloor and the beach need to be considered as well.
State of the Art
There are several processes influencing the intensity of SGD such as waves and sea level variability as well as the pressure head. Once in the ocean, the fate of the discharged water and the substances included depends on various factor of the sea state such as wind-driven currents and vertical mixing as well as wave-driven near-shore circulation. Various wave-related near-shore processes are known to drive transports in shallow water such as rip currents, intensified vertical mixing due to breaking waves or wave motion interacting with the sea floor, vertical return currents due to on-shore Stokes transport as well as generation of coast parallel currents. Many aspects of these wave-current-turbulence interactions have been investigated using coupled coastal ocean models, but the necessary comprehensive consideration of interactions between these processes has not yet been carried out. Specifically, the interaction with density stratification caused by freshwater discharges, precipitation and heating and cooling with wave-related dynamics is poorly understood.
A comprehensive three-dimensional model system will be set up for the shallow water coastal areas in front of the study site NSG „Heiligensee & Hütelmoor“, including an SGD model to supply groundwater discharge. To provide consistent external forcing, this local model will be nested into a hierarchy of larger scale models ranging up to the scale of the entire Baltic Sea. A shallow water surface wave model will be interactively coupled to this circulation model in order to quantitatively investigate. Interactions with stratification and vertical mixing are established by means of second-order turbulence closure models. Using this model system, process studies, hindcast simulations using in-situ observations as validation as well as scenario studies to investigate system sensitivities to external forcing will be carried out.