Physics Linking Shelf Circulation to Estuarine Inflow

University Of Washington, Seattle WA

Investigators

Abstract

The physics controlling the source of waters flowing from the coastal ocean into the mouth of an estuary or fjord will be explored using theory and idealized numerical experiments. The specific goals are to develop theoretical predictions of the depth from which source water is drawn and the geographical region from which it is drawn. These two properties will be expressed as functions of controlling environmental variables. The parameter space will span a wide variety of systems, from shallow coastal plain estuaries on a gently sloping shelf, to deep fjords adjoining a shelf-crossing canyon. This research will inform numerical modelers about what physics must be included on the shelf in order to successfully predict the properties of water flowing into an estuary. This will allow improved future predictions of the change in estuarine biogeochemical function due to changing water properties in the coastal ocean. The principal investigator and a grad student will connect the results of the proposed research directly with stakeholders in their own region, and will communicate results to scientists working toward desired societal outcomes in other regions. Parts of a theoretical framework already exist, based on extensive previous work on coastal upwelling, canyons, river plumes, and the estuarine exchange flow. However the dynamics of the inflow on the shelf before it reaches the estuary remain relatively unexplored, with substantially less observational evidence than has been gathered for river plumes. Early analytical solutions for two-layer flow will be a key starting point. Idealized numerical experiments will be conducted to test the assumed force balance and inflow paths of this set of solutions. Force balances in the numerical experiments will be analyzed using three methods: (i) Lagrangian momentum budgets along inflow particle tracks, (ii) backward-in-time particle tracking to efficiently determine inflow pathways, and (iii) averaging in density (salinity) classes to separate purely advective transport from that requiring mixing. Each offers advantages and drawbacks, but in combination they should provide clear guidance for advancing the theory, particularly moving from two layers to continuous stratification. Throughout the project the ability of a theory to explain important properties of the numerical solutions will be the test of success.