Bottom Boundary Layer Dynamics

Oceanic bottom boundary layers (BBL) are thin layers above the seafloor and are characterized by enhanced velocity shear and turbulence. Processes within the BBL exert strong constraints on the energy budget of the large-scale ocean circulation and facilitate material exchanges such as heat and nutrients between the BBL and interior ocean. Our work aims to address the dynamics and turbulent characteristics of the BBL where mean flows, stratification and sloping topography interact and we used theoretical derivations and three-dimensional large-eddy simulations (LES) as our main tools.

Southern Ocean Dynamics

The Southern Ocean connects the Pacific, Atlantic and Indian Oceans and plays a disproportionately large role in modulating Earth’s climate. The Southern Ocean circulation is notoriously complex, especially near the Antarctic margins, with the dominant deep-reaching Antarctic Circumpolar Currents interacting with energetic atmosphere and ice dynamics. We use in-situ observational data collected from autonomous ocean robots and ship-board measurements to quantify the key water mass transformation rates both at the Antarctic continental slopes and within the ice-cavities over the shallow continental shelves.

Submesoscale Turbulence

Spanning horizontal scales of 0.1–10 km, submesoscale ocean currents provide a crucial energy dissipation pathway from quasi-balanced mesoscale motions to three-dimensional turbulence. These submesoscale currents are also efficient in redistributing water properties, including momentum, buoyancy, freshwater, and biogeochemical tracers in the global ocean. We focus on submesoscale features near the oceanic surface and bottom boundary layers under the direct impacts of turbulent mixing and surface forcing and we use idealized numerical General Circulation Models (GCM) to explore these fascinating processes.

Ocean Mixing

Turbulent mixing regulates mass transport across density surfaces in the vast interior ocean away from direct external forcing. It has been demonstrated lately that small-scale turbulent mixing near the ocean seafloor exerts a profound, direct influence on the global abyssal ocean circulation. Our work is centered on the detailed mixing mechanisms near the seafloor as a result of tidal currents interacting with topography. Our goal is to bring a more complete picture on how deep-ocean mixing regulates the mass exchange between the bottom boundary layers and interior ocean and shape the pathways of the abyssal ocean circulation.

Coastal Upwelling

Coastal upwelling is the process in which cold subsurface water is brought up to the surface near coastlines. This typically occurs when winds blow along the coasts of continents and cause surface water to move away from shore due to the Earth's rotation. The upwelled water is often rich in nutrients and can thus stimulate phytoplankton growth and result in high levels of primary and fishery production. We explore coastal upwelling dynamics by including the recent theoretical developments of small-scale ocean physics, including boundary layer dynamics, meso and submesoscale turbulence and tides over three-dimensional complex topography.

Contact

Email: xruan@bu.edu， Phone: 617-353-9678

Earth & Environment, Boston University

CAS 135, 685 Commonwealth Ave

Boston, MA 02215