Abyssal Boundary Layers
A multi-University Research Initiative (MURI) to understand the ocean near the seafloor
Abyssal boundary layer MURI - Recent News
WHAT is Boundary Layer Turbulence and why does it matter?
The ocean, once thought to be a “swamp,” is a vigorous and energetic place filled with breaking waves the size of skyscrapers (right). These lead to turbulence via a variety of complex processes, the details of which can affect the efficiency of the mixing, the ocean’s energetics and the strength of the general circulation which includes the Gulf Stream. A number of fundamental fluid mechanics problems come in to play, which will require us to make detailed observations and to contextualize them with numerical computer simulations.
Additionally, the seafloor is a complicated and dynamic place, with sediment able to be suspended into the water above when bed stresses are strong enough. This sediment can spread due to the turbulence and background currents, and can blanket seafloor biological communities. Additionally, the flux of nutrients to these life forms can be affected by the turbulence and other processes. So the turbulence, the ecosystem, the sediment and any other human seafloor activities or emplacements on the seafloor are all intertwined. A complex problem worthy of two combined projects! These Multi-University Research Initiatives (MURIs) are designed to help researchers across the nation work together on really hard problems.
Temperature measured from a moored chain of thermistors with spacing as shown. By measuring so densely in time and space, the details of the complex processes that break and lead to ocean mixing are resolved. We aim to use this technique and others to understand ocean mixing over flat and sloping seafloors.
A schematic plan of our observations, which include a dye release, moorings, fast turbulence sampling, an autonomous turbulence float and coring measurements.
Project details.
This Multi-University Research Initiative (MURI) is collaborative with another MURI led by Dr. Kelly Dorgan. Together the two coupled projects will examine the processes occurring at and above the ocean’s sea floor. In our MURI, Matthew Alford and Gunnar Voet of MOD, Professor YT Lin of Scripps and Professor Tom Peacock of MIT will field a dense set of shipboard and autonomous measurements aimed at understanding the processes in the ocean that keep the abyssal bottom boundary layer well mixed, as well as potentially radiating internal waves upward towards the shallower parts of the ocean.
Experiment plan. Combining acoustic, coring and our novel high-resolution turbulence sampling techniques, we will aim to measure and model the ocean’s bottom few hundred meters. In this region, breaking internal waves create turbulence, whose bed stresses can suspend sediment that impacts nearby seafloor biological communities. Because these processes are very different on flat versus sloping sea floors, we aim to sample them both. We will have cruises in fall 2025, 2026 and 2028.