UNH Ocean Seminar

Enhancing and Parameterizing interfacial Fluxes: Exploring Impacts of Waves, Wakes, and Secondary Currents

Katherine Adler, Ph.D.
Postdoctoral Research Associate
UNH School of Marine Science and Ocean Engineering
Friday, Jan. 24, 2025, 3:10pm
Chase 105
Abstract

Fluxes of nutrients and other materials through environmental interfaces are difficult to quantify and often play a key role in controlling environmental conditions. For instance, the rates at which gases, like carbon dioxide and oxygen, are absorbed into or released from water bodies are difficult to measure directly and depend on the physical properties of the water surface and near-surface motions. Several empirical models and scaling laws exist to relate gas transfer to more easily measured bulk flow conditions, such as wind speed, or to parameters describing a local surface renewal time scale, such as the integral time scale, turbulence intensity, turbulent kinetic energy (TKE), TKE dissipation rate, and divergence. However, challenges arise when selecting a model and empirical coefficient to apply, especially in the presence of less documented flow structures, such as longitudinal vortices or surface ripples. Velocity data, from surface particle image velocimetry (PIV) and a subsurface acoustic doppler velocimeter, and reoxygenation data were compared across flow cases in recirculating flumes to determine the extent to which these flow mechanisms enhance gas transfer and to identify the most accurate gas transfer parameterizations for use in these and similar contexts.  For example, surface perturbations in the form of static, hanging, 1-mm-diameter cylinders increased gas transfer rate by up to 68% at speeds which resulted in capillary bow waves, and longitudinal bed ridges which generated depth-scale roller vortices increased gas transfer up to 15%. Models based on different representations of the renewal time scale were compared and a new, apparently more accurate representation was developed. Stereo PIV measurements around a 1-cm-diameter cylinder, representing a vegetation stalk, in a recirculating flume suggest that the presence of the cylinder more than doubled local gas transfer rate compared to upstream conditions.

Bio

Katherine (Katie) Adler joined the School of Marine Science and Ocean Engineering at the University of New Hampshire as a postdoctoral research associate in November 2024. Her research during her B.S. at MIT, Ph.D. at Cornell University, and postdoctoral fellowship at the University of Idaho involved laboratory investigation of environmental flow-structure interactions and turbulence impacting mass and momentum transport. Katie is particularly interested in quantifying fluxes of mass, as gases or solids, at air-water and water-sediment interfaces of marginal aquatic systems with implications for future climate outcomes and resilience.