CAREER: A new perspective on the transformation of internal waves on the inner shelf

University Of California-Irvine, Irvine CA

Investigators

Abstract

In a layered fluid like the ocean, waves can occur in the interface between the different density layers of water. These are called internal waves and they have been largely studied in deep ocean basins and mid-to-outer continental shelf regions. However, steep internal waves are common in the inner shelf and can modify turbulent mixing, exchange of materials across the continental shelf, and biological productivity of coastal waters. This research will conduct an intensive field campaign and numerical modeling aiming at resolving the transformation of internal waves across the shelf including breaking and dissipation. Historically, internal waves are detected using observations of subsurface ocean temperature that are made at fixed locations using moorings or vertical profiles of temperature, each with their own limitations in resolution. This research uses a fiber optic distributed temperature sensing (DTS) system, a new method that provides measurement over large areas over the shelf (kilometers), with high spatial (<1 meter) and temporal resolutions. These measurements will be combined with more traditional point measurements for hydrographic and turbulence variables. Results from this work will yield insights into benthic ecology, cross-shelf exchange of nutrients and pollutants, turbulent mixing, larval connectivity, coastal hypoxia, and ocean acidification. The educational component of this CAREER project is based on the idea that one of the best ways to help students succeed in the sciences, and to shape the innovators of the next generation is to inspire passion for science. This is achieved through the integration of research and teaching and activities that relate curricular concepts to societal issues that excite the students, and by demonstrating how perseverance is an important part for success. At the university level, courses will be re-designed to include: (i) socio-scientific issues related to ongoing research, and (ii) active learning techniques that encourage risk-taking and perseverance as a constructive path to scientific discovery. At primary and secondary education levels, the investigator will develop a mentor-toolkit to help professionals in STEM careers, who desire to serve as a role model but lack training in elementary education, to most effectively communicate their path to science and the struggles that they faced and overcame along the way. The inner shelf is, in effect, a "swash zone" for nonlinear internal waves (NLIWs) and their intermittency and small spatiotemporal scales pose challenges to observation. Consequently, there are few comprehensive field measurements of NLIWs on the inner shelf to test dynamical theories derived from numerous laboratory and numerical studies. This project will use high resolution DTS measurements, coupled with a dense array of hydrographic instruments and turbulence measurements, to capture a continuous view of the cross-shelf evolution of NLIWs. Results from a pilot study in the South China Sea demonstrate that DTS measurements can provide a unique perspective on NLIWs - allowing for detection of internal wave characteristics (form and path), variable propagation speed, reflection, wave-wave interactions, and "internal tidepools" (cool water left behind after the wave has run back down the slope). Furthermore, as opposed to boat-based measurements, which must physically follow a wave across the shelf, the proposed measurements are capable of capturing a cross-shelf view of many waves and will be useful for understanding variability in internal wave "weather" on the shelf. The observations will be performed at two locations, representing different shelf geometries and characteristic internal wave fields, and the data will be analyzed to advance our knowledge on NLIW transformation over the inner shelf, the fate of internal wave energy, and the effects of NLIWs on mass flux and turbulent mixing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.