Available at: https://digitalcommons.calpoly.edu/theses/3060
Date of Award
6-2025
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Derek Manheim
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
Marine heatwaves (MHWs) are increasing in frequency and intensity globally, with grave effects on marine ecosystems and their dependent industries. There are significant gaps in knowledge of the subsurface behavior and geographic distribution of MHWs, especially in eastern boundary upwelling systems like the California Current. Here, two decades of full water-column temperature observations from a shallow autonomous profiler in San Luis Obispo Bay (~10m) revealed that while MHWs have similar average durations and intensities across all depths, one-third of bottom MHWs occur without a concurrent surface signal. MHWs across the water column initiated during anomalously weak upwelling or downwelling conditions and displayed stratification-driven seasonal shifts in vertical structure. Next, two decades of NOAA NDBC surface buoy temperature measurements distributed along the US West Coast shelf revealed the latitudinal variation of MHWs in the California Current. MHWs displayed various spatial extents, from coast- wide events to site-specific occurrences, and various drivers, from basin-scale climate modes (e.g., Pacific Decadal Oscillation, El Niño Southern Oscillation) to site-specific conditions. Upwelling contributed to MHW occurrence across the coast, with both initiation and termination of MHWs linked to weak and strong upwelling anomalies, respectively. Central and Northern California displayed the strongest link between upwelling and MHWs, while Oregon/Washington and Southern California displayed higher regional co-occurrences. Across 7 MHW metrics and 22 sites, there was only one statistically significant positive long-term trend (i.e., increase in MHWs), suggesting that the US West Coast could serve as a thermal refuge for marine organisms. These findings improve the understanding of MHW variability in upwelling systems and highlight the need for sustained long-term observations and depth-resolved, geographically distributed observational infrastructure to support forecasting, ecosystem resilience planning, and sustainable offshore infrastructure development in a changing and warming ocean.