MSCI Dissertation Comprehensive Exam - Blaire UmhauWednesday, October 11, 2017 - 2:00pm
Title: A novel use of 238U-234Th disequilibrium to measure Domoic acid flux in the Santa Barbara Basin and Juan de Fuca Eddy region
Toxic blooms of the diatom Pseudo-nitzschia are particularly problematic in coastal upwelling regions because they produce the neurotoxin domoic acid (DA) which may result in commercial fishery closures and harm to marine birds and mammals, including humans. Recent, but limited work argues that DA is delivered to depth when Pseudo-nitzschia form aggregates that sink quickly, before DA trapped in the particles can “leak” into the surrounding water column. The current body of literature, however, has very little information on the timing and magnitude of the vertical flux of Pseudo-nitzschia and DA to depth, and much of this information relies on sediment traps as a sampling mechanism, resulting in poor sampling resolution. Using Thorium-234 as a proxy for particle flux can provide much higher spatial resolution by sampling fluxes at several depths in the water column simultaneously. This project aims to test the use of the 234Th method to identify where in the water column DA is produced and remineralized and to calculate DA fluxes in regions considered to be hotspots of Pseudo-nitzschia blooms: The Santa Barbara Basin and the Juan de Fuca Ridge.These regions are the subject of numerous research on Pseudo-nitzschia blooms and DA toxicity, with several ongoing monitoring programs that provide a basis for comparison with our new measurement technique. However, the two regions have very different circulation regimes that will influence the vertical and horizontal flux of Pseudo-nitzschia and DA. This project will provide valuable information for bloom monitoring and prediction programs especially for benthic systems, such as razor clam beds.