Date: Friday, April 7, 2023

Time: 2pm

Location: ES&T 1114 AND via Zoom at https://us06web.zoom.us/j/9357307122?pwd=V01uSVdnWHJSV0VwZGZuRFdyajdxQT09

Erin K. Griffith, PE, PhD(c)

Thesis title: Understanding zinc incorporation in Antarctic diatom frustules

Committee members: Dr. Ellery D. Ingall; Dr. Julia M Diaz; Dr. Jennifer B. Glass; Dr. Pete L. Morton; Dr. Yuanzhi Tang

Abstract:

Our understanding of the composition and uptake of zinc into Southern Ocean diatom frustules has been enhanced by X-ray fluorescence (XRF) microscopy and X-ray absorption spectroscopy (XAS). These findings potentially resolve decades of debate about the close correlation of zinc and silicate in the global ocean. In most of our sampled diatoms, there is a high correlation of zinc to silica within the diatom’s frustule, regardless of oceanic conditions. Consistent with this hypothesis is the enrichment of zinc in the silica frustule, with frustule Zn/Si ratios approximately 15 times higher than dissolved Zn/Si ratios in the surrounding water. Furthermore, frustule zinc occurs in a form similar to a zinc silicate or a zinc sulfide in all of the samples. The XRF and XAS results suggest a structural incorporation of zinc into the siliceous frustule, even if the precise reason is unknown.

The low solubility of zinc silicates and zinc sulfides results in much of the incorporated zinc surviving transport through the global ocean with eventual burial in the sediments. The burial of zinc associated with silica frustules is a new, major, ocean zinc sink which adjusts the residence time of oceanic dissolved zinc to 5,100 years.