Tessa Spano

I have an undergraduate degree in Physical Geography and a Masters in International Development from the University of Sheffield. I joined the department in 2014 and started my PhD in 2021.

Understanding fluvial sediment transport using infra-red stimulated luminescence

I am developing a new technique for tracing the movement of sediment in fluvial systems using multiple elevated temperature infra-red stimulated luminescence (MET-IRSL). Understanding sediment transport dynamics has important implications for landscape evolution, water-borne disease transmission, and carbon cycling. My project involves a combination of fieldwork, single grain MET-IRSL, multiple grain MET-IRSL, laboratory experimentation, numerical modelling, and statistical. I am working with fluvial samples from Scotland and California.

Luminescence exploits the ability of quartz and feldspar to trap electrons in their crystal structure. Trapped electrons accumulate when sediment grains are buried, and are released when grains are exposed to light or heat. We can measure accumulated trapped electrons as a luminescence signal by exposing a sample to light in controlled conditions, which is a well-established technique for determining how long sediments have been buried for.

By measuring luminescence signals at different temperatures using MET-IRSL, we can access different populations of trapped charge, with different bleaching behaviours (the rate at which electrons vacate their traps when material is exposed to heat or light) and thermal stabilities. Low temperature signals bleach quickly whilst high temperature signals bleach quickly. As a result, in fluvial systems where grains are repeatedly subject to light exposure and burial, incomplete bleaching of MET-IRSL signals is common, which poses as a challenge for conventional luminescence dating. However for sediment transport, the relative differences between high and low temperature signals provides a signature that reflects past and present geomorphic processes characteristic of that system. I aim to produce a method for extracting information from a given configuration of signals, such as transport rate, lateral input, storage history, and light exposure history beyond the most recent bleaching event.

My project also looks to contribute to detailed understanding of the bleaching process, which is essential for constructing accurate luminescence-based sediment transport models. Specifically, I am interested in understanding the controls on bleaching parameter variation, within and between samples, in order to improve how accurately we can recover the light exposure history of individual grains in different contexts.

Supervisors: Prof Edward Rhodes, Dr Jeremy Ely