The Role of Siliceous Rhizaria in the Silicon Cycle in the Northeast Subarctic Pacific Ocean
| dc.contributor.author | Melville, Anna Olivia | |
| dc.contributor.supervisor | Varela, Diana Esther | |
| dc.date.accessioned | 2024-04-30T20:21:29Z | |
| dc.date.available | 2024-04-30T20:21:29Z | |
| dc.date.issued | 2024 | |
| dc.degree.department | Department of Biology | |
| dc.degree.level | Master of Science MSc | |
| dc.description.abstract | Siliceous Rhizaria are zooplankton protists found in all ocean basins from the surface to the deep aphotic zone. Like diatoms, a group of phytoplankton with silica cell walls, siliceous Rhizaria utilize silicon (Si) to form their skeletons. While diatom production is known to strongly control the marine Si cycle, an important biogeochemical process that modulates global long-term stability, the role of Rhizaria on Si cycling is poorly understood. Therefore, the Si cycle is not fully constrained in the ocean. Furthermore, long-term shifts in community composition and seasonal changes to Si uptake rate (ρSi) in siliceous Rhizaria have never been studied. To address these knowledge gaps, field work was conducted in the Northeast Subarctic Pacific Ocean (NESP) and Pacific Arctic Region (PAR) between 2010-2023. Stations were sampled with bongo net tows which were vertically hauled from 250 m and 1200 m to the ocean surface. In this thesis, chapter 2 presents a historical time series (summers 2010-2020) of siliceous Rhizaria community composition in the NESP. The results showed that there were no yearly trends in species abundance, richness, or composition. Rhizaria abundance data from 2010-2020 were incorporated into a published dataset to update the estimated Si production by Rhizaria from 0.4 – 6.4 Tmol Si year-1 to 0.4 – 5.5 Tmol Si year-1 in global waters >40°N/S. Chapter 3 compares Rhizaria community composition in the NESP (March, July, and August 2022) and the PAR (July 2022). In the NESP, wintertime conditions promoted mixotrophic taxa of Rhizaria, while summer favoured phagotrophic Rhizaria. The sampling locations in the PAR displayed an absence of siliceous Rhizaria during this study. Chapter 4 presents the results from diatom and Rhizaria ρSi experiments conducted in August 2022 and May 2023 in the NESP. Overall, the contribution of siliceous Rhizaria to total daily ρSi was less than 0.12% and their contribution to total silica biomass was less than 4% confirming that diatoms are the main drivers of Si cycling in the NESP. However, it can be estimated that more than 38% of silica produced by Rhizaria could be buried along Line P suggesting that Rhizaria contribution to Si flux might be higher than expected. This work provides a novel contribution to our understanding of the ecology of Rhizaria in the NESP and PAR. Furthermore, this thesis provides new data which can be used to constrain the global Si cycle and predict how the Si cycle might shift with climate change. | |
| dc.description.scholarlevel | Graduate | |
| dc.identifier.uri | https://hdl.handle.net/1828/16447 | |
| dc.language | English | eng |
| dc.language.iso | en | |
| dc.rights | Available to the World Wide Web | |
| dc.subject | Siliceous Rhizaria | |
| dc.subject | Silicon cycle | |
| dc.subject | Diatom | |
| dc.subject | Biogeochemistry | |
| dc.subject | Uptake rates | |
| dc.title | The Role of Siliceous Rhizaria in the Silicon Cycle in the Northeast Subarctic Pacific Ocean | |
| dc.type | Thesis |