Nutrient physiology of siliceous phytoplankton under warming and acidification in Arctic and subtropical oceans
| dc.contributor.author | Wyatt, Shea | |
| dc.contributor.supervisor | Varela, Diana Esther | |
| dc.date.accessioned | 2025-01-10T18:07:06Z | |
| dc.date.available | 2025-01-10T18:07:06Z | |
| dc.date.issued | 2024 | |
| dc.degree.department | Department of Biology | |
| dc.degree.level | Doctor of Philosophy PhD | |
| dc.description.abstract | Steadily rising atmospheric CO2 concentrations have the potential to impact marine ecosystems by increasing the temperature and acidity of the world’s oceans. In the sunlit upper ocean, phytoplankton affect elemental cycling and contribute to nutrient export to deeper waters by incorporating nutrients into biomass and supporting higher tropic levels. One unique group of phytoplankton, diatoms, are characterized by their typically larger size and heavy silica frustules, and they make considerable contributions to global primary productivity. Diatoms are expected to be impacted by oceanic change in various ways, but the degree of this effect is still uncertain. The overall objective of this thesis is to improve our understanding of how marine diatom physiology, specifically the utilization of silicon (Si), and the contribution by diatoms to the cycles of carbon (C) and nitrogen (N), are affected by climate-induced increases in temperature and acidification. I investigated the impact of mesoscale physical processes on diatom contributions to utilization rates of C (ρC) and nitrate (ρNO3) in the Sargasso Sea in the North Atlantic subtropical gyre, an ecosystem impacted by increased stratification due to ocean warming. Diatoms played a minor role in nutrient utilization and biomass during the lowest-productivity time of year, but they dominated nutrient utilization rates in the deeper euphotic zone of the Sargasso Sea when nutrient concentrations were enhanced by eddy-driven upwelling. In the contrasting environment of the Bering and Chukchi Seas, I investigated the effects of a warming ocean on diatom physiology and elemental composition as part of an on-going oceanographic time-series in the Pacific Arctic Region (PAR). I found significant trends in ocean temperature and sea ice breakup dates for different regions of the PAR, and evidence for declining diatom biomass in one area of the northern Bering Sea. Anomalously low particulate C:N values were observed across the PAR during the 2019 MHW, but otherwise the response of diatom assemblages in the PAR to a sustained warming period and marine heatwave (MHW) in 2019 varied substantially. Estimates of diatom contributions to ρC and ρNO3 in the PAR were improved compared to previous studies, demonstrating that diatoms were responsible for most of the nutrient utilization in all regions. Ocean acidification experiments were conducted with a model diatom species and two natural phytoplankton assemblages to assess the effects of decreased pH on nutrient physiology. Overall, diatom Si utilization and silicification in laboratory and field culture experiments were unaffected by pH. I found that the cell size of a model species of diatom, Thalassiosira rotula, decreased under OA, while in subtropical and Arctic phytoplankton assemblages, OA had no conclusive meaningful impacts on other measures of physiology, or assemblage composition. This dissertation provides valuable insights into how siliceous phytoplankton, particularly diatoms, interact with marine cycles of Si, C, and N across cold and warm marine ecosystems. It also deepens our understanding of how these dynamic systems may respond to oceanic change, and sets the stage for future research on the evolving impacts of climate-driven physical processes. | |
| dc.description.embargo | 2025-12-18 | |
| dc.description.scholarlevel | Graduate | |
| dc.identifier.bibliographicCitation | Wyatt S, McNabb B, Varela D. (2024). Morphological and physiological responses of the cosmopolitan marine diatom Thalassiosira rotula to acidification. Diatom Research, 1-14. DOI: 10.1080/0269249X.2024.2369049 | |
| dc.identifier.uri | https://hdl.handle.net/1828/20929 | |
| dc.language | English | eng |
| dc.language.iso | en | |
| dc.rights | Available to the World Wide Web | |
| dc.subject | Diatoms | |
| dc.subject | Phytoplankton | |
| dc.subject | Climate change | |
| dc.subject | Ocean acidification | |
| dc.subject | Arctic | |
| dc.subject | Sargasso Sea | |
| dc.subject | Distributed Biological Observatory | |
| dc.subject | Bermuda-Atlantic Time-series Study | |
| dc.subject | Silicon | |
| dc.subject | Nutrient cycles | |
| dc.title | Nutrient physiology of siliceous phytoplankton under warming and acidification in Arctic and subtropical oceans | |
| dc.type | Thesis |