UBC Theses and Dissertations
Particulate trace metals & iron availability to phytoplankton in a changing Arctic Ocean Li, Jingxuan
This thesis, focusing on the Canadian Arctic Ocean, investigates the cycling of particulate trace metals, and the bioavailability of iron to phytoplankton in this rapidly changing ocean. Full depth profiles of particulate Al, Cd, Pb, P, V, Mn, Fe, Co, Cu, Zn and Ba were determined. Trace elements displayed various vertical distributions. Firstly, some elements had a strong lithogenic component (Al, Fe and V), and were characterized by a maximum at the surface. Indeed, their concentrations strongly correlated with each other across basins. Secondly, elements with a significant biogenic component (Cd and Cu) were characterized by a decrease in concentration with depth. Furthermore, preferential remineralization of P over Cd at shallow depths in numerous stations is reported. In some stations across basins, the molar ratio of particulate Cu and P approached a plateau at the meso- or bathy-pelagic zone, suggesting the presence of ammonium oxidizing archaea, which require Cu-dependent enzymes. Thirdly, Mn, a trace metal with a predominant redox cycle, showed a spike in concentration between 100-200 m, as well as a bottom enrichment. In the Canada Basin, we suggest interactions between the production of manganese oxide, cobalt oxide and barite by manganese oxidizing bacteria. The Arctic Ocean is experiencing the greatest decrease in seawater pH, as well as rapid ice melting which elevates light intensity in surface waters. To examine changes in Fe bioavailability to Arctic phytoplankton under a varying environment, two incubation experiments were conducted. After natural phytoplankton assemblages were acclimated to different light/CO2 treatments for one week, short-term Fe uptake assays were performed to assess the capability of phytoplankton to access Fe. Generally, Fe uptake capability was positively influenced by CO₂ level, and negatively impacted by light level in the incubations. These observations imply that high CO₂ has a significant negative effect on Fe bioavailability, while high light has a positive effect. Furthermore, when comparing future scenario (higher atmospheric CO₂ and underwater irradiance) with present-day conditions, the bioavailability of Fe to phytoplankton appeared to be similar.
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