Biological cycling of carbon, nitrogen and silicon in Arctic and sub-Arctic Marine waters: insights from phytoplankton studies in the laboratory and the field




Kelly, Brianne

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This thesis characterizes the cycling of carbon, nitrogen and silicon by marine polar diatoms through the aid of a field study and a laboratory study. Field studies were conducted along a transect from Victoria, Canada to Barrow, Alaska and particulate carbon, nitrogen and silicon, chlorophyll a, nitrate, phosphate, silicic acid, and carbon and nitrogen incorporation, along with biogenic silica net incorporation were measured. Total primary production was lowest in the NE Pacific (0.3 to 1.0 mmol m-3 day-1), with new production contributing 17 to 38% of total production. Biogenic silica net incorporation in the upper 250 m of the water column in the NE Pacific was relatively low (0 to 0.12 mmol m-3 day-1), but positive, indicating the opportunity for export from the euphotic zone. Total primary, new production and production by siliceous plankton was highest in the Chukchi Sea, due to the influence of nutrient influx from the Anadyr Stream. Total primary production ranged from 1.0 to 3.2 mmol m-3 day-1, new production contributed as much as 56% of total production, and the production by siliceous phytoplankton was as high as 5.6 mmol m-3 day-1. Siliceous biomass was usually recycled in the upper water column of the Bering and the Chukchi Seas, in contrast to the NE Pacific. The interference of lithogenic material on the measurement of biogenic silica was explored using data from the Bering and Chukchi Seas. Results show that lithogenic interference is location specific. Sediment clay composition data should be considered when high concentrations of lithogenic silica are present. The laboratory study examined the effects of different irradiance and temperature conditions on two polar diatom species: Thalassiosira antarctica and Porosira glacialis. Temperature and irradiance had species-specific effects on the cellular content of carbon, nitrogen and silicon. The relationship between growth rate and silicon content for T. antarctica showed that silicon content increased as growth rate decreased, which is in agreement with previous studies. However, this relationship did not hold for P. glacialis at low temperatures. These species-specific effects complicate the understanding of how environmental change will influence phytoplankton populations in Arctic and sub-Arctic marine areas. In general, primary production was lower in the Bering and Chukchi Seas when compared to previous studies, however it is unknown whether differences are due to interannual variability or a trend of decreasing production. Data from both the field and laboratory component indicate a high amount of biological silicon cycling in polar environments. This study represents the first time net silicon incorporation has been measured as far north as the Chukchi Sea.



marine, phytoplankton, nutrient cycling, Arctic, sub-Arctic