Seasonality in primary production, Nitrogen sources for primary production and primary producers response to light intensity

Abstract

Several functional aspects of pelagic and simpagic primary producers were studied during the Nansen Legacy Q3 cruise. In open water stations (P1, P4, P5), water was sampled from the standard depths 10, 20, 40, 60, 90 and Chl a max. Water from these depths was spiked with radioactively labelled carbon in order to determine to the Carbon fixation rate (i.e. the Primary Production rate) of phototrophic organisms throughout the water column and latitudinal gradient. Additionally, water from 10m and Chla max was spiked with stable isotopes of Carbon (13C) and Nitrogen (15N) to determine the F-ratio (which fraction of the estimated primary production is new production). One incubation bottle was also treated to assess the nitrification activity of microbes. These incubations were deployed attached to the sediment trap moorings and exposed to in situ light and temperature conditions for 24 hours. In parallel, water from the Chla max was used to determine the photosynthetic response of the community to light intensity (P vs I curves). At the ice-covered stations (P6 and P7), the aforementioned water sampling and experimental work was carried as described, and additionally the bottom 3cm of 4 ice cores were sampled and pooled for similar in situ incubations: Under-ice Primary production, Nitrogen uptake and PvsI curve. Water from a meltpond was sampled, spiked and incubated in situ for Primary Production and Nitrogen uptake. A reciprocal transplant experiment was conducted with surface water from stations P1 and P6 and will be analyzed for abundance and community shifts due to changes in environmental factors.