In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard

2020-10-01T00:00:00Z

Title: In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard Authors: Kim, Bo Kyung; Joo, Hyoung Min; Jung, Jinyoung; Lee, Boyeon; Ha, Sun-Yong Abstract: Rapid climate warming and the associated melting of glaciers in high-latitude open fjord systems can have a significant impact on biogeochemical cycles. In this study, the uptake rates of carbon and nitrogen (nitrate and ammonium) of total phytoplankton and picophytoplankton (<2 mu m) were measured in Kongsfjorden in early May 2017 using the dual stable isotope technique. The daily uptake rates of total carbon and nitrogen ranged from 0.3 to 1.1 g C m(-2) day(-1), with a mean of 0.7 +/- 0.3 g C m(-2) day(-1), and 0.13 to 0.17 g N m(-2) day(-1), with a mean of 0.16 +/- 0.02 g N m(-2) day(-1). Microphytoplankton (20-200 mu m) accounted for 68.1% of the total chlorophyll a (chl-a) concentration, while picophytoplankton (<2 mu m) accounted for 19.6% of the total chl-a, with a high contribution to the carbon uptake rate (42.9%) due to its higher particulate organic carbon-to-chl-a ratio. The contributions of picophytoplankton to the total nitrogen uptake rates were 47.1 +/- 10.6% for nitrate and 74.0 +/- 16.7% for ammonium. Our results indicated that picophytoplankton preferred regenerated nitrogen, such as ammonium, for growth and pointed to the importance of the role played by picophytoplankton in the local carbon uptake rate during the early springtime in 2017. Although the phytoplankton community, in terms of biovolume, in all samples was dominated by diatoms and Phaeocystis sp., a higher proportion of nano- and picophytoplankton chl-a (mean +/- SD = 71.3 +/- 16.4%) was observed in the relatively cold and turbid surface water in the inner fjord. Phytoplankton production (carbon uptake) decreased towards the inner fjord, while nitrogen uptake increased. The contrast in carbon and nitrogen uptake is likely caused by the gradient in glacial meltwater which affects both the light regime and nutrient availability. Therefore, global warming-enhanced glacier melting might support lower primary production (carbon fixation) with higher degrees of regeneration processes in fjord systems.

Optical and molecular characterization of dissolved organic matter (DOM) in the Arctic ice core and the underlying seawater (Cambridge Bay, Canada): Implication for increased autochthonous DOM during ice melting

2018-06-15T00:00:00Z

Title: Optical and molecular characterization of dissolved organic matter (DOM) in the Arctic ice core and the underlying seawater (Cambridge Bay, Canada): Implication for increased autochthonous DOM during ice melting Authors: Simona Retelletti Brogi; Hur, Jin; Lee, Yun Kyung; Morgane Derrien; Kim, Kwanwoo; Ha, Sun-Yong Abstract: Sea ice contains a large amount of dissolved organic matter (DOM), which can be released into the ocean once it melts. In this study, Arctic sea ice DOM was characterized for its optical (fluorescence) properties as well as the molecular sizes and composition via size exclusion chromatography and Fourier transformation ion cyclotron resonancemass spectrometry (FT-ICR MS). Ice cores were collected along with the underlying seawater samples in Cambridge Bay, an Arctic area experiencing seasonal ice formation. The ice core samples revealed a marked enrichment of dissolved organic carbon (DOC) compared to the seawater counterparts (up to 6.2 times greater). The accumulation can be attributed to in situ production by the autotrophic and heterotrophic communities. Fluorescence excitation emission matrices (EEMs) elaborated with parallel factor analysis (PARAFAC) evidenced the prevalence of protein-like substances in the ice cores,which likely results fromin situ production followed by accumulation in the ice. Size exclusion chromatography further revealed the in situ production of all DOM size fractions, with the exception of the humic substance fraction. The majority of DOM in both the ice and seawater consists of lowmolecularweight compounds (b350 Da) probably derived by the microbial degradation/transformation of freshly produced DOM. Molecular characterization also supported the in situ production of DOM and highlighted the marked difference in molecular composition between sea ice and seawater. This study provides new insights into the possible role of sea ice DOM in the Arctic carbon cycle under climate change.

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In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard

Optical and molecular characterization of dissolved organic matter (DOM) in the Arctic ice core and the underlying seawater (Cambridge Bay, Canada): Implication for increased autochthonous DOM during ice melting