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- Fripiat, F., et al.
(författare)
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Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes
- 2017
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Ingår i: Elementa. - : University of California Press. - 2325-1026. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- Antarctic pack ice is inhabited by a diverse and active microbial community reliant on nutrients for growth. Seeking patterns and overlooked processes, we performed a large-scale compilation of macro-nutrient data (hereafter termed nutrients) in Antarctic pack ice (306 ice-cores collected from 19 research cruises). Dissolved inorganic nitrogen and silicic acid concentrations change with time, as expected from a seasonally productive ecosystem. In winter, salinity-normalized nitrate and silicic acid concentrations (C∗) in sea ice are close to seawater concentrations (Cw), indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C∗ < Cw), commensurate with the seasonal build-up of ice microalgae promoted by increased insolation. Stronger and earlier nitrate than silicic acid consumption suggests that a significant fraction of the primary productivity in sea ice is sustained by flagellates. By both consuming and producing ammonium and nitrite, the microbial community maintains these nutrients at relatively low concentrations in spring. With the decrease in insolation beginning in late summer, dissolved inorganic nitrogen and silicic acid concentrations increase, indicating imbalance between their production (increasing or unchanged) and consumption (decreasing) in sea ice. Unlike the depleted concentrations of both nitrate and silicic acid from spring to summer, phosphate accumulates in sea ice (C∗ > Cw). The phosphate excess could be explained by a greater allocation to phosphorus-rich biomolecules during ice algal blooms coupled with convective loss of excess dissolved nitrogen, preferential remineralization of phosphorus, and/or phosphate adsorption onto metal-organic complexes. Ammonium also appears to be efficiently adsorbed onto organic matter, with likely consequences to nitrogen mobility and availability. This dataset supports the view that the sea ice microbial community is highly efficient at processing nutrients but with a dynamic quite different from that in oceanic surface waters calling for focused future investigations. Copyright © 2017 The Author(s).
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| 2. |
- Fransson, Agneta, 1964, et al.
(författare)
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Impact of sea-ice processes on the carbonate system and ocean acidification at the ice-water interface of the Amundsen Gulf, Arctic Ocean
- 2013
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Ingår i: Journal of Geophysical Research - Oceans. - 0148-0227 .- 2156-2202. ; 118:12, s. 7001-7023
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Tidskriftsartikel (refereegranskat)abstract
- From sea-ice formation in November 2007 to onset of ice melt in May 2008, we studied the carbonate system in first-year Arctic sea ice, focusing on the impact of calcium-carbonate (CaCO3) saturation states of aragonite (ΩAr) and calcite (ΩCa) at the ice-water interface (UIW). Based on total inorganic carbon (CT) and total alkalinity (AT), and derived pH, CO2, carbonate ion ([CO3 2-]) concentrations and Ω, we investigated the major drivers such as brine rejection, CaCO3 precipitation, bacterial respiration, primary production and CO2-gas flux in sea ice, brine, frost flowers and UIW. We estimated large variability in sea-ice CT at the top, mid, and bottom ice. Changes due to CaCO3 and CO2-gas flux had large impact on CT in the whole ice core from March to May, bacterial respiration was important at the bottom ice during all months, and primary production in May. It was evident that the sea-ice processes had large impact on UIW, resulting in a five times larger seasonal amplitude of the carbonate system, relative to the upper 20 m. During ice formation, [CO2] increased by 30 μmol kg-1, [CO3 2-] decreased by 50 μmol kg-1, and the ΩAr decreased by 0.8 in the UIW due to CO2-enriched brine from solid CaCO3. Conversely, during ice melt, [CO3 2-] increased by 90 μmol kg -1 in the UIW, and Ω increased by 1.4 between March and May, likely due to CaCO3 dissolution and primary production. We estimated that increased ice melt would lead to enhanced oceanic uptake of inorganic carbon to the surface layer. Key Points Evidence of impact of sea-ice dynamics on CO2 system at ice-water interface Larger variability of CO 2 system in upper 2 m than upper 20 m from solid CaCO3 Ice melt promote enhanced oceanic CO2 uptake © 2013. American Geophysical Union. All Rights Reserved.
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