New insights into sea ice nitrogen biogeochemical dynamics from the nitrogen isotopes

Fripiat, François; Sigman, Daniel M.; Fawcett, Sarah E.; Rafter, Patrick A.; Weigand, M. Alexandra; Tison, Jean-Louis

doi:10.1002/2013gb004729

Cited by 57 publications

(86 citation statements)

References 64 publications

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“…The likely dilution of labeled ammonium by the production of unlabeled ammonium in the melted samples (as nitrogen-containing osmolytes were respired during the salinity downshift associated with melting) means that the in situ rates may have been even higher. These corrections place the measured nitrification rates at the upper end of the range for the pelagic realm, pointing to nitrification as a more important pathway in the sea-ice nitrogen cycle than previously assumed, as also recently suggested by Fripiat et al (2014) and Baer et al (2015).…”

supporting

confidence: 73%

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Bacterial use of choline to tolerate salinity shifts in sea-ice brines

Firth

Carpenter

Sørensen

et al. 2016

Elementa: Science of the Anthropocene

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Bacteria within the brine network of sea ice experience temperature-driven fluctuations in salinity on both short and long temporal scales, yet their means of osmoprotection against such fluctuations is poorly understood. One mechanism used to withstand the ion fluxes caused by salinity shifts, well-known in mesophilic bacteria, is the import and export of low molecular weight organic solutes that are compatible with intracellular functions. Working with the marine psychrophilic gammaproteobacterium, Colwellia psychrerythraea 34H, and with natural microbial assemblages present in sackhole brines drained from sea ice in Kanajorsuit Bay (2013) and Kobbefjord (2014), Greenland, we measured the utilization of 14 C-choline (precursor to glycine betaine, a common compatible solute) at −1°C upon salinity shifts to double and to half the starting salinity. In all cases and across a range of starting salinities, when salinity was increased, 14 C-solute (choline or derivatives) was preferentially retained as an intracellular osmolyte; when salinity was decreased, 14 C-choline was preferentially respired to 14 CO 2 . Additional experiments with cold-adapted bacteria in culture indicated that an abrupt downshift in salinity prompted rapid (subsecond) expulsion of retained 14 C-solute, but that uptake of 14 C-choline and solute retention resumed when salinity was returned to starting value. Overall, the results indicate that bacteria in sea-ice brines use compatible solutes for osmoprotection, transporting, storing and cycling these molecules as needed to withstand naturally occurring salinity shifts and persist through the seasons. Because choline and many commonly used compatible solutes contain nitrogen, we suggest that when brines freshen and bacteria respire such compatible solutes, the corresponding regeneration of ammonium may enhance specific biogeochemical processes in the ice, possibly algal productivity but particularly nitrification. Measurements of potential nitrification rates in parallel sea-ice samples are consistent with a link between use of the compatible solute strategy and nitrification.

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confidence: 73%

“…Evidence that nitrification occurs in sea ice exists for both Arctic and Antarctic sea ice (Priscu et al, 1990;Bowman, 2015;Fripiat et al, 2014Fripiat et al, , 2015, but rates have Elementa: Science of the Anthropocene • 4: 000120 • doi: 10.12952/journal.elementa.000120…”

Section: Choline As a Metabolitementioning

confidence: 99%

Bacterial use of choline to tolerate salinity shifts in sea-ice brines

Firth

Carpenter

Sørensen

et al. 2016

Elementa: Science of the Anthropocene

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“…Two processes can be responsible for such an increase in *NO 3 -concentrations: (i) an increase in the exchange with nutrient-rich seawater in porous decaying sea ice (Fritsen et al, 1994;Kattner et al, 2004;Haas et al, 2001), or (ii) an imbalance between the processes of NO 3 -production (nitrification, partly light-inhibited) and consumption (assimilation, light-dependent) with the decrease in solar radiation. Nitrification has been shown to be significant in sea ice (Priscu et al, 1990;Fripiat et al, 2014aFripiat et al, , 2015Baer et al, 2015;Firth et al, 2016), with the microbial community being embedded in biofilms and exposed to both low-light and high NH 4 + concentrations from decaying organic matter (Hagopian and Riley, 1998;Meiners et al, 2004;Ward, 2007;Deming, 2010).…”

Section: Nutrient Seasonal Trends and Processesmentioning

confidence: 99%

“…Although many nutrient transformations (e.g., converting one form to another) have been either documented or inferred in Antarctic pack ice, the overall pattern of nutrient concentrations has remained elusive (Arrigo et al, 1995;Gleitz et al, 1995;Rysgaard et al, 2004Rysgaard et al, , 2008Fransson et al 2011;Fripiat et al, 2014aFripiat et al, , 2014bBaer et al, 2015;Roukaerts et al, 2016). Previous studies are based on a few ice cores only, limited in space and time (e.g., Thomas et al, 1998;Becquevort et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes

Fripiat

Meiners

Vancoppenolle

et al. 2017

Elementa: Science of the Anthropocene

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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 (C w ), indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C* < C w ), 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* > C w ). 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.

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“…Potential pathways for NO 3 − consumption are NO 3 − respiration to NO 2 − (Fripiat et al, 2014) and/or denitrification (Kaartokallio, 2001;Rysgaard et al, 2008) with production of NO 2 − , N 2 O and N 2 . However, NO 2 − in ice (Table 3) or N 2 O in brine (data not shown) did not increase significantly, suggesting that NO 3 − reduction and denitrification were minor.…”

Section: Physical Imprints On Nutrient Incorporationmentioning

confidence: 99%

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

et al. 2014

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a b s t r a c t a r t i c l e i n f oWe investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14°C for 14 days after which ice decay was induced by increasing the air temperature to −1°C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.

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New insights into sea ice nitrogen biogeochemical dynamics from the nitrogen isotopes

Cited by 57 publications

References 64 publications

Bacterial use of choline to tolerate salinity shifts in sea-ice brines

Bacterial use of choline to tolerate salinity shifts in sea-ice brines

Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes

Physical and bacterial controls on inorganic nutrients and dissolved organic carbon during a sea ice growth and decay experiment

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