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See detailEvidence of freezing pressure in sea ice discrete brine inclusions and its impact on aqueous-gaseous equilibrium
Crabeck, Odile; Galley, R.J.; Mercury, L. et al

in Journal of Geophysical Research. Oceans (in press)

Sea ice in part controls surface water properties and the ocean-atmosphere exchange of greenhouse gases at high latitudes. In sea ice gas exists dissolved in brine and as air bubbles contained in liquid ... [more ▼]

Sea ice in part controls surface water properties and the ocean-atmosphere exchange of greenhouse gases at high latitudes. In sea ice gas exists dissolved in brine and as air bubbles contained in liquid brine inclusions, or as bubbles trapped directly within the ice matrix. Current research on gas dynamics within the ocean-sea ice-atmosphere interface has been based on the premise that brine with dissolved air becomes supersaturated with respect to the atmosphere during ice growth. Based on Henry’s Law, gas bubbles within brine should grow when brine reaches saturation during cooling, given that the total partial pressure of atmospheric gases is above the implicit pressure in brine of 1 atm. Using high-resolution light microscopy time series imagery of gas bubble evolution inside discrete brine pockets, we observed bubbles shrinking during cooling events in response to the development of freezing pressure above 3 atm. During warming of discrete brine pockets, existing bubbles expand and new bubbles nucleate in response to depressurization. Pressure variation within these inclusions has direct impacts on aqueous-gaseous equilibrium, indicating that Henry's Law at a constant pressure of 1 atm is inadequate to assess the partitioning between dissolved and gaseous fractions of gas in sea ice. This new evidence of pressure build-up in discrete brine inclusions controlling the solubility of gas and nucleation of bubbles in these inclusions has the potential to affect the transport pathways of air bubbles and dissolved gases within sea ice-ocean-atmosphere interface and modifies brine biochemical properties. [less ▲]

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See detailPIPERS: Air-sea-Ice Interactions during a Very Anomalous Season in the Ross Sea
Stammerjohn, Sharon; Ackley, Stephen; Maksym, Ted et al

Conference (2018, June 21)

The PIPERS (Polynyas, Ice Production and seasonal Evolution in the Ross Sea) project conducted a research expedition to the southwestern Ross Sea aboard the RVIB Palmer during April-June 2017. Its main ... [more ▼]

The PIPERS (Polynyas, Ice Production and seasonal Evolution in the Ross Sea) project conducted a research expedition to the southwestern Ross Sea aboard the RVIB Palmer during April-June 2017. Its main objective was to assess the local/large-scale controls on sea ice production, water mass transformation, and carbon/trace metal inventories during an autumn-winter transition. Between 1979 and 2015 the Ross Sea was notable for showing strong positive sea ice trends in all seasons (strongest in autumn and spring). The PIPERS expedition however took place prior to the lowest austral summer sea ice extent ever observed in the Ross Sea since 1979. This anomalous 2017 summer season followed record-breaking anomalies that first emerged the preceding winter-spring of 2016. Subsequently, during the autumn of 2017, the ice edge was slow to recover during March-April, but by late May, the ice edge east of ~165W finally reached its climatological location,while the ice edge between 165E to 165W remained anomalously south (by ~240km). This ice edge anomaly then shifted eastward during winter-spring 2017. To help explain these anomalous sea ice conditions, air-seaice and ice-climate interactions leading up to and during the PIPERS cruise will be described and discussed. These regional analyses will then be compared to the ship-based observations acquired during PIPERS to help validate and distinguish local/large-scale controls on sea ice production and thickness evolution. [less ▲]

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See detailECV-Ice: Measuring Essential Climate Variables in Sea Ice-SCOR Working Group 152
Nomura, D.; Fripiat, François ULiege; Else, B. et al

Poster (2018, June 20)

Observations over recent decades suggest that sea ice plays a significant role in global biogeochemical cycles, providing an active biogeochemical interface at the ocean-atmosphere boundary. However, a ... [more ▼]

Observations over recent decades suggest that sea ice plays a significant role in global biogeochemical cycles, providing an active biogeochemical interface at the ocean-atmosphere boundary. However, a pressing need exists to perform methodological intercalibration experiments in order to obtain reliable measurements of basic biogeochemical properties, including many of the Essential Climate Variables of the Global Climate Observing System. With newly emerging techniques, and pressed by the rapid changes in sea ice, the time has come to evaluate and improve our approach to study sea-ice systems. In 2016, the Scientific Committee on Oceanic Research (SCOR) launched Working Group 152 on Measuring Essential Climate Variables in Sea Ice (ECV-Ice). This working group will synthesize past intercalibration exercises and design and coordinate new experiments. Our ultimate goal is to provide the international community with standardized protocols for processing sea-ice samples and collecting data for key variables, including CO2 partial pressure, nutrients, algal biomass and production, and gas exchange. We will also establish the effectiveness of new techniques to address sea-ice heterogeneity (often referred to as “patchiness”). These tasks will directly benefit the longterm community goal of understanding the response of polar marine environments to ongoing climate change. [less ▲]

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See detailUnderstanding the Origin(s) of Methane in Sea Ice Using Stable Isotope Ratios
Sapart, C.; Jacques, Caroline; Carnat, Gauthier et al

Poster (2018, June 20)

In 2012, an unexpected CH4 excess has been reported above open leads in the Arctic Ocean showing that sea ice plays a role in the ocean-atmosphere CH4 dynamics. However, the processes involved there have ... [more ▼]

In 2012, an unexpected CH4 excess has been reported above open leads in the Arctic Ocean showing that sea ice plays a role in the ocean-atmosphere CH4 dynamics. However, the processes involved there have not yet been identified. We performed CH4 stable isotope (d13C and dD) analyses on sea ice samples, as well as geochemical and physical measurements, to determine the possible pathways involved in CH4 production/removal in or under sea ice. We present results from ice cores collected above the shallow shelf of Barrow (Alaska) from January to June 2009 as well as in the landfast ice of McMurdo Sound (Antarctica) from September to November 2012. We found a clear difference in isotopic signature between the two sites. The McMurdo ice was supersaturated in CH4 and showed isotopic signatures surprisingly enriched in heavy isotopes (d13C between -47 and -12 ‰ and dD between -87 and -350‰). No natural pathways have yet been identified with such isotopic signatures, but we suggest that aerobic CH4 formation in or under the ice might be a candidate. In contrast, the CH4 concentrations were much larger in ice overlying the shallow shelf of Barrow and there the origin of CH4 was clearly biogenic (d13C between -48 and -68 ‰ and dD between -180 and -250‰), thus likely originating from the sediment. In the McMurdo ice, the seasonal evolution shows that CH4 was becoming more enriched in heavy isotopes with time, suggesting the occurrence of aerobic oxidation processes in the ice. [less ▲]

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See detailInter-comparison between chambers for CO2 flux measurements over sea ice
Nomura, D.; Delille, Bruno ULiege; Tison, J.-L. et al

Poster (2018, June 20)

In order to validate the difference of air-sea ice CO2 flux measurements by different types of CO2 chamber, inter-comparison experiments were carried out on winter Antarctic pack ice in the Weddell Sea (R ... [more ▼]

In order to validate the difference of air-sea ice CO2 flux measurements by different types of CO2 chamber, inter-comparison experiments were carried out on winter Antarctic pack ice in the Weddell Sea (R.V. Polarstern AWECS cruise, July-August 2013). Our ultimate goal is to understand the methodological gaps for the CO2 flux measurements betweem chamber and eddy covariance methods over sea ice as an activity for SCOR Working Group 152 (ECV-Ice). Two kinds of CO2 chamber systems were used: semi-automated CO2 chambers developed at Hokkaido University and automated long-term CO2 chambers (Li-8100A, LI-COR Biosciences, USA). These chambers were installed at the same ice/snow surface conditions within a 2-m × 2-m area. Based on the quantitative comparisons using least squares linear regression analyses, slope was 1.08, suggesting that the airsea ice CO2 flux from two chambers were good agreement. Therefore, our inter-comparison experiments confirmed that there was no instrumental bias between two chambers, thereby the past data for air-sea ice CO2 flux obtained by each chamber's group in the world polar oceans could be shared. [less ▲]

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See detailBiogeochemistry at the Early Stages of Ice Tormation: Insights from PIPERS
Delille, Bruno ULiege; Van der Linden, Fanny ULiege; Carnat, G. et al

Poster (2018, June 20)

The PIPERS cruise on N. B. Palmer into the early winter Ross Sea took place between April and June 2017. PIPERS was a unique opportunity to investigate biogeochemistry of pack ice during early stages of ... [more ▼]

The PIPERS cruise on N. B. Palmer into the early winter Ross Sea took place between April and June 2017. PIPERS was a unique opportunity to investigate biogeochemistry of pack ice during early stages of ice formation. We will present insights of the dynamics of sympagic microalgae assemblages, nutrients, particulate organic carbon and 2 potent greenhouse gases (carbon dioxide and nitrous oxide) during early ice growth. The comparison of CO2 fluxes over consolidated and unconsolidated ice show that 1) sea ice acts as a source of CO2 for the atmosphere 2) largest fluxes occur at the earliest sea ice growth stages (i.e. frazil ice, unconsolidated grey ice, pancake ice). Large fluxes are due to ongoing active rejection of impurities, high porosity of highly saline/high temperature young ice, and the absence of snow. Overall, snow appears to restrict CO2 fluxes. In some cases, fluxes over snow appears to be nil or even opposite to fluxes over bare ice. Therefore, while snow is often view as a transient buffer for air-ice gases fluxes, the role of snow appears to be more complicated. The new measurements of CO2 fluxes over young ice carried out during PIPERS potentially allow to complete a budget of CO2 fluxes over Antarctic pack ice by filling a significant gap. [less ▲]

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See detailCycling of DMS,P in Early-winter Ross Sea Pack Ice during the PIPERS Project
Carnat, G.; Delille, Bruno ULiege; Van der Linden, Fanny ULiege et al

Poster (2018, June 20)

Ice-algal assemblages are known to produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), and of its volatile degradation product dimethylsulfide (DMS). Sea ice DMS is ... [more ▼]

Ice-algal assemblages are known to produce large amounts of the sulfur metabolite dimethylsulfoniopropionate (DMSP), and of its volatile degradation product dimethylsulfide (DMS). Sea ice DMS is subsequently released to the polar ocean and atmosphere where it plays multiple roles in the sulfur and carbon cycle, and mediates the formation of climate cooling sulfate aerosols. Previous studies on the cycling of DMS and DMSP in sea ice are mostly limited to the spring/summer seasons, when large blooms develop in firstyear ice due to favourable light and nutrient regimes. In contrast, there is much less information about the production of DMS,P during the first stages of sea ice formation in light-limited early-winter. In this context, we carried out measurements of sea ice DMS,P concentrations in the Ross Sea from April until June 2017 in the framework of the PIPERS project. Multiple ice types and thicknesses were sampled (frazil, unconsolidated and consolidated pancakes, first-year ice) together with sea water and brine, in contrasted areas (marginal ice zones, polynyas, and the central Ross sea pack ice). Sea ice DMS,P concentrations (maximum of 95 and 492 nM) were lower than values typically reported during ice-algal spring blooms, but still significantly higher than sea water concentrations at the time of sampling (maximum of 3 and 15 nM). We present and discuss working hypotheses to explain how these concentrations build up through the different steps of sea ice formation. [less ▲]

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See detailBiogeochemistry of Antarctic Landfast Sea Ice and the Potential Role of Biofilm
Deman, Florian; Roukaerts, A.; Fripiat, François ULiege et al

Poster (2018, June 20)

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See detailPhysical and Biogeochemical Properties of Winter Sea Ice during Pipers, Ross Sea
Tison, J.-L.; Maksym, T.; Lieser, J. et al

Conference (2018, June 20)

The PIPERS (Polynyas, Ice Production and its seasonal Evolution in the Ross Sea) cruise on N. B. Palmer into the early winter Ross Sea took place between April 11 and June 14 2017. The main objective was ... [more ▼]

The PIPERS (Polynyas, Ice Production and its seasonal Evolution in the Ross Sea) cruise on N. B. Palmer into the early winter Ross Sea took place between April 11 and June 14 2017. The main objective was to investigate the Atmosphere-Ice-Ocean interactions in the Terra Nova Bay and Ross Ice Shelf coastal polynyas. The cruise however extended these polynyas studies to a series of ice stations transects “in” and “out” of the Ross Sea. It involved a large set of multidisciplinary activities aiming at the detailed documentation of processes across the ocean-ice-atmosphere continuum. This paper presents the basic physical (Temperature, bulk salinity, brine volume, Rayleigh number) and biogeochemical properties (water stable isotopes, Chl-a) of the sea ice cover at 27 ice stations. The cruise encountered unusual sea-ice conditions in the 2016/2017 season, where exceptionally low sea-ice summer extent was recorded Antarctica-wide as early as November 2016, which stayed below previous records of the satellite era for the rest of the austral summer. It is also a year where active primary production was evidenced within the Ross Sea and Terra Nova Bay Polynya, a few weeks before the cruise took place. We will show how these conditions have potentially affected (or not) the physical and biogeochemical properties of the sea ice cover in the Central Ross Sea and discuss the contrasts with the sea ice properties of the Terra Nova Bay polynya and the MIZ. [less ▲]

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See detailPIPERS: Role of Polynyas on the Atmospheric Budget of Methane and Carbon Dioxide
Sapart, C.; Thornton, B.; Crill, P. et al

Conference (2018, June 20)

Coastal polynyas are areas of anomalous open water and thin ice in regions that are otherwise covered by sea ice. They frequently occur around the Antarctic continent in response to strong offshore ... [more ▼]

Coastal polynyas are areas of anomalous open water and thin ice in regions that are otherwise covered by sea ice. They frequently occur around the Antarctic continent in response to strong offshore katabatic wind stresses. The loss of heat from the open ocean to the cold atmosphere can enormously enhance rates of ice production. In polynya areas, the coupling between the atmosphere, sea ice and ocean is complex, and the role of ice formation on the budget of the main climate forcing carbon gases remains unknown. During the PIPERS expedition on the N.B. Palmer from April to June 2017, we performed continuous measurements of methane and carbon dioxide concentrations in the atmosphere and in the surface water from New Zealand to the polynyas of the Ross Sea. Discrete sampling was carried out in parallel to calibrate the continuous systems and to later measure the stable isotope ratios of both gases in the water and in the air. The stable isotope data enable unravelling the pathways involved in gas formation and removal. While the concentrations of both gases were relatively low in the surface waters of polynyas, the preliminary atmospheric data show higher methane and carbon dioxide levels in the atmosphere at locations where sea ice formation was most intense. These data together with the isotopic ratios of both gases and with meteorological data will be discussed to better understand the role of sea ice formation on the exchange of climate forcing gases. [less ▲]

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See detailPIPERS: Ocean Observations during an Anomalous Autumn-winter in the Ross Sea
Stammerjohn, Sharon; Ackley, Stephen; Maksym, Ted et al

Conference (2018, June 18)

There are very few ocean observations during autumn-winter south of the Antarctic ice edge, particularly as far south as the coastal polynyas. In the Ross Sea alone, we know of only three prior autumn ... [more ▼]

There are very few ocean observations during autumn-winter south of the Antarctic ice edge, particularly as far south as the coastal polynyas. In the Ross Sea alone, we know of only three prior autumn-winter U.S. oceanographic expeditions. In 2017 the PIPERS (Polynyas, Ice Production and seasonal Evolution in the Ross Sea) project conducted an oceanographic expedition to the southwestern Ross Sea aboard the RVIB Palmer during April-June. Its main objective was to assess the local/large-scale controls on sea ice production, water mass transformation, and carbon/trace metal inventories during an autumn-winter transition. In contrast to the strong positive sea ice trends observed over 1979-2015, the PIPERS ocean observations were acquired prior to, and during, very anomalous air-sea-ice conditions in the Ross Sea. These hydrographic observations extended from north of the ice edge, to the advancing ice edge, and along south/north transects to/from the coastal polynyas under an anomalously thin ice cover. Extensive observations were collected in Terra Nova Bay before/after several strong katabatic wind events, as well as in front of the Ross Ice Shelf under milder katabatic conditions. These ocean observations (water mass types, mixed layer evolution, heat/salt inventories) will be discussed within the context of the anomalous air-sea-ice conditions that occurred prior to and during PIPERS, as well as to the few autumn-winter ocean observations available for the Ross Sea. [less ▲]

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See detailSCOR Working Group 152: Measuring Essential Climate Variables in Sea Ice (ECV-Ice)
Nomura, D; Fripiat, François ULiege; Else, B. et al

Poster (2018, January 15)

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See detailChlorophyll- a in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data
Meiners, K. M.; Vancoppenolle, M.; Carnat, G. et al

in Journal of Geophysical Research. Oceans (2018), 123(11), 8444-8459

Abstract Historical sea‐ice core chlorophyll‐a (Chla) data are used to describe the seasonal, regional and vertical distribution of ice algal biomass in Antarctic landfast sea ice. The analyses are based ... [more ▼]

Abstract Historical sea‐ice core chlorophyll‐a (Chla) data are used to describe the seasonal, regional and vertical distribution of ice algal biomass in Antarctic landfast sea ice. The analyses are based on the Antarctic Fast Ice Algae Chlorophyll‐a dataset, a compilation of currently available sea‐ice Chla data from landfast sea‐ice cores collected at circum‐Antarctic nearshore locations between 1970 and 2015. Ice cores were typically sampled from thermodynamically grown first‐year ice and have thin snow depths (mean = 0.052 ± 0.097 m). The dataset comprises 888 ice cores, including 404 full vertical profile cores. Integrated ice algal Chla biomass (range: ‐2 – 219.9 mg m‐2, median = 4.4 mg m‐2, interquartile range = 9.9 mg m‐2) peaks in late spring and shows elevated levels in autumn. The seasonal Chla development is consistent with the current understanding of physical drivers of ice algal biomass, including the seasonal cycle of irradiance and surface temperatures driving landfast sea‐ice growth and melt. Landfast ice regions with reported platelet‐ice formation show maximum ice algal biomass. Ice algal communities in the lower‐most third of the ice cores dominate integrated Chla concentrations during most of the year, but internal and surface communities are important, particularly in winter. Through comparison of biomass estimates based on different sea‐ice sampling strategies, i.e., analysis of full cores versus bottom‐ice section sampling, we identify biases in common sampling approaches and provide recommendations for future survey programs: e.g., the need to sample fast ice over its entire thickness and to measure auxiliary physico‐chemical parameters. [less ▲]

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See detailThe first known virus isolates from Antarctic sea ice have complex infection patterns
Luhtanen, A.-M.; Eronen-Rasimus, E.; Oksanen, H. M. et al

in FEMS Microbiology Ecology (2018), 94(4),

Viruses are recognized as important actors in ocean ecology and biogeochemical cycles, but many details are not yet understood. We participated in a winter expedition to the Weddell Sea, Antarctica, to ... [more ▼]

Viruses are recognized as important actors in ocean ecology and biogeochemical cycles, but many details are not yet understood. We participated in a winter expedition to the Weddell Sea, Antarctica, to isolate viruses and to measure virus-like particle abundance (flow cytometry) in sea ice. We isolated 59 bacterial strains and the first four Antarctic sea-ice viruses known (PANV1, PANV2, OANV1 and OANV2), which grow in bacterial hosts belonging to the typical sea-ice genera Paraglaciecola and Octadecabacter. The viruses were specific for bacteria at the strain level, although OANV1 was able to infect strains from two different classes. Both PANV1 and PANV2 infected 11/15 isolated Paraglaciecola strains that had almost identical 16S rRNA gene sequences, but the plating efficiencies differed among the strains, whereas OANV1 infected 3/7 Octadecabacter and 1/15 Paraglaciecola strains and OANV2 1/7 Octadecabacter strains. All the phages were cold-active and able to infect their original host at 0°C and 4°C, but not at higher temperatures. The results showed that virus-host interactions can be very complex and that the viral community can also be dynamic in the winter-sea ice. © FEMS 2018. All rights reserved. [less ▲]

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See detailAn active bacterial community linked to high chl-a concentrations in Antarctic winter-pack ice and evidence for the development of an anaerobic sea-ice bacterial community
Eronen-Rasimus; Luhtanen, A.-M.; Rintala, J.-M. et al

Poster (2017, September)

Detailed reference viewed: 25 (2 ULiège)
See detailWhere does the methane entrapped in Antarctic sea ice come from?
Jacques, C.; Sapart, Célia Julia ULiege; Carnat, G. et al

Poster (2017, July)

Methane (CH4) atmospheric concentrations have increased by a factor of 2.5 since the beginning of the Industrial Era, mainly because of anthropogenic activities. However, between 1999 and 2006, CH4 growth ... [more ▼]

Methane (CH4) atmospheric concentrations have increased by a factor of 2.5 since the beginning of the Industrial Era, mainly because of anthropogenic activities. However, between 1999 and 2006, CH4 growth rate declined to a near-zero level, suggesting that an equilibrium had been reached. But, from 2007 on, atmospheric concentrations underwent a renewed growth, implying major ongoing changes in the CH4 global budget (Nisbet et al., 2016). These changes challenge our understanding on the contribution of existing sources, and in particular natural sources. Sea ice can strongly affect emissions of CH4 from the ocean, but the precise mechanisms are not well understood. Sea ice has long been considered as an inert and impermeable barrier, but recent studies have highlighted the existence of gas fluxes at the atmosphere-sea ice and sea ice-seawater interfaces (Kort et al., 2012; He et al., 2013; Zhou et al., 2014; Sapart et al., 2016). However, these fluxes are to date poorly understood and quantified. To improve future climate projections, we aim to investigate the control exerted by sea ice on the CH4 atmospheric budget. To unravel the impacts of the Antarctic sea ice physical environment on biogeochemical cycles, the AWECS (Antarctic Winter Ecosystem Climate Study) expedition was conducted between the 8th of June and the 12th of August 2013 in the Weddell Sea. Such an expedition provides a rare opportunity to obtain insights on the behaviour of sea ice during winter. Ice cores specifically dedicated to the investigation of gas dynamics were collected at ten different stations. In order to determine CH4 formation and removal pathways in sea ice, we used concentration and stable isotope analysis, which can help to distinguish different processes. Here, we present and discuss our first results of the isotopic composition of CH4 (δ13C and δ D) on sea ice cores from the Weddell Sea and the Ross Ice Shelf. This new dataset will help to determine the origin of the CH4 entrapped in Antarctic sea ice and its potential impact on the current and future atmospheric CH4 budget. [less ▲]

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See detailN2O production and cycling within Antarctic sea ice
Kotovitch, Marie ULiege; Tison, J.-L.; Fripiat, François ULiege et al

Poster (2017, July)

Nitrous oxide (N2O) is a potent greenhouse gas that has a lifetime of 114 years in the atmosphere and a global warming potential 300 time higher than that of CO2. However there are still large ... [more ▼]

Nitrous oxide (N2O) is a potent greenhouse gas that has a lifetime of 114 years in the atmosphere and a global warming potential 300 time higher than that of CO2. However there are still large uncertainties and gaps in the understanding of the N2O cycle in polar oceans and particularly associated to sea ice. Sources and sinks of N2O are therefore poorly quantified. To date, only one study by Randall et al. 2012 present N2O measurements in sea ice. They pointed out that sea ice formation and melt has the potential to generate sea-air or air-sea fluxes of N2O, respectively. The main processes (except the transport processes) involved in the N2O cycle within the aquatic environment are nitrification and denitrification. Recent observations of significant nitrification in Antarctic sea ice shed a new light on nitrogen cycle within sea ice. It has been suggested that nitrification supplies up to 70% of nitrate assimilated within Antarctic spring sea ice. Corollary, production of N2O, a by-product of nitrification, can potentially be significant. Our recent studies in Antarctic land fast ice in McMurdo Sound, confirmed this suggestion, where N2O release to the atmosphere was estimated to reach 4µmol.m-2.yr-1. But this assessment is probably an underestimation since it only accounts for dissolved N2O while a significant amount of N2O is likely to occur in the gaseous form like N2, O2 and Ar. We will then address the new tools to measure the bulk concentration of N2O (dissolved and gaseous) in sea ice, and the production of N2O by sympagic microorganisms - what process is dominant and how much N2O is produced - based on the first time series of N2O measurement in sea ice. The determination of the isotopic composition of N2O using cavity enhanced laser absorption spectroscopy technique (Off-axis ICOS) will allow us to determine the origin of these processes. [less ▲]

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See detailMacro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes
Fripiat, François ULiege; Meiners, K.M.; Vancoppenolle, M. et al

in Elementa: Science of the Anthropocene (2017), 5(13),

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 ... [more ▼]

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. [less ▲]

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See detailGases in sea ice
Tison, J.-L.; Delille, Bruno ULiege; Papadimitriou, Stathys

in Thomas, D.N. (Ed.) Sea ice (third edition) (2017)

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See detailBiogeochemical Impact of Snow Cover and Cyclonic Intrusions on the Winter Weddell Sea Ice Pack
Tison, J.-L.; Schwegmann, S.; Dieckmann, G. et al

in Journal of Geophysical Research. Oceans (2017), 122(12), 9548--9571

Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and ... [more ▼]

Sea ice is a dynamic biogeochemical reactor and a double interface actively interacting with both the atmosphere and the ocean. However, proper understanding of its annual impact on exchanges, and therefore potentially on the climate, notably suffer from the paucity of autumnal and winter data sets. Here we present the results of physical and biogeochemical investigations on winter Antarctic pack ice in the Weddell Sea (R. V. Polarstern AWECS cruise, June–August 2013) which are compared with those from two similar studies conducted in the area in 1986 and 1992. The winter 2013 was characterized by a warm sea ice cover due to the combined effects of deep snow and frequent warm cyclones events penetrating southward from the open Southern Ocean. These conditions were favorable to high ice permeability and cyclic events of brine movements within the sea ice cover (brine tubes), favoring relatively high chlorophyll-a (Chl-a) concentrations. We discuss the timing of this algal activity showing that arguments can be presented in favor of continued activity during the winter due to the specific physical conditions. Large-scale sea ice model simulations also suggest a context of increasingly deep snow, warm ice, and large brine fractions across the three observational years, despite the fact that the model is forced with a snowfall climatology. This lends support to the claim that more severe Antarctic sea ice conditions, characterized by a longer ice season, thicker, and more concentrated ice are sufficient to increase the snow depth and, somehow counterintuitively, to warm the ice. [less ▲]

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