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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 (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

This study was conducted to estimate the potential for natural iron fertilization in the Bellingshausen Sea, a remote region in the Pacific sector of the Southern Ocean. Seawater samples were collected during early austral spring 2007 near the continental margin, in the wake of an iceberg and near Peter I Island in order to identify and quantify Fe sources to the upper ocean. We concomitantly collected sea ice cores for Fe analysis during a time series sampling program on an ice floe. Looking at the upper 200m, our seawater data together with other published data suggest a large-scale exponential meridional decrease of DFe concentrations with increasing distance from the coastline noticeable up to 1400km to the north into the ACC. From this DFe gradient we estimated DFe fluxes into the upper mixed layer of the Bellingshausen Sea using a simple one-dimensional horizontal and vertical diffusion/advection model. We also estimated the melting input from sea ice and icebergs. DFe fluxes were compared for three biogeochemical provinces: ice covered continental shelf, marginal ice zone near the continental margin, and the open ocean. Fe in sea ice decreased with time enabling us to estimate a melt flux of 0.3μmol/m2/d DFe. We found that going from the continental shelf to the open ocean the dominant Fe fluxes gradually change from horizontal advection on the continental shelf (54% of a total DFe flux of 7.6±5.0μmol/m2/d) via sea ice melt in the pack ice near the continental margin (56% of a total DFe flux of 0.55±0.18μmol/m2/d) to vertical advection (58% of a total DFe flux of 0.038±0.027μmol/m2/d) in the ice free open ocean. A significant DFe flux of 0.6μmol/m2/d was estimated for iceberg melting, but this flux took place below the upper mixed layer and was not taken into further account. Fueling the high horizontal flux on the continental shelf is likely benthic diffusion and sediment resuspension. This is indicated by enhanced total dissolvable Fe (TD-Fe) and dissolved, SCOPUS: ar.j, info:eu-repo/semantics/published

Mineral dust is a major source of micronutrients (e.g. Fe) in open oceans and HNLC zones. In the Southern Ocean in particular, the properties and impacts of current dust deposition are not well constrained. Here, several dust-bearing snow samples collected in the NE Antarctica coast are investigated in order to :(i) characterize the mineralogy, size, and morphology of dust by single particle analyses (automated-FEG-SEM-EDS and TEM-SAED), (ii) trace the origin and the relative contribution of natural and anthropogenic particles in dusts through elemental and multi-isotopic analyses (HR-ICP-MS and MC-ICP-MS) and (iii) quantify the Fe bioavailability in dusts (via extractions). Our first results show a fine size distribution (98% of particles < 5 µm, n=1550). A large fraction exhibits a Fe contribution, either from mineralogy or coating. While the mineralogy suggest a substantial contribution of proximal rocks, a high Pb enrichment factor (x7 relative to upper continental crust - UCC) indicates an anthropogenic contribution to the dust deposition. Overall, this study will improve our understanding of dust reaching the coast of NE-Antarctica, which may represent a proxy for the dust material supplied to the Southern Ocean, by far the largest HNLC., info:eu-repo/semantics/nonPublished

Growth limitation of marine algae due to lack of iron occurs in up to 40% of the global ocean. Despite important advances on the impact of organic compounds on iron biogeochemistry, their roles in controlling iron availability to prokaryotic and eukaryotic phytoplankton remain unclear. Whether algal and bacterial exopolymeric substances (EPS) include organic ligands which may help iron-limited phytoplankton growth remains an unknown. If so, then EPS could relieve phytoplankton iron limitation with implications for the biological carbon pump and hence the regulation of atmospheric CO2. Here we compared the biological impact of algal, bacterial and in situ EPS with model compounds, a siderophore and two saccharides on biological parameters including, iron bioavailability, phytoplankton growth, photo-physiology and community structure. Laboratory and field experiments demonstrated that EPS produced by marine microorganisms are efficient in sustaining biological iron uptake as well as algal growth, and can affect natural phytoplankton community structure. Our data suggest that natural phytoplankton growth enhancement in the presence of EPS was not solely due to highly bioavailable iron forms, but also because EPS contains other micronutrients. Stronger ligands were detected following iron-siderophore enrichments (log KFe'L=12.0) and weaker ligands were measured in the presence of EPS (log KFe'L=10.4-11.0). The trend of the conditional stability constants of organic ligands did not seem to be affected as a result of biological activity and photo-chemistry during our four day incubations. The shift in the phytoplankton community observed during our field experiments was not uniformly observed between different sites rendering it difficult to extrapolate which functional group(s) would benefit the most from iron bound to EPS., SCOPUS: ar.j, info:eu-repo/semantics/published

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The characteristics of the dissolved iron (DFe) binding organic ligands were determined during 3 Dutch GEOTRACES cruises covering the length of the West Atlantic Ocean. Adsorptive Differential Pulse Cathodic Stripping Voltammetry (AdDPCSV) with TAC as competing ligand was used to measure Fe binding organic ligands. Although the distribution of DFe is related to its sources, sinks and vertical processes, ultimately it is the solubility of Fe in seawater that determines its concentrations in the oceans. The Fe binding organic ligands increase the solubility of Fe. The total ligand concentration and the excess ligand over Fe concentration showed a decreasing trend from north to south in the surface ocean as well as in the North Atlantic Deep Water (NADW). This trend could be extended further north to the Arctic Ocean, where ligand concentrations were even higher. The Arctic might be a source of ligands to the northern West Atlantic Ocean. We calculated a residence time of 779 to 1039. years for dissolved organic ligands in the NADW. This is 2.5 to 4 times larger than the estimated residence time of DFe in the NADW.The highest concentrations of excess ligands were found in the surface where the dissolved Fe concentrations were the lowest. This resulted in high ratios of [Lt]/DFe in the surface decreasing with depth to a value close to 2 below 500. m, where more ligands were saturated. Dissolved organic ligands were saturated with Fe in a large part of the southern West Atlantic at mid-depth, where DFe concentrations increased due to hydrothermal activity.The inorganic Fe concentrations, [Fe'], were surprisingly uniform for the western Atlantic Ocean. Values ranged between 0.2 and 1. pM in the deep Atlantic as well as in the surface, where ligands were unsaturated with Fe. However, in the hydrothermal influenced region, where ligands were (nearly) saturated, [Fe'] was high, possibly larger than the solubility product of the Fe(oxy)hydroxides and thus suggesting either hi, SCOPUS: ar.j, info:eu-repo/semantics/published

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YROSIAE survey aimed to carry out a year-round survey of land-fast sea ice focusing on the study of sea ice physics and biogeochemistry in order to a) better understand and budget exchanges of energy and matter across the ocean-sea ice-atmosphere interfaces during sea ice growth and decay and b) quantify their potential impact on fluxes of climate gases (CO2, DMS, CH4, N2O) to the atmosphere and on carbon and macro- nutrients and micro-nutrients export to the ocean. Ice cores, sea water, brines and exported material were collected at regular intervals about 1 km off cape Evans from November 2011 to December 2011 and from September 2012 to December 2012 in trace-metal clean conditions. Samples are processed to characterize both the vertical distribution and temporal changes of climate gases (CO2, DMS, CH4, N2O), CO2-related parameters (dissolved inorganic carbon, total alkalinity and CaCO3 amount), physical parameters (salinity, temperature, texture, 18O), biogeochemical parameters (macro-nutrients, particulate and dissolved organic carbon, δ13C, δ30Si and δ15N, micro-nutrients - including iron) and biological parameters ( chlorophyll a, primary production within sea ice derived from O2:Ar and O2:N ratios, autotrophic species determination, bacterial cell counts a.s.o.). In addition, we deployed a micro-meterological tower and automatic chambers to measure air-ice CO2 fluxes. Continuous measurements of ice temperature and ice accretion or melting, both at the ice-ocean and the ice-atmosphere interfaces were provided by an “Ice-T” ice mass balance buoy. Sediment traps collected particles below the ice between 10 and 70 m, while dust collectors provided a record of a full suite of trace metal and dust at different levels above the ground. We will present the aims, overall approach and sampling strategy of the YROSIAE survey. In addition we will also discuss CO2 dynamics within the ice and present temporal air-ice CO2 fluxes over the year. We will provide a first budget, info:eu-repo/semantics/nonPublished

We report first direct measurements of the partial pressure of CO2 (pCO2) within Antarctic pack sea ice brines and related CO2 fluxes across the air-ice interface. From late winter to summer, brines encased in the ice change from a CO2 large oversaturation, relative to the atmosphere, to a marked undersaturation while the underlying oceanic waters remains slightly oversaturated. The decrease from winter to summer of pCO2 in the brines is driven by dilution with melting ice, dissolution of carbonate crystals, and net primary production. As the ice warms, its permeability increases, allowing CO2 transfer at the air-sea ice interface. The sea ice changes from a transient source to a sink for atmospheric CO2. We upscale these observations to the whole Antarctic sea ice cover using the NEMO-LIM3 large-scale sea ice-ocean and provide first estimates of spring and summer CO2 uptake from the atmosphere by Antarctic sea ice. Over the spring-summer period, the Antarctic sea ice cover is a net sink of atmospheric CO2 of 0.029 Pg C, about 58% of the estimated annual uptake from the Southern Ocean. Sea ice then contributes significantly to the sink of CO2 of the Southern Ocean., FLWIN, info:eu-repo/semantics/published

We report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover, with emphasis on the ice texture and brine dynamics. Isolated DMS and DMSP maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture. We show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates (strong DMSP producers) in the ice cover. We also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of DMS,P concentrations. We show that during the winter-spring transition in 2012, the DMS,P profiles were strongly influenced by the development and decline of a diatom-dominated bloom in the bottom ice, with DMSP variations remarkably following chl a variations. During the spring-summer transition in 2011, the increase in brine volume fraction (influencing ice permeability) on warming was shown to trigger (1) an important release of DMS to the under-ice water through brine convection and (2) a vertical redistribution of DMSP across the ice. Key Points Incorporated platelet ice can strongly influence fast ice DMS,P dynamics The seasonal bloom of diatoms governs DMSP production in bottom ice Brine convection at the end of spring triggers strong DMS release to the ocean © 2014. American Geophysical Union. All Rights Reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

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Although algal growth in the iron-deficient Southern Ocean surface waters is generally low, there is considerable evidence that winter sea ice contains high amounts of iron and organic matter leading to ice-edge blooms during austral spring. We used field observations and ship-based microcosm experiments to study the effect of the seeding by sea ice microorganisms, and the fertilization by organic matter and iron on the planktonic community at the onset of spring/summer in the Weddell Sea. Pack ice was a major source of autotrophs resulting in a ninefold to 27-fold increase in the sea ice-fertilized seawater microcosm compared to the ice-free seawater microcosm. However, heterotrophs were released in lower numbers (only a 2- to 6-fold increase). Pack ice was also an important source of dissolved organic matter for the planktonic community. Small algae (<10 μm) and bacteria released from melting sea ice were able to thrive in seawater. Field observations show that the supply of iron from melting sea ice had occurred well before our arrival onsite, and the supply of iron to the microcosms was therefore low. We finally ran a "sequential melting" experiment to monitor the release of ice constituents in seawater. Brine drainage occurred first and was associated with the release of dissolved elements (salts, dissolved organic carbon and dissolved iron). Particulate organic carbon and particulate iron were released with low-salinity waters at a later stage. © 2013 The Author(s)., SCOPUS: ar.j, info:eu-repo/semantics/published

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In large parts of the Southern Ocean, primary production is limited due to shortage of iron (Fe). We measured vertical Fe profiles in the western Weddell Sea, Weddell-Scotia Confluence, and Antarctic Circumpolar Current (ACC), showing that Fe is derived from benthic Fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography. Our data together with literature data reveal an exponential decrease of dissolved Fe (DFe) concentrations with increasing distance from the continental shelves of the Antarctic Peninsula and the western Weddell Sea. This decrease can be observed 3500 km eastward of the Antarctic Peninsula area, downstream the ACC. We estimated DFe summer fluxes into the upper mixed layer of the Atlantic sector of the Southern Ocean and found that horizontal advection dominates DFe supply, representing 54 ± 15% of the total flux, with significant vertical advection second most important at 29 ± 13%. Horizontal and vertical diffusion are weak with 1 ± 2% and 1 1%, respectively. The atmospheric contribution is insignificant close to the Antarctic continent but increases to 15 ± 10% in the remotest waters (>1500 km offshore) of the ACC. Translating Southern Ocean carbon fixation by primary producers into biogenic Fe fixation shows a twofold excess of new DFe input close to the Antarctic continent and a one-third shortage in the open ocean. Fe recycling, with an estimated "fe" ratio of 0.59, is the likely pathway to balance new DFe supply and Fe fixation. Copyright 2012 by the American Geophysical Union., SCOPUS: ar.j, info:eu-repo/semantics/published

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