We studied the temporal variations of CO 2 , O 2 , and dimethylsulfide (DMS) concentrations within three environments (sea-ice brine, platelet ice-like layer, and underlying water) in the coastal area of Adélie Land, Antarctica, during spring 1999 before ice breakup. Temporal changes were different among the three environments, while similar temporal trends were observed within each environment at all stations. The underlying water was always undersaturated in O 2 (around 85%) and oversaturated in CO 2 at the deepest stations. O 2 concentrations increased in sea-ice brine as it melted, reaching oversaturation up to 160% due to the primary production by the sea-ice algae community (chlorophyll a in the bottom ice reached concentrations up to 160 mg L 21 of bulk ice). In parallel, DMS concentrations increased up to 60 nmol L 21 within sea-ice brine and the platelet ice-like layer. High biological activity consumed CO 2 and promoted the decrease of partial pressure of CO 2 (pCO 2 ). In addition, melting of pure ice crystals and calcium carbonate (CaCO 3 ) dissolution promoted the shift from a state of CO 2 oversaturation to a state of marked CO 2 undersaturation (pCO 2 , 30 dPa). On the whole, our results suggest that late spring land fast sea ice can potentially act as a sink of CO 2 and a source of DMS for the neighbouring environments, i.e., the underlying water or/and the atmosphere.Sea ice covers about 7% of Earth's surface at its maximum seasonal extent, representing one of the largest biomes on the planet. For decades, sea ice was assumed to be an impermeable and inert barrier for air-sea exchanges of CO 2 , and global climate models did not include CO 2 exchanges between this compartment and the atmosphere. However, there is a growing body of evidence that sea ice exchanges CO 2 with the atmosphere. While estimating permeation constants of sulfur hexafluoride (SF 6 ) and CO 2 within sea ice, Gosink et al. (1976) stressed that sea ice is a permeable medium for gases. These authors suggested that gas migration through sea ice could be an important factor in winter ocean-atmosphere exchange at sea-ice surface temperature above 210uC. More recently, uptake of atmospheric CO 2 over sea-ice cover has been reported (Semiletov et al. 2004;Delille 2006;Zemmelink et al. 2006) supporting the need to further investigate pCO 2 dynamics in the sea-ice realm and related CO 2 fluxes.Very few studies have been carried out on the dynamics of the carbonate system within natural sea ice. They have generally been aimed at investigating CaCO 3 precipitation or dissolution (Gleitz et al. 1995), or they have focused on measurements of dissolved inorganic carbon (DIC) and total alkalinity (TA) (Anderson and Jones, 1985;Rysgaard et al. 2007) rather than on pCO 2 . As pointed out by 1 Corresponding author (Bruno.Delille@ulg.ac.be).

[1] Year-round composition of bulk and size-segregated aerosol was examined at a coastal Antarctic site (Dumont d'Urville). Sea-salt particles display a summer depletion of chloride relative to sodium, which reaches $10%. The mass chloride loss is maximum on 1-to 3-mm-diameter particles, nitrate being often the anion causing the chloride loss. The summer SO 4 2À /Na + ratio exceeds the seawater value on submicron particles due to biogenic sulfate and on coarse particles due to ornithogenic (guano-enriched soils) sulfate and to heterogeneous uptake of SO 2 (or H 2 SO 4 ). HCl levels range from 47 ± 28 ng m À3 in the winter to 130 ± 110 ng m À3 in the summer, being close to the mass chloride loss of sea-salt aerosols. In the winter, sea-salt particles exhibit Cl À /Na + and SO 4 2À /Na + mass ratios of 1.9 ± 0.1 and 0.13 ± 0.04, respectively. Resulting from precipitation of mirabilite during freezing of seawater, this sulfate-depletion-relative sodium takes place from May to October. From March to April, warmer temperatures and/or smaller sea ice extent offshore the site limit the phenomenon. A range of 14-50 ng m À3 of submicron sulfate is found, confirming the existence of nssSO 4 2À in the winter at a coastal Antarctic site, highest values being found in the winters of 1992-1994 due to the Pinatubo volcanic input. Apart from these three winters, nssSO 4 2À levels range between 15 and 30 ng m À3 , but its origin is still unclear (quasi-continuous SO 2 emissions from the Mount Erebus volcano or local wintertime dimethyl sulfide [DMS] oxidation, in addition to long-range transported byproduct of DMS oxidation).

The Sentinel Application Platform (SNAP) architecture facilitates Earth Observation data processing. In this work, we present results from a new Snow Processor for SNAP. We also describe physical principles behind the developed snow property retrieval technique based on the analysis of Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3A/B measurements over clean and polluted snow fields. Using OLCI spectral reflectance measurements in the range 400–1020 nm, we derived important snow properties such as spectral and broadband albedo, snow specific surface area, snow extent and grain size on a spatial grid of 300 m. The algorithm also incorporated cloud screening and atmospheric correction procedures over snow surfaces. We present validation results using ground measurements from Antarctica, the Greenland ice sheet and the French Alps. We find the spectral albedo retrieved with accuracy of better than 3% on average, making our retrievals sufficient for a variety of applications. Broadband albedo is retrieved with the average accuracy of about 5% over snow. Therefore, the uncertainties of satellite retrievals are close to experimental errors of ground measurements. The retrieved surface grain size shows good agreement with ground observations. Snow specific surface area observations are also consistent with our OLCI retrievals. We present snow albedo and grain size mapping over the inland ice sheet of Greenland for areas including dry snow, melted/melting snow and impurity rich bare ice. The algorithm can be applied to OLCI Sentinel-3 measurements providing an opportunity for creation of long-term snow property records essential for climate monitoring and data assimilation studies—especially in the Arctic region, where we face rapid environmental changes including reduction of snow/ice extent and, therefore, planetary albedo.