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This study explores the role of snowpack in polar boundary layer chemistry, especially as a direct source of reactive bromine (BrOX=BrO+Br) and nitrogen (NOX=NO+NO2) in the Arctic springtime. Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80° N, 86° W) from the end of February to the end of March in 2018 and 2019. The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level (asl). At the inland sites, surface snow salinity has a double-peak distribution with the first and lowest peak at 0.001–0.002 practical salinity unit (psu), which corresponds to the precipitation effect, and the second peak at 0.01–0.04 psu, which is likely related to the salt accumulation effect (due to loss of water vapour by sublimation). Snow salinity on sea ice has a triple-peak distribution; its first and second peaks overlap with the inland peaks, and the third peak at 0.2–0.4 psu is likely due to the sea water effect (due to upward migration of brine on sea ice). At all sites, snow sodium and chloride concentrations increase by almost 10-fold from the top 0.2 cm to ~1.5 cm in depth. Surface snow bromide at sea level is significantly enriched, indicating a net sink of atmospheric bromine. Moreover, surface snow bromide at sea level has an increasing trend over the measurement time period, with mean slopes of 0.024 in the 0–0.2 cm layer and 0.016 μM d-1 in the 0.2–0.5 cm layer. Surface snow nitrate at sea level also shows a significant increasing trend, with mean slopes of 0.27, 0.20, and 0.07 μM d-1 in the top 0.2 cm, 0.2–0.5 cm, and 0.5–1.5 cm layers, respectively. Using these trends, an integrated net deposition flux of bromide of 1.01×107 molecules cm-2 s-1 and an integrated net deposition flux of nitrate of 2.6×108 molecules cm-2 s-1 were derived. In addition, nitrate and bromide in the morning samples are significantly higher than the afternoon samples, indicating a strong photochemistry effect. However, the mean bromide loss rate (0.027–0.040 μM) is smaller than the nitrate loss rate (0.23–0.362 μM) by an order of magnitude, implying the reactive bromine emission flux from snowpack is significantly smaller than the reactive nitrogen emission flux, which is consistent with the large difference between their derived net deposition fluxes. After considering the photochemical loss effect, the corrected bromide deposition flux at sea level is 2.73×107 molecules cm-2 s-1; for nitrate, the corrected deposition flux is 5.98×108 molecules cm-2 s-1. In addition, the surface snow nitrate and bromide at inland sites were found to be significantly correlated (R=0.48–0.76), and the [NO3-]/[Br-] ratio of 4–7 indicates a possible acceleration effect of reactive bromine in atmospheric NOX-to-nitrate conversion. This is the first time such an effect has been seen in snow chemistry data obtained with a sampling frequency as short as one day. [ABSTRACT FROM AUTHOR]

This study explores the role of snowpack in polar boundary layer chemistry, especially as a direct source of reactive bromine (BrOX=BrO+Br) and nitrogen (NOX=NO+NO2) in the Arctic springtime. Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80°N, 86°W) from the end of February to the end of March in 2018 and 2019. The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level (asl). At the inland sites, surface snow salinity has a double-peak distribution with the first and lowest peak at 0.001-0.002 practical salinity unit (psu), which corresponds to the precipitation effect, and the second peak at 0.01-0.04 psu, which is likely related to the salt accumulation effect (due to loss of water vapour by sublimation). Snow salinity on sea ice has a triple-peak distribution; its first and second peaks overlap with the inland peaks, and the third peak at 0.2-0.4 psu is likely due to the sea water effect (due to upward migration of brine on sea ice). At all sites, snow sodium and chloride concentrations increase by almost 10-fold from the top 0.2 cm to ~1.5 cm in depth. Surface snow bromide at sea level is significantly enriched, indicating a net sink of atmospheric bromine. Moreover, surface snow bromide at sea level has an increasing trend over the measurement time period, with mean slopes of 0.024 in the 0-0.2 cm layer and 0.016 μM d-1 in the 0.2-0.5 cm layer. Surface snow nitrate at sea level also shows a significant increasing trend, with mean slopes of 0.27, 0.20, and 0.07 μM d-1 in the top 0.2 cm, 0.2-0.5 cm, and 0.5-1.5 cm layers, respectively. Using these trends, an integrated net deposition flux of bromide of 1.01×107 molecules cm-2 s-1 and an integrated net deposition flux of nitrate of 2.6×108 molecules cm-2 s-1 were derived. In addition, nitrate and bromide in the morning samples are significantly higher than the afternoon samples, indicating a strong photochemistry effect. However, the mean bromide loss rate (0.027-0.040 μM) is smaller than the nitrate loss rate (0.23-0.362 μM) by an order of magnitude, implying the reactive bromine emission flux from snowpack is significantly smaller than the reactive nitrogen emission flux, which is consistent with the large difference between their derived net deposition fluxes. After considering the photochemical loss effect, the corrected bromide deposition flux at sea level is 2.73×107 molecules cm-2 s-1; for nitrate, the corrected deposition flux is 5.98×108 molecules cm-2 s-1. In addition, the surface snow nitrate and bromide at inland sites were found to be significantly correlated (R=0.48-0.76), and the [NO3-]/[Br-] ratio of 4-7 indicates a possible acceleration effect of reactive bromine in atmospheric NOX-to-nitrate conversion. This is the first time such an effect has been seen in snow chemistry data obtained with a sampling frequency as short as one day. [ABSTRACT FROM AUTHOR]

This study explores the role of snowpack in polar boundary layer chemistry, especially as a di-rect source of reactive bromine (BrOX=BrO+Br) and nitrogen (NOX=NO+NO2) in the Arctic springtime. Surface snow samples were collected daily from a Canadian high Arctic location at Eureka, Nunavut (80° N, 86° W) from the end of February to the end of March in 2018 and 2019. The snow was sampled at several sites representing distinct environments: sea ice, inland close to sea level, and a hilltop ~600 m above sea level (asl). At the inland sites, surface snow salinity has a double-peak distribution with the first and low-est peak at 0.001–0.002 practical salinity unit (psu), which corresponds to the precipitation ef-fect, and the second peak at 0.01–0.04 psu, likely due to the condensation effect. Snow salinity on sea ice has a triple-peak distribution; its first and second peaks overlap with the inland peaks, and the third peak at 0.2–0.4 psu can be clearly attributed to sea water contamination. At all sites, sodium and chloride concentrations in surface snow increase by almost 10-fold from the top 0.2 cm to ~1 cm in depth. Bromide in surface snow is significantly enriched, indi-cating that surface snow at Eureka is a net sink of atmospheric bromine. Moreover, daily data show that top surface snow bromide at all sampling sites has an increasing trend over the measurement time period (late February to late March), with mean slopes of 1.9 and 1.3 ppb d-1 in the 0–0.2 cm and the 0.2–0.5 cm layers, respectively. At the sea level sites, snow nitrate also shows a significant increasing trend, with mean slopes of 12.1, 12.4, and 4.3 ppb d-1 in the top 0.2 cm, 0.2–0.5 cm, and 0.5–1.5 cm layers, respectively. Using these trends, we derive a novel method to calculate deposition flux of bromide and nitrate to the snowpack. For bromide, the integrated deposition flux is 1.29×107 molecules cm-2 s-1 at sea level and 1.01×107 molecules cm-2 s-1 at ~600 m. For nitrate, the integrated deposition flux is 2.4×108 molecules cm-2 s-1 at sea level and -1.0×108 molecules cm-2 s-1 at ~600 m; the negative flux indicates that snow at the hilltop sites is losing nitrate. The smaller vertical gradient of bromide deposition flux strongly indicates that local snowpack emission on sea ice and inland is not likely to be a large source of reactive bromine. In contrast, nitrate deposition flux has a large vertical gradient, e.g., with a positive flux at sea level and a negative flux at ~600 m, indicating that snowpack at sea level is a large source of reactive nitrate. In addition, we found a significant correlation (with coefficient R values of 0.48-0.76) between surface snow nitrate and bromide at the inland sites. The [NO3-] / [Br-] ratio ranges from 4 to 7, highlighting the effect of reactive bromine in accelerating the atmospheric NOX-to-nitrate con-version. This is the first time we see such an effect over the course of one day. [ABSTRACT FROM AUTHOR]

Ongoing climate change in the Arctic has caused tidewater glacier retreat and increased discharge of freshwater and terrestrial material into fjords. These land inputs bring nutrients into the fjords and their cycling within the fjord system can vary with the influence of tidewater glaciers and the presence of sub-glacial meltwater plumes. In this study, we assess the influence of tidewater glaciers on nitrogen inputs and cycling in two fjords in Svalbard during the summer using stable isotopic analyses of dissolved nitrate (δ15N and δ18O) in combination with nutrients and hydrographic data. Kongsfjorden receives inputs from tidewater glaciers, whereas Rijpfjorden mainly receives surface inputs from land-terminating glaciers. Results showed that both fjords are enriched in nutrients from terrestrial inputs, where the inputs exceed Redfield ratios with excess Si and P relative to N. In both fjords, terrestrial nitrate from snowpack and glacier melting are identified as the dominant sources based on high δ18O-NO3- and low δ15N-NO3- of dissolved nitrate. In Kongsfjorden, mixed-layer nitrate is completely consumed within the fjord system which we attribute to vigorous circulation at the glacial front influenced by the subglacial plume and longer residence time in the fjord. This is in contrast with Rijpfjorden where nutrients are only partially consumed perhaps due to surface river discharge and light limitation. In Kongsfjorden, we estimate terrestrial and marine N contributions to the nitrate pool from nitrogen isotopic values (δ15N-NO3-) and this suggests that nearly half the nitrate in the subglacial plume (50 ± 3 %) and the water column (44 ± 3 %) originates from terrestrial sources. In addition, we show that terrestrial N also contributes significantly to regenerated N pool (63–88 %) within this fjord suggesting its importance in sustaining productivity within Kongsfjorden. Given this importance of terrestrial nutrient sources within the fjords, increase in these inputs due to climate change can enhance the fjord nutrient inventory, productivity and nutrient export offshore. Specifically, increasing Atlantification and warmer Atlantic Water will encourage tidewater glacier retreat and in turn increase surface discharge. In fjords akin to Rijpfjorden this is expected to foster more light limitation and less dynamic circulation, ultimately aiding the export of nutrients offshore contributing to coastal productivity. Climate change scenario postulated for fjords such as Kongsfjorden include more terrestrial N-fuelled productivity and N cycling within the fjord, less vigorous circulation and the expansion of oxygen depleted deep waters inside the sill. [ABSTRACT FROM AUTHOR]