scholarly journals Temperature and sunlight controls of mercury oxidation and deposition atop the Greenland ice sheet

2011 ◽  
Vol 11 (2) ◽  
pp. 3663-3691 ◽  
Author(s):  
S. Brooks ◽  
C. Moore ◽  
D. Lew ◽  
B. Lefer ◽  
G. Huey ◽  
...  
Keyword(s):  
Thermal Dissociation ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Halogen Chemistry ◽  
Marine Source ◽  
Remote Environment ◽  
Marine Boundary Layers

Abstract. We conducted the first ever mercury speciation measurements atop the Greenland ice sheet at Summit Station (Latitude 72.6° N, Altitude 3200 m) in the Spring and Summer of 2007 and 2008. These measurements were part of the GSHOX campaigns investigating the importance of halogen chemistry in this remote environment. Significant levels of BrO (1–5 pptv) in the near surface air were often accompanied by depletions of gaseous elemental mercury (GEM) below background levels, and in-situ production of reactive gaseous mercury (RGM). While halogen (i.e. Br) chemistry is normally associated with marine boundary layers, at Summit, Greenland, far from any marine source, we have conclusively detected bromine and mercury chemistry in the near surface air. We suggest that the fate of the formed mercury-bromine radical (HgBr) is further oxidation to stable RGM (HgBr2, HgBrOH, HgBrCl, etc.), or thermal decomposition. These fates appear to be controlled by the availability of Br, OH, Cl, etc. to produce RGM (Hg(II)), verses the lifetime of HgBr by thermal dissociation. At Summit, the availability of Br appears to be controlled by J(Br2), requiring a sun angle of > 5 degrees, while the formation of RGM from HgBr requires a temperature < −15 °C. The majority of the deposited RGM is readily photoreduced and re-emitted to the air as GEM. However, a very small fraction becomes buried at depth. Extrapolating to the entire Greenland ice sheet, we calculate an estimated net annual sequestration of ~ 13 metric tons Hg per year, buried long-term under the sunlit photoreduction zone.

scholarly journals Temperature and sunlight controls of mercury oxidation and deposition atop the Greenland ice sheet

2011 ◽  
Vol 11 (16) ◽  
pp. 8295-8306 ◽  
Author(s):  
S. Brooks ◽  
C. Moore ◽  
D. Lew ◽  
B. Lefer ◽  
G. Huey ◽  
...  
Keyword(s):  
Thermal Dissociation ◽  
Elevation Angle ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Halogen Chemistry ◽  
Marine Source ◽  
Remote Environment

Abstract. We conducted the first ever mercury speciation measurements atop the Greenland ice sheet at Summit Station (Latitude 72.6° N, Longitude 38.5° W, Altitude 3200 m) in the Spring and Summer of 2007 and 2008. These measurements were part of the collaborative Greenland Summit Halogen-HOx experiment (GSHOX) campaigns investigating the importance of halogen chemistry in this remote environment. Significant levels of BrO (1–5 pptv) in the near surface air were often accompanied by diurnal dips in gaseous elemental mercury (GEM), and in-situ production of reactive gaseous mercury (RGM). While halogen (i.e. Br) chemistry is normally associated with marine boundary layers, at Summit, Greenland, far from any marine source, we have conclusively detected bromine and mercury chemistry in the near surface air. The likely fate of the formed mercury-bromine radical (HgBr) is further oxidation to stable RGM (HgBr2, HgBrOH, HgBrCl...), or thermal decomposition. These fates appear to be controlled by the availability of Br, OH, Cl, etc. to produce RGM (Hg(II)), versus the lifetime of HgBr by thermal dissociation. At Summit, the production of RGM appears to require a sun elevation angle of >5 degrees, and an air temperature of 5 degrees, while the formation of RGM from HgBr requires a temperature

scholarly journals Overview of the 2007 and 2008 campaigns conducted as part of the Greenland Summit Halogen-HO<sub>x</sub> Experiment (GSHOX)

2012 ◽  
Vol 12 (7) ◽  
pp. 17135-17150
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
J. Stutz ◽  
R. von Glasow ◽  
S. Brooks ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Vertical Mixing ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
The North ◽  
Polar Snow ◽  
Active Bromine

Abstract. From 10 May through 17 June, 2007 and 6 June through 9 July, 2008 intensive sampling campaigns at Summit, Greenland confirmed that active bromine chemistry is occurring in and above the snow pack at the highest part of the Greenland ice sheet (72°36' N, 38° 25' W and 3.2 km a.s.l.). Direct measurements found BrO and soluble gas phase Br− mixing ratios in the low pptv range on many days (maxima <10 pptv). Conversion of up to 200 pg m−3 of gaseous elemental mercury (GEM) to reactive gaseous mercury (RGM) and enhanced OH relative to HO2 plus RO2 confirm that active bromine chemistry is impacting chemical cycles even at such low abundances of reactive bromine species. However, it does not appear that Bry chemistry can fully account for observed perturbations to HOx partitioning, suggesting unknown additional chemical processes may be important in this unique environment, or that our understanding of coupled NOx-HOx−Bry chemistry above sunlit polar snow is incomplete. Rapid transport from the North Atlantic marine boundary layer occasionally caused enhanced BrO at Summit (just two such events observed during the 12 weeks of sampling over the two seasons). In general observed reactive bromine was linked to activation of bromide (Br−) in, and release of reactive bromine from, the snowpack. A coupled snow-atmosphere one-dimensional model that assumed snow photochemistry as the only source successfully simulated observed NO and BrO at Summit during a three day interval when winds were weak (transport not a factor). The source of Br− in surface and near surface snow at Summit is not entirely clear, but concentrations were observed to increase when stronger vertical mixing brought free tropospheric air to the surface. Reactive Bry mixing ratios above the snow often increased in the day or two following increases in snow concentration, but this response was not consistent. On seasonal time scales concentrations of Br− in snow and reactive bromine in the air were directly related.

scholarly journals Overview of the 2007 and 2008 campaigns conducted as part of the Greenland Summit Halogen-HO<sub>x</sub> Experiment (GSHOX)

2012 ◽  
Vol 12 (22) ◽  
pp. 10833-10839 ◽  
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
J. Stutz ◽  
R. von Glasow ◽  
S. Brooks ◽  
...  
Keyword(s):  
Marine Boundary Layer ◽  
Vertical Mixing ◽  
Greenland Ice Sheet ◽  
Elemental Mercury ◽  
Near Surface ◽  
Gaseous Elemental Mercury ◽  
Mixing Ratios ◽  
The North ◽  
Polar Snow ◽  
Active Bromine

Abstract. From 10 May through 17 June 2007 and 6 June through 9 July 2008 intensive sampling campaigns at Summit, Greenland confirmed that active bromine chemistry is occurring in and above the snow pack at the highest part of the Greenland ice sheet (72°36´ N, 38°25´ W and 3.2 km above sea level). Direct measurements found BrO and soluble gas phase Br− mixing ratios in the low pptv range on many days (maxima < 10 pptv). Conversion of up to 200 pg m−3 of gaseous elemental mercury (GEM) to reactive gaseous mercury (RGM) and enhanced OH relative to HO2 plus RO2 confirm that active bromine chemistry is impacting chemical cycles even at such low abundances of reactive bromine species. However, it does not appear that Bry chemistry can fully account for observed perturbations to HOx partitioning, suggesting unknown additional chemical processes may be important in this unique environment, or that our understanding of coupled NOx-HOx-Bry chemistry above sunlit polar snow is incomplete. Rapid transport from the north Atlantic marine boundary layer occasionally caused enhanced BrO at Summit (just two such events observed during the 12 weeks of sampling over the two seasons). In general observed reactive bromine was linked to activation of bromide (Br−) in, and release of reactive bromine from, the snowpack. A coupled snow-atmosphere model simulated observed NO and BrO at Summit during a three day interval when winds were weak. The source of Br− in surface and near surface snow at Summit is not entirely clear, but concentrations were observed to increase when stronger vertical mixing brought free tropospheric air to the surface. Reactive Bry mixing ratios above the snow often increased in the day or two following increases in snow concentration, but this response was not consistent. On seasonal time scales concentrations of Br− in snow and reactive bromine in the air were directly related.

Estimating near-surface climatology of multi-reanalyses over the Greenland Ice Sheet

2021 ◽  
pp. 105676
Author(s):  
Wuying Zhang ◽  
Yetang Wang ◽  
Paul C.J.P. Smeets ◽  
Carleen H. Reijmer ◽  
Baojuan Huai ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Near Surface

scholarly journals Seasonal variability in the dynamics of marine-terminating outlet glaciers in Greenland

2010 ◽  
Vol 56 (198) ◽  
pp. 601-613 ◽  
Author(s):  
Ian M. Howat ◽  
Jason E. Box ◽  
Yushin Ahn ◽  
Adam Herrington ◽  
Ellyn M. McFadden
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Surface Air Temperature ◽  
Greenland Ice Sheet ◽  
Flow Speed ◽  
High Temporal Resolution ◽  
Sea Ice Concentration ◽  
Seasonal Behavior ◽  
Near Surface ◽  
Front Position

AbstractRecent studies indicate that the dynamics of fast-flowing, marine-terminating outlet glaciers of the Greenland ice sheet may be sensitive to climate and ocean forcing on sub-annual timescales. Observations of seasonal behavior of these glaciers at such high temporal resolution, however, are currently few. Here we present observations of front position, flow speed, near-surface air temperature and ocean conditions for six large marine-terminating glaciers in the Uummannaq region of West Greenland, to investigate controls on short-term glacier dynamics. As proposed by other studies, we find that seasonal front advance and retreat correlates with the formation and disappearance of an ice melange. Our data suggest that high sea-surface temperature, anomalously low sea-ice concentration and reduced melange formation in early 2003 have triggered multi-year retreat of several glaciers in the study area, which is consistent with other regions in Greenland. Of the stable glaciers, only Rink Isbræ exhibits a seasonal speed variation that correlates with variations in front position, with the others undergoing mid-summer deceleration that indicates the effects of subglacial meltwater discharge and drainage system evolution. Drainage of supraglacial lakes and water-filled crevasses results in substantial decreases in speed (40–60%) on fast-flowing glaciers. Our results demonstrate that attempts to model ice-sheet evolution must take into account short-timescale flow dynamics resulting from drainage events and oceanographic conditions.

scholarly journals PROMICE automatic weather station data

2021 ◽  
Author(s):  
Robert S. Fausto ◽  
Dirk van As ◽  
Kenneth D. Mankoff ◽  
Baptiste Vandecrux ◽  
Michele Citterio ◽  
...  
Keyword(s):  
Surface Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Weather Station ◽  
Automatic Weather Station ◽  
Atmospheric Conditions ◽  
Production Chain ◽  
Near Surface ◽  
Surface Mass ◽  
Future Assessment

Abstract. The Programme for Monitoring of the Greenland Ice Sheet (PROMICE) has been measuring climate and ice sheetproperties since 2007. Currently the PROMICE automatic weather station network includes 25 instrumented sites in Greenland.Accurate measurements of the surface and near-surface atmospheric conditions in a changing climate is important for reliablepresent and future assessment of changes to the Greenland ice sheet. Here we present the PROMICE vision, methodology,and each link in the production chain for obtaining and sharing quality-checked data. In this paper we mainly focus on thecritical components for calculating the surface energy balance and surface mass balance. A user-contributable dynamic webbaseddatabase of known data quality issues is associated with the data products at (https://github.com/GEUS-PROMICE/PROMICE-AWS-data-issues/). As part of the living data option, the datasets presented and described here are available atDOI: 10.22008/promice/data/aws, https://doi.org/10.22008/promice/data/aws (Fausto and van As, 2019).

scholarly journals The darkening of the Greenland ice sheet: trends, drivers, and projections (1981–2100)

2016 ◽  
Vol 10 (2) ◽  
pp. 477-496 ◽  
Author(s):  
Marco Tedesco ◽  
Sarah Doherty ◽  
Xavier Fettweis ◽  
Patrick Alexander ◽  
Jeyavinoth Jeyaratnam ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Aerosol Deposition ◽  
Near Surface ◽  
Multispectral Data ◽  
Warming Climate ◽  
Air Temperatures ◽  
Increasing Trends ◽  
Snow And Ice

Abstract. The surface energy balance and meltwater production of the Greenland ice sheet (GrIS) are modulated by snow and ice albedo through the amount of absorbed solar radiation. Here we show, using space-borne multispectral data collected during the 3 decades from 1981 to 2012, that summertime surface albedo over the GrIS decreased at a statistically significant (99 %) rate of 0.02 decade−1 between 1996 and 2012. Over the same period, albedo modelled by the Modèle Atmosphérique Régionale (MAR) also shows a decrease, though at a lower rate ( ∼ −0.01 decade−1) than that obtained from space-borne data. We suggest that the discrepancy between modelled and measured albedo trends can be explained by the absence in the model of processes associated with the presence of light-absorbing impurities. The negative trend in observed albedo is confined to the regions of the GrIS that undergo melting in summer, with the dry-snow zone showing no trend. The period 1981–1996 also showed no statistically significant trend over the whole GrIS. Analysis of MAR outputs indicates that the observed albedo decrease is attributable to the combined effects of increased near-surface air temperatures, which enhanced melt and promoted growth in snow grain size and the expansion of bare ice areas, and to trends in light-absorbing impurities (LAI) on the snow and ice surfaces. Neither aerosol models nor in situ and remote sensing observations indicate increasing trends in LAI in the atmosphere over Greenland. Similarly, an analysis of the number of fires and BC emissions from fires points to the absence of trends for such quantities. This suggests that the apparent increase of LAI in snow and ice might be related to the exposure of a "dark band" of dirty ice and to increased consolidation of LAI at the surface with melt, not to increased aerosol deposition. Albedo projections through to the end of the century under different warming scenarios consistently point to continued darkening, with albedo anomalies averaged over the whole ice sheet lower by 0.08 in 2100 than in 2000, driven solely by a warming climate. Future darkening is likely underestimated because of known underestimates in modelled melting (as seen in hindcasts) and because the model albedo scheme does not currently include the effects of LAI, which have a positive feedback on albedo decline through increased melting, grain growth, and darkening.

scholarly journals Supercooled liquid fogs over the central Greenland Ice Sheet

2019 ◽  
Vol 19 (11) ◽  
pp. 7467-7485
Author(s):  
Christopher J. Cox ◽  
David C. Noone ◽  
Max Berkelhammer ◽  
Matthew D. Shupe ◽  
William D. Neff ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Extreme Case ◽  
Supercooled Liquid ◽  
Surface Radiation ◽  
Radiative Properties ◽  
Small Contribution ◽  
Near Surface ◽  
Radiation Fogs

Abstract. Radiation fogs at Summit Station, Greenland (72.58∘ N, 38.48∘ W; 3210 m a.s.l.), are frequently reported by observers. The fogs are often accompanied by fogbows, indicating the particles are composed of liquid; and because of the low temperatures at Summit, this liquid is supercooled. Here we analyze the formation of these fogs as well as their physical and radiative properties. In situ observations of particle size and droplet number concentration were made using scattering spectrometers near 2 and 10 m height from 2012 to 2014. These data are complemented by colocated observations of meteorology, turbulent and radiative fluxes, and remote sensing. We find that liquid fogs occur in all seasons with the highest frequency in September and a minimum in April. Due to the characteristics of the boundary-layer meteorology, the fogs are elevated, forming between 2 and 10 m, and the particles then fall toward the surface. The diameter of mature particles is typically 20–25 µm in summer. Number concentrations are higher at warmer temperatures and, thus, higher in summer compared to winter. The fogs form at temperatures as warm as −5 ∘C, while the coldest form at temperatures approaching −40 ∘C. Facilitated by the elevated condensation, in winter two-thirds of fogs occurred within a relatively warm layer above the surface when the near-surface air was below −40 ∘C, as cold as −57 ∘C, which is too cold to support liquid water. This implies that fog particles settling through this layer of cold air freeze in the air column before contacting the surface, thereby accumulating at the surface as ice without riming. Liquid fogs observed under otherwise clear skies annually imparted 1.5 W m−2 of cloud radiative forcing (CRF). While this is a small contribution to the surface radiation climatology, individual events are influential. The mean CRF during liquid fog events was 26 W m−2, and was sometimes much higher. An extreme case study was observed to radiatively force 5 ∘C of surface warming during the coldest part of the day, effectively damping the diurnal cycle. At lower elevations of the ice sheet where melting is more common, such damping could signal a role for fogs in preconditioning the surface for melting later in the day.

Depth and properties of freshwater export from the Greenland Ice Sheet modulated by ice-ocean processes

2020 ◽  
Author(s):  
Donald Slater ◽  
Fiamma Straneo
Keyword(s):  
Large Scale ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Regional Variability ◽  
Near Surface ◽  
Fjord Circulation ◽  
Ocean Reanalyses ◽  
Freshwater Export ◽  
Ocean Processes

&lt;p&gt;Freshwater export from the Greenland Ice Sheet to the surrounding ocean has increased by 50% since the early 1990s, and may triple over the coming century under high greenhouse gas emissions. This increasing freshwater has the potential to influence both the regional and large-scale ocean, including marine ecosystems. Yet quantification of these impacts remains uncertain in part due to poor characterization of freshwater export, and in particular the transformation of freshwater around the ice sheet margin by ice-ocean processes, such as submarine melting, plumes and fjord circulation. Here, we combine in-situ observations, ocean reanalyses and simple models for ice-ocean processes to estimate the depth and properties of freshwater export around the full Greenland ice sheet from 1991 to present. The results show significant regional variability driven primarily by the depth at which freshwater runoff leaves the ice sheet. Areas with deeply-grounded marine-terminating glaciers are likely to export freshwater to the ocean as a dilute mixture of freshwater and externally-sourced deep water masses, while freshwater from areas with many land-terminating glaciers is exported as a more concentrated mixture of freshwater and near-surface waters. A handful of large glacier-fjord systems dominate ice sheet freshwater export, and the vast majority of freshwater export occurs subsurface. Our results provide an ice sheet-wide first-order characterization of how ice-ocean processes modulate Greenland freshwater export, and are an important step towards accurate representation of Greenland freshwater in large-scale ocean models.&lt;/p&gt;

Direct Detection of Atmospheric Atomic Bromine Leading to Mercury and Ozone Depletion

2020 ◽  
Author(s):  
Kerri Pratt ◽  
Siyuan Wang ◽  
Stephen McNamara ◽  
Christopher Moore ◽  
Daniel Obrist ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Direct Detection ◽  
Bromine Atom ◽  
Critical Role ◽  
Elemental Mercury ◽  
Atmospheric Mercury ◽  
The Arctic ◽  
Molecular Bromine ◽  
Near Surface ◽  
Halogen Chemistry

&lt;p&gt;Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. Yet, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic near Utqiagvik, Alaska in March 2012. Measured bromine atom levels reached up to 14 ppt (4.2&lt;strong&gt;&amp;#215;&lt;/strong&gt;10&lt;sup&gt;8 &lt;/sup&gt;atoms cm&lt;sup&gt;-3&lt;/sup&gt;) and were up to 3-10 higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study shows that measured bromine atoms, resulting from photochemical snowpack production of molecular bromine, can quantitatively explain ozone and mercury loss in the near-surface polar atmosphere.&lt;/p&gt;

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