scholarly journals An improved estimate of microbially mediated carbon fluxes from the Greenland ice sheet

2012 ◽  
Vol 58 (212) ◽  
pp. 1098-1108 ◽  
Author(s):  
J.M. Cook ◽  
A.J. Hodson ◽  
A.M. Anesio ◽  
E. Hanna ◽  
M. Yallop ◽  
...  
Keyword(s):  
Carbon Fixation ◽  
Ice Sheet ◽  
Stable State ◽  
Greenland Ice Sheet ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Biological Production ◽  
Spatial Uniformity ◽  
Annual Carbon ◽  
Order Of Magnitude

AbstractMicrobially mediated carbon fluxes on the surface of the Greenland ice sheet (GrIS) were recently quantified by Hodson and others (2010) using measurements of the surface coverage of debris (cryoconite) and rates of biological production associated with debris near the ice-sheet margin. We present updated models that do not assume the same spatial uniformity in key parameters employed by Hodson and others (2010) because they make use of biomass distribution and biological production data from a 79 km transect of the GrIS. Further, the models presented here also include for the first time biomass associated with both cryoconite holes and surficial algae. The predicted annual carbon flux for a small (1600 km2) section of ice surrounding the field transect is about four times that estimated using spatially uniform biomass and production in this area. When surficial algae are included, the model predicts about 11 times more carbon fixation via photosynthesis per year than the cryoconite-only models. We therefore suggest that supraglacial carbon fluxes from the GrIS have previously been underestimated by more than an order of magnitude and that the hitherto overlooked surficial algal ecosystem can be the most crucial contributor. The GrIS is shown to be in a relatively stable state of net autotrophy according to our model and so a strong link between bare-ice area and total carbon fluxes is evident. The implication is a biomass feedback to surface albedo and enhanced ablation as a result. Climate predictions for the year 2100 show that greater carbon fixation could also result from climate warming.

scholarly journals The cryoconite ecosystem on the Greenland ice sheet

2010 ◽  
Vol 51 (56) ◽  
pp. 123-129 ◽  
Author(s):  
Andy Hodson ◽  
Carl Bøggild ◽  
Edward Hanna ◽  
Phillipe Huybrechts ◽  
Harry Langford ◽  
...  
Keyword(s):  
Biological Activity ◽  
Carbon Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Balance Model ◽  
Surface Mass ◽  
Ice Surface ◽  
Accurate Quantification

AbstractThis paper presents an assessment of biological activity associated with ice surface debris (cryoconite) at the ice-sheet scale. Estimates of the mass distribution of cryoconite over the Greenland ice sheet (GIS) and the biological activity associated with it are presented and then coupled with a surface mass-balance model to estimate total carbon fluxes due to respiration and photosynthesis. We find an average loading of 66gm−2 at Kangerlussuaq, southwest Greenland, which compares well with recent estimates from Kronprins Christians Land (17–440 gm−2: Bøggild and others, 2010) in northeast Greenland. We also report a significant microbial biomass in cryoconite at both these places (103–104 cells mg−1) and carbon fluxes of the order of 1–3 μM C g−1d−1 for both respiration and photosynthesis. The modelling indicates that total respiration and photosynthesis fluxes are likely to be ∼101–102 GgCa−1 and thus far from trivial. However, estimation of the net ecosystem impact across the entire ice sheet on atmospheric CO2 concentrations is problematic because photosynthesis rates were almost certainly low during our field campaign. Therefore, like its water balance, the carbon balance of the GIS is now known to be important, but its accurate quantification will remain elusive until more data are forthcoming.

scholarly journals Hydraulic transmissivity inferred from ice-sheet relaxation following Greenland supraglacial lake drainages

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ching-Yao Lai ◽  
Laura A. Stevens ◽  
Danielle L. Chase ◽  
Timothy T. Creyts ◽  
Mark D. Behn ◽  
...  
Keyword(s):  
Laboratory Experiments ◽  
Ice Sheet ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Field Observations ◽  
Surface Uplift ◽  
Drainage Networks ◽  
Order Of Magnitude ◽  
Lake Drainage ◽  
Magnitude Increase

AbstractSurface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye and gas-tracing studies conducted in the western margin sector of the ice sheet have directly observed drainage efficiency to evolve seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we infer drainage system transmissivity based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity (from 0.8 ± 0.3 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 to 215 ± 90.2 $${\rm{m}}{{\rm{m}}}^{3}$$ m m 3 ) as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes driven by seasonal meltwater input.

scholarly journals Discharge of debris from ice at the margin of the Greenland ice sheet

2002 ◽  
Vol 48 (161) ◽  
pp. 192-198 ◽  
Author(s):  
Peter G. Knight ◽  
Richard I. Waller ◽  
Carrie J. Patterson ◽  
Alison P. Jones ◽  
Zoe P. Robinson
Keyword(s):  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
High Rate ◽  
Outlet Glacier ◽  
Tidewater Glaciers ◽  
Sediment Production ◽  
Basal Ice ◽  
Order Of Magnitude ◽  
Sediment Transfer ◽  
A Minor

AbstractSediment production at a terrestrial section of the ice-sheet margin in West Greenland is dominated by debris released through the basal ice layer. The debris flux through the basal ice at the margin is estimated to be 12–45 m3 m−1 a−1. This is three orders of magnitude higher than that previously reported for East Antarctica, an order of magnitude higher than sites reported from in Norway, Iceland and Switzerland, but an order of magnitude lower than values previously reported from tidewater glaciers in Alaska and other high-rate environments such as surging glaciers. At our site, only negligible amounts of debris are released through englacial, supraglacial or subglacial sediment transfer. Glaciofluvial sediment production is highly localized, and long sections of the ice-sheet margin receive no sediment from glaciofluvial sources. These findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin. These data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the Greenland ice sheet.

scholarly journals Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

2013 ◽  
Vol 10 (12) ◽  
pp. 19311-19345 ◽  
Author(s):  
E. C. Lawson ◽  
J. L. Wadham ◽  
M. Tranter ◽  
M. Stibal ◽  
G. P. Lis ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
River System ◽  
The Arctic ◽  
Marine Microorganisms ◽  
The North ◽  
Glacial Runoff ◽  
Order Of Magnitude ◽  
Free Carbohydrates

Abstract. Runoff from small glacier systems contains dissolved organic carbon (DOC), rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr−1). We report high and episodic fluxes of POC and DOC from a large (1200 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70–89% on average), is sourced from the ice sheet bed and contains a significant bioreactive component (9% carbohydrates). A major source for the "bioavailable" (free carbohydrates) LMW-DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW-DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (30–58%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the ~ 2 fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating supply-limitation of suspended sediment in runoff. Scaled to the GrIS, the combined DOC and POC fluxes (0.13–0.17 Tg C yr−1 DOC, 0.36–1.52 Tg C yr−1 mean POC) are of a similar order of magnitude to a large Arctic river system, and hence represent an important OC source to the North Atlantic, Greenland and Labrador Seas.

scholarly journals Open fires in Greenland: an unusual event and its impact on the albedo of the Greenland Ice Sheet

2018 ◽  
Author(s):  
Nikolaos Evangeliou ◽  
Arve Kylling ◽  
Sabine Eckhardt ◽  
Viktor Myroniuk ◽  
Kerstin Stebel ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Dispersion Model ◽  
Large Fraction ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Particle Dispersion ◽  
Data Sets ◽  
Average Value ◽  
Unusual Event ◽  
Order Of Magnitude

Abstract. Highly unusual open fires burned in Western Greenland between 31 July and 21 August 2017, after a period of warm, dry and sunny weather. The fires burned on peat lands that became vulnerable to fires by permafrost thawing. We used several satellite data sets to estimate that the total area burned was about 2345 hectares. Based on assumptions of typical burn depths and BC emission factors for peat fires, we estimate that the fires consumed a fuel amount of about 117 kt C and produced BC emissions of about 23.5 t. We used the Lagrangian particle dispersion model to simulate the atmospheric BC transport and deposition. We find that the smoke plumes were often pushed towards the Greenland Ice Sheet by westerly winds and thus a large fraction of the BC emissions (7 t or 30 %) was deposited on snow or ice covered surfaces. The calculated BC deposition was small compared to BC deposition from global sources, but not entirely negligible. Analysis of aerosol optical depth data from three sites in Western Greenland in August 2017 showed strong influence of forest fire plumes from Canada, but little impact of the Greenland fires. Nevertheless, CALIOP lidar data showed that our model captured very effectively the presence and structure of the plume from the Greenland fires. The albedo changes and instantaneous surface radiative forcing in Greenland due to the fire BC emissions were estimated with the SNICAR model and the uvspec model from the libRadtran radiative transfer software package. We estimate that the maximum albedo change due to the BC deposition was about 0.006, too small to be measured by satellites or other means. The average instantaneous surface radiative forcing over Greenland at noon on 31 August was 0.03 W m−2, with locally occurring maximum values of 0.63 W m−2. The average value is at least an order of magnitude smaller than the radiative forcing due to BC from other sources. Overall, the fires burning in Greenland in summer of 2017 had little impact on BC deposition on the Greenland Ice Sheet, causing almost negligible extra radiative forcing. This was due to the – in a global context – still rather small size of the fires. However, the very large fraction of the BC emissions deposited on the Greenland Ice Sheet makes these fires very efficient climate forcers on a per unit emission basis. If the expected further warming of Greenland produces much larger fires in the future, this could indeed cause substantial albedo changes and thus lead to accelerated melting of the Greenland Ice Sheet. The fires burning in 2017 may be a harbinger of such future changes.

scholarly journals Modelling the genesis of equatorial podzols: age and implications for carbon fluxes

2017 ◽  
Vol 14 (9) ◽  
pp. 2429-2440 ◽  
Author(s):  
Cédric Doupoux ◽  
Patricia Merdy ◽  
Célia Régina Montes ◽  
Naoise Nunan ◽  
Adolpho José Melfi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Organic C ◽  
Perched Water Table ◽  
C Dynamics ◽  
14C Age ◽  
Order Of Magnitude ◽  
Over Time ◽  
Main Carbon

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon River. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retrocalculations to take into account the bomb carbon in the young topsoil horizons (calculated apparent 14C age from 62 to 109 years). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (calculated apparent 14C age 6.8  ×  103 and 8.4  ×  103 years) and two profiles with a very old Bh (calculated apparent 14C age 23.2  ×  103 and 25.1  ×  103 years). The calculated fluxes from the topsoil to the perched water table indicate that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15  ×  103 and 130  ×  103 years for the two younger and two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15  ×  103–25  ×  103 and 150  ×  103–250  ×  103 years, respectively.

scholarly journals Carbon fixation prediction during a bloom of <i>Emiliania huxleyi</i> is highly sensitive to the assumed regulation mechanism

2009 ◽  
Vol 6 (3) ◽  
pp. 5339-5372 ◽  
Author(s):  
O. Bernard ◽  
A. Sciandra ◽  
S. Rabouille
Keyword(s):  
Large Scale ◽  
Carbon Fixation ◽  
Co2 Concentration ◽  
Carbon Fluxes ◽  
Emiliania Huxleyi ◽  
Regulation Mechanism ◽  
Fixation Rate ◽  
Saturation State ◽  
Calcite Saturation ◽  
Order Of Magnitude

Abstract. Large scale precipitation of calcium carbonate in the oceans by coccolithophorids plays an important role in carbon sequestration. However, there is a controversy on the effect of an increase in atmospheric CO2 concentration on both calcification and photosynthesis of coccolithophorids. Indeed recent experiments, performed under nitrogen limitation, revealed that the associated fluxes may be slowed down, while other authors claim the reverse. We designed models to account for various scenarii of calcification and photosynthesis regulation in chemostat cultures of Emiliania huxleyi, based on different hypotheses on the regulation mechanism. These models consider that either carbon dioxide, bicarbonate, carbonate or calcite saturation state (Ω) is the regulating factor. All were calibrated to predict the same carbon fixation rate in nowadays pCO2, but they turn out to respond differently to an increase in CO2 concentration. Thus, using the four possible models, we simulated a large bloom of Emiliania huxleyi. It results that models assuming a regulation by CO32− or Ω predicted much higher carbon fluxes. The response when considering a doubled pCO2 was different and models controlled by CO2 or HCO3 − led to increased carbon fluxes. In addition, the variability between the various scenarii proved to be in the same order of magnitude than the response to pCO2 increase. These sharp discrepancies reveal the consequences of model assumptions on the simulation outcome.

scholarly journals Greenland Ice Sheet exports labile organic carbon to the Arctic oceans

2014 ◽  
Vol 11 (14) ◽  
pp. 4015-4028 ◽  
Author(s):  
E. C. Lawson ◽  
J. L. Wadham ◽  
M. Tranter ◽  
M. Stibal ◽  
G. P. Lis ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
River System ◽  
The Arctic ◽  
Marine Microorganisms ◽  
Glacial Runoff ◽  
Order Of Magnitude ◽  
Free Carbohydrates ◽  
Bioavailable Carbon

Abstract. Runoff from small glacier systems contains dissolved organic carbon (DOC) rich in protein-like, low molecular weight (LMW) compounds, designating glaciers as an important source of bioavailable carbon for downstream heterotrophic activity. Fluxes of DOC and particulate organic carbon (POC) exported from large Greenland catchments, however, remain unquantified, despite the Greenland Ice Sheet (GrIS) being the largest source of global glacial runoff (ca. 400 km3 yr−1). We report high and episodic fluxes of POC and DOC from a large (>600 km2) GrIS catchment during contrasting melt seasons. POC dominates organic carbon (OC) export (70–89% on average), is sourced from the ice sheet bed, and contains a significant bioreactive component (9% carbohydrates). A major source of the "bioavailable" (free carbohydrate) LMW–DOC fraction is microbial activity on the ice sheet surface, with some further addition of LMW–DOC to meltwaters by biogeochemical processes at the ice sheet bed. The bioavailability of the exported DOC (26–53%) to downstream marine microorganisms is similar to that reported from other glacial watersheds. Annual fluxes of DOC and free carbohydrates during two melt seasons were similar, despite the approximately two-fold difference in runoff fluxes, suggesting production-limited DOC sources. POC fluxes were also insensitive to an increase in seasonal runoff volumes, indicating a supply limitation in suspended sediment in runoff. Scaled to the GrIS, the combined DOC (0.13–0.17 Tg C yr−1 (±13%)) and POC fluxes (mean = 0.36–1.52 Tg C yr−1 (±14%)) are of a similar order of magnitude to a large Arctic river system, and hence may represent an important OC source to the near-coastal North Atlantic, Greenland and Labrador seas.

scholarly journals Modelling the genesis of equatorial podzols: age and implications on carbon fluxes

2017 ◽  
Author(s):  
Cédric Doupoux ◽  
Patricia Merdy ◽  
Célia Régina Montes ◽  
Naoise Nunan ◽  
Adolpho José Melfi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Carbon Fluxes ◽  
Total Carbon ◽  
Organic C ◽  
Perched Water Table ◽  
C Dynamics ◽  
14C Age ◽  
Order Of Magnitude ◽  
Over Time ◽  
Main Carbon

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon river. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carbon-containing horizons, i.e. the topsoil and deep Bh. We performed retro calculations to take in account the bomb carbon in the young topsoil horizons (14C age from 62 to 109 y). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (14C age 6.8 × 103 and 8.4 × 103 y) and two profiles with a very old Bh (14C age 23.2 × 103 and 25.1 × 103 y). The calculated fluxes from the topsoil to the perched water-table indicates that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15 × 103 and 130 × 103 y for the two younger and the two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15 × 103–25 × 103 and 150 × 103–250 × 103 y, respectively.

Seasonally evolving hydraulic transmissivity beneath Greenland supraglacial lakes

2020 ◽  
Author(s):  
Ching-Yao Lai ◽  
Laura Stevens ◽  
Danielle Chase ◽  
Timothy Creyts ◽  
Mark Behn ◽  
...  
Keyword(s):  
Ice Sheet ◽  
Drainage System ◽  
Greenland Ice Sheet ◽  
Dye Tracing ◽  
Surface Uplift ◽  
Supraglacial Lakes ◽  
Drainage Networks ◽  
Order Of Magnitude ◽  
Novel Method ◽  
Lake Drainage

Abstract Surface meltwater reaching the base of the Greenland Ice Sheet transits through drainage networks, modulating the flow of the ice sheet. Dye-tracing studies indicate that drainage efficiency evolves seasonally along the drainage pathway. However, the local evolution of drainage systems further inland, where ice thicknesses exceed 1000 m, remains largely unknown. Here, we develop a novel method to infer transmissivity of the drainage system based on surface uplift relaxation following rapid lake drainage events. Combining field observations of five lake drainage events with a mathematical model and laboratory experiments, we show that the surface uplift decreases exponentially with time, as the water in the blister formed beneath the drained lake permeates through the subglacial drainage system. This deflation obeys a universal relaxation law with a timescale that reveals hydraulic transmissivity and indicates a two-order-of-magnitude increase in subglacial transmissivity as the melt season progresses, suggesting significant changes in basal hydrology beneath the lakes.

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