Projecting circum-Arctic excess ground ice melt with a sub-grid representation in the Community Land Model

Abstract. To address the longstanding underrepresentation of the influences of highly variable ground ice content on the trajectory of permafrost conditions simulated in Earth System Models under a warming climate, we implement a sub-grid representation of excess ground ice within permafrost soils using the latest version of the Community Land Model (CLM5). Based on the original CLM5 tiling hierarchy, we duplicate the natural vegetated landunit by building extra tiles for up to three different excess ice conditions for each grid cell. For the same total amount of excess ice, introducing sub-grid variability in excess ice contents leads to different excess ice melting rates at the grid level. In addition, there are impacts on permafrost thermal properties and local hydrology with sub-grid representation. We evaluate this new development at a single-point at the Lena river delta, Siberia, where three sub-regions with distinctively different excess ice conditions are observed. A triple-landunit case accounting for this spatial variability conforms well to previous model studies for the Lena river delta and displays a markedly different dynamics of future excess ice thaw compared to a single-landunit case initialized with average excess ice contents. We prescribed a tiling scheme combined with our sub-grid representation to the global permafrost region using the dataset “Circum-Arctic Map of Permafrost and Ground-Ice Conditions” (Brown et al., 2002). The sub-grid scale excess ice produces significant melting of excess ice under a warming climate and enhances the representation of sub-grid variability of surface subsidence on a global scale. Our model development makes it possible to portray more details on the permafrost degradation trajectory depending on the sub-grid soil thermal regime and excess ice melting. The modeled permafrost degradation with sub-grid excess ice follows the pathway that continuous permafrost transforms into discontinuous permafrost before it disappears, including surface subsidence and talik formation, which are highly permafrost-relevant landscape changes excluded from most land models. Our development of sub-grid representation of excess ice demonstrates a way forward to enhance improve the realism of excess ice melt in global land models, but further developments rely on additional global observational datasets on both the horizontal and vertical distributions of excess ground ice.

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Projecting circum-Arctic excess-ground-ice melt with a sub-grid representation in the Community Land Model

The Cryosphere ◽

10.5194/tc-14-4611-2020 ◽

2020 ◽

Vol 14 (12) ◽

pp. 4611-4626

Author(s):

Lei Cai ◽

Hanna Lee ◽

Kjetil Schanke Aas ◽

Sebastian Westermann

Keyword(s):

Surface Subsidence ◽

Permafrost Degradation ◽

Ice Melting ◽

Ground Ice ◽

Lena River ◽

Land Unit ◽

Ice Melt ◽

Community Land Model ◽

Warming Climate ◽

Lena River Delta

Abstract. To address the long-standing underrepresentation of the influences of highly variable ground ice content on the trajectory of permafrost conditions simulated in Earth system models under a warming climate, we implement a sub-grid representation of excess ground ice within permafrost soils using the latest version of the Community Land Model (CLM5). Based on the original CLM5 tiling hierarchy, we duplicate the natural vegetated land unit by building extra tiles for up to three cryostratigraphies with different amounts of excess ice for each grid cell. For the same total amount of excess ice, introducing sub-grid variability in excess-ice contents leads to different excess-ice melting rates at the grid level. In addition, there are impacts on permafrost thermal properties and local hydrology with sub-grid representation. We evaluate this new development with single-point simulations at the Lena River delta, Siberia, where three sub-regions with distinctively different excess-ice conditions are observed. A triple-land-unit case accounting for this spatial variability conforms well to previous model studies for the Lena River delta and displays markedly different dynamics of future excess-ice thaw compared to a single-land-unit case initialized with average excess-ice contents. For global simulations, we prescribed a tiling scheme combined with our sub-grid representation to the global permafrost region using presently available circum-Arctic ground ice data. The sub-grid-scale excess ice produces significant melting of excess ice under a warming climate and enhances the representation of sub-grid variability of surface subsidence on a global scale. Our model development makes it possible to portray more details on the permafrost degradation trajectory depending on the sub-grid soil thermal regime and excess-ice melting, which also shows a strong indication that accounting for excess ice is a prerequisite of a reasonable projection of permafrost thaw. The modeled permafrost degradation with sub-grid excess ice follows the pathway that continuous permafrost transforms into discontinuous permafrost before it disappears, including surface subsidence and talik formation, which are highly permafrost-relevant landscape changes excluded from most land models. Our development of sub-grid representation of excess ice demonstrates a way forward to improve the realism of excess-ice melt in global land models, but further developments require substantially improved global observational datasets on both the horizontal and vertical distributions of excess ground ice.

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Projecting Circum-Arctic Excess Ground Ice Melt with a sub-grid representation in the Community Land Model

10.5194/tc-2019-230 ◽

2019 ◽

Author(s):

Lei Cai ◽

Hanna Lee ◽

Sebastian Westermann ◽

Kjetil Schanke Aas

Keyword(s):

Grid Point ◽

Melting Rate ◽

The Arctic ◽

Active Layer Thickness ◽

Ground Ice ◽

Soil Layers ◽

Ice Melt ◽

Community Land Model ◽

Vertical Distributions ◽

Ice Conditions

Abstract. We implement a sub-grid representation of excess ground ice within permafrost soils and its melting using the latest version of Community Land Model (CLM5). Based on the original CLM5 tiling hierarchy, we duplicate the natural vegetated landunit by building extra tiles for up to three different excess ice conditions in each grid point. Single-grid simulation cases initialize the same amount of excess ice in same soil layers, while prescribing different volumetric ice contents and sub-grid distributions. For the same total amount of excess ice initialized at the same soil layers, different sub-grid variability of excess ice leads to different excess ice melting rates on the grid level, as well as to different impacts to permafrost thermal properties and local hydrology. We prescribed a tiling scheme based on the dataset “Circum-Arctic Map of Permafrost and Ground-Ice Conditions” (Brown et al., 2002) within horizontal and vertical distributions of three different types of excess ice in the CLM grid to test applicability of sub-grid representation. Compared to the excess ice initialized homogeneously in each grid, the sub-grid scale excess ice and the tiling scheme amend the overly early timing of initial melting and the overly high melting rate of excess ice in warming climate. Initializing the excess ice depths according to local active layer thickness reduces underestimation of excess ice melt for the Arctic coastal regions. Further developments rely on additional global observational datasets on both the spatial and vertical distributions of excess ground ice, where our development of sub-grid representation demonstrated the potential for more realistically projecting excess ice melt in the circum-Arctic domain.

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Spatial analyses of thermokarst lakes and basins in Yedoma landscapes of the Lena Delta

The Cryosphere ◽

10.5194/tc-5-849-2011 ◽

2011 ◽

Vol 5 (4) ◽

pp. 849-867 ◽

Cited By ~ 83

Author(s):

A. Morgenstern ◽

G. Grosse ◽

F. Günther ◽

I. Fedorova ◽

L. Schirrmeister

Keyword(s):

Spatial Analyses ◽

Lena River ◽

Thermokarst Lakes ◽

Thermokarst Lake ◽

Warming Climate ◽

Future Potential ◽

Lake Drainage ◽

Carbon Balances ◽

Lena River Delta ◽

Ice Complex

Abstract. Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2% of the study area compared to 20.0% occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Future thermokarst lake expansion is similarly limited in most of Siberia's Yedoma regions covering about 106 km2, which has to be considered for water, energy, and carbon balances under warming climate scenarios.

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Spatial analyses of thermokarst lakes and basins in Yedoma landscapes of the Lena Delta

The Cryosphere Discussions ◽

10.5194/tcd-5-1495-2011 ◽

2011 ◽

Vol 5 (3) ◽

pp. 1495-1545 ◽

Cited By ~ 12

Author(s):

A. Morgenstern ◽

G. Grosse ◽

F. Günther ◽

I. Fedorova ◽

L. Schirrmeister

Keyword(s):

Developmental Stages ◽

Permafrost Degradation ◽

Lena River ◽

Thermokarst Lakes ◽

Carbon Release ◽

Future Potential ◽

Lake Drainage ◽

Landscape Units ◽

Lena River Delta ◽

Ice Complex

Abstract. Distinctive periglacial landscapes have formed in late-Pleistocene ice-rich permafrost deposits (Ice Complex) of Northern Yakutia, Siberia. Thermokarst lakes and thermokarst basins alternate with ice-rich Yedoma uplands. We investigate different thermokarst stages in Ice Complex deposits of the Lena River Delta using remote sensing and geoinformation techniques. The morphometry and spatial distribution of thermokarst lakes on Yedoma uplands, thermokarst lakes in basins, and thermokarst basins are analyzed, and possible dependence upon relief position and cryolithological context is considered. Of these thermokarst stages, developing thermokarst lakes on Yedoma uplands alter ice-rich permafrost the most, but occupy only 2.2 % of the study area compared to 20.0 % occupied by thermokarst basins. The future potential for developing large areas of thermokarst on Yedoma uplands is limited due to shrinking distances to degradational features and delta channels that foster lake drainage. Further thermokarst development in existing basins is restricted to underlying deposits that have already undergone thaw, compaction, and old carbon mobilization, and to deposits formed after initial lake drainage. Therefore, a distinction between developmental stages of thermokarst and landscape units is necessary to assess the potential for future permafrost degradation and carbon release due to thermokarst in Siberian Yedoma landscapes.

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Spatiotemporal variability of methane emissions of tundra landscapes in the Lena River Delta, Siberia

10.5194/egusphere-egu2020-17937 ◽

2020 ◽

Author(s):

Lars Kutzbach ◽

Norman Rößger ◽

Tim Eckhardt ◽

Christian Knoblauch ◽

Torsten Sachs ◽

...

Keyword(s):

Spatial Variability ◽

Growing Season ◽

Landscape Scale ◽

River Delta ◽

The Other ◽

Permafrost Degradation ◽

River Terrace ◽

Lena River ◽

River Terraces ◽

Lena River Delta

Increased methane (CH4) release from a warming Arctic is expected to be a major feedback on the global climate. However, due to the complex effects of climate change on arctic geoecosystems, projections of future CH4 emissions are highly uncertain. CH4 emissions from complex tundra landscapes will be controlled not only by direct climatic effects on production, oxidation and transport of CH4 but, importantly, also by geomorphology and hydrology changes caused by gradual or abrupt permafrost degradation. Therefore, improving our understanding of both the temporal dynamics and the spatial heterogeneity of CH4 fluxes on multiple scales is still necessary.Here, we present pedon- and landscape-scale CH4 flux measurements at two widespread tundra landscapes (active floodplains and late-holocene river terraces) of the Lena River Delta in the Siberian Arctic (72.4&#176; N, 126.5&#176; E). The dominating scales of spatial variability of soil, vegetation and CH4 fluxes differ between the two landscapes of different geological development stage. The active floodplains are characterized by sandy beaches and ridges, and backswamp depressions, forming a mesorelief with height differences of several meters on horizontal scales of 10-1000 m. On the other hand, the river terraces are characterized by the formation of ice-wedge polygons, which lead to a regular microrelief with height differences of several decimeters on horizontal scales of 1 to 10 meters. CH4 fluxes were investigated on the landscape scale with the eddy covariance method (15 campaigns during 2002-2018 at the river terrace, 2 campaigns 2014-2015 at the floodplain) and on the pedon scale with chamber methods (campaigns at different sites in 2002, 2006, 2013, 2014, 2015).Average growing season (June-September) CH4 flux for the floodplain was 166 &#177; 4 mmol m-2 (n=2) and for the river terrace 100 &#177; 25 mmol m-2 (n=15). There was pronounced spatial variability of CH4 fluxes within both tundra landscapes types. On the river terrace, growing season CH4 flux was only 20-40 mmol m-2 at elevated polygon rims and polygon high centers, respectively, and up to 300 mmol m-2 at polygon low centers. On the floodplain, CH4 flux was as low as 5 mmol m-2 at sandy ridges and above 400 mmol m-2 in backswamp depressions. Mean growing season CH4 fluxes at the river terrace were positively linearly correlated (r2 = 0.9, n=15) to growing-degree-days (base temperature of 5 &#176;C). Our findings suggest that a warmer climate stimulates the production of CH4, which is directly reflected in increased CH4 emissions. On the other hand, warming effects on CH4 oxidation appear limited because transport processes that bypass the soil oxidation zone, i.e. plant-mediated transport and ebullition, dominate CH4 emission from wet tundra landscapes. However, since CH4 emissions strongly vary with (micro-)topographical situation within tundra landscapes, the changes of geomorphology and hydrology due to permafrost degradation will probably be the dominating driver of future CH4 emissions from arctic tundra landscapes.

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Supplementary material to "Projecting circum-Arctic excess ground ice melt with a sub-grid representation in the Community Land Model"

10.5194/tc-2020-91-supplement ◽

2020 ◽

Author(s):

Lei Cai ◽

Hanna Lee ◽

Kjetil Schanke Aas ◽

Sebastian Westermann

Keyword(s):

Ground Ice ◽

Ice Melt ◽

Community Land Model ◽

Supplementary Material

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Subrecent Spore-Pollen Spectra and Modern Vegetation from the Lena River Delta, Russian Arctic

Сибирский экологический журнал ◽

10.15372/sej20170407 ◽

2017 ◽

Keyword(s):

River Delta ◽

Russian Arctic ◽

Lena River ◽

Lena River Delta

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Hydrological Response of a Patchy High Arctic Wetland

Hydrology Research ◽

10.2166/nh.2000.0019 ◽

2000 ◽

Vol 31 (4-5) ◽

pp. 317-338 ◽

Cited By ~ 21

Author(s):

Kathy L. Young ◽

Ming-ko Woo

Keyword(s):

Weather Conditions ◽

High Arctic ◽

Ground Ice ◽

Ice Melt ◽

Snow Storage ◽

Streamflow Response ◽

Dry Seasons ◽

And Storage ◽

Surface And Subsurface Flow ◽

Present Understanding

High Arctic patchy wetlands are ecological oases in a polar desert environment and are vulnerable to climatic warming. At present, understanding of their responses to external factors (climate and terrain) is limited. This study examines a wetland located in a topographic depression maintained by seasonal snowmelt, ground ice melt and lateral inflows. The wetland is located on Cornwallis Island, Nunavut, Canada. Hydrological, climatological and soil observations were made over several summers with different weather conditions. The summers of 1996 and 1997 were cool and wet but the summer of 1998 was warm and dry. The melt in 1996 was rapid due to rain on snow events and only lasted six days. Deeper snow in 1997 prolonged the melt season to 18 days. A shallow snow-cover in 1998 and early melt depleted the snow by early June. Surface, groundwater and storage fluctuations in the wetland were dictated by snowmelt, rainfall, evaporation loss from the wetland and lateral inputs which in turn were controlled by the melting of the late-lying snow storage in the catchment. Soil factors influence the spatial variations in ground thaw which affects the surface and subsurface flow. Streamflow response of the wetland reflects a nival regime and augmentation of streamflow thoughout the summer season in all three years is supported by multiple water sources: ground ice melt and suprapermafrost water from a large late-lying snowpack. Overall, this study suggests that the survival of some patchy wetlands depends on their interaction with the surrounding basin, with a dependency probably being more important during warm and dry seasons.

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