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Ghislain Picard, Marion Leduc-Leballeur, Alison F. Banwell, Ludovic Brucker, Giovanni Macelloni. (2022). The sensitivity of satellite microwave observations to liquid water in the Antarctic snowpack (Vol. 16).
Abstract: Surface melting on the Antarctic Ice Sheet has been monitored by satellite microwave radiometry for over 40 years. Despite this long perspective, our understanding of the microwave emission from wet snow is still limited, preventing the full exploitation of these observations to study supraglacial hydrology. Using the Snow Microwave Radiative Transfer (SMRT) model, this study investigates the sensitivity of microwave brightness temperature to snow liquid water content at frequencies from 1.4 to 37 GHz. We first determine the snowpack properties for eight selected coastal sites by retrieving profiles of density, grain size and ice layers from microwave observations when the snowpack is dry during wintertime. Second, a series of brightness temperature simulations is run with added water. The results show that (i) a small quantity of liquid water (≈0.5 kg m−2) can be detected, but the actual quantity cannot be retrieved out of the full range of possible water quantities; (ii) the detection of a buried wet layer is possible up to a maximum depth of 1 to 6 m depending on the frequency (6–37 GHz) and on the snow properties (grain size, density) at each site; (iii) surface ponds and water-saturated areas may prevent melt detection, but the current coverage of these waterbodies in the large satellite field of view is presently too small in Antarctica to have noticeable effects; and (iv) at 1.4 GHz, while the simulations are less reliable, we found a weaker sensitivity to liquid water and the maximal depth of detection is relatively shallow (<10 m) compared to the typical radiation penetration depth in dry firn (≈1000 m) at this low frequency. These numerical results pave the way for the development of improved multi-frequency algorithms to detect melt intensity and the depth of liquid water below the surface in the Antarctic snowpack.
Programme: 1110
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Dominic Saunderson, Andrew Mackintosh, Felicity McCormack, Richard Selwyn Jones, Ghislain Picard. (2022). Surface melt on the Shackleton Ice Shelf, East Antarctica (2003–2021) (Vol. 16).
Abstract: Melt on the surface of Antarctic ice shelves can potentially lead to their disintegration, accelerating the flow of grounded ice to the ocean and raising global sea levels. However, the current understanding of the processes driving surface melt is incomplete, increasing uncertainty in predictions of ice shelf stability and thus of Antarctica's contribution to sea-level rise. Previous studies of surface melt in Antarctica have usually focused on either a process-level understanding of melt through energy-balance investigations or used metrics such as the annual number of melt days to quantify spatiotemporal variability in satellite observations of surface melt. Here, we help bridge the gap between work at these two scales. Using daily passive microwave observations from the AMSR-E and AMSR-2 sensors and the machine learning approach of a self-organising map, we identify nine representative spatial distributions (“patterns”) of surface melt on the Shackleton Ice Shelf in East Antarctica from 2002/03–2020/21. Combined with output from the RACMO2.3p3 regional climate model and surface topography from the REMA digital elevation model, our results point to a significant role for surface air temperatures in controlling the interannual variability in summer melt and also reveal the influence of localised controls on melt. In particular, prolonged melt along the grounding line shows the importance of katabatic winds and surface albedo. Our approach highlights the necessity of understanding both local and large-scale controls on surface melt and demonstrates that self-organising maps can be used to investigate the variability in surface melt on Antarctic ice shelves.
Programme: 1110
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Gauthier Vérin, Florent Domine, Marcel Babin, Ghislain Picard, Laurent Arnaud. (2022). Metamorphism of snow on Arctic sea ice during the melt season: impact on spectral albedo and radiative fluxes through snow (Vol. 16).
Abstract: The energy budget of Arctic sea ice is strongly affected by the snow cover. Intensive sampling of snow properties was conducted near Qikiqtarjuaq in Baffin Bay on typical landfast sea ice during two melt seasons in 2015 and 2016. The sampling included stratigraphy, vertical profiles of snow specific surface area (SSA), density and irradiance, and spectral albedo (300–1100 nm). Both years featured four main phases: (I) dry snow cover, (II) surface melting, (III) ripe snowpack, and (IV) melt pond formation. Each phase was characterized by distinctive physical and optical properties. A high SSA value of 49.3 m2 kg−1 was measured during phase I on surface wind slabs together with a corresponding broadband albedo (300–3000 nm) of 0.87. Phase II was marked by alternating episodes of surface melting, which dramatically decreased the SSA below 3 m2 kg−1, and episodes of snowfall re-establishing pre-melt conditions. Albedo was highly time-variable, with minimum broadband values around 0.70. In phase III, continued melting led to a fully ripe snowpack composed of clustered rounded grains. Albedo began to decrease in the visible as snow thickness decreased but remained steady at longer wavelengths. Moreover, significant spatial variability appeared for the first time following snow depth heterogeneity. Spectral albedo was simulated by radiative transfer using measured SSA and density vertical profiles and estimated impurity contents based on limited measurements. Simulations were most of the time within 1 % of measurements in the visible and within 2 % in the infrared. Simulations allowed the calculations of albedo and of the spectral flux at the snow–ice interface. These showed that photosynthetically active radiation fluxes at the bottom of the snowpack durably exceeded 5 W m−2 (∼9.2 µmol m−2 s−1) only when the snowpack thickness started to decrease at the end of phase II.
Programme: 1042
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Georg Lackner, Florent Domine, Daniel F. Nadeau, Matthieu Lafaysse, Marie Dumont. (2022). Snow properties at the forest–tundra ecotone: predominance of water vapor fluxes even in deep, moderately cold snowpacks (Vol. 16).
Abstract: The forest–tundra ecotone is a large circumpolar transition zone between the Arctic tundra and the boreal forest, where snow properties are spatially variable due to changing vegetation. The extent of this biome through all circumpolar regions influences the climate. In the forest–tundra ecotone near Umiujaq in northeastern Canada (56∘33′31′′ N, 76∘28′56′′ W), we contrast the snow properties between two sites, TUNDRA (located in a low-shrub tundra) and FOREST (located in a boreal forest), situated less than 1 km apart. Furthermore, we evaluate the capability of the snow model Crocus, initially developed for alpine snow, to simulate the snow in this subarctic setting. Snow height and density differed considerably between the two sites. At FOREST, snow was about twice as deep as at TUNDRA. The density of snow at FOREST decreased slightly from the ground to the snow surface in a pattern that is somewhat similar to alpine snow. The opposite was observed at TUNDRA, where the pattern of snow density was typical of the Arctic. We demonstrate that upward water vapor transport is the dominant mechanism that shapes the density profile at TUNDRA, while a contribution of compaction due to overburden becomes visible at FOREST. Crocus was not able to reproduce the density profiles at either site using its standard configuration. We therefore implemented some modifications for the density of fresh snow, the effect of vegetation on compaction, and the lateral transport of snow by wind. These adjustments partly compensate for the lack of water vapor transport in the model but may not be applicable at other sites. Furthermore, the challenges using Crocus suggest that the general lack of water vapor transport in the snow routines used in climate models leads to an inadequate representation of the density profiles of even deep and moderately cold snowpacks, with possible major impacts on meteorological forecasts and climate projections.
Programme: 1042
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Georg Lackner, Florent Domine, Daniel F. Nadeau, Annie-Claude Parent, François Anctil, Matthieu Lafaysse, Marie Dumont. (2022). On the energy budget of a low-Arctic snowpack (Vol. 16).
Abstract: Arctic landscapes are covered in snow for at least 6 months of the year. The energy balance of the snow cover plays a key role in these environments, influencing the surface albedo, the thermal regime of the permafrost, and other factors. Our goal is to quantify all major heat fluxes above, within, and below a low-Arctic snowpack at a shrub tundra site on the east coast of Hudson Bay in eastern Canada. The study is based on observations from a flux tower that uses the eddy covariance approach and from profiles of temperature and thermal conductivity in the snow and soil. Additionally, we compared the observations with simulations produced using the Crocus snow model. We found that radiative losses due to negative longwave radiation are mostly counterbalanced by the sensible heat flux, whereas the latent heat flux is minimal. At the snow surface, the heat flux into the snow is similar in magnitude to the sensible heat flux. Because the snow cover stores very little heat, the majority of the upward heat flux in the snow is used to cool the soil. Overall, the model was able to reproduce the observed energy balance, but due to the effects of atmospheric stratification, it showed some deficiencies when simulating turbulent heat fluxes at an hourly timescale.
Programme: 1042
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Pierre Stephan, Lancelot Massé, David Dider, Ronan Autret, Antoine Soloy, Serge Suanez. (2022). Pluri-annual morphological and sedimentological changes of the Valahnúkur boulder barrier, SW Iceland.
Abstract: While recent studies highlighted the great mobility of boulder beaches related to the impact of storm waves, numerous researches are still needed to better understand the morphodynamic of coastal boulder accumulations. This paper provides original data about pluri-annual morphological and sedimentological changes, as well as storm-induced geomorphic processes and their impact on the Valahnúkur boulder barrier, in the south-west of Iceland. First described by Etienne & Paris (2010), this massive accumulation of boulders shows numerous evidences of coastal barrier flooding and intense boulder mobility. Between May 2015 and May 2021, a topo-morphological survey was undertaken to analyze and quantify both cross-shore and longshore morphosedimentary processes of the Valahnúkur boulder barrier and surrounding areas. Annual campaigns of UAV (Unmanned Aerial Vehicle) flights were conducted in order to produce a set of Digital Elevation Models (DEMs) and Orthophotographs using Structure-from-Motion photogrammetry. DEMs were compared to deduce the morphological changes. Orthophotographs were analyzed from a deep learning-based method to estimate the changes in the spatial distribution of boulder sizes. Hydrodynamic conditions were reconstructed using wave buoy and tide gauge measurements. Wave runup were calibrated from the analysis of a wave/swash motion data set acquired by video monitoring related to different hydrodynamic conditions. The chronology of extreme water levels has been reconstructed on this high refective beach to estimate the elevation of the wave action during the survey period. From the sediment budget calculation, a significant northward longshore drift of around 1000 m3/a is highlighted on the beachface. The ridge and back-barrier areas were dominated by accretion related to cross-shore boulder transport from the beach. The volume of transported boulders is highly variable according to hydrodynamic conditions. Although the morphogenic impact of winter storms is difficult to assess, the observed morphological changes suggest processes dominated by swash, overtopping and overwash. The boulder size analysis highlights a link between the boulders mass and their movement landward. Video monitoring indicates that the amplitude of the swash is quite similar whether the hydrodynamic conditions are normal or energetic. The high porosity of the barrier appears to be a key factor in the dissipation of wave energy.
Programme: 1216
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Ole Richter, David E. Gwyther, Benjamin K. Galton-Fenzi, Kaitlin A. Naughten. (2022). The Whole Antarctic Ocean Model (WAOM v1.0): development and evaluation (Vol. 15).
Abstract: The Regional Ocean Modeling System (ROMS), including an ice shelf component, has been applied on a circum-Antarctic domain to derive estimates of ice shelf basal melting. Significant improvements made compared to previous models of this scale are the inclusion of tides and a horizontal spatial resolution of 2 km, which is sufficient to resolve on-shelf heat transport by bathymetric troughs and eddy-scale circulation. We run the model with ocean–atmosphere–sea ice conditions from the year 2007 to represent nominal present-day climate. We force the ocean surface with buoyancy fluxes derived from sea ice concentration observations and wind stress from ERA-Interim atmospheric reanalysis. Boundary conditions are derived from the ECCO2 ocean state estimate; tides are incorporated as sea surface height and barotropic currents at the open boundary. We evaluate model results using satellite-derived estimates of ice shelf melting and established compilations of ocean hydrography. The Whole Antarctic Ocean Model (WAOM v1.0) qualitatively captures the broad scale difference between warm and cold regimes as well as many of the known characteristics of regional ice–ocean interaction. We identify a cold bias for some warm-water ice shelves and a lack of high-salinity shelf water (HSSW) formation. We conclude that further calibration and development of our approach are justified. At its current state, the model is ideal for addressing specific, process-oriented questions, e.g. related to tide-driven ice shelf melting at large scales.
Programme: 688
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Bruyant, F., Amiraux, R., Amyot, M. P., Archambault, P., Artigue, L., Bardedo de Freitas, L., ...Fort, J.,... & Babin, M. (2022). The Green Edge cruise: Understanding the onset, life and fate of the Arctic phytoplankton spring bloom.
Abstract: The Green Edge project was designed to investigate the onset, life and fate of a phytoplankton spring bloom (PSB) in the Arctic Ocean. The lengthening of the ice-free period and the warming of seawater, amongst other factors, have induced major changes in arctic ocean biology over the last decades. Because the PSB is at the base of the Arctic Ocean food chain, it is crucial to understand how changes in the arctic environment will affect it. Green Edge was a large multidisciplinary collaborative project bringing researchers and technicians from 28 different institutions in seven countries, together aiming at understanding these changes and their impacts into the future. The fieldwork for the Green Edge project took place over two years (2015 and 2016) and was carried out from both an ice-camp and a research vessel in the Baffin Bay, canadian arctic. This paper describes the sampling strategy and the data set obtained from the research cruise, which took place aboard the Canadian Coast Guard Ship (CCGS) Amundsen in spring 2016. The dataset is available at https://doi.org/10.17882/59892 (Massicotte et al., 2019a).
Programme: 388
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Pierre Friedlingstein, Michael O'Sullivan, Matthew W. Jones, Robbie M. Andrew, Luke Gregor, Judith Hauck, Corinne Le Quéré, Ingrid T. Luijkx, Are Olsen, Glen P. Peters, Wouter Peters, Julia Pongratz, Clemens Schwingshackl, Stephen Sitch, Josep G. Canadell, Philippe Ciais, Robert B. Jackson, Simone R. Alin, Ramdane Alkama, Almut Arneth, Vivek K. Arora, Nicholas R. Bates, Meike Becker, Nicolas Bellouin, Henry C. Bittig, Laurent Bopp, Frédéric Chevallier, Louise P. Chini, Margot Cronin, Wiley Evans, Stefanie Falk, Richard A. Feely, Thomas Gasser, Marion Gehlen, Thanos Gkritzalis, Lucas Gloege, Giacomo Grassi, Nicolas Gruber, Özgür Gürses, Ian Harris, Matthew Hefner, Richard A. Houghton, George C. Hurtt, Yosuke Iida, Tatiana Ilyina, Atul K. Jain, Annika Jersild, Koji Kadono, Etsushi Kato, Daniel Kennedy, Kees Klein Goldewijk, Jürgen Knauer, Jan Ivar Korsbakken, Peter Landschützer, Nathalie Lefèvre, Keith Lindsay, Junjie Liu, Zhu Liu, Gregg Marland, Nicolas Mayot, Matthew J. McGrath, Nicolas Metzl, Natalie M. Monacci, David R. Munro, Shin-Ichiro Nakaoka, Yosuke Niwa, Kevin O'Brien, Tsuneo Ono, Paul I. Palmer, Naiqing Pan, Denis Pierrot, Katie Pocock, Benjamin Poulter, Laure Resplandy, Eddy Robertson, Christian Rödenbeck, Carmen Rodriguez, Thais M. Rosan, Jörg Schwinger, Roland Séférian, Jamie D. Shutler, Ingunn Skjelvan, Tobias Steinhoff, Qing Sun, Adrienne J. Sutton, Colm Sweeney, Shintaro Takao, Toste Tanhua, Pieter P. Tans, Xiangjun Tian, Hanqin Tian, Bronte Tilbrook, Hiroyuki Tsujino, Francesco Tubiello, Guido R. van der Werf, Anthony P. Walker, Rik Wanninkhof, Chris Whitehead, Anna Willstrand Wranne, Rebecca Wright, Wenping Yuan, Chao Yue, Xu Yue, Sönke Zaehle, Jiye Zeng, Bo Zheng. (2022). Global Carbon Budget 2022 (Vol. 14).
Abstract: Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize data sets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the year 2021, EFOS increased by 5.1 % relative to 2020, with fossil emissions at 10.1 ± 0.5 GtC yr−1 (9.9 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 1.1 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission (including the cement carbonation sink) of 10.9 ± 0.8 GtC yr−1 (40.0 ± 2.9 GtCO2). Also, for 2021, GATM was 5.2 ± 0.2 GtC yr−1 (2.5 ± 0.1 ppm yr−1), SOCEAN was 2.9 ± 0.4 GtC yr−1, and SLAND was 3.5 ± 0.9 GtC yr−1, with a BIM of −0.6 GtC yr−1 (i.e. the total estimated sources were too low or sinks were too high). The global atmospheric CO2 concentration averaged over 2021 reached 414.71 ± 0.1 ppm. Preliminary data for 2022 suggest an increase in EFOS relative to 2021 of +1.0 % (0.1 % to 1.9 %) globally and atmospheric CO2 concentration reaching 417.2 ppm, more than 50 % above pre-industrial levels (around 278 ppm). Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2021, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use change emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extratropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and data sets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this data set. The data presented in this work are available at https://doi.org/10.18160/GCP-2022 (Friedlingstein et al., 2022b).
Programme: 416
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Casado, M., Leroy-Dos Santos, C., Fourré, E., Favier, V., Agosta, C., Arnaud, L., Prié, F., Akers, P. D., Janssen, L., Kittel, C., Savarino, J., and Landais, A.. (2022). Water vapor isotopic signature along the EAIIST traverse.
Abstract: Stable Water Isotopes Are A Tracer Of Hydrological Processes And A Paleoclimate Proxy From Ice Core Records. The Interpretation Of The Latter Relies On Fractionation Processes Throughout The Hydrological Cycle, From The Evaporation Over The Ocean, During Each Precipitation Event, And During Post-deposition Processes, In Particular Due To The Exchanges Between The Snow And The Moisture In The Atmosphere. Thanks To New Developments In Infrared Spectroscopy, It Is Now Possible To Monitor Not Only The Snow Isotopic Composition But Also The Vapour Continuously, And Thus Document Exchanges Between The Snow And The Vapour. On The East Antarctic Plateau, Records Of Water Vapour Isotopic Composition In Kohnen And Dome C During Summer Have Revealed Significant Diurnal Variability Which Can Be Used To Address The Exchange Between Surface Snow And Atmospheric Water Vapour As Well As The Stability Of The Atmospheric Boundary Layer. in This Study, We Present The First Vapour Monitoring On A Transect Across East Antarctica For A Period Of 3 Months From November 2019 To February 2020 During The Eaiist Traverse, Covering More Than 3600 Km. In Parallel, We Also Monitored The Vapour Isotopic Composition At Two Stations: Dumont D’urville (Ddu), The Starting Point, And Dome C, Half Way Through. Efforts On The Calibration On Each Monitoring Station, As Well As Cross-calibration Of The Different Instruments Offer A Unique Opportunity To Compare Both The Spatial And Temporal (Diurnal Variability Or At The Scale Of Several Days) Gradients Of Humidity, Temperature And Water Vapour Isotopic Composition In East Antarctica During The Summer Season. with The Use Of The Modele Atmospherique Régional (Mar), We Compare The Variability Measured In Water Vapour Isotopic Composition, Temperature And Humidity With The Different Systems (Fixed Or Mobile Location). Although Further Comparisons With The Surface Snow Isotopic Composition Are Required To Quantify The Impact Of The Snow-atmosphere Exchanges On The Local Surface Mass Balance, These Three Simultaneous Measurements Of The Vapour Isotopic Composition Show The Potential Of Using Water Stables Isotopes To Evaluate Hydrological Processes In East Antarctica.
Programme: 1205
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