Search

Your search keyword '"King, Michalea"' showing total 30 results
Start Over Author "King, Michalea"
30 results on '"King, Michalea"'

1. Greenland Mass Trends From Airborne and Satellite Altimetry During 2011–2020

Author

Khan, Shfaqat A, Bamber, Jonathan L, Rignot, Eric, Helm, Veit, Aschwanden, Andy, Holland, David M, Broeke, Michiel, King, Michalea, Noël, Brice, Truffer, Martin, Humbert, Angelika, Colgan, William, Vijay, Saurabh, and Munneke, Peter Kuipers

Subjects
Earth Sciences, Physical Geography and Environmental Geoscience, Climate Action, Greenland Ice Sheet, satellite altimetry, mass loss, ice dynamics, vertical land motion, surface mass balance, Earth sciences, Environmental sciences
Abstract

We use satellite and airborne altimetry to estimate annual mass changes of the Greenland Ice Sheet. We estimate ice loss corresponding to a sea-level rise of 6.9 ± 0.4 mm from April 2011 to April 2020, with a highest annual ice loss rate of 1.4 mm/yr sea-level equivalent from April 2019 to April 2020. On a regional scale, our annual mass loss timeseries reveals 10-15 m/yr dynamic thickening at the terminus of Jakobshavn Isbræ from April 2016 to April 2018, followed by a return to dynamic thinning. We observe contrasting patterns of mass loss acceleration in different basins across the ice sheet and suggest that these spatiotemporal trends could be useful for calibrating and validating prognostic ice sheet models. In addition to resolving the spatial and temporal fingerprint of Greenland's recent ice loss, these mass loss grids are key for partitioning contemporary elastic vertical land motion from longer-term glacial isostatic adjustment (GIA) trends at GPS stations around the ice sheet. Our ice-loss product results in a significantly different GIA interpretation from a previous ice-loss product.

Published
2022

4. Accelerating the Renewable Energy Revolution to Get Back to the Holocene

Author

Abbott, Benjamin W., primary, Abrahamian, Chelsea, additional, Newbold, Nicholas, additional, Smith, Peter, additional, Merritt, Marina, additional, Sayedi, Sayedeh Sara, additional, Bekker, Jeremy, additional, Greenhalgh, Mitchell, additional, Gilbert, Sophie, additional, King, Michalea, additional, Lopez, Gabriel, additional, Zimmermann, Nils, additional, and Breyer, Christian, additional

Published
2023
Full Text
View/download PDF

8. Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020

Author

Otosaka, Inès N., primary, Shepherd, Andrew, additional, Ivins, Erik R., additional, Schlegel, Nicole-Jeanne, additional, Amory, Charles, additional, van den Broeke, Michiel R., additional, Horwath, Martin, additional, Joughin, Ian, additional, King, Michalea D., additional, Krinner, Gerhard, additional, Nowicki, Sophie, additional, Payne, Anthony J., additional, Rignot, Eric, additional, Scambos, Ted, additional, Simon, Karen M., additional, Smith, Benjamin E., additional, Sørensen, Louise S., additional, Velicogna, Isabella, additional, Whitehouse, Pippa L., additional, A, Geruo, additional, Agosta, Cécile, additional, Ahlstrøm, Andreas P., additional, Blazquez, Alejandro, additional, Colgan, William, additional, Engdahl, Marcus E., additional, Fettweis, Xavier, additional, Forsberg, Rene, additional, Gallée, Hubert, additional, Gardner, Alex, additional, Gilbert, Lin, additional, Gourmelen, Noel, additional, Groh, Andreas, additional, Gunter, Brian C., additional, Harig, Christopher, additional, Helm, Veit, additional, Khan, Shfaqat Abbas, additional, Kittel, Christoph, additional, Konrad, Hannes, additional, Langen, Peter L., additional, Lecavalier, Benoit S., additional, Liang, Chia-Chun, additional, Loomis, Bryant D., additional, McMillan, Malcolm, additional, Melini, Daniele, additional, Mernild, Sebastian H., additional, Mottram, Ruth, additional, Mouginot, Jeremie, additional, Nilsson, Johan, additional, Noël, Brice, additional, Pattle, Mark E., additional, Peltier, William R., additional, Pie, Nadege, additional, Roca, Mònica, additional, Sasgen, Ingo, additional, Save, Himanshu V., additional, Seo, Ki-Weon, additional, Scheuchl, Bernd, additional, Schrama, Ernst J. O., additional, Schröder, Ludwig, additional, Simonsen, Sebastian B., additional, Slater, Thomas, additional, Spada, Giorgio, additional, Sutterley, Tyler C., additional, Vishwakarma, Bramha Dutt, additional, van Wessem, Jan Melchior, additional, Wiese, David, additional, van der Wal, Wouter, additional, and Wouters, Bert, additional

Published
2023
Full Text
View/download PDF

9. Closing Greenland's Mass Balance: Frontal Ablation of Every Greenlandic Glacier From 2000 to 2020.

Author

Kochtitzky, William, Copland, Luke, King, Michalea, Hugonnet, Romain, Jiskoot, Hester, Morlighem, Mathieu, Millan, Romain, Khan, Shfaqat Abbas, and Noël, Brice

Subjects
GLACIERS, GREENLAND ice, ICE sheets
Abstract

In Greenland, 87% of the glacierized area terminates in the ocean, but mass lost at the ice‐ocean interface, or frontal ablation, has not yet been fully quantified. Using measurements and models we calculate frontal ablation of Greenland's 213 outlet and 537 peripheral glaciers and find a total frontal ablation of 481.8 ± 24.0 for 2000–2010 and 510.2 ± 18.6 Gt a−1 for 2010–2020. Ice discharge accounted for ∼90% of frontal ablation during both periods, while mass loss due to terminus retreat comprised the remainder. Only 16 glaciers were responsible for the majority (>50%) of frontal ablation from 2010 to 2020. These estimates, along with the climatic‐basal balance, allow for a more complete accounting of Greenland Ice Sheet and peripheral glacier mass balance. In total, Greenland accounted for ∼90% of Northern Hemisphere frontal ablation for 2000–2010 and 2010–2020. Plain Language Summary: We estimate the mass of ice lost from all Greenland glaciers that entered the ocean during each of the last two decades. This ice loss at the front of these marine‐terminating glaciers is called frontal ablation and is approximately equal to the mass of icebergs entering the ocean. Frontal ablation is important because 87% of glacier area in Greenland ends in the ocean, through 750 outlets, and previous work has only approximated frontal ablation. This study quantifies it for the first time, helping to close the mass budget for the Greenland Ice Sheet and better partition its mass balance into components. We find that Greenland accounts for ∼90% of all Northern Hemisphere frontal ablation and, of that contribution, just 17 glaciers for 2000–2010 and 16 glaciers for 2010–2020 account for more than half of total Greenland frontal ablation. Key Points: Frontal ablation of the Greenland Ice Sheet averaged 510.2 ± 18.6 Gt a−1 for 2010–2020, ∼90% of which came from ice dischargeThe frontal ablation we measured is larger than the total mass loss from the ice sheet, indicating a positive climatic‐basal balanceOnly 16 glaciers account for 50% of the total frontal ablation from the Greenland Ice Sheet [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

10. Progress toward globally complete frontal ablation estimates of marine-terminating glaciers.

Author

Kochtitzky, William, Copland, Luke, Van Wychen, Wesley, Hock, Regine, Rounce, David R., Jiskoot, Hester, Scambos, Ted A., Morlighem, Mathieu, King, Michalea, Cha, Leo, Gould, Luke, Merrill, Paige-Marie, Glazovsky, Andrey, Hugonnet, Romain, Strozzi, Tazio, Noël, Brice, Navarro, Francisco, Millan, Romain, Dowdeswell, Julian A., and Cook, Alison

Subjects
GLACIERS, ICE calving, ICE sheets
Abstract

Knowledge of frontal ablation from marine-terminating glaciers (i.e., mass lost at the calving face) is critical for constraining glacier mass balance, improving projections of mass change, and identifying the processes that govern frontal mass loss. Here, we discuss the challenges involved in computing frontal ablation and the unique issues pertaining to both glaciers and ice sheets. Frontal ablation estimates require numerous datasets, including glacier terminus area change, thickness, surface velocity, density, and climatic mass balance. Observations and models of these variables have improved over the past decade, but significant gaps and regional discrepancies remain, and better quantification of temporal variability in frontal ablation is needed. Despite major advances in satellite-derived large-scale datasets, large uncertainties remain with respect to ice thickness, depth-averaged velocities, and the bulk density of glacier ice close to calving termini or grounding lines. We suggest ways in which we can move toward globally complete frontal ablation estimates, highlighting areas where we need improved datasets and increased collaboration. [ABSTRACT FROM AUTHOR]

Published
2023
Full Text
View/download PDF

12. Progress toward globally complete frontal ablation estimates of marine-terminating glaciers

Author

Kochtitzky, William, primary, Copland, Luke, additional, Van Wychen, Wesley, additional, Hock, Regine, additional, Rounce, David R., additional, Jiskoot, Hester, additional, Scambos, Ted A., additional, Morlighem, Mathieu, additional, King, Michalea, additional, Cha, Leo, additional, Gould, Luke, additional, Merrill, Paige-Marie, additional, Glazovsky, Andrey, additional, Hugonnet, Romain, additional, Strozzi, Tazio, additional, Noël, Brice, additional, Navarro, Francisco, additional, Millan, Romain, additional, Dowdeswell, Julian A., additional, Cook, Alison, additional, Dalton, Abigail, additional, Khan, Shfaqat, additional, and Jania, Jacek, additional

Published
2022
Full Text
View/download PDF

13. Data supporting 'Atlantic Water intrusion triggers rapid retreat and regime change at previously stable Greenland glacier'

Author

Chudley, Thomas R, Howat, Ian M, King, Michalea D, and Negrete, Adelaide

Subjects
remote sensing, glacier, greenland, glacier terminus, glacier position, oceanography, ice sheet
Abstract

Data supporting the paper: Chudley, T. R., Howat, I. M., King, M. D., and Negrete, A. (2023). Atlantic Water intrusion triggers sudden and rapid retreat of Greenlandic glacier following long-term stability. Nature Communications, 14, 2151. https://doi.org/10.1038/s41467-023-37764-7 Methods are described in the full text of the paper. Please consult the README.md file for information as to how to interpret datasets., This project was supported by grants 80NSSC18K1027 and NNX13AI21A from the National Aeronautics and Space Administration.

Published
2022
Full Text
View/download PDF

14. Mass Balance of the Greenland and Antarctic Ice Sheets from 1992 to 2020

Author

Otosaka, Inès N., primary, Shepherd, Andrew, additional, Ivins, Erik R., additional, Schlegel, Nicole-Jeanne, additional, Amory, Charles, additional, van den Broeke, Michiel, additional, Horwath, Martin, additional, Joughin, Ian, additional, King, Michalea, additional, Krinner, Gerhard, additional, Nowicki, Sophie, additional, Payne, Tony, additional, Rignot, Eric, additional, Scambos, Ted, additional, Simon, Karen M., additional, Smith, Benjamin, additional, Sandberg Sørensen, Louise, additional, Velicogna, Isabella, additional, Whitehouse, Pippa, additional, A, Geruo, additional, Agosta, Cécile, additional, Ahlstrøm, Andreas P., additional, Blazquez, Alejandro, additional, Colgan, William, additional, Engdahl, Marcus, additional, Fettweis, Xavier, additional, Forsberg, Rene, additional, Gallée, Hubert, additional, Gardner, Alex, additional, Gilbert, Lin, additional, Gourmelen, Noel, additional, Groh, Andreas, additional, Gunter, Brian C., additional, Harig, Christopher, additional, Helm, Veit, additional, Khan, Shfaqat Abbas, additional, Konrad, Hannes, additional, Langen, Peter, additional, Lecavalier, Benoit, additional, Liang, Chia-Chun, additional, Loomis, Bryant, additional, McMillan, Malcolm, additional, Melini, Daniele, additional, Mernild, Sebastian H., additional, Mottram, Ruth, additional, Mouginot, Jeremie, additional, Nilsson, Johan, additional, Noël, Brice, additional, Pattle, Mark E., additional, Peltier, William R., additional, Pie, Nadege, additional, Sasgen, Ingo, additional, Save, Himanshu, additional, Seo, Ki-Weon, additional, Scheuchl, Bernd, additional, Schrama, Ernst, additional, Schröder, Ludwig, additional, Simonsen, Sebastian B., additional, Slater, Thomas, additional, Spada, Giorgio, additional, Sutterley, Tyler, additional, Vishwakarma, Bramha Dutt, additional, van Wessem, Jan Melchior, additional, Wiese, David, additional, van der Wal, Wouter, additional, and Wouters, Bert, additional

Published
2022
Full Text
View/download PDF

15. Greenland Mass Trends From Airborne and Satellite Altimetry During 2011–2020

Author

Khan, Shfaqat A., Bamber, Jonathan L., Rignot, Eric, Helm, Veit, Aschwanden, Andy, Holland, David M., van den Broeke, Michiel, King, Michalea, Noël, Brice, Truffer, Martin, Humbert, Angelika, Colgan, William, Vijay, Saurabh, Kuipers Munneke, Peter, Sub Dynamics Meteorology, Marine and Atmospheric Research, Sub Dynamics Meteorology, and Marine and Atmospheric Research

Subjects
Climate Action, Geophysics, surface mass balance, Greenland Ice Sheet, Earth Sciences, GlobalMass, ice dynamics, satellite altimetry, vertical land motion, mass loss, Earth-Surface Processes
Abstract

We use satellite and airborne altimetry to estimate annual mass changes of the Greenland Ice Sheet. We estimate ice loss corresponding to a sea-level rise of 6.9±0.4mm from April 2011 to April 2020, with a highest annual ice loss rate of 1.4mm/yr sea-level equivalent from April 2019 to April 2020. On a regional scale, our annual mass loss timeseries reveals 10–15m/yr dynamic thickening at the terminus of Jakobshavn Isbræ from April 2016 to April 2018, followed by a return to dynamic thinning. We observe contrasting patterns of mass loss acceleration in different basins across the ice sheet and suggest that these spatiotemporal trends could be useful for calibrating and validating prognostic ice sheet models. In addition to resolving the spatial and temporal fingerprint of Greenland's recent ice loss, these mass loss grids are key for partitioning contemporary elastic vertical land motion from longer-term glacial isostatic adjustment (GIA) trends at GPS stations around the ice sheet. Our ice-loss product results in a significantly different GIA interpretation from a previous ice-loss product.

Published
2022

16. Greenland ice sheet mass balance from 1840 through next week

Author

Mankoff, Kenneth D., Fettweis, Xavier, Langen, Peter L., Stendel, Martin, Kjeldsen, Kristian K., Karlsson, Nanna B., Noël, Brice, Van Den Broeke, Michiel R., Solgaard, Anne, Colgan, William, Box, Jason E., Simonsen, Sebastian B., King, Michalea D., Ahlstrøm, Andreas P., Andersen, Signe Bech, Fausto, Robert S., Sub Dynamics Meteorology, Marine and Atmospheric Research, Sub Dynamics Meteorology, and Marine and Atmospheric Research

Subjects
geography, QE1-996.5, geography.geographical_feature_category, Ice calving, Greenland ice sheet, Earth and Planetary Sciences(all), Glacier, Geology, Atmospheric sciences, Snow, Environmental sciences, Glacier mass balance, SDG 13 - Climate Action, General Earth and Planetary Sciences, Environmental science, Climate model, GE1-350, SDG 14 - Life Below Water, Meltwater, Surface runoff
Abstract

The mass of the Greenland ice sheet is declining as mass gain from snow accumulation is exceeded by mass loss from surface meltwater runoff, marine-terminating glacier calving and submarine melting, and basal melting. Here we use the input–output (IO) method to estimate mass change from 1840 through next week. Surface mass balance (SMB) gains and losses come from a semi-empirical SMB model from 1840 through 1985 and three regional climate models (RCMs; HIRHAM/HARMONIE, Modèle Atmosphérique Régional – MAR, and RACMO – Regional Atmospheric Climate MOdel) from 1986 through next week. Additional non-SMB losses come from a marine-terminating glacier ice discharge product and a basal mass balance model. From these products we provide an annual estimate of Greenland ice sheet mass balance from 1840 through 1985 and a daily estimate at sector and region scale from 1986 through next week. This product updates daily and is the first IO product to include the basal mass balance which is a source of an additional ∼24 Gt yr−1 of mass loss. Our results demonstrate an accelerating ice-sheet-scale mass loss and general agreement (coefficient of determination, r2, ranges from 0.62 to 0.94) among six other products, including gravitational, volume, and other IO mass balance estimates. Results from this study are available at https://doi.org/10.22008/FK2/OHI23Z (Mankoff et al., 2021).

Published
2021

18. Mass Balance of the Greenland and Antarctic Ice Sheets from 1992 to 2020.

Author

Otosaka, Inès N., Shepherd, Andrew, Ivins, Erik R., Schlegel, Nicole-Jeanne, Amory, Charles, van den Broeke, Michiel R., Horwath, Martin, Joughin, Ian, King, Michalea D., Krinner, Gerhard, Nowicki, Sophie, Payne, Antony J., Rignot, Eric, Scambos, Ted, Simon, Karen M., Smith, Benjamin E., Sørensen, Louise S., Velicogna, Isabella, Whitehouse, Pippa L., and A., Geruo

Subjects
ICE sheets, GREENLAND ice, ANTARCTIC ice, SEA level, MELTWATER, SUBGLACIAL lakes
Abstract

Ice losses from the Greenland and Antarctic Ice Sheets have accelerated since the 1990s, accounting for significant increase in global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0 ± 1.9 mm to global mean sealevel, with the rate of mass loss rising from 105 Gt yr-1 between 1992 and 1996 to 372 Gt yr-1 between 2016 and 2020. In Greenland, the rate of mass loss is 169 ± 9 Gt yr-1 between 1992 and 2020 but there are large inter-annual variations in mass balance with mass loss ranging from 86 Gt yr-1 in 2017 to 444 Gt yr-1 in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (-82 ± 9 Gt yr-1) and to lesser extent from the Antarctic Peninsula (-13 ± 5 Gt yr-1). East Antarctica remains close to a state of balance (3 ± 15 Gt yr- 1), but is the most uncertain component of Antarctica's mass balance. [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

19. Author Correction: Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat (Communications Earth & Environment, (2020), 1, 1, (1), 10.1038/s43247-020-0001-2)

Author

King, Michalea D., Howat, Ian M., Candela, Salvatore G., Noh, Myoung J., Jeong, Seongsu, Noël, Brice P.Y., van den Broeke, Michiel R., Wouters, Bert, Negrete, Adelaide, Sub Dynamics Meteorology, and Marine and Atmospheric Research

Subjects
Environmental Science(all), Earth and Planetary Sciences(all)
Abstract

The original version of this Article contained an error in the spelling of the author Seongsu Jeong, which was incorrectly given as Seonsgu Jeong. This has now been corrected in both the PDF and HTML versions of the Article.

Published
2020

20. GrSMBMIP: Intercomparison of the modelled 1980-2012 surface mass balance over the Greenland Ice Sheet

Author

Fettweis, Xavier, Hofer, Stefan, Krebs-Kanzow, Uta, Amory, Charles, Aoki, Teruo, Berends, Constantijn J., Born, Andreas, Box, Jason E., Delhasse, Alison, Fujita, Koji, Gierz, Paul, Goelzer, Heiko, Hanna, Edward, Hashimoto, Akihiro, Huybrechts, Philippe, Kapsch, Marie Luise, King, Michalea D., Kittel, Christoph, Lang, Charlotte, Langen, Peter L., Lenaerts, Jan T.M., Liston, Glen E., Lohmann, Gerrit, Mernild, Sebastian H., Mikolajewicz, Uwe, Modali, Kameswarrao, Mottram, Ruth H., Niwano, Masashi, Noël, Brice, Ryan, Jonathan C., Smith, Amy, Streffing, Jan, Tedesco, Marco, Jan Van De Berg, Willem, Van Den Broeke, Michiel, Van De Wal, Roderik S.W., Van Kampenhout, Leo, Wilton, David, Wouters, Bert, Ziemen, Florian, Zolles, Tobias, Sub Dynamics Meteorology, Proceskunde, Sub Algemeen Marine & Atmospheric Res, and Marine and Atmospheric Research

Subjects
Water Science and Technology, Earth-Surface Processes
Abstract

Observations and models agree that the Greenland Ice Sheet (GrIS) surface mass balance (SMB) has decreased since the end of the 1990s due to an increase in meltwater runoff and that this trend will accelerate in the future. However, large uncertainties remain, partly due to different approaches for modelling the GrIS SMB, which have to weigh physical complexity or low computing time, different spatial and temporal resolutions, different forcing fields, and different ice sheet topographies and extents, which collectively make an inter-comparison difficult. Our GrIS SMB model intercomparison project (GrSMBMIP) aims to refine these uncertainties by intercomparing 13 models of four types which were forced with the same ERA-Interim reanalysis forcing fields, except for two global models. We interpolate all modelled SMB fields onto a common ice sheet mask at 1 km horizontal resolution for the period 1980-2012 and score the outputs against (1) SMB estimates from a combination of gravimetric remote sensing data from GRACE and measured ice discharge; (2) ice cores, snow pits and in situ SMB observations; and (3) remotely sensed bare ice extent from MODerate-resolution Imaging Spectroradiometer (MODIS). Spatially, the largest spread among models can be found around the margins of the ice sheet, highlighting model deficiencies in an accurate representation of the GrIS ablation zone extent and processes related to surface melt and runoff. Overall, polar regional climate models (RCMs) perform the best compared to observations, in particular for simulating precipitation patterns. However, other simpler and faster models have biases of the same order as RCMs compared with observations and therefore remain useful tools for long-term simulations or coupling with ice sheet models. Finally, it is interesting to note that the ensemble mean of the 13 models produces the best estimate of the present-day SMB relative to observations, suggesting that biases are not systematic among models and that this ensemble estimate can be used as a reference for current climate when carrying out future model developments. However, a higher density of in situ SMB observations is required, especially in the south-east accumulation zone, where the model spread can reach 2 m w.e. yr-1 due to large discrepancies in modelled snowfall accumulation.

Published
2020

22. Supplementary material to "GrSMBMIP: Intercomparison of the modelled 1980–2012 surface mass balance over the Greenland Ice sheet"

Author

Fettweis, Xavier, primary, Hofer, Stefan, additional, Krebs-Kanzow, Uta, additional, Amory, Charles, additional, Aoki, Teruo, additional, Berends, Constantijn J., additional, Born, Andreas, additional, Box, Jason E., additional, Delhasse, Alison, additional, Fujita, Koji, additional, Gierz, Paul, additional, Goelzer, Heiko, additional, Hanna, Edward, additional, Hashimoto, Akihiro, additional, Huybrechts, Philippe, additional, Kapsch, Marie-Luise, additional, King, Michalea D., additional, Kittel, Christoph, additional, Lang, Charlotte, additional, Langen, Peter L., additional, Lenaerts, Jan T. M., additional, Liston, Glen E., additional, Lohmann, Gerrit, additional, Mernild, Sebastian H., additional, Mikolajewicz, Uwe, additional, Modali, Kameswarrao, additional, Mottram, Ruth H., additional, Niwano, Masashi, additional, Noël, Brice, additional, Ryan, Jonathan C., additional, Smith, Amy, additional, Streffing, Jan, additional, Tedesco, Marco, additional, van de Berg, Willem Jan, additional, van den Broeke, Michiel, additional, van de Wal, Roderik S. W., additional, van Kampenhout, Leo, additional, Wilton, David, additional, Wouters, Bert, additional, Ziemen, Florian, additional, and Zolles, Tobias, additional

Published
2020
Full Text
View/download PDF

23. GrSMBMIP: Intercomparison of the modelled 1980–2012 surface mass balance over the Greenland Ice sheet

Author

Fettweis, Xavier, primary, Hofer, Stefan, additional, Krebs-Kanzow, Uta, additional, Amory, Charles, additional, Aoki, Teruo, additional, Berends, Constantijn J., additional, Born, Andreas, additional, Box, Jason E., additional, Delhasse, Alison, additional, Fujita, Koji, additional, Gierz, Paul, additional, Goelzer, Heiko, additional, Hanna, Edward, additional, Hashimoto, Akihiro, additional, Huybrechts, Philippe, additional, Kapsch, Marie-Luise, additional, King, Michalea D., additional, Kittel, Christoph, additional, Lang, Charlotte, additional, Langen, Peter L., additional, Lenaerts, Jan T. M., additional, Liston, Glen E., additional, Lohmann, Gerrit, additional, Mernild, Sebastian H., additional, Mikolajewicz, Uwe, additional, Modali, Kameswarrao, additional, Mottram, Ruth H., additional, Niwano, Masashi, additional, Noël, Brice, additional, Ryan, Jonathan C., additional, Smith, Amy, additional, Streffing, Jan, additional, Tedesco, Marco, additional, van de Berg, Willem Jan, additional, van den Broeke, Michiel, additional, van de Wal, Roderik S. W., additional, van Kampenhout, Leo, additional, Wilton, David, additional, Wouters, Bert, additional, Ziemen, Florian, additional, and Zolles, Tobias, additional

Published
2020
Full Text
View/download PDF

30. Seasonal to Multidecadal Drivers of Variability at Greenland Outlet Glaciers

Author

King, Michalea Dianne

Subjects
Earth, Geophysics, Geophysical, Geological, Environmental Studies, Climate Change, Greenland, glaciers, cryosphere, glaciology, climate change, Arctic
Abstract

The Greenland Ice Sheet (GrIS) is losing mass at accelerated rates in the 21st century, due in part to faster flow at large outlet glaciers. Chapter 2 presents work published in The Cryosphere (King et al., 2018). Here, we sample rapid changes in thickness and velocity at all large outlet glaciers to derive the first continuous, GrIS-wide record of total ice sheet discharge, or the volume of ice glaciers export, for the 2000-2016 period. We resolve a distinct pattern of seasonal variability with an amplitude of 6%, and analyze how seasonal to annual variability in the discharge time series relates to both meltwater runoff and glacier front position changes over the same period. We find that the annual magnitude of discharge is closely related to cumulative front position change (r2 = 0.79), averaging over 2 km of retreat since 2000. We find that larger seasonal quantities of runoff do not relate to increased annual discharge, although seasonal acceleration of ice discharge does closely coincide with the onset of the melt season. These results suggest that changes in glacier front position drive secular trends in discharge, whereas the impact of runoff is likely limited to the summer months when observed seasonal variations are substantially controlled by the timing of meltwater input.In Chapter 3, we extend our 2000-2016 discharge time series to the period 1985-2018, combining more than three decades of GrIS-wide observational products of outlet glacier velocity, elevation, and front position changes, and compare decadal variability in discharge with calving front position. We find that the close relationship between frontal change and ice discharge identified over the 2000-2016 record holds true for the 34-year record, and that increased glacier discharge can be attributed almost entirely to the retreat of glacier fronts, rather than inland ice sheet processes, such as changes in meltwater runoff. Discharge sensitivity to retreat is remarkably consistent across the ice sheet, with all main regions showing an increase in discharge of 4-5% per km of retreat. Most importantly, we show that widespread retreat between 2000 and 2005 resulted in a step-increase in discharge and a switch to a new dynamic state of sustained mass loss. The increase in discharge was large enough to alone ensure persistent negative ice sheet mass balance, even before including more recent negative trends in surface mass balance. This study is published in Nature Communications Earth & Environment (King et al., 2020). Lastly, we revisit seasonal impacts of meltwater on short temporal variability in glacier dynamics. Chapter 4 work describes how, in lieu of widespread direct observations of subglacial systems, we derive a novel runoff index that quantifies the potential of a given melt season to sustain fast outlet glacier flow. This index, "Basal Pumping Index'', is based on the distribution and relative magnitude of individual runoff events throughout the summer, and reflects the current understanding of how subglacial drainage systems evolve over time to modulate water pressures at the ice bed. We also categorize glaciers based on several unique patterns of variability, and discuss how particular glacier properties impact seasonality and sensitivity to our index. We compare net GrIS discharge between low and highly effective runoff years, and find that particular runoff distributions can increase total GrIS dynamic ice losses by 3% in the late summer/autumnal months. In total, our results provide new insights into the large scale, ice sheet-wide drivers of variability in Greenland's ice discharge and mass balance on seasonal to decadal timescales. These insights will guide projections of future glacier response to ongoing climate change, improving our estimates of Greenland's contribution to global sea level rise and impacts on ocean salinity and circulation.

Published
2020

Catalog

Books, media, physical & digital resources
See catalog results