Atmosphere-Ocean Coupling Causing Ice Shelf Melt in Antarctica (ACCIMA)

News
Description
ACCIMA animations
ROMS results
Presentations
Publications
Links


News related to ACCIMA project:

  • 2014/06/05: Is It Too Late to Save Our Cities from Sea-Level Rise?
  • 2014/05/16: West Antarctic Ice Sheet collapse is underway (Study 1, Study 2)
  • 2014/01/16: Pine Island Glacier, West Antarctica: Dramatic retreat about to start?
  • 2014/01/16: Pine Island Glacier, West Antarctica: Bottom melting modulated by tropical climate variability? (see also in NSF Press Release 14-013)

  • Description:

    The ACCIMA project has adapted a regional climate system model (similar to the Regional Arctic System Model, RASM) to the Southern Ocean and Antarctica with the goal of better understanding the ice shelf melt occurring in the Amundsen Sea embayment of West Antarctica that is contributing significantly to sea-level rise (Bromwich et al. 2014). The component models are the polar version of the Weather Research and Forecasting model (Polar WRF; Bromwich et al. 2013a; Hines et al. 2014), the Parallel Ocean Program (POP2), the Los Alamos sea-ice model (CICE), and the Community Land Model (CLM). The models are coupled through the NCAR flux coupler (CPL7).

    ACCIMA simulations have been run for 1999-2010 driven by the ERA-Interim global atmospheric reanalysis (Bromwich et al. 2014). Results provide realistic representations of atmosphere, ocean, and sea-ice characteristics, including wind and precipitation fields over the Southern Ocean, the annual cycle of sea-ice cover, the ocean volume transport through the Drake Passage, the meridional overturning circulation in the Southern Ocean, and the oceanic heat transport across the continental shelf directed toward the base of major ice shelves (ACCIMA does not yet represent ice shelves).

    Coupled ocean-sea ice-ice shelf simulations with the Regional Ocean Modeling System (ROMS) model (10 km grid spacing) forced by surface winds from ERA-Interim and a Polar WRF simulation (30 km grid spacing) are compared with the ACCIMA fully-coupled runs to test the effects of changes in the atmospheric model resolution (Dinniman et al. 2014). Major ice shelf melting rates are similar to observational estimates and consistent with the ACCIMA oceanic heat transport across the continental shelf. Simulations show that the total basal ice shelf melt increased by ~15% with higher resolution winds, due to changes in the open ocean heat delivered to the continental shelves as well as changes in the heat lost to the atmosphere over the continental shelves.

    Analysis of the atmospheric temperature regime over Antarctica, and West Antarctica in particular, has demonstrated that the Southern Annular Mode (SAM) has restrained the atmospheric warming in recent decades (Nicolas and Bromwich 2014). Today, the average summer atmospheric temperatures in the coastal Amundsen Sea region are significantly cooler because of SAM influence. Depending on SAM behavior, ice-shelf retreat in the coming decades may be influenced by both summer surface melting and the currently-observed melting from below due to warm ocean temperatures.

    An extensive review of the role of sea ice and floating ice shelves in modifying global ocean circulation has been carried out by Holland (2013), with an emphasis on the southern hemisphere and recent changes in sea ice and land ice. This peer-reviewed book chapter was preceded by a shorter review article by Joughin et al. (2012) which, among other issues, highlighted the pressing research areas in which large gaps in knowledge currently exist. These review papers have motivated research to investigate underlying mechanisms for Antarctic climate change, and has resulted in a recent paper showing the impacts of tropical ocean temperature variability on West Antarctic climate (Li et al. 2014).

    Examination of the ice mass balance of the coastal Amundsen Sea region by the in/out method (Medley et al. 2014) demonstrated that while Thwaites Glacier lost the most ice in the mid-1990s, losses from Pine Island Glacier increased substantially by 2006, overtaking Thwaites as the largest regional contributor to sea-level rise. The trend of increasing discharge for both glaciers, however, appears to have leveled off since 2008 (through 2012).


    Animations of results produced by the ACCIMA regional climate system model during 1999-2010:

  • Monthly mean temperature at 2m (C): Note very cold temperature over Antarctica. The freezing line (0 degrees) migration reflects the expansion and contraction of the sea ice cover. (gif)
  • Monthly total precipitation (mm): Note the orographic maxima on the western tip of South America and western side of the Antarctic Peninsula. (gif)
  • Monthly mean wind at 10m (m/s): Streamlines plus wind speed (m/s, colors). Note the very strong westerly winds around Antarctica. (gif)
  • July 2005, 10m wind, every 6hrs: Streamlines plus wind speed (m/s, colors). Illustrates the storm systems over the Southern Ocean circulating clockwise around Antarctica. (gif)
  • Monthly katabatic wind pattern over Antarctica: Streamlines plus wind speed (m/s, colors). Illustrates the strong wind zones at Byrd Glacier, Adelie Land, and just west of Amery Ice Shelf. (gif)
  • Monthly average surface wind stress magnitude (N/m^2): The band of high speed westerly (eastward) surface winds between 40S and 50S are evident as is the strong fluctuations of the winds from one month to the next. Some regions near the Antarctic Continent have higher stress which are associated with polar easterlies (westward). Contour intervals are 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35 N/m^2. (gif)
  • Monthly averaged sea ice concentration: Sea ice extends to roughly 60S at mid-winter (Aug/Sept) of each year and retreats to the edge of the continent in late summer (Jan/Feb). The timing of maximum and minimum ice as well as the area of ice at maximum extent agree with observations from the National Snow and Ice Data Center. Too much ice melts in the summer leaving about half of the observed ice area. Locations of the summer ice (mainly the Weddell Sea and sections of the Antarctic coast) agree with observations. Contours intervals are 15, 50, 75 and 90%. The outermost contour (15% ice concentration) is the defining boundary for ice extent. The light green contour indicates ice concentrations of 90 to 100%, which is essentially complete ice cover with a few leads. The date for each image is given in the center of the figure. (gif)
  • Monthly averaged sea surface height (m): Sea surface height is a proxy for surface pressure which is proportional to the streamfunction for flow. Sea surface is low around Antarctica (blue) and high in the subtropics (magenta). The Weddell Gyre clearly shows as the dark blue area near the upper coast of Antarctica. A similar dark blue patch near the bottom represents the Ross Gyre. The yellow band is the northern part of the Antarctic Circumpolar Current (ACC) - the Sub Antarctic Frontal area, while the green band in the center of the ACC - the Polar Frontal area. The small scale features on the figure are mesoscale eddies and meanders of the flow which are marginally represented by the 20 km grid spacing in this simulation. Contours intervals are -1.5, -1.0, -0.5, 0., 0.5, and 1.0 m. The date for each image is given in the center of the figure. (gif)
  • Monthly averaged sea surface temperature (degree C): Water temperature under sea ice is effectively the freezing temperature (-1.8C) so the expansion and contraction of the dark blue area is due to the summer/winter cycle of sea ice freezing and melting. At subtropical latitudes (the outer part of the domain), there is a clear seasonal cycle of warming and cooling. The surface temperature contours do not closely match ACC fronts due to the strong seasonal heat exchange with the atmosphere. The small scale features are due to mesoscale eddies and meanders of the flow. Contours intervals are -2, -1, 0, 1, 2, 4, 6, 8, 10, 15, and 20C. The date for each image is given in the center of the figure. (gif)
  • Monthly averaged temperature (C) at 550 m depth: Water at this depth is not strongly affected by seasonal surface forcing. Waters colder than 0C show the Weddell and Ross Gyres. The northward extension of the ACC east of Drake Passage is clear in the cool (light blue) water along the east coast of South America. Contour intervals are -1.8, -1, 0, 1, 1.8, 2, 4, 6, 8, 10 C. (gif)
  • Monthly averaged salinity (PSU) at 550 m depth: Water at this depth is not strongly affected by seasonal surface forcing. The low salinity band (blue) around 50S is where Subantarctic Mode Water is being created by deep mixing in the winter. The deepest mixing occurs in the western South Pacific and through the Atlantic sector. Salinity in the Weddell Sea is increasing in the first few years of the model simulation. Near the coast, dense, but lower salinity water, is evident. Contour intervals are 34, 34.1, 34.2, 34.3, 34.4, 34.5, 34.6, 34.7, 34.8, 34.9, 35 PSU. (gif)
  • Meridional section of monthly averaged temperature at 90W: This section is across the western South Pacific showing the Antarctic Circumpolar Current between 55S and 70S. The thick surface layer of warm water north of 55S is the region of Subantarctic Mode Water where winter mixing extends 400 to 600 m. Circumpolar Deep Water is indicated by the tongue of warm water (darker green) ascending from 2000 m at 60S to the surface at 70S. The winter surface mixed layer of 100 m or more appears in winter and is capped during summer by a warm surface layer of a few 10's of m thickness. Contour intervals are -2, -1.5, -1, -.5, 0, .5, 1, 1.5, 2, 3, 5, 7 C. (gif)
  • Meridional section of monthly averaged salinity at 90W: This section is across the western South Pacific showing the Antarctic Circumpolar Current between 55S and 70S. The thick surface layer of lower salinity north of 55S is the region of Subantarctic Mode Water where winter mixing extends 400 to 600 m. Circumpolar Deep Water is indicated by the higher salinity band (yellow green) rising from 3000m at 53S to 500 m at 70S. A wedge of lower salinity water occurs at the far south but there is no indication of dense water formation. Contour intervals are 33, 33.5, 34, 34.4, 34.5, 34.6, 34.65, 34.7, 34.75, 34.8, 35, 35.5, 36 PSU. (gif)
  • Meridional section of monthly averaged temperature at 30E: This section extends through the Weddell Sea to the tip of Africa. The very warm water at the north end is the Agulhas Current carrying warm tropical water around Africa. The Antarctic Circumpolar Current is between 58S and 48S, having been displaced north by its passage through Drake Passage and the Scotia Sea. South of 58S is the Weddell Gyre with water colder than 0C but with a warm subsurface layer as a cooled remnant of Circumpolar Deep Water. Very cold 100 m thick surface layers are created in the winter. At the southern end of this section, dense water plumes are evident in late winter and early spring. Contour intervals are -2, -1.5, -1, -.5, 0, .5, 1, 1.5, 2, 3, 5, 7 C. (gif)
  • Meridional section of monthly averaged salinity at 30E: This section extends through the Weddell Sea to the tip of Africa. The very salty at the north end is the Agulhas Current. The Antarctic Circumpolar Current is between 58S and 48S, having been displaced north by its passage through Drake Passage and the Scotia Sea. The tongue of higher salinity Circumpolar Deep Water is disrupted by a lower salinity water in the northern part of the ACC. The northern buffer zone is creating CDW which is moving to the south. South of 58S is the Weddell Gyre. High salinity water at the bottom is a sign of dense Antarctic Bottom Water. Contour intervals are 33, 33.5, 34, 34.4, 34.5, 34.6, 34.65, 34.7, 34.75, 34.8, 35, 35.5, 36 PSU. (gif)
  • Meridional section of monthly averaged temperature at Greenwich Meridian: The Antarctic Circumpolar Current is between 45S and 55S occuring on and north of the America-Antarctic Ridge. The higher temperature tongue is southward intruding Circumpolar Deep water across the ACC. The Weddell Gyre is south of 58S. The subsurface temperature maximum is clearly connected to the tongue of CDW that has crossed the ACC. The seasonal cycle of surface layers is clear in the deep cold layers in the winter and thin warm layers in the summer. Dense plumes occur along the continental slope in the south. Contour intervals are -2, -1.5, -1, -.5, 0, .5, 1, 1.5, 2, 3, 5, 7 C. (gif)
  • Meridional section of monthly averaged salinity at Greenwich Meridian: The Antarctic Circumpolar Current is between 45S and 55S occuring on and north of the America-Antarctic Ridge. The high salinity tongue clearly shows the southward intruding Circumpolar Deep water across the ACC. The northward deepening tongue of low salinity (50S to 45S) is the subducting Antarctic Intermediate Water. High salinity Antarctic Bottom Water occurs in the deep Weddell Sea (60S to 65S). Dense plumes occur at the Antarctic Continent in winter and spring as incidated by the lower salinity water along the continental slope. Contour intervals are 33, 33.5, 34, 34.4, 34.5, 34.6, 34.65, 34.7, 34.75, 34.8, 35, 35.5, 36 PSU. (gif)

  • Sensitivity of ROMS simulations of the Southern Ocean to differing atmospheric forcings:

  • A climatology over the last five years of each of the three model runs showing the total Ice Shelf Basal Melt (Gt/yr) around the entire continent. ERA-Int is the base forcing run (ERA-Interim forcing), PWRF Winds are where just the winds are switched from ERA-Interim to 30km PWRF, and PWRF-Winds+ are where the winds and 2m air temperatures are switched from ERA-Int to PWRF. The number in parenthesis is the average total melt over the climatology. (png)
  • The top panel shows a climatology from the last five years of the model run of the different terms in the heat budget for the entire volume of water on the Antarctic continental shelves (including the ice shelf cavities) for just the base (ERA-Int) run. You can see the positive contribution from the lateral advection of heat onto the shelves and the seasonal gain from/loss to the atmosphere of heat. The middle panel shows the difference in the lateral advection of heat onto the continental shelf for the PWRF run vs. ERA-Int and for PWRF+ vs. ERA-Int. Adding the PWRF winds increases the heat advected onto the continental shelf. The bottom panel shows the difference in the surface heating over the continental shelf for the PWRF run vs. ERA-Int and PWRF+ vs. ERA-Int. Adding the PWRF winds increases the heat lost to the atmosphere (negative difference in the term). (png)

  • Presentations:

  • Yoo, C., E. P. Gerber, L.-S. Bai, D. H. Bromwich, M. S. Dinniman, K. M. Hines, D. M. Holland, and J. M. Klinck: Impact of Souther Annular Mode on cross shelf exchange around the Antarctica. 2013 AGU Fall Meeting, San Francisco, CA, Dec. 9-13, 2013. pdf
  • Bromwich, D. H., K. M. Hines, C. Yoo, J. M. Klinck, D. M. Holland, M. Dinniman, E. P. Gerber, L. Bai, and J. P. Nicolas: The ACCIMA Project - Coupled Modeling of the High Southern Latitudes. 18th Annual CESM Workshop, 17-20 June 2013, Breckenridge, CO. pdf
  • Bromwich, D., L.-S. Bai, M. Dinniman, E. Gerber, K. Hines, D. Holland, J. Klinck, J. Nicolas and C. Yoo: The ACCIMA Project - Coupled Modeling of the High Southern Latitudes. 27th International Forum for Research into Ice Shelf Processes, June 2013. pdf
  • Bromwich, D. H., L.-S. Bai, M. S. Dinniman, E. P. Gerber, K. M. Hines, D. M. Holland, J. M. Klinck, J. P. Nicolas, and C. Yoo: The ACCIMA Project - Coupled Modeling of the High Southern Latitudes. 12th AMS Conference on Polar Meteorology and Oceanography, April 2013. pdf
  • Bromwich, D. H., L.-S. Bai, M. S. Dinniman, E. P. Gerber, K. M. Hines, D. M. Holland, J. M. Klinck, J. P. Nicolas, and C. Yoo: How important is atmosphere-ocean coupling on fine scales for communicating the large scale ozone signature ro Antarctica? 2013 WCRP ozone meeting, Buenos Aires, Argentina, Feb. 25 - Mar. 1, 2013. pdf
  • Bromwich, D. H., and K. M. Hines: ACCIMA. XXXII SCAR Open Science Conf., Portland, OR, 16-19 July 2012. pdf
  • Hines, K. M., D. H. Bromwich, L.-S. Bai, J. P. Nicolas, D. M. Holland, J. M. Klinck, M. Dinniman, C. Yoo, and E. P. Gerber:Atmosphere-Ocean Coupling Causing Ice Shelf Melt in Antarctica (ACCIMA). 17th Annual CESM Workshop, 18-21 June 2012, Breckenridge, CO. pdf
  • Bromwich, D., L.-S. Bai, M. Dinniman, E. Gerber, K. Hines, D. Holland, J. Klinck, J. Nicolas and C. Yoo: The ACCIMA Project - Coupled Modeling of the High Southern Latitudes. 26th International Forum for Research into Ice Shelf Processes, June, 2012. pdf
  • Hines, K. M., and D. H. Bromwich: Polar WRF 3.3.1. ACCIMA Project Meeting. NYU, NYC, Dec. 16, 2011. ppt
  • Dinniman, M., and J. Klinck: ACCIMA ROMS Issues. ACCIMA Project Meeting. NYU, NYC, Dec. 16, 2011. ppt
  • Nicolas, J. P: Polar WRF over Antarctica. ACCIMA Project Meeting. NYU, NYC, Dec. 16, 2011. pptx

  • Publications:

  • Bromwich, D. H, C. Yoo, K. M. Hines, L.-S. Bai, D. Holland, J. Klinck, M. Dinniman, and E. Gerber, 2014: ACCIMA: A regional climate system model for the Southern Ocean and Antarctica. J. Climate, in review. Manuscript (PDF)
  • Dinniman, M., J. Klinck, L.-S. Bai, D. Bromwich, K. M. Hines and D. Holland, 2014: The effect of atmospheric forcing resolution on the delivery of ocean heat to the Antarctic floating ice shelves. J. Climate, in review. Manuscript (PDF)
  • Hines, K. M., D. H. Bromwich, L. Bai, C. M. Bitz, J. G. Powers, and K. W. Manning, 2014: Sea ice enhancements to Polar WRF. Mon. Wea. Rev., in review. Manuscript (PDF)
  • Li, X., E. P. Gerber, D. M. Holland, and C. Yoo, 2014: A Rossby wave bridge from the tropical Atlantic to Antarctica. J. Climate, submitted. Manuscript (PDF)
  • Li, X., D. M. Holland, E. P. Gerber, and C. Yoo, 2014: Decadal timescale impact of tropical oceans on Southern Hemisphere circulation. Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice. Nature, 505, 538-542, doi: 10.1038/nature12945. The full text and supplementary materials are available at www.nature.com
  • Medley, B., I. Joughin, B. E. Smith, S. B. Das, E. J. Steig, H. Conway, S. Gogineni, C. Lewis, A. S. Criscitiello, J. R. McConnell, M. R. van den Broeke, J. T. M. Lenaerts, D. H. Bromwich, J. P. Nicolas, and C. Leuschen, 2014: Constraining the recent mass balance of Pine Island and Thwaites glaciers, West Antarctica with airborne observations of snow accumulation. The Cryosphere Dicuss, 8, 953-998, doi: 10.5194/tcd-8-953-2014. Full Text (PDF)
  • Nicolas, J. P., and D. H. Bromwich, 2014: Antarctic temperatures since the late 1950s: SAM cooling, background warming, and West Antarctica heating up. J. Climate, submitted. Manuscript (PDF)
  • Bromwich, D. H., F. O. Otieno, K. M. Hines, K. W. Manning, and E. Shilo, 2013: Comprehensive evaluation of polar weather research and forecasting performance in the Antarctic. J. Geophys. Res., 118, 274-292, doi: 10.1029/2012JD018139. Full Text (PDF)
  • Holland, D. M., 2013: The Marine Cryosphere, in Ocean Circulation and Climate, Eds. G. Seidler, S. Griffies, J. Gould, and J. Church. Elsevier, 413-442, ISBN: 978-0-12-391851-2. Full Text (PDF)
  • Joughin, I, R. B. Alley, and D. M. Holland, 2012: Ice sheet response to oceanic forcing. Science, 338 (6111), 1172-1176, doi: 10.1126/science.1226481. The full text and supplementary materials are available at www.sciencemag.org

  • Links:

  • The Ohio State University, Polar Meteorology Group (PMG)
  • New York University, Courant Institute of Mathematical Sciences (CIMS)
  • Old Dominion University, Center for Coastal Physical Oceanography (CCPO)
  • Regional Arctic System Model (RASM)

  • Last updated: January 16, 2014

    Byrd Polar Research Center The Ohio State University