David Holland Courant Institute of Mathematical Sciences New York

Document Sample
David Holland Courant Institute of Mathematical Sciences New York Powered By Docstoc
					Ice-Shelf – Ocean Interaction: Observations & Modeling




                      David Holland
       Courant Institute of Mathematical Sciences
               New York University, USA


            The Fourth CLIVAR/CliC/SCAR
         Southern Ocean Region Panel Meeting
                   Buenos Aires, AR
                  November 13, 2006
   Why Study Ice Shelf – Ocean Interaction?


Glaciological Perspective:
       Ice Shelves may buttress an ice sheet.

Oceanographic Perspective:
       Antarctic Shelf Waters are modified by presence of ice
shelf cavity.

Climatic Perspective:
       Catastrophic sea-level rise can only occur through the
intermediary of ice-shelf ocean interaction.
IPCC 2001 Prediction Sea-Level Rise
   Update: WCRP 2006
Schematic of Ice Shelf – Ocean Interaction
        Observations & Modeling

Observational Advances
  O.1   Ice-Shelf-Front Hydrography
  O.2   Hot-Water Drilling
  O.3   Radio-Echo Sounding
  O.4   Phase-Sensitive Radar
  O.5   Topographic Soundings
  O.6   Autonomous Underwater Vehicles


Numerical Modeling
  M.1 Z-level
  M.2 Terrain-Following
  M.3 Isopycnic-Coordinate
  M.4 ISOMIP
  M.5 Coupled 2-D
Notable Ice Shelves of West Antarctica




                 FRIS




                     RIS
       PIG
Main Seas Bordering West Antarctica


        WEDDELL




BELLINGS-
HAUSEN



 AMUNDSEN
            ROSS
            Observational Techniques
Radio Echo Sounding      Hot-Water Drilling
  via airplane

                                         Ice-Front Cruises
Phase-
Sensitive
Radar



                                Ice-Front Moorings



Topographic
Soundings
              Autonomous vehicles
O.1   Ice-Shelf-Front Hydrography
O.1   Ice-Shelf-Front Hydrography




                         Foldvik et al., Antarct. Res. Ser., 1985
O.1   Ice-Shelf-Front Hydrography
   O.1                     Ice-Shelf-Front Hydrography

                                                   Temperature
                                                   Section
                   Temperature
                   Section
                                     Pine Island
    Sea Ice
                                     Glacier
                     Polynya




Jacobs et al., Geophys. Res. Lett., 1996
Jenkins et al., J. Glaciol., 1997
Hellmer et al., Antarct. Res. Ser., 1998
O.2   Hot-Water Drilling
O.2        Hot-Water Drilling


Melting 12 tonnes of snow
                                 Drill Stand




             Heaters and pumps


                                    Courtesy of Keith Nicholls, B.A.S.
   O.2                     Hot-Water Drilling
                                                  T

                                                          Thermistor
                                                          cable

                                                      Inductive loop
                                                      for CT and CM
                                                                       Glacier
                                     820 m

                                                               T

CM = current meter                                T

CT = conductivity+temperature                                  T




                                                        40 m
                                                  T
T = thermistor                                    T
                                                               T
                                                               T
                                        CT+CM                  T
                                                               T
                                             CT
                                                               T

                                                               T
                                     485 m   CT
                                                                       Ocean
                                             CT

                                                               T
                                        CT+CM



                                                                       Bedrock
Courtesy of Keith Nicholls, B.A.S.
O.3   Radio-Echo Sounding
O.3   Radio-Echo Sounding




                                          Flight
                                         Tracks




                            Thyssen et al.,
                            Polarforschung , 1993
O.3           Radio-Echo Sounding


 Marine-Ice
 Thickness:
 … 300 m

                                             Marine-
 (> 50 % of                                 Only Ice
 total                                     Thickness
 thickness)




                                    Thyssen et al.,
                                    Polarforschung , 1993
O.4   Phase-Sensitive Radar
O.4   Phase-Sensitive Radar




                         Courtesy of Craig Stewart, B.A.S.
O.4   Phase-Sensitive Radar
O.4                                    Phase-Sensitive Radar
                             0.14


                             0.12


                              0.1
      Thickness change (m)




                             0.08


                             0.06


                             0.04

                             0.0
                             2

                                   0


                         -0.02
                             380       382   384   386    388    390   392    394      396
                                                         Day number

                                                                        Jenkins et al., FRISP Report 14, 2003
O.5          Topographic Soundings




      BEDMAP
       Bedrock
         Depth




                                     Bedmap Web Pages, 2001
O.5          Topographic Soundings




 BEDMAP
       Ice
 Thickness




                                     Bedmap Web Pages, 2001
O.6   Autonomous Underwater Vehicles




                           Courtesy of Nick Millard, S.O.C.
M.1   Z-Level
M.1   Z-Level




                Grosfeld et al., 2001
M.2   Terrain-Following




                          Hellmer, GRL, 2004
M.3   Isopycnic-Coordinate
M.3   Isopycnic-Coordinate
M.3   Isopycnic-Coordinate




         Flow Schema
M.3   Isopycnic-Coordinate
M.3       Isopycnic-Coordinates




      2-Year Simulation:     MICOM
M.4    A Coupled Ice-Shelf – Ocean Model
A two-dimensional coupled model for ice shelf-ocean interaction




                                      PhD Thesis: Ryan Walker, NYU
M.4 A Coupled Ice-Shelf – Ocean Model

              Modeling goals and strategy

 • Question: How does interaction with the ocean affect
   the equilibrium state of an ice shelf?
 • Ice shelves are slow (~1 km/yr), so reaching equilibrium
   can take centuries
 • A simplified coupled model is needed to make this
   computationally reasonable
 • Solution: Model the ocean circulation and ice shelf
   profile in a vertical plane
M.4 A Coupled Ice-Shelf – Ocean Model

              What’s new about this model?

 • First simplified process model to include both ice shelf
   thermodynamics and dynamics coupled with ocean
 • Advantages of process models vs. OGCMs
    – Computationally inexpensive
        • Well-suited to long term simulations
        • Extensive sensitivity studies are feasible
    – Straightforward physics and numerics
        • Model output and performance are easily analyzed
M.4 A Coupled Ice-Shelf – Ocean Model
      Sensitivity to Ocean Warming over Time
Assessments of Ice-Shelf-Ocean Interaction
     Ice-Shelf – Ocean Interaction Summary
• Good News:
  – there exists an ever growing (?) and diverse group of researchers
  studying ice-shelf ocean interaction


• Not So Good News:
  – Topography poorly known
  – Hydrographic Observations in the cavity are inadequate
  – Models are poorly constrained
  – Parameterizations of melting are inaccurate by at least 100%
  – Most 3-D models have static ice shelf and dynamic ocean (or vice
  versa)


• Really Bad News:
  – No existing capability to model future sea level change
  – The capability is not going to emerge anytime soon
  – There is no plan