Team Updated Draft Ice Sheet Science Goals and Assignments

1. Team Updated Draft Ice Sheet Science Goals and Assignments September 27

2. OIB Ice Sheet Science Themes • What is the present state of the ice sheet? What is the flux of ice from the polar ice sheets and what is required to improve the estimates for the IPCC on the contribution of ice sheets to global sea level rise [1]? OIB will collect surface elevation change data and ice thickness measurements. In combination with available spaceborne radar interferometry measurements of surface velocity, OIB will enable ongoing assessments of the evolution of mass fluxes from the Greenland Ice Sheet and from important sectors of the Antarctic Ice sheet . • How and why are the ice sheets changing? What causes observed abrupt changes in ice sheet motion? Does a rapid change in a glacier always lead to a large change in the ice sheet volume [2]? OIB will map the sea water cavity beneath ice shelves, depth of grounded glaciers below sea level, how far inland they remain below sea level, and the basal slopes. OIB will inform on subglacial geology and basal boundary conditions. These data will feed ice sheet process studies and numerical models assessing areas capable of sustained contribution to sea level rise. • How will the mass balance and dynamics of the ice sheets change in the future [1,2,3]? High fidelity surface and basal topographies and other measurements (eg InSAR velocities from other projects) will provide input to material properties, forcings and boundary conditions. • What do we learn across glacier systems? By documenting changing glacier systems in Alaska/Greenland/Antarctica can we identify common forcings and responses that drive future evolution? The Greenland Ice sheet, rimmed by outlet glaciers, is an analog for the future of the Antarctic Ice sheet, rimmed by outlet-glacier-fed ice shelves. Alaskan/Canadian glaciers and ice caps are analogs for the eventual fates of both Greenland and Antarctica. IceBridge will explore these relationships to identify key processes and characteristize glacier systems where information on local processes can be extended regionally

3. Ice Sheet Science Questions • Where are glaciers continuing to thin and where may they be slowing/ thickening (1,2) • How can the ICESat, OIB, Cryosat, ICESat -2 measurements be optimized to characterize the state of the ice sheets over several decades? • What are the major forces and mechanisms causing the ice sheets to lose mass and change velocity, and how are these processes changing over time? (2, 3, 4) • How does the ice sheet/glacier surface topography, bed topography, bed geology, ice shelves/tongues, and grounding line configurations effect ice dynamics? • How and how far are horizontal stresses transmitted in the ice sheet? • How far downstream do changing processes near the ice divide effect glacier flow • What is the important scale for measuring geophysical parameters so as to substantially improve modeling fidelity? • Where is the subglacial water produced and where is it going? • What is the sliding law and can repeat measurements be used to refine estimates of the sliding law parameters? • How do ocean, sea ice, ice sheet interactions influence ice sheet behavior (1, 2,3, 4) • How does the bathymetry beneath ice shelves and the ocean/ice sheet interaction effect ice sheet/glacier flow dynamics? • How does bathymetry in fjords influence tide-water glaciers about Greenland?

4. Ice Sheet Science Questions • When do ice shelves become unstable? (2,3,4) • What creates "granularity" in ice shelves?  By granularity, we mean the bumpy texture that creates the meltwater features that exist on entities like the pre-collapse Larsen B Ice Shelf.  Why should water fill crevasses on Larsen in a geometry such that the fragments of the ice shelf created during collapse can capsize rather than float "top up" as a tabular iceberg?  This (the development of the proper granularity) is the key constraint that differentiates a stable ice shelf from an ice shelf that can collapse explosively. • At what scale are ice rises/rumples important for understanding ice shelf and upstream ice sheet stability? • What are yearly snow accumulation rates over the ice sheets? (1,3) • How do changing accumulation rates (and hence near surface densities and firn structure) impact altimetry measurements • What is the relative importance of ice sheet surface melt, and melt hydrology on ice sheet mass balance and dynamics? (1,2,3) • What are the surface-melt flow-patterns and how much surface melt drains directly from the surface and how much drains through channels within the ice sheet? • How much annual surface melt refreezes in place and how much results in net wastage? • What is the magnitude and spatial distribution of basal melt/freeze on ice shelves? • Are there commonalities in bed geomorphology, surface/base hydrology etc, that can be used to extend IceBridge-derived process-knowledge to glaciers not overflown by IceBridge? (characterisitic systems like fast glaciers with high slope, fast glaciers with low slope etc.) (4) • What is the current surface mass balance and dynamic thinning of ice sheets? (1,2,4)

5. OIB Ice Sheet Program Goals • Make airborne altimetry measurements over the ice sheets and sea ice to extend the record of observations begun by ICESat. (A-H) • Link the measurements made by aircraft,ICESat, ICESat-2, and CryoSat-2 to allow accurate comparison and production of a long-term, ice altimetry record. (A-D, H) • Use airborne altimetry to monitor key, rapidly changing areas of ice in the Arctic and Antarctic to maintain a long term observation record, improve understanding of glacial dynamics and surface mass balance, and improve predictive models of sea level rise and sea ice cover. (A-H) • In conjunction with altimetry measurements, collecting other remotely sensed data, improve predictive models of sea level rise and sea ice cover, especially the following: (A-H) • Ice thickness and structure; • Bed topography underlying land-based ice; • Bathymetry beneath floating ice shelves; • Snow accumulation and firn structure; and • Other geophysical constraints that will improve estimates of the geothermal and oceanic heat flux. • Adapt existing instruments for airborne remote sensing of ice by unmanned aerial systems such as NASA’s Global Hawk. (A-H)

6. Ice Sheet Observation Requirementsoriginally in section 1.3.1 of Draft Project Plan • Provide a dataset for cross-calibration and validation of ice-sheet elevations from satellite lidars (ICESat-1, ICESat-2, DesDynI-Lidar) and radars (CryoSat-2 and Envisat). (a, b, c) • Provide a dataset for improving and linking ICESat and ICESat-2 the ice-sheet elevation time series, including better characterization of ICESat-1 errors. (a,b) • Provide a data sets for investigating critical ice sheet processes (c,d) • Provide a dataset for improving and comparing numerical models of ice-sheet dynamics, especially maps of the bed beneath glaciers and ice shelves. (a,b,c,d) • Provide a dataset for improving instrument simulation and performance analysis in support of future missions, such as ICESat-2 and DesDynI-Lidar. (a,c,d,e) • Collaborate with field programs that will enhance interpretationo f ice bridge data.  (d,e)

7. Science Requirements – Spatial Coverage • Detailed requirements deleted here and awaiting an update by Halloween

8. Process toward Requirements • Assignments refering back to vu-graph 6 • 1. Michele/Scott, Duncan • 2. Ben, Bea • 3. Ken, Bea, Robin • 4. Sophie, Eric, Eric, Robin, Ian, Ben • 5. Scott , Bea(check with Science leads on Icesat etc) • 6. Michael, Ken, Mark • What is the format of the requirements and level of detail.

9. Issues and Random Thoughts • Cal val sensor intercal plan • Concise explanation/justification on each objective/requirement • Update tracability throughout the bullets • Objectives and Requirements as a check list for flight planning and instrument priorities • What are the risks to the gravity measurement inversions for sub ice shelf cavities in the presence of undetected basal marine ice?