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Ocean melting has thinned Antarctica’s ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean–atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet. The boundary between West and East Antarctica is a tectonic feature that bisects the Ross Ice Shelf. This boundary constrains ocean circulation under the ice, which affects ice stability, according to airborne survey data and ocean simulations.

Author(s): MacGregor, JA; Boisvert, LN; Medley, B; Petty, AA; Harbeck, JP; Bell, RE; Blair, JB; Blanchard-Wrigglesworth, E; Buckley, EM; Christoffersen, MS; Cochran, JR; Csatho, BM; De Marco, EL; Dominguez, RAT; Fahnestock, MA; Farrell, SL; Gogineni, SP; Greenbaum, JS; Hansen, CM; Hofton, MA; Holt, JW; Jezek, KC; Koenig, LS; Kurtz, NT; Kwok, R; Larsen, CF; Leuschen, CJ; Locke, CD; Manizade, SS; Martin, S; Neumann, TA; Nowicki, SMJ; Paden, JD; Richter-Menge, JA; Rignot, EJ; Rodriguez-Morales, F; Siegfried, MR; Smith, BE; Sonntag, JG; Studinger, M; Tinto, KJ; Truffer, M; Wagner, TP; Woods, JE; Young, DA; Yungel, JK | Abstract: The National Aeronautics and Space Administration (NASA)’s Operation IceBridge (OIB) was a 13-year (2009–2021) airborne mission to survey land and sea ice across the Arctic, Antarctic, and Alaska. Here, we review OIB’s goals, instruments, campaigns, key scientific results, and implications for future investigations of the cryosphere. OIB’s primary goal was to use airborne laser altimetry to bridge the gap in fine-resolution elevation measurements of ice from space between the conclusion of NASA’s Ice, Cloud, and land Elevation Satellite (ICESat; 2003–2009) and its follow-on, ICESat-2 (launched 2018). Additional scientific requirements were intended to contextualize observed elevation changes using a multisensor suite of radar sounders, gravimeters, magnetometers, and cameras. Using 15 different aircraft, OIB conducted 968 science flights, of which 42% were repeat surveys of land ice, 42% were surveys of previously unmapped terrain across the Greenland and Antarctic ice sheets, Arctic ice caps, and Alaskan glaciers, and 16% were surveys of sea ice. The combination of an expansive instrument suite and breadth of surveys enabled numerous fundamental advances in our understanding of the Earth’s cryosphere. For land ice, OIB dramatically improved knowledge of interannual outlet-glacier variability, ice-sheet, and outlet-glacier thicknesses, snowfall rates on ice sheets, fjord and sub-ice-shelf bathymetry, and ice-sheet hydrology. Unanticipated discoveries included a reliable method for constraining the thickness within difficult-to-sound incised troughs beneath ice sheets, the extent of the firn aquifer within the Greenland Ice Sheet, the vulnerability of many Greenland and Antarctic outlet glaciers to ocean-driven melting at their grounding zones, and the dominance of surface-melt-driven mass loss of Alaskan glaciers. For sea ice, OIB significantly advanced our understanding of spatiotemporal variability in sea ice freeboard and its snow cover, especially through combined analysis of fine-resolution altimetry, visible imagery, and snow radar measurements of the overlying snow thickness. Such analyses led to the unanticipated discovery of an interdecadal decrease in snow thickness on Arctic sea ice and numerous opportunities to validate sea ice freeboards from satellite radar altimetry. While many of its data sets have yet to be fully explored, OIB’s scientific legacy has already demonstrated the value of sustained investment in reliable airborne platforms, airborne instrument development, interagency and international collaboration, and open and rapid data access to advance our understanding of Earth’s remote polar regions and their role in the Earth system.

As a part of the Software Engineering Institute's Real-Time Software in Ada project, personnel from IBM, the Naval Weapons Center, and SEI carried out an effort to construct a realistic hard real-time avionics application using Ada, including Ada tasking and rendezvous. In this joint study, an important goal was to determine how to use the Ada language as it was designed to be used in a hard real-time system, rather than continuing the current practice of avoiding the very constructs Ada's designers created to meet real-time requirements. In this paper, we present the avionics problem considered, as well as a high-level overview of an Ada solution to the problem which uses Ada tasking and rendezvous, resulting in a solution fully capable of predictably meeting its time constraints.

In an effort to promote the use of Ada in embedded system development, a realistic avionics application model whose hard real-time properties are fully predictable has been generated. This was done starting with a rate monotonic analysis of a set of typical fully synchronized periodic and aperiodic avionics tasks drawn from an idealized attack aircraft mission computer. The authors describe this avionics case study and its goals, examine the resulting design issues and trade-offs, and investigate the ability of the rate monotonic analysis model to predict its performance under a heavy load. >

This position paper explores the application of a new priority management protocol for bringing a heretofore unknown level of response time predictability to the design of real-time programs in Ada. While the protocol is not itself dependent on the use of Ada, we believe that when used in an Ada design, it will enable a much more complete use of modern software engineering in the implementation of real-time software, enhancing not only performance, but also quality, reliability, and maintainability. Thus, the protocol helps to separate timing issues from the logical structure of a set of tasks, thereby helping to provide a better basis for engineering real-time software. This new protocol, called the ceiling protocol, is described in a companion position. Although the protocol provides what we believe are extremely important benefits to the design of real-time systems, it is not without cost; the ceiling protocol imposes several significant limitations on the use of Ada in software design. It is the purpose of this paper to explore some of the ramifications of these limitations, illustrating the issues raised by the use of an actual problem encountered in modern avionics systems. We hope to demonstrate the likelihood that, in spite of these limitations, there are many existing real-time problems which could greatly benefit from the application of this protocol. (kr)