National Academies Press: OpenBook
« Previous: 1 Introduction
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

2
Priority I: Changing Antarctic Ice Sheets

Priority I, the “Changing Antarctic Ice Sheets Initiative” as identified in NASEM (2015) addresses “how fast and by how much will sea level rise,” and consists of two interconnected components:

  1. Understanding why ice sheets are changing now and how they will change in the future, and
  2. Using multiple records of past ice sheet change to understand rates and processes.

The urgency of research addressing this topic is now more apparent than at the publication of NASEM (2015). The Special Report on the Ocean and Cryosphere in a Changing Climate by the Intergovernmental Panel on Climate Change (IPCC, 2019) noted that global mean sea level “is rising, with acceleration in recent decades due to increasing rates of mass loss from the Greenland and Antarctic ice sheets (very high confidence).” In particular, the IPCC report stated that uncertainty in global sea level rise by 2100 is “mainly determined by the ice sheets, especially in Antarctica.” Regions considered especially vulnerable are the Amundsen Sea embayment (including Thwaites Glacier; see Figure 2-1) in West Antarctica and the Wilkes Land region of East Antarctica (see Figure 2-2).

Recent studies have illuminated the role of basal melt in accelerated grounding-line1 retreat and ice-shelf thinning and calving (e.g., Jacobs et al., 2011; Golledge et al., 2012; Pritchard et al., 2012; Christianson et al., 2016; Davis et al., 2018; Milillo et al., 2019; Joughin et al., 2021). These processes have been accelerated by changing winds that push warmer ocean waters closer to the continental shelves (Thompson et al., 2011; Holland et al., 2019). Basal melt reduces ice-shelf buttressing, which enhances grounded-ice loss and ice discharge to the ocean (Furst et al., 2016; Seroussi et al., 2017; Jenkins et al., 2018; Smith et al., 2020). Current observations indicate accelerated mass loss in marine-based regions of both East and West Antarctica, raising concerns about the future stability of these regions and near-term contributions to sea level rise (Morlighem et al., 2020; Smith et al., 2020).

Modeling has improved process understanding necessary for accurate sea level projections, but uncertainty in projections of ice mass loss remains (Cornford et al., 2020; Seroussi et al., 2020). This highlights the importance of understanding

___________________

1 A grounding line or grounding zone is the area of transition from a grounded ice sheet to a freely floating ice shelf. Grounding lines often extend for a kilometer or more below sea level.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Image
FIGURE 2-1 The U.S. Nathaniel B. Palmer research vessel sits in the water by the Thwaites Glacier front. Scientists on this ship collected data about Thwaites Glacier in 2019.
SOURCE: Aleksandra Mazur.

processes and feedbacks driving the behavior of marine-terminating ice sheets, including sea ice and solid earth components, and then parameterizing them accurately in models to improve sea level rise projections (Pattyn and Morlighem, 2020). Studies seeking to understand past Antarctic ice sheet behavior, particularly during past warm climate intervals (e.g., Golledge et al., 2015; DeConto and Pollard, 2016; Gilford et al., 2020; DeConto et al., 2021), are needed to constrain the range of future sea level projections and will explicitly test whether the processes hypothesized to lead to high rates of ice mass loss actually occurred and whether they are accurately parameterized in models.

Progress in advancing the Changing Antarctic Ice Sheets Initiative is discussed in this chapter, along with key implementation challenges and opportunities to improve progress toward the research goals. Evaluation of progress will be considered separately for the two components of Priority I (Components i and ii) because they are at rather different stages of maturity. Implementation challenges and opportunities for progress are considered for the two components together.

EVALUATION OF PROGRESS

The National Science Foundation (NSF) has recognized the urgency associated with Priority I and is currently addressing it within the International Thwaites Glacier Collaboration (ITGC) as well as other funded projects. Priority I,

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Image
FIGURE 2-2 Location of sites central to Priority I research on a map showing rates of change in Antarctic ice sheet mass during 2003-2019 using ICESat. The bottom panel shows rates of ice mass change at the grounding line starting at the Antarctic Peninsula and moving counterclockwise around the continent during the same time period.
SOURCE: Modified from Smith et al., 2020.

Component i (I.i) is emphasized in the ITGC; to date, Priority I, Component ii (I.ii) has not experienced a similar level of financial and logistical support or focus from the NSF Antarctic Sciences Program.

Priority I, Component i

Component i of Priority I represents “a multidisciplinary initiative to understand why the Antarctic ice sheets are changing now and how they will change in the future.” Building from the West Antarctic Ice Sheet (WAIS) Initiative,2NASEM (2015) recommended a coordinated research effort with multidisciplinary aspects

___________________

2 See waisworkshop.org.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

(ice, ocean, atmosphere), systematic measurements of key drivers of change (e.g., sea ice, ocean circulation, ice flow, sub-ice-shelf and grounding-line environments), mapping of unknown territory beneath ice shelves and elsewhere (airborne, marine geophysical, sub-ice rover surveys), and advancing atmosphere–ice sheet–ocean–sea ice models. Critical targets were recommended to include the Amundsen Sea sector and the Ross Ice Shelf and its grounding lines. NSF joined with the UK Natural Environment Research Council (NERC) to develop the ITGC (see Box 2-1), focused specifically on the Thwaites Glacier, a climatically sensitive component of the West Antarctic Ice Sheet.

NASEM (2015) noted that such an effort would require funding from most NSF Antarctic Science programs, but should not affect its capacity to maintain a broad program of investigator-driven Antarctic research (see Chapter 5). The report suggested that this could be achieved by forging international collaborations and partnerships with other federal agencies. The report, however, did recommend that NSF should seek additional funding for this research, given the magnitude of the task and the projected costs of adaptation to sea level rise, which are orders of magnitude greater than funding currently provided for this research.

Overall, Priority I, Component i, among the NASEM (2015) strategic priorities, has been pursued most directly by NSF, providing a pathway for major scientific advances in a critical sector of West Antarctica. Despite the importance of this effort, the ITGC initiative is limited in scope compared with the scale and magnitude of the scientific issues at hand and the urgency required to address them. A detailed evaluation of Component i is provided in the following sections.

Progress Toward Science Goals

Substantial progress is under way toward the goals of Priority I, Component i, via the ITGC, which focuses on the Thwaites Glacier—widely hypothesized as the weak underbelly of WAIS—and Amundsen Sea embayment (see Figures 2-1 and 2-2). The ITGC is expected to make major science advances, but it is early to quantify scientific advances because most publications have not been submitted. Two successful field seasons were organized—one preparatory season in 2018-2019 and the first full-fledged field season in 2019-2020. Subsequently, the COVID-19 pandemic resulted in cancellation of field work in 2020-2021; at the time of writing this report, the scope of a 2021-2022 campaign is still uncertain. The first full season provided more than 2,000 km of multibeam echo sounder data and high-resolution bathymetry immediately offshore of Thwaites Glacier (Hogan et al., 2020). High-resolution bathymetry helps resolve ocean water pathways and pinning points and is critical to improve our understanding and modeling of ocean circulation and heat transport underneath the ice shelves and near grounding zones. Other ITCG studies using seismic and swath radar data revealed specific bed properties near bed ridges that are critical for stability (e.g., Muto et al., 2019; Clyne et al., 2020; Holschuh et al., 2020). Finally, robotic underwater devices have surveyed the sub-ice-shelf cavity of

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Image
FIGURE 2-4 The Icefin autonomous underwater vehicle was used by the International Thwaites Glacier Collaboration in January 2020 to study the ocean underside of the Thwaites Glacier and its grounding line.
SOURCE: International Thwaites Glacier Collaboration.

Thwaites for the first time and reported the presence of warm (0°C) water temperature near the grounding line (B. Schmidt, Georgia Tech, personal communication, 2020).

The ITGC has used technological advances to improve understanding of sub-ice-shelf and grounding-line environments. Ocean robotics, if further developed, will provide critical observations about sub-ice bathymetry and key oceanographic parameters necessary to constrain the physical processes operating at the ice–ocean interface, both in West Antarctica and in other climatically sensitive regions of Antarctica. Early demonstrations of autonomous underwater vehicle (AUV) technology indicate a high rate of success with respect to studying ice–ocean interactions (see Figure 2-4). AUV multibeam echo sounding will be essential to complete sub-ice bathymetric mapping in front of Thwaites Glacier. The ITGC will be transformative to addressing how and when WAIS might collapse. Despite delays, significant advances have already been demonstrated with critical novel observations and improved process-based modeling since the ITGC started.

Other ongoing non-ITGC projects and research avenues are critical to the science goals of Priority I, Component i. Airborne geophysical surveys with improved sensor technologies and ground penetrating radars are crucial for high-resolution mapping of bedrock elevation beneath ice sheets, inferring subglacial hydrology, imaging ice-shelf basal morphology crevasse characteristics, and quantifying accumulation rates and ice-shelf basal melt (see Figure 2-5). In situ surface observations of accumulation rates, firn3 characteristics, and weather data such as temperature, wind fields, and radiation have been used to understand long-term

___________________

3 Firn is partly compacted granular snow from prior seasons that represents an intermediate stage between snow and glacial ice.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Image
FIGURE 2-5 Airborne observation equipment for Priority I science. (Top) IcePod geophysical sensor package mounted on an LC-130 aircraft during the ROSETTA-Ice project. (Bottom) Center for Remote Sensing of Ice Sheets radar and antenna configuration on a Basler aircraft in flight.
SOURCES: M. Lucibella, USAP. https://photolibrary.usap.gov/PhotoDetails.aspx?filename=Rosetta_Icepod_Prep_Ground.jpg; CRESIS, https://cresis.ku.edu/content/research/field-programs/Antarctica.

trends and improve regional climate models. In situ surface mass balance measurements are missing from the ITGC, a critical gap in data collection to be addressed. More efforts are warranted to improve the projection capability and uncertainty reduction in a hierarchy of climate models.

The Autonomous Global Navigation Satellite System (GNSS) and seismic instruments, deployed by the Antarctic Network’s Polar Earth Observing Network (ANET-POLENET) and partner projects, provide critical information on rates of vertical land motion and laterally varying Earth structure (see Figure 2-6). An important application of the GNSS vertical uplift data is to reduce uncertainties in glacial isostatic adjustment (GIA) models required to achieve more precise ice mass balance estimates from satellite data, especially the Gravity Recovery and Climate Experiment (GRACE) and GRACE follow-on missions. Terrestrial seismic data are critical in constraining geothermal heat flux and ice dynamics. Longer time series and expanded geographic coverage of POLENET, particularly in East Antarctica, would further reduce GIA uncertainties, provide supplementary evidence for ongoing mass changes, and establish how ice sheet–solid earth interactions influence ice sheet stability and sea level contributions (see Box 2-2). In addition, including reliable GIA trends and parameterizations into coupled models can reduce

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Image
FIGURE 2-6 In situ observations under way by the Antarctic Network’s Polar Earth Observing Network using autonomous Global Navigation Satellite System instruments at the Pecora Escarpment.
SOURCES: E. Kendrick; http://polenet.org/wp-content/gallery/polenet-sites_1/3_polenet4.jpg.

uncertainties on how future ice sheet retreat would proceed, particularly for the marine-based glaciers including Thwaites.

Research in the Ross Sea sector of Antarctica, such as the interdisciplinary Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) and Subglacial Antarctic Lakes Scientific Access (SALSA) projects are improving understanding of grounding-line behavior in cold shelf regions (Thompson et al., 2018). Using an integrated systems framework, the multidisciplinary ROSETTA project collected critical airborne geophysical data and improved our understanding of how the Ross Ice Shelf interacts with the underlying ocean and land surface, helping to elucidate how complex ice shelf systems respond to climate change (Tinto et al., 2019; Das et al., 2020) (see Figure 2-5). These efforts are complementary to the ITGC research or to research that could be conducted in East Antarctica (e.g., Kingslake et al., 2018; Begeman et al., 2020; Venturelli et al., 2020).

East Antarctica, including Cook, Ninnis, Totten, and Denman glaciers, the Wilkes Subglacial Basin, the Aurora Subglacial Basin (see Figure 2-2), and their associated ice shelves, is a region of growing concern (e.g., Greenbaum et al., 2015; Li et al., 2015; Greene et al., 2017; Rintoul et al., 2018; Silvano et al., 2019). Although the ITGC focuses on the most important vector of rapid sea level rise at present, the prospect of changes in the large marine-based East Antarctic glacial catchments may have larger implications for future sea level rise, as is outlined in Box 2-3. Understanding future sea level rise requires more exploration of these East Antarctic systems.

To advance Priority I, Component i, NASEM (2015) encouraged the development of coupled models that address processes and conditions across the atmosphere, ocean, land, and ice. The ITGC funded two modeling projects that use coupled or semi-coupled models that focus on understanding basal conditions, basal sliding, calving mechanisms, and ice–ocean interactions (e.g., Gudmundsson et al., 2019; Barnes et al., 2021). Some modeling efforts have specifically focused on

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

improving the physical basis and understanding of theoretical instabilities such as the marine ice-cliff instability that could lead to large and runaway ice mass change (Bassis et al., 2021; Crawford et al., 2021). Further challenges for reducing modeling uncertainties include improving model parameterizations of grounding-line physics, subglacial hydrology, basal sliding, and a universal calving law. Observations that can constrain grounding-line physics and basal conditions, critical for ice sheet models, are difficult to obtain, leaving large uncertainties in coupled ice–ocean models. Technological advances and renewed efforts are needed to tackle these issues. Coupled GIA–ice sheet–sea level models that can simulate the impacts of earth deformation on ice sheet dynamics and sea level contributions are also needed (see Box 2-2). The committee agrees with input from the scientific community that modeling efforts should be more strongly supported and should include a broadening and growing range of scientists (e.g., ocean modelers, physical oceanographers, meteorologists, paleoclimatologists, and geodynamicists).

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Promotion of Research Priority

Overall, NSF responded quickly to NASEM (2015) in this priority area and, beginning in 2016, called out the “Changing Ice Initiative” in the introduction to their regular solicitation (NSF, 2016), encouraging proposals in this area, although noting that “major new investments in field resources are not expected to be available until the 2018-2019 austral summer field season due to existing commitments.” In later solicitations, they encouraged and added support for workshops, coordination, and synthesis efforts. In 2017, NSF released a solicitation titled “The Future of Thwaites Glacier and Its Contribution to Sea-level Rise,” a joint program with NERC (NSF, 2017). Community feedback to the committee (see Chapter 1) indicated that the special call was effective in launching the initiative. Community feedback suggested, however, that the ITGC special call favored established researchers and their long-term collaborators, contributing to perceptions that the call was not open to all. Early-career U.S. scientists indicated that they felt disadvantaged by the process, because they did not have existing collaborations with UK scientists or the leadership experience to pull together a team of multidisciplinary scientists. Overall, Priority I would benefit from engaging a broader set of disciplines and proposers to work on these critical questions.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Science Funding

Based on the committee’s classification of Priority I projects into Components i and ii, NSF has contributed $29.7 million to Priority I, Component i (I.i) since 2016 (see Figure 2-7). NSF funding for Priority I.i research from 2016 to 2020 ($5.9 million/year average) has increased substantially compared to 2011-2015 ($3.8 million/year average), as a result of NSF funding for the ITGC. The NERC collaboration has further expanded the available effort. The ITGC work started in 2018, with estimated funding of $25 million over 5 years (50 percent from NSF, 50 percent from NERC), and it is the largest glaciology collaboration between the United States and the United Kingdom in Antarctica in the last 70 years, involving 60 scientists and students. Within Priority I.i, the ITGC funding has supported two modeling studies and four key process studies (see Box 2-1). The overall funding fits the current budget of the U.S. Antarctic research program but is not necessarily commensurate with the scope, breadth, and urgency of Priority I.i science. To put the funding into context, projected costs of adaptation of vulnerable, large cities to sea level rise range in the billions of dollars per city (e.g., MacOr, 2021).

Investment in new technologies, engineering development, and computing are critical to support the science goals of this priority. For example, NSF’s investment in the Polar Geospatial Center has resulted in the high resolution

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Antarctic digital elevation model (Howat et al., 2019).4 New investment, however, has largely been directed within individual proposals. The committee agrees with feedback from the research community that there is potential for major scientific advances from investments in technological resources that would be shared across research teams (e.g., new ocean robotics).

Scientific Community

Priority I.i research builds on prior efforts of a strong and longstanding U.S. science community, organized for over two decades as the WAIS Initiative. WAIS Initiative science plans from 2002, 2014, and 2016 all outlined multidisciplinary research programs aimed at understanding ice sheet stability and projections of the contributions of the WAIS to current and future sea level rise. These community science plans were a starting point for the Changing Ice Initiative (Priority I) articulated in NASEM (2015).

The ITGC has drawn from the WAIS Initiative to establish a broad collaborative scientific community. Each Thwaites project is co-led by two principal investigators—one from the United States and one from the United Kingdom—with a

Image
FIGURE 2-7 National Science Foundation (NSF) funding awarded for Priority I.i and I.ii initiatives by year; logistics funding is not included. Project classifications of Priority I were determined by NSF, and the committee identified projects within Priority I that fit Components i or ii based on information in the project title and abstract.
SOURCE: Project funding data from Paul Cutler, NSF, personal communication, 2020.

___________________

4 Text was added to recognize the contribution of the Polar Geospatial Center after a prepublication version was provided to NSF.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

number of co-investigators, early-career researchers, postdoctoral fellows, graduate students, and technicians. Results of the ITGC have been shared among the project teams via Web conferencing, as well as at annual WAIS workshops and American Geophysical Union meetings. There is, however, a need for more focused Priority Ii science workshops to organize a wider community (beyond ITGC participants) that provides guidance and feedback on ongoing and future research priorities.

All science efforts will benefit from welcoming research contributions from scientists with diverse backgrounds, levels of experience, and career stages. The ITGC was established without a concerted effort to improve the accessibility of NSF funding to early-career researchers, researchers from diverse backgrounds, or researchers from universities supporting underrepresented minorities. As previously discussed, the ITGC favored more senior scientists, and establishing collaborations with UK counterparts was challenging for those new to the community. ITGC team members have recognized the need to improve the access of underrepresented minorities and women, and there is a grassroots effort within the ITGC to include researchers from various career levels, disciplines, and backgrounds in team leadership. Additionally, the ITGC developed community values and norms of behavior (ITGC, 2020). Community input suggests that additional top-down steps to address diversity, equity, and inclusion would also be beneficial. The WAIS workshop is another effort geared toward making the community more accessible to junior members and underrepresented minorities in the community with a commitment to providing an inclusive and equal opportunity platform for future scientific advancement and international collaborations for all. No publicly available data on diversity, equity, and inclusion within the ITGC was available for the committee to review.

Partnerships

The ITGC established international collaborations where resources and modeling efforts are shared between countries. The international agreement between NSF and NERC for the ITGC has been a substantial benefit, in terms of logistics and science funding, to address Priority I.i questions, and both agencies are to be commended for fostering this partnership. The projects are also enhanced by involvement of collaborators from Korea, Germany, and Sweden. Additionally, airborne surveys in East Antarctica have been conducted in coordination with Australia and China; the results of initial surveys are coming out (Cui et al., 2020). A few agency partnerships have also assisted Priority I.i efforts. For example, aerogeophysical surveys were coordinated with NASA’s Operation IceBridge in 2018 in the Amundsen Sea, which builds on a background of extensive surveys since 2009.

Nevertheless, the committee observes that NSF could do more to lead these Priority I.i research partnerships, because of its great scientific and logistics capacity, and establish broader and more diverse partnerships to extend its research portfolio beyond the ITGC. For example, NSF could build collaborations and

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

partnerships to advance work in East Antarctica. NSF can encourage leadership and participation in international Scientific Committee on Antarctic Research (SCAR) science programs, including the SCAR Instabilities and Thresholds in Antarctica (INSTANT) research program, which aims to quantify the Antarctic ice sheet contribution to past and future global sea level change, and the SCAR RINGS Action Group, which aims to map bed topography and grounding zone position around the circumference of the Antarctic ice sheet coastal margin, both key to advancing Priority I science objectives.5 The success of existing efforts indicates the critical role of partnerships with national and international agencies to bridge technology gaps and provide access to remote locations. If the priorities of NASEM (2015) are to be realized, then NSF should engage internationally through program-to-program bilateral agreements, multinational consortiums, and coordinating umbrella organizations such as the Council of Managers of National Antarctic Programs, SCAR, and the World Climate Research Program (WCRP).

Priority I, Component ii

The second component of the first strategic priority (I.ii) involves “using multiple records of past ice sheet change to understand rates and processes.” NASEM (2015) recommended “an integrated program of sediment and ice core observations that can directly inform and test models used to predict future WAIS melting.” Two specific science questions were highlighted:

  1. How fast did WAIS collapse in the past?
  2. How much sea level rise was caused by past WAIS collapse?

Although Component ii focuses on the WAIS, the report left open the possibility that EAIS studies could contribute to the overarching scientific goals.

To answer the first question, paleoclimate and paleoceanographic studies are necessary to determine timing and rates of past WAIS retreat. When combined with reconstructions of ocean and ice surface climate conditions at times of retreat, this may provide insights into the underlying processes and climatic conditions that lead to retreat, and hence to more robust estimates of future retreat rates. NASEM (2015) highlighted the last interglacial period (~125,000 years before present) as a possible target, because this may have been when the WAIS most recently collapsed. This period is also aligned with international ice core science priorities (IPICS, n.d.). The report recommended drilling one or more new, annually resolved ice cores extending back to 130,000 years before present and suggested that such records might be found on the WAIS margins. NASEM (2015) recommended site surveys, but highlighted the Hercules Dome site at the intersection of the WAIS and EAIS, which is thought to have well-preserved ice of the last interglacial age (Jacobel et al., 2005;

___________________

5 See https://www.scar.org/science/instant/home and https://www.scar.org/science/rings/home.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Steig et al., 2015). The report also recommended identifying and recovering high-resolution (up to annual-scale) marine sediment sequences from Antarctica’s continental margins. Previously recovered sequences from the western Antarctic Peninsula and Wilkes Land continental shelves provide decadal- to centennial-scale records of ocean temperature and sea ice history over the past 12,000 years (Leventer et al., 2006; Escutia et al., 2011; Shevenell et al., 2011; Ashley et al., 2021), with the implication that similar records should exist proximal to the WAIS. NASEM (2015) also recommended collecting new marine sediment records from past warm climate intervals to determine how ice sheets behaved under different climate boundary conditions, also a scientific priority of the International Ocean Discovery Program (IODP, 2011). Such studies improve understanding of the timing and rates of past ice retreat as well as linkages between retreat, ocean temperatures, and sea ice required to assess the relative roles of oceanic and atmospheric temperatures on past ice retreat.

To answer the second question, NASEM (2015) recognized the importance of reconstructing the geographic footprint and thickness of the past WAIS. In addition to marine sedimentologic and marine geophysical studies of past ice extent and the timing and style of ice retreat, the report recommended glacial geological mapping. This included cosmogenic nuclide techniques for surface exposure dating of terrestrial and subglacial bedrock samples to determine past ice sheet thickness and minimum extent on land. Together, these datasets can be used to refine glaciological models essential for furthering the understanding of when and how the WAIS retreated and to estimate its past sea level contributions.

Although NSF has focused on pursuing the scientific questions promoted in Priority I, currently funded projects addressing Priority I.ii science questions are limited in scope, geography, and funding (see Figure 2-7). As an example, progress toward deep ice drilling targets and marine geological studies to assess past ice extent and retreat rates has been slow and not commensurate with the ambition or urgency expressed in the 2015 report. A detailed evaluation of Priority I.ii follows.

Progress Toward Science Goals

Priority I.ii goals are being addressed by two NSF-NERC collaborative efforts funded as part of the ITGC to address past WAIS ice extent, thickness, and ice sheet dynamics in the Thwaites Glacier region. To date, terrestrial surface and subglacial bedrock samples were successfully recovered during the 2019 field season and are being analyzed to reconstruct regional ice sheet and relative sea level changes during the Holocene (the last 11,700 years) and to understand the amount and timing of terrestrial ice thinning associated with past and present Thwaites grounding-line retreat. Two of three shipboard field seasons were completed by the NSF-NERC-funded Thwaites Offshore Research (THOR) project; results from marine geophysical surveys are emerging (Kirkham et al., 2019, 2020; Hogan et al., 2020; Wåhlin et al., 2021), and marine sediment studies are ongoing. Significant additional efforts will be

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

needed to integrate data from Priority I.i and I.ii ITGC-funded studies to achieve a holistic view of past and present glacier response in the Thwaites catchment.

Both deep ice core drilling through the Antarctic ice sheet (e.g., WAIS Divide Project Members, 2013, 2015) and sediment drilling near the continent (e.g., Naish et al., 2009; Escutia et al., 2019) have made essential contributions to knowledge of Earth’s climate system and Antarctic ice sheet evolution. NASEM (2015) recommended drilling a long ice core to access the last interglacial-age ice. Preparatory work that is required for drilling this ice core at the NSF-funded Ice Drilling Program (IDP) facility is well-advanced (Johnson et al., 2020). Initial site survey work at Hercules Dome has been carried out, and potential target sites have been identified, as required for initiating the ice drilling program. An award has been issued by NSF for deep drilling at this site, and the project team has a target for drilling to start in 2024, almost a decade after this project was prioritized, although the final implementation schedule has not been set.

Since 2015, NSF has made modest investments in investigator-led programs (outside of the ITGC) focused on understanding the timing, rates, and forcing mechanisms of past ice retreat in a variety of geographic settings and time intervals. Funded geochronology research on marine sediments and terrestrial-based geology, including site characterization, is expected to improve known weaknesses in site-selection techniques (e.g., Spector et al., 2018), dating techniques (see Box 2-4; e.g., Subt et al., 2016; Venturelli et al., 2020), and proxies used to reconstruct past ocean temperatures (e.g., Shevenell et al., 2011). Such fundamental research is essential to develop systematic sampling strategies and accurate and precise chronologies of ice retreat and to understand past forcings. NSF investments in subglacial bedrock drilling technology (e.g., Goodge and Severinghaus, 2016; Boeckmann et al., 2020; Kuhl et al., 2020) have improved recovery of bedrock suitable for terrestrial cosmogenic geochronology studies. Projects to cosmogenically date past ice extent in Antarctica have been funded since 2015 and are documenting ice retreat rates and drivers for ice sheet change around the Ross Embayment (e.g., Kingslake et al., 2018; Shakun et al., 2018; Balter-Kennedy et al., 2020). In the central and western Ross Sea catchments, terrestrial-to-marine transects are providing a more complete picture of ice sheet evolution in the Cenozoic era (past 66 million years), and modelers are using constraints on past ice sheet extent and retreat rates to understand how ice might respond during warmer climate intervals (McKay et al., 2012, 2019; Levy et al., 2016; Kingslake et al., 2017; Goehring et al., 2019; Halberstadt et al., 2021).

Although there is important work under way, the geographic coverage of Priority I.ii marine- and terrestrial-based geochronologic studies remains limited. IODP expeditions related to Priority I.ii science goals (2018-2019) have focused on the Ross Sea, Amundsen Sea, and Scotia Sea (see Figure 2-2), while terrestrial studies have focused in the Ross Sea sector, Marie Byrd Land, and proximal to Thwaites. NSF has done an excellent job supporting the new Antarctic Core Collection and

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

continuing to support the Polar Rock repositories6 at Oregon State University and The Ohio State University, respectively. It is clear that analysis of existing sedimentary and rock samples can increase geographic coverage of research on past ice sheet collapse while improving access to materials to a broader, more diverse scientific community. However, Priority I.ii science cannot be addressed using only previously collected samples. Additional geophysical surveys and coordinated interdisciplinary marine and terrestrial field sampling programs in climatically sensitive East Antarctic catchments (e.g., Wilkes Land/Sabrina Coast, Filchner-Ronne; e.g., Golledge et al., 2017; see Figure 2-2) will be necessary to address Priority I.ii questions in a systematic way.

Promotion of Science Priority

As discussed previously, the science objectives of Priority I.ii were briefly mentioned in the annual announcements of opportunities for NSF funding. Without any specific solicitation or Dear Colleague Letter, some investigators may not have known that paleoclimate/paleo-ice sheet proposals were encouraged under the Priority I umbrella. In the ITGC funding call (NSF 17-505), paleo aspects were not mentioned in the program synopsis. “Past Change” was mentioned as a theme in the program description, but few details were provided on what constitutes past change, or the time frame considered. Community input indicated that many people did not know that the ITGC contained a paleo component.

Science Funding

Funding for Priority I.ii projects declined slightly in 2016-2020 ($2.2 million/year average) compared to the 2011-2015 interval ($2.3 million/year average) (see Figure 2-7). This funding trend is not commensurate with the relative importance of ice core and sub-ice to ice-proximal geological research and data collection required for addressing Priority I.ii science, or for constraining climate and ice sheet models.

Scientific Community

In terms of community, there has not yet been a specific effort by NSF or NSF-funded Antarctic researchers to bring together the different Antarctic-centric paleoclimate communities addressing past ice sheet change. There are encouraging signs of community building among the ice core researchers associated with

___________________

6 These facilities receive and curate marine sediment samples, rocks, and their associated data and metadata, enforce moratorium access, and are working toward providing up-to-date searchable databases.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Hercules Dome ice core planning, and the Antarctic marine geology community is currently developing via recent IODP initiatives. Although paleoclimate researchers have other opportunities to converge in international community efforts (e.g., the SCAR Past Antarctic Ice Sheet Dynamics, SCAR INSTANT, Past Global Changes, PALeo constraints on SEA level rise [PALSEA]), these groups typically do not merge terrestrial, ice, and marine communities. The annual U.S.-focused WAIS and Interdisciplinary Antarctic Earth Sciences meetings have traditionally been excellent opportunities for ice core and terrestrial geologists to gather, and the marine geological community has recently joined these meetings.

Partnerships

International partnerships, such as the successful UK-U.S. partnership for the ITGC, have been key to advancing Priority I.ii science, particularly in regions far from U.S. bases. Collaboration with international programs, including IODP, has offered NSF an opportunity to leverage large field program investments by supporting post-expedition science. Between 2018 and 2019, three IODP expeditions were conducted in Antarctic waters as part of an ongoing initiative to address IODP scientific challenges complementary to those outlined in Priority I.ii, including How do ice sheets and sea level respond to a warming climate? A total of 12 sites were drilled and ~5.4 km of marine sediments were recovered from the Ross (McKay et al., 2019), Amundsen (Gohl et al., 2021), and Scotia seas (Weber et al., 2019). U.S. scientists are developing proposals to address Priority I.ii-aligned science using IODP samples, and three IODP-related projects have already been funded.

KEY IMPLEMENTATION CHALLENGES ACROSS PRIORITIES I.i AND I.ii

The committee identified three key challenges affecting the pace of implementation across Priorities I.i and I.ii—the magnitude of the science goal, limited NSF logistical support capacity, and the lack of integrated community strategies for advancing Priority I science.

The Challenge of the Science Goal

The science questions highlighted in Priority I are challenging because understanding why Antarctica’s ice sheets are changing requires studying both ongoing processes and past ice sheet behavior at many locations with integration and holistic assessment of research findings across time and space. Recent observations have identified significant ice sheet thinning and mass loss over multiple decades in many regions of Antarctica (Paolo et al., 2015; Adusumilli et al., 2020; Das et al., 2020; Smith et al., 2020). As has been demonstrated by the ITGC,

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

addressing these questions at one location requires significant scientific and logistical resources. Thus, it is likely that after a decade of effort, scientists will have only begun to scratch the surface of understanding what makes portions of Antarctica’s ice sheets sensitive to climate variations in the present, and how these regions might respond with continued warming. Focusing on just one region (Thwaites Glacier in the Amundsen Sea), at the expense of other rapidly evolving regions may result in a missed opportunity to capture key processes in other climatically sensitive glacial catchments. The societal urgency of sea level rise necessitates that Antarctic researchers and their funding agencies broaden the geographic scope to more holistically address Priority I science questions. Such an effort would require substantially increased resources, as initially stated in NASEM (2015).

Answering fundamental Priority I science questions continues to be challenging because sub-ice-shelf and subglacial environments are difficult to access, but such access is required to understand the processes and environmental conditions that influence glacial flow, rapid grounding-line retreat, and ice shelf melt, rifting, and calving (Dupont and Alley, 2005; Scambos et al., 2017; Rintoul et al., 2018; Milillo et al., 2019). Additional challenges arise when determining the hierarchy of physical processes acting on ice retreat, parameterizing these processes in models, and increasing the resolution of these models to capture temporally rapid processes.

Priority I.ii calls not just for determination of past ice sheet extent, but also for assessment of past rates of change. Determining past rates of ice sheet change is a notoriously hard problem to address because of the difficulty of producing ice, rock, and sediment records with sufficient resolution and chronology in any one catchment. This is particularly acute for marine sediments, which are the most direct archive for determining maximum ice extent at any given time or for estimating retreat rates (see Box 2-4). Knowledge of regional bedrock and erosion history is essential, and linking local ice levels to broader ice sheet behavior requires substantial spatial data coverage (Spector et al., 2019, 2020). At present, outside the western and central Ross Sea regions, there are no large-scale coordinated campaigns to systematically sample terrestrial-to-marine transects to establish past ice extent, thickness, and retreat rates. This type of holistic assessment would be valuable in all climatically sensitive catchments, including Thwaites, to improve understanding of Antarctica’s ice sheet sensitivity to anthropogenic warming.

Logistical Challenges

At present, Priority I research focuses on Thwaites Glacier and West Antarctica. Although the ITGC includes research funding from NERC and logistics support from the British Antarctic Survey, NSF has carried a major part of the large logistics support load for this initiative (e.g., flight hours, ship days). Even with prioritization of ITGC logistics, strained logistics capacity has affected the pace of

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Priority I progress. NSF made it clear in its 2016 call for proposals that new major field projects (such as the Hercules Dome ice drilling) could not be supported for some years. In 2018-2019, NSF used LC-130s to transport 50,000 gallons of fuel to the ITGC, which impacted LC-130 availability for other deep-field research support. A planned field season of work at Hercules Dome (Priority I.ii) in 2018-2019 necessary for site selection was almost completely lost due to logistical challenges including those associated with LC-130 landing site assessments. This resulted in a slow start for many aspects of the Priority I.ii component; Hercules Dome drilling is unlikely to start before 2024.

Marine access is a primary logistical concern for Priority I science in the circum-Antarctic. At present, the aging Research Vessel/Ice Breaker Nathaniel B. Palmer (see Box 1-2) is required for any marine access in remote West and East Antarctica, and three recent cruises of the vessel have been dedicated for ITGC activities.7 To address Priority I science questions, researchers must be able to access the inner continental shelf, which is complicated by icebergs, multiyear landfast ice,8 and sea ice. While the Nathaniel B. Palmer is a polar-capable vessel, it is not able to operate in the heavy ice conditions often encountered in inner shelf regions. Furthermore, the Nathaniel B. Palmer does not have enough deck space, a sufficient moon pool, or the equipment required to safely deploy and recover state-of-the-art AUVs and remotely operated vehicles to access, image, and sample glacial grounding zones and sub-ice-shelf environments. The vessel also lacks the space and equipment required to safely conduct geological drilling operations (e.g., over-the-side and/or seabed drilling systems) to recover marine sediments older than the last deglaciation (~18 ka). As such, it is currently difficult, if not impossible, to use the Nathaniel B. Palmer to recover data from Antarctica’s continental shelves, grounding zones, and beneath ice shelves to addresses Priority I science questions.

Overall, NSF logistics support capacity, which has diminished in recent years (see Boxes 1-1 and 1-2), limits the scope of science in Antarctica and the Southern Ocean and the accessibility to remote areas of interest. With NSF logistics alone at current levels of support, access to East Antarctica to pursue research in other vulnerable areas such as Totten Glacier, the Wilkes Subglacial Basin, or the Ronne-Filchner Ice Shelf is all but impossible. Scientists are not involved in logistics planning, so the science community is not aware of how trade-offs across science goals are being assessed.

Community Challenges

Integrative analysis of current processes and past change, including complementary data from the ice, terrestrial, and marine communities, is needed to develop a holistic understanding of current and future rates of ice mass loss.

___________________

7 See https://www.usap.gov/USAPgov/vesselScienceAndOperations/documents/nbp_history.pdf.

8 Ice that is attached to the shoreline and survives at least one melt season.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

However, there is little sense of a joint initiative to comprehensively address Priority I questions across these communities, both within and across paleo, current, and future components. For example, there does not seem to be much attempt to involve the paleo community in workshops focused on understanding current processes (particularly within the ITGC). Without discussions between all who might contribute to answering questions about how fast and how much sea level will rise, it is unlikely that meaningful progress will be made.

Although feedback from the science community suggests that field and remote sensing data were reasonably well shared among the ITGC project members, the committee and community note that the current framework of data collection, analysis, processing, distribution, and incorporation of these data in advanced, gridded, validated products needs to be improved in order to meet the needs of ice sheet modelers in a more timely fashion. There is a danger that these products will only be ready by the end of the project, rather than being a part of the ongoing activities during the project. Data collection, processing, validation, and publication require time, and finding a fair balance between data moratorium conditions and the value of data sharing is challenging.

The ITGC community has been actively involved in efforts to increase its diversity, equity, and inclusion (DEI). DEI activities planned through large programs, such as the ITGC and workshops, are a great way to involve larger sections of the community. At present, these activities are largely shouldered by junior to mid-career scientists, which takes focus away from funded research, with little recognized career benefits in current academic promotion structures.

OPPORTUNITIES TO IMPROVE PROGRESS

The following sections discuss strategies and opportunities to improve progress toward Priority I science goals. Strategies to address logistics are discussed separately in Chapter 6, because these issues affect all of the strategic priorities.

Research and Funding Priorities

To target Priority I.i goals, the large and rapidly changing Thwaites Glacier was identified as the primary research focus. In light of the enormity of the science objectives, the societal utility of the research findings, and COVID-19-related delays, continuation of international Thwaites Glacier region research with a second phase of 5 more years should be considered so that its research activities and goals can be completed. A range of research, discussed under the sections on Progress Toward Science Goals, that supplements ITGC projects also needs to be supported to more fully understand future WAIS change and sea level contributions. These include the completion of high-resolution bathymetric mapping beneath regional ice shelves, sampling of water properties beneath ice shelves using ocean robotic devices,

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

longer-term monitoring of surface and firn conditions using automated weather stations and in situ firn measurements, improving climate models, and supporting ANET-POLENET observations of GIA for supplementary mass balance estimates, among others. Analysis of existing IODP marine sediment cores collected from West Antarctica’s margins and the Hercules Dome ice core is also needed, which could engage a broader community of paleoclimate and paleoceanographic scientists.

Improvements in sea level rise projections require better integration of the components such as ice dynamics, surface mass balance, sea ice changes, solid earth feedbacks, and ice–ocean–atmosphere interactions into Earth system models. More emphasis on modeling efforts, including coupled climate–ice sheet–solid earth models and enhanced integration of observations and modeling, should be prioritized. Increasing the resolution of ice sheet and ocean models and improving the ability of models to capture evolving grounding lines, fracture processes, surface, englacial, and basal processes would enhance progress toward Priority I objectives. Sea ice variability and GIA trends also need to be included to assess their potential to reduce uncertainties in ice sheet retreat projections.

Scientists are increasingly aware that there are other vulnerable regions with potentially large impacts on future sea levels, including several East Antarctic catchments (see Box 2-3; Paolo et al., 2015; Rignot et al., 2019; Morlighem et al., 2020; Smith et al., 2020). To achieve Priority I goals of understanding how fast sea level will rise, research focus also needs to be directed toward the most vulnerable and rapidly changing sectors of East Antarctica to assess their potential for near-term and future sea level contributions. Targeted funding opportunities akin to the scale of the ITGC with international partners will be needed to make significant contributions in this region. NSF should develop and lead international partnerships to explore the stability of East Antarctica’s Pacific sector marine-terminating outlet glaciers. Such a field campaign could include marine to land-based geophysical surveys and in situ measurements; marine sediment, terrestrial bedrock, and ice core drilling; and atmosphere, ice surface, and oceanographic studies. Such a campaign would serve Priority I.i and I.ii and inform our nation and society about the risks of rapid sea level rise from East Antarctica, complementing the new understanding of sea level contributions of the Amundsen Sea Embayment sector of West Antarctica from the ITGC.

Beyond the ITGC, additional coordinated terrestrial-to-marine transects in climatically sensitive regions (including East Antarctica), along with specialized funding calls, could help to systematically address Priority I.ii science questions with the breadth and urgency required. A special call highlighting Priority I.ii topics might generate geographically focused proposals and foster a sense of community. Such research would require use of recent advances in marine and ice drilling discussed in the next section.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Opportunities Afforded by Recent Technological and Scientific Developments

A number of recent technological and scientific developments offer opportunities to advance Antarctic research.

Ocean Technologies

Technologies to explore the ocean and sub-ice-shelf environment continue to develop and offer opportunities for accessing sites currently out of reach with existing research vessels. Understanding the sub-ice-shelf environment is key to understanding changes in the marine-based parts of the ice sheets. The scientific community emphasized the need for increased technological capabilities for sub-ice-shelf exploration to significantly advance science, including Argo float capabilities for critical information about the water column, AUV technologies for access to the sub-ice-shelf environment and crossing grounding lines, and sea-bottom transponder arrays for the navigation of AUVs under sea ice and ice shelves and for the positioning of floats during the ice-covered winter season. Improved AUV technologies, such as tether-free Icefins,9 can cover longer distances to provide access to subglacial channels and can be equipped with upward- and downward-looking multibeam sonar and improved sampling and monitoring. These technologies exist today, and if NSF implemented a shared instrument pool, similar to the ice-core drilling model, these technologies could be more widely applied.

An upgraded heavy-ice–breaking research vessel with heave compensation could greatly expand Antarctic research capabilities to address Priority I. A new vessel could also provide state-of-the-art instruments for marine sediment recovery and geophysical surveys.

Ice Sheet Technologies and Opportunities

Understanding the nature of the ice-bedrock interface is key to assessing ice dynamic change. The community identified a need for an increased capacity for rapid-access drilling for basal properties, ice-flow studies, and past bedrock exposure. Although drilling continuous cores (as envisaged at Hercules Dome) remains the most straightforward solution to obtaining last interglacial ice, the prospect of obtaining ice from previous interglacials in areas with no net accumulation of snow (known as blue-ice zones) has emerged more prominently since 2015 as a further option (e.g., Shackleton et al., 2020).

The community also identified swath-radar imaging capabilities as an emergent area for enhanced understanding of, and higher-resolution assessments of, ice sheet bed topography and tomography. Ice cores can be used to provide chronology to the radar datasets collected during extensive airborne radar

___________________

9 See https://schmidt.eas.gatech.edu/icefin.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

campaigns and can be used to study basal conditions, accumulation rates, and past climate conditions (e.g., MacGregor et al., 2009; Bell et al., 2011; Das et al., 2013; Medley et al., 2014). Another technology yielding novel types of data is phase-sensitive radar (e.g., Kingslake et al., 2016), now being used to estimate vertical strain rates within the ice sheet, critical information for understanding ice dynamics.

Improved sensor, power, and data transfer technologies for in situ measurements are also needed. Installing automated weather stations with improved sensors in climatically sensitive regions is important for obtaining a longer-term record of Antarctic surface parameters, including snow accumulation and firn temperatures. Oceanographic measurements of temperature and salinity profiles on the continental shelf and beneath ice shelves using Argo-float-like instruments and robotic devices complement satellite observations of glacier, ice shelf, and ocean conditions. Enhanced data transfer technologies would allow autonomous instrument operations with full remote data recovery from regions that are logistically difficult to access. Advancing technologies to acquire observational records of critical parameters is challenging on an individual investigator level, but can be done as a part of a facility. The advantages in investing in facilities to collect longer-term data are that they becomes immediately available to anyone who needs them and bypasses the need to go through complicated data sharing procedures.

Coupled Ice Sheet–Ocean–Solid Earth and Climate Modeling

Improvements in sea level rise projections require additional development of continental-scale coupled ice sheet–ocean–atmosphere–sea ice and solid earth models. With recent advances in the availability of high-resolution, remote sensing data and increased availability of field-based observations, there is ample opportunity for assimilating these data into continental-scale coupled models as well as their evaluation. The process of data assimilation into coupled models and their evaluation is by no means trivial, requiring dedicated approaches by teams of data scientists and modelers. This could be facilitated in proposal calls and workshops that would provide an opportunity for teams from varying disciplines to collaborate on improving models. At present, there is still a disconnect between big-data scientists (e.g., remote sensing experts) and modelers. There is also need of support for community-driven model intercomparison exercises (e.g., Seroussi et al., 2020).

Improvements in resolution and data assimilation, as well as developing coupled continental-scale models, require improved computing and storage facilities and technical support. Collaboration with computer scientists with expertise in data assimilation, machine learning, and optimization of large computer codes is needed to further improvements in developing continental-scale coupled models. Model development, evaluation, and validation are generally a process that takes longer than the typical 3-year project timeframe.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

Increasing Scientific Community Involvement

To advance integrated science, NSF should encourage and fund proposals for workshops specifically aimed at bringing together disparate communities (e.g., marine and terrestrial, modern and paleo observations, and observational and modeling) addressing Priority I questions. Topical workshops that bring together researchers from a variety of backgrounds to discuss Priority I science questions in different geographic regions are likely to generate new collaborations of interdisciplinary groups. For Priority I.i, in particular, the disconnect between observational scientists and modelers can be reduced via these topical workshops. Workshops on Hercules Dome involving component I.ii researchers outside the ice core community could help build a multidisciplinary community. To improve Priority I.ii community collaborations, Gordon Conference–style meetings on terrestrial and marine paleoclimate science might encourage scientists to come together to exchange ideas and develop collaborations. Such gatherings are important for building trust and discussing integrated field programs that seek to understand sensitive climate catchments from the ice sheet to the continental margin.

Chapter 6 includes discussions of ways to help address the strained logistics burden through communication forums for scientists working in similar areas, which would also help to foster collaborations. Implementing geographic focus groups might assist in streamlining logistics and equipment usage, as has been done with previous efforts such as the Shackleton Glacier camp. A similar mechanism has been successful in NSF-funded IDP and NSF-funded IODP, both of which have Science Advisory Boards or Panels tasked with gathering community input for prioritizing drilling tool usage and ship tracks.

International and Interagency Collaboration

The ITGC and many multinational collaborations during the International Polar Year demonstrated that comprehensive programs that involve simultaneous airborne, ship-based, drilling, and ground-based work are best addressed by developing international and interagency collaborations. The ITGC is an example of an ambitious plan that has benefited from NSF-NERC and NASA collaboration. East Antarctica is an important target in the coming years because of its potential contribution to sea level rise. Coastal East Antarctica is difficult to access logistically from U.S. research stations, and an ambitious program will need collaborations with foreign agencies as well as domestic partners such as NASA. The U.S. and international science communities have long recognized the need for international collaboration to meet ambitious science agendas in Antarctica (see Kennicutt et al., 2014, 2016, 2019; NASEM, 2015), but new and transparent mechanisms to develop internationally supported programs need to be developed. To realize Priority I science objectives more fully, NSF should consider multiple mechanisms to engage internationally, including bilateral agreements between national programs,

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

multinational consortiums, and through international umbrella organizations such as SCAR and WCRP.

Priority I.i scientists supported by NSF regularly collaborate with NASA scientists on using remote sensing observations and ice sheet models, but interagency policies to facilitate collaborative work are lacking and should be developed. Similar agreements could be worked out between NSF and the U.S. Department of Energy, the National Oceanic and Atmospheric Administration, and other agencies, to encourage larger initiatives in coupled model developments. Leveraging Antarctic and Southern Ocean drilling projects through enhanced coordination with IODP could advance Priority I.ii science in particular.

CONCLUSIONS AND RECOMMENDATIONS

Priority I science questions are urgent, complex, and essential to global adaptation planning, requiring research initiatives that are ambitious in vision and funding. Priority I research addresses how fast and how much sea level will rise, including a focus on both current rates of ice sheet change and studies of past major ice sheet retreat episodes to better understand current events. The ITGC is a large, multinational research initiative that is making important progress, with a focus on understanding current ice sheet and ocean interactions as drivers of ongoing ice mass loss at the Thwaites Glacier and Amundsen Sea region in West Antarctica. Research progress in understanding the ice mass loss rates and sea level rise associated with past ice sheet collapse events is proceeding at a slower pace. Despite the important progress to date, the potential magnitude of the threats to humans posed by Antarctic ice sheet collapse demands a more aggressive, comprehensive, and ambitious research approach; the scientific response to this immense challenge should be commensurate with the task at hand.

To more fully address the major science objectives of Priority I, NSF should consider expanding initiatives beyond the International Thwaites Glacier Collaboration to include the Wilkes Land sector of East Antarctica. Multiple studies since 2015 have demonstrated that parts of East Antarctica are rapidly losing mass and have a greater potential for contributions to sea level rise than West Antarctica. East Antarctic research initiatives at the scale of the ITGC supported by new collaborations with foreign agencies as well as domestic partners such as NASA could provide critical information to inform the understanding of current and future sea level rise.

Given the scientific urgency of Priority I, NSF should take a leadership role in initiating additional international and interagency partnerships to enable ambitious Priority-I–focused terrestrial- and marine-based science campaigns to progress, in parallel, in both West and East Antarctica. The International Thwaites Glacier Collaboration and International Polar Year collaborations demonstrated that multidisciplinary projects that involve airborne, ship-based, drilling, and ground-based work are best addressed (scientifically and logistically) by developing

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

international and interagency collaborations. International partnerships can also help address existing logistics constraints.

NSF should expand and continue international Thwaites Glacier region research. ITGC efforts are advancing well, despite COVID-19-associated challenges, and promise important and essential scientific advances on the physical processes driving the retreat of this sector of Antarctica, thereby reducing uncertainties in projections of sea level rise from Antarctica. This highly innovative collaboration is challenging, but it provides significant benefits in terms of discovery and impacts on the science of sea level rise. It is very difficult to envision, however, that most of the key scientific questions will be addressed with only a couple of field campaigns to a sector of Antarctica that is changing very rapidly and has never been investigated at this level of detail. Additional years of study of this sector by an expanded international community are warranted given our current state of knowledge of the underlying processes and rates of ice sheet loss. Detailed study of the evolution of the Antarctic ice sheet will remain important for decades to come to significantly reduce uncertainties of sea level rise projections. Increased investments in new technologies, such as underwater robotics, will provide critical data and enhance the understanding of ice–ocean interactions at grounding lines.

NSF should issue a specific call for proposals directed toward increasing knowledge of past ice sheet behavior, rates of change, and climate forcings—information essential to place ongoing environmental change in context and accurately predict future sea level rise. The committee and community perceive a lack of urgency from NSF toward funding and supporting Priority I.ii-focused research. This perception arises from the slow pace of progress in drilling the Hercules Dome ice core, the limited NSF Antarctic Sciences involvement in preexpedition planning, logistical support, and post-expedition scientific funding in support of the three 2018-2019 IODP Antarctic Margin expeditions, and the limited number and scope of funded projects studying past episodes of ice sheet loss (either within or outside of the ITGC). A focused call for proposals could increase attention to this important science area.

Limited logistical support capacity and funding are slowing implementation of Priority I. Aging infrastructure—specifically the LC-130 fleet and the limited polar icebreaker and research vessel capacity for science support—and increasing costs of logistics are having a negative impact on access and support provided to research, particularly affecting deep-field sites. These constraints force NSF to make difficult decisions on distributing the limited logistics resources among various science teams. Increasing access for science, cargo, and fuel into the deep field would significantly increase research progress toward Priority I objectives. The seagoing capacity and capabilities of U.S. Antarctic science need to be enhanced to provide critical access to the oceanic margins of the WAIS and EAIS and address Priority I questions in a timely way. Recommendations to address cross-cutting logistics issues are discussed in Chapter 6.

NSF should increase support for interdisciplinary research and modeling efforts to advance progress toward Priority I objectives. Specifically, NSF should

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

continue support for research to improve coupled atmosphere–ocean–ice–earth models, which need substantial additional development and data to improve parameterizations of important processes into an Earth system modeling framework. Specific calls for workshops and other initiatives that bring together terrestrial, marine, and modeling communities interested in studying past and ongoing change in key marine-based catchments in both West and East Antarctica are also recommended.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×

This page intentionally left blank.

Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 25
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 26
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 27
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 28
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 29
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 30
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 31
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 32
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 33
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 34
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 35
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 36
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 37
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 38
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 39
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 40
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 41
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 42
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 43
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 44
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 45
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 46
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 47
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 48
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 49
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 50
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 51
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 52
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 53
Suggested Citation:"2 Priority I: Changing Antarctic Ice Sheets." National Academies of Sciences, Engineering, and Medicine. 2021. Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research. Washington, DC: The National Academies Press. doi: 10.17226/26338.
×
Page 54
Next: 3 Priority II: Using Genomics to Understand How Antarctic Biota Evolve and Adapt »
Mid-Term Assessment of Progress on the 2015 Strategic Vision for Antarctic and Southern Ocean Research Get This Book
×
Buy Paperback | $48.00 Buy Ebook | $38.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

The Antarctic's unique environment and position on the globe make it a prime location to gain insights into how Earth and the universe operate. This report assesses National Science Foundation (NSF) progress in addressing three priority research areas identified in a 2015 National Academies report: (1) understanding the linkages between ice sheets and sea-level rise, including both a focus on current rates of ice sheet change and studies of past major ice sheet retreat episodes; (2) understanding biological adaptations to the extreme and changing Antarctic environment; and (3) establishing a next-generation cosmic microwave background (CMB) program, partly located in Antarctica, to study the origins of the universe.

NSF has made important progress understanding the impacts of current ice sheet change, particularly through studies focused on the ice sheet and ocean interactions driving ongoing ice mass loss at the Thwaites Glacier and Amundsen Sea region in West Antarctica. Less progress has been made on studies of past major ice sheet retreat episodes. Progress is also strong on CMB research to understand the origins of the universe. Progress has lagged on understanding biological adaptations, in part because of limited community organization and collaboration toward the priority. To accelerate progress during the second half of the initiative, NSF could issue specific calls for proposals, develop strategies to foster collaborations and partnerships, and commission a transparent review of logistical capacity to help illuminate strategies and priorities for addressing resource constraints. Such efforts would also help optimize science and proposal development in an environment of inherently constrained logistics.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!