New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations

Jordan, Tom A.; Porter, David; Tinto, Kirsty; Millan, Romain; Muto, Atsuhiro; Hogan, Kelly; Larter, Robert D; Graham, Alastair G C; Paden, John

doi:10.5194/tc-2019-294

Cited by 16 publications

(35 citation statements)

References 32 publications

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“…Troughs and channels in the adjacent eastern part of Pine Island Bay have been described comprehensively by Nitsche et al (2013) and Kirkham et al (2019). The larger troughs in our study area, which have also been identified on gravity-derived regional bathymetry maps (Millan et al, 2017;Jordan et al, 2020. ), are considered important as potential pathways for the transport of CDW towards the grounding zone of TG and warrant full description here.…”

Section: Trough and Channel Metricssupporting

confidence: 67%

“…During ITGC cruise NBP19-02, the marine areas in front of TG were unusually clear of sea-ice and icebergs providing a unique opportunity for bathymetric data acquisition at the margin of Thwaites Ice Shelf (Larter et al, 2020). MBES data was acquired using a hull-mounted 1° x 1° Kongsberg EM122 echo sounder with 288 across-track beams and an operational frequency in the range 11.25-12.75 kHz.…”

Section: Multibeam Echosounder Datasets (Mbes)mentioning

confidence: 99%

“…For NBP19-02, data processing was performed on board using MB-System (Caress and Chayes, 1996;Caress et al, 2019) in order to apply optimal sound velocity profiles (SVPs) to each data file and to remove erroneous soundings. Ray tracing and sea-floor depths were calculated using SVPs generated from conductivity-temperature-depth and expendable bathythermograph casts made during NBP19-02 (Larter et al, 2020). Most of the other bathymetry datasets were also initially ping-edited during each respective cruise; however, minor additional cleaning was performed in MB-System and QPS Fledermaus (Mayer et al, 2000) after the datasets were collated when clear outliers could be easily identified.…”

Section: Multibeam Echosounder Datasets (Mbes)mentioning

confidence: 99%

“…1) (Ferrigno et al, 1993;Rabus et al, 2003;MacGregor et al, 2012). In contrast, the EIS remains pinned on a sea-floor high that restricts its flow (Rignot et al, 2001; Tinto and Bell, 2011;Jordan et al, 2020) and induces shear between the EIS and TGT. Satellite imagery confirms that since 2006 increased crevassing and fracturing has weakened the shear zone between the EIS and TGT (Kim et al, 2015), with the two ice shelves remaining connected until 2010 (MacGregor et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

“…Regional bathymetric compilations for the ASE shelf use multibeam echo-sounder data (MBES) where available in offshore regions (Nitsche et al, 2007(Nitsche et al, , 2013Arndt et al, 2013) and gravity inversions and a limited amount of echo-sounding data from autonomous underwater vehicles for sub-ice shelf cavities (Jenkins et al, 2010;Tinto and Bell, 2011;Millan et al, 2017;Jordan et al, 2020.). These datasets have identified glacially-modified depressions on the continental shelf that act as conduits for CDW transport towards present-day ocean-terminating glacier margins in the ASE (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Hogan

Larter

Graham

et al. 2020

Preprint

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Abstract. The geometry of the sea floor beyond Thwaites Glacier (TG) is a major control on the routing of warm ocean waters towards the ice stream’s grounding zone, which has led to increased mass loss through sub-ice-shelf melting and resulting accelerated ice flow. Nearshore topographic highs act as pinning points for the Thwaites Ice Shelf and potentially provide barriers to warm water incursions. To date, few vessels have been able to access this area due to persistent sea-ice and iceberg cover. This critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project, with more than 2000 km2 of new multibeam echo-sounder data (MBES) were acquired offshore TG. Here, these data along with legacy MBES datasets are compiled to produce a set of standalone bathymetric grids for the inner Amundsen Sea shelf beyond both Pine Island and Thwaites glaciers. At TG, the bathymetry is dominated by a > 1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some parts having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf, suggesting a positive feedback mechanism for ice-shelf ungrounding. Knowing that this offshore area is a former bed for TG, we applied a novel spectral approach to investigate bed roughness and find that derived power spectra can be approximated using an inverse-square law, a result that is consistent with spectra for bed profiles from the modern TG. Using existing ice-flow theory, we also make a first assessment of the form drag (basal drag contribution) for ice flow over this topography. Ice flowing over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting in the grounding zone today. We show that the sea-floor bathymetry is an analogue for extant bed areas of TG and that more can be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. Comparisons with existing regional bathymetric compilations for the area show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the capacity of bathymetric troughs, and thus oceanic heat flux, may be significantly underestimated. This work meets the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

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Section: Trough and Channel Metricssupporting

confidence: 67%

Section: Multibeam Echosounder Datasets (Mbes)mentioning

confidence: 99%

Section: Multibeam Echosounder Datasets (Mbes)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Hogan

Larter

Graham

et al. 2020

Preprint

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Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures

et al. 2020

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While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty, the Intergovernmental Panel on Climate Change (IPCC) reported that sea-level rise from the 1950s levels would likely be within 0.61-1.10 m if warming exceeds 4 C by 2100. The IPCC acknowledged greater sea-level increases were possible through mechanisms not fully incorporated in models used in the assessment. In this perspective, we discuss challenges faced in projecting sea-level change and discuss why the IPCC's sea-level range for 2100 under strong warming is focused at the low end of possible outcomes. We argue outcomes above this range are far more probable than below it and discuss how decision makers may benefit from reframing IPCC's terminology to avoid unintentionally masking worst-case scenarios.

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Seafloor Depth of George VI Sound, Antarctic Peninsula, From Inversion of Aerogravity Data

Constantino

Tinto

Bell

et al. 2020

Geophysical Research Letters

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George VI Sound is an~600 km-long curvilinear channel on the west coast of the southern Antarctic Peninsula separating Alexander Island from Palmer Land. The Sound is a geologically complex region presently covered by the George VI Ice Shelf. Here we model the bathymetry using aerogravity data. Our model is constrained by water depths from seismic measurements. We present a crustal density model for the region, propose a relocation for a major fault in the Sound, and reveal a dense body,~200 km long, flanking the Palmer Land side. The southern half of the Sound consists of two distinct basins~1,100 m deep, separated by a −650 m-deep ridge. This constricting ridge presents a potential barrier to ocean circulation beneath the ice shelf and may account for observed differences in temperature-salinity (T-S) profiles. Plain Language Summary Knowing the seafloor depth beneath ice shelves is crucial for understanding the interaction between the ocean and the overlying ice, as the shape of the sea floor influences water circulation pathways. We present a new bathymetric model of the seafloor beneath George VI Ice Shelf on the Antarctica Peninsula. The data for our model were collected from airborne surveys, including the ice surface elevation, ice thickness, and gravity field measurements. We first present a new geological model of the Sound and use our improved data coverage to relocate a previously interpreted geological fault. The new bathymetry model shows that in the southern segment of the Sound, an area with shallow bathymetry and deep ice might be acting as a barrier to the water flow. This information can change our understanding of the circulation between the northern and southern segments of the Sound and can be used in models of how this impacts the melt in the base of the ice shelf. High basal melt rates around Antarctica have been interpreted as responses to variations in oceanic temperature and circulation (e.g., Holland et al., 2008; Jacobs et al., 2011). Over George VI Ice Shelf, estimated basal melt rates range from 2.8 m/a (Corr et al., 2002) to 6.0 m/a (Dinniman et al., 2012) with a recent study report-ing~4 m/a over a 23 year period (Adusumilli et al., 2018). Future changes in basal melt depend on changes in ocean temperature as well as subsurface currents, steered by the cavity shape, highlighting the importance of accurate bathymetry data for future predictions (e.g.,

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New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations

Cited by 16 publications

References 32 publications

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures

Seafloor Depth of George VI Sound, Antarctic Peninsula, From Inversion of Aerogravity Data

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