Modeling Ocean Eddies on Antarctica's Cold Water Continental Shelves and Their Effects on Ice Shelf Basal Melting

Mack, Stefanie; Dinniman, Michael S.; Klinck, John M.; McGillicuddy, Dennis J.; Padman, Laurie

doi:10.1029/2018jc014688

Cited by 21 publications

(27 citation statements)

References 82 publications

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“…15) and inferred from observations (J9). Closer to the ice front, models predict higher mean melt rates (O ∼ 1 m/y) and stronger seasonal variability (7,11,15,18,19,24), features confirmed by recent observations (5,25,26). The largest rates, near the front, are associated with inflow of local summer surface water (5,27).…”

Section: Significancesupporting

confidence: 71%

“…In order to generate the observed behavior, tidal interactions with upper and lower solid boundaries must be adequately represented over a wide spatial domain and so require tide-resolving time steps and sufficient spatial resolution to resolve ice basal topographic features (4,12,46). Comparable reliability in benthic topography also appears to be required to adequately resolve what appears to be, at HWD2 at least, a thin inflowing benthic boundary layer that can take advantage of even quite small topographic variations to transport heat toward the grounding line (4,19,46,47).…”

Section: Water Massesmentioning

confidence: 99%

“…1 and Methods ) and 300 km from the ice shelf front. The site is predicted to be on the western flank of an outward flowing zone of the ocean cavity with speeds of between 1 to 2 ( 18 ) and 5 cm s −1 ( 19 ), but it is clear that the circulation varies on small scales relative to the horizontal dimensions of the cavity ( 19 ). While the margins of the RIS cavity have been previously sampled ( 11 , 16 , 20 ), the central cavity has been sampled only once previously.…”

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confidence: 99%

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Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting

Stevens

Hulbe

Brewer

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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The stability of large Antarctic ice shelves has important implications for global sea level, sea ice area, and ocean circulation. A significant proportion of ice mass loss from these ice shelves is through ocean-driven melting which is controlled by largely unobserved oceanic thermodynamic and circulatory processes in the cavity beneath the ice shelf. Here we use direct measurements to provide evidence of the changing water column structure in the cavity beneath the Ross Ice Shelf, the planet’s largest ice shelf by area. The cavity water column data exhibit both basal and benthic boundary layers, along with evidence of tidally modulated and diffusively convecting internal mixing processes. A region of thermohaline interleaving in the upper–middle water column indicates elevated diffusion and the potential to modify the cavity circulation. The measurements were recorded using the Aotearoa New Zealand Ross Ice Shelf Program hot water drill borehole melted in the central region of the shelf in December 2017 (HWD2), only the second borehole through the central region of the ice shelf, following J9 in 1977. These data, and comparison with the 1977 data, provide valuable insight into ice shelf cavity circulation and aid understanding of the evolution of the presently stable Ross Ice Shelf.

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Section: Significancesupporting

confidence: 71%

Section: Water Massesmentioning

confidence: 99%

mentioning

confidence: 99%

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Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting

Stevens

Hulbe

Brewer

et al. 2020

Proc. Natl. Acad. Sci. U.S.A.

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“…As we did not obtain direct measurements of ocean mixed layer currents, we estimate them by inserting our measured temperatures, salinities, and basal melt rates into the boundary layer parameterization described by Holland and Jenkins (1999). This yields a time‐varying ocean current speed, potentially driven by a combination of buoyancy, tides, wind stress acting outside of the sub‐ice shelf cavity, and eddies (e.g., Jenkins, 2011; Mack et al, 2019; Makinson & Nicholls, 1999).…”

Section: Methodsmentioning

confidence: 99%

Tidal Modulation of Buoyant Flow and Basal Melt Beneath Petermann Gletscher Ice Shelf, Greenland

et al. 2020

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A set of collocated, in situ oceanographic and glaciological measurements from Petermann Gletscher Ice Shelf, Greenland, provides insights into the dynamics of under-ice flow driving basal melting. At a site 16 km seaward of the grounding line within a longitudinal basal channel, two conductivity-temperature (CT) sensors beneath the ice base and a phase-sensitive radar on the ice surface were used to monitor the coupled ice shelf-ocean system. A 6 month time series spanning 23 August 2015 to 12 February 2016 exhibited two distinct periods of ice-ocean interactions. Between August and December, radar-derived basal melt rates featured fortnightly peaks of ∼15 m yr −1 which preceded the arrival of cold and fresh pulses in the ocean that had high concentrations of subglacial runoff and glacial meltwater. Estimated current speeds reached 0.20-0.40 m s −1 during these pulses, consistent with a strengthened meltwater plume from freshwater enrichment. Such signals did not occur between December and February, when ice-ocean interactions instead varied at principal diurnal and semidiurnal tidal frequencies, and lower melt rates and current speeds prevailed. A combination of estimated current speeds and meltwater concentrations from the two CT sensors yields estimates of subglacial runoff and glacial meltwater volume fluxes that vary between 10 and 80 m 3 s −1 during the ocean pulses. Area-average upstream ice shelf melt rates from these fluxes are up to 170 m yr −1 , revealing that these strengthened plumes had already driven their most intense melting before arriving at the study site. Plain Language Summary Petermann Gletscher is a large glacier in northern Greenland that transports 4% of the ice sheet by area into the ocean. At its marine terminus it extends into a 16 km wide and 50 km long floating ice shelf. The ice shelf has retreated by 30% over the last decade, likely due to increasing melting of its base. Regions of faster melting result in channels carved into the ice base, where ice thicknesses are half that of the surrounding ice. Here, we investigate the cause of this melting using 6 months of oceanographic and glaciological measurements from August 2015 to February 2016 in the ice shelf's central basal channel. We find that under-ice ocean current speeds played the primary role in mixing ocean heat upward and controlling melting in the channel. During the first 3 months of data, freshwater periodically flowed from land into the ocean beneath the ice shelf, causing currents to accelerate and melting to increase. This behavior changed in the second 3 months, when freshwater discharge stopped and tides instead drove weaker currents and low melting. Hence, the timing of subglacial freshwater outflow into the ocean controlled when the ice shelf experienced the strongest melting in its central basal channel.

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“…Even though the shelf temperature of the total domain still decreases slightly at the second resolution step, the Amundsen-Bellingshausen Seas is warming. As mentioned earlier, this phenomenon is often associated with shoreward heat transport by eddies that need a grid spacing on the order of 1 km to be resolved by ocean models (Dinniman et al, 2016;Mack et al, 2019). The cooling north of Nickerson, Sulzberg and Swinburne Ice Shelves might be a consequence of this warming, as the continental shelf current drives melt water from the Amundsen-Bellingshausen Seas mostly westward (Nakayama et al, 2017).…”

Section: Resolution Effectsmentioning

confidence: 97%

The Whole Antarctic Ocean Model (WAOM v1.0): Development and Evaluation

Richter

Gwyther

Naughten

2020

Preprint

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Abstract. The Regional Ocean Modeling System (ROMS), including an ice shelf component, has been applied on a circum-Antarctic domain to derive estimates of ice shelf basal melting. Significant improvements made compared to previous models of this scale are the inclusion of tides and a horizontal spatial resolution of 2 km, which is sufficient to resolve onshelf heat transport by bathymetric troughs and eddy scale circulation. We run the model with ocean-atmosphere-sea ice conditions from the year 2007, to represent nominal present day climate. We force the ocean surface with buoyancy fluxes derived from sea ice concentration observations and wind stress from ERA-Interim atmospheric reanalysis. At the northern boundaries ocean conditions are derived from the ECCO2 reanalysis and tides are incorporated as sea surface height and barotropic currents. The accuracy of tidal height signals close to the coast is comparable to those simulated from widely-used barotropic tide models, while off-shelf hydrography agrees well with the Southern Ocean State Estimate (SOSE) model. On the shelf, most details of ice shelf-ocean interaction are consistent with results from regional modelling and observational studies, although a paucity of observational data (particularly taken during 2007) prohibits a full verification. We conclude that our improved model is well suited to derive a new estimate of present day Antarctic ice shelf melting at high resolution and is able to quantify its sensitivity to tides.

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Modeling Ocean Eddies on Antarctica's Cold Water Continental Shelves and Their Effects on Ice Shelf Basal Melting

Cited by 21 publications

References 82 publications

Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting

Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting

Tidal Modulation of Buoyant Flow and Basal Melt Beneath Petermann Gletscher Ice Shelf, Greenland

The Whole Antarctic Ocean Model (WAOM v1.0): Development and Evaluation

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