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Modeling the dynamic response of outlet glaciers to observed ice-shelf thinning in the Bellingshausen Sea Sector, West Antarctica

TitleModeling the dynamic response of outlet glaciers to observed ice-shelf thinning in the Bellingshausen Sea Sector, West Antarctica
Publication TypeJournal Article
Year of Publication2018
AuthorsMinchew B.M, Gudmundsson G.H, Gardner AS, Paolo F.S, Fricker H.A
JournalJournal of Glaciology
Date Published2018/04
Type of ArticleArticle
ISBN Number0022-1430
Accession NumberWOS:000430422000014
Keywordscollapse; CryoSat-2; discharge; flow; Geology; glacier flow; glacier modeling; glaciological model experiments; greenland; ice shelves; ice-ocean interactions; peninsula; Physical Geography; pine island glacier; sheet; stability; surface mass-balance

Satellite observations of gravity anomalies, ice-surface elevation and glacier velocity show significant increases in net grounded-ice-mass loss over the past decade along the Bellingshausen Sea sector (BSS), West Antarctica, in areas where warm (> 1 degrees C) sea water floods the continental shelf. These observations provide compelling but indirect evidence that mass losses are driven primarily by reduced buttressing from the floating ice shelves caused by ocean-driven ice-shelf thinning. Here, we combine recent observations of ice velocity, thickness and thickness changes with an ice flow model to study the instantaneous dynamic response of BSS outlet glaciers to observed ice-shelf thinning, alone. Our model results show that multiple BSS outlet glaciers respond instantaneously to observed ice-shelf thinning, particularly in areas where ice shelves ground at discrete points. Increases in modeled and observed dynamic mass losses, however, account for similar to 5% of the mass loss rates estimated from gravity anomalies and changes in ice-surface elevation, suggesting that variations in surface mass balance may be key to understanding recent BSS mass loss. Our approach isolates the impact of ice-shelf thinning on glacier flow and shows that if ice-shelf thinning continues at or above current rates, total BSS mass loss will increase in the next decade.

Short TitleJ. Glaciol.

We used recent observations of ice surface velocity and ice-shelf thinning rates along with an ice flow model to isolate the impact of ice-shelf thinning on glacier mass loss in Bellingshausen Sea sector (BSS). Our results indicate that increases in ice discharge contributed to observed changes in surface elevation and gravitational potential in BSS, in agreement with previous studies. We find instantaneous increases in glacier speeds and dynamically induced thinning rates in response to changes in ice-shelf thickness (alone) that broadly agree with observations. Glacier speedup and increases in dynamic thinning rates are most pronounced in the southern English Coast, where George VI Ice Shelf is rapidly thinning in areas with numerous pinning points. Modeled instantaneous increases in grounding line flux agree with changes in grounding line flux calculated from observed changes in surface velocity (Gardner and others, 2018), but are markedly lower than (~ 5% of) rates of dynamic mass loss estimated from observations of gravity anomalies and inland surface elevation along with outputs from a regional climate model (Wouters and others, 2015). We postulate that disparities in the estimates of grounding line flux and dynamic mass losses in BSS may be due primarily to variations in surface mass balance not accounted for in the regional climate model. Projections of dynamic mass loss over the next decade indicate that, in the absence of grounding line retreat in the English Coast, ice-shelf thinning alone could drive further BSS mass loss; these losses are unlikely to exceed 15% of the total discharge from this area. We are unable to model the dynamic response of BSS outlet glacier to local grounding line retreat, a potentially important process for understanding the future evolution of the ice sheet, because the bed in BSS is poorly resolved. Thus, our projections of BSS mass loss may be an underestimate, and it is important to continue to monitor mass changes in BSS using multiple observational platforms and to collect finer resolution, spatially comprehensive data on ice thickness and bed topography to enable more detailed model studies.

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