Bistability of the Filchner‐Ronne Ice Shelf Cavity Circulation and Basal Melt

Hazel, J.; Stewart, Andrew L.

doi:10.1029/2019jc015848

Cited by 32 publications

(36 citation statements)

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“…Thermocline heaving alone does not cause an increased inflow of warm water since the pathway along the deep Filchner Trough is blocked by the presence of DSW masses. In agreement with Hellmer et al (2017) and Hazel and Stewart (2020), we find that the density structure in Filchner Trough is crucial for determining the water exchange across its sill. The blocking effect decreases when the DSW becomes fresher and ceases if the DSW becomes lighter than the WDW.…”

Section: Resultssupporting

confidence: 92%

“…A positive meltwater feedback, where enhanced freshwater input from FRIS basal melt reduces the shelf salinity and further strengthens the warm inflow, may contribute to drive the system past a tipping point (Hellmer et al, 2017). These results are supported by a regional model study (Hazel & Stewart, 2020), which also suggests that offshore katabatic winds may affect the FRIS cavity circulation through modulation of sea ice formation and the freshwater flux. The uncertainties in the high‐melt model studies (BRIOS and RAnGO) and the CMIP5 scenarios are pronounced (see Figure 1b), and the oceanic processes controlling the warm inflows are strongly related to the projected atmospheric forcing (Timmermann & Hellmer, 2013).…”

Section: Introductionsupporting

confidence: 74%

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Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea

Daae

Hattermann

Darelius

et al. 2020

Geophysical Research Letters

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Understanding changes in Antarctic ice shelf basal melting is a major challenge for predicting future sea level. Currently, warm Circumpolar Deep Water surrounding Antarctica has limited access to the Weddell Sea continental shelf; consequently, melt rates at Filchner-Ronne Ice Shelf are low. However, large-scale model projections suggest that changes to the Antarctic Slope Front and the coastal circulation may enhance warm inflows within this century. We use a regional high-resolution ice shelf cavity and ocean circulation model to explore forcing changes that may trigger this regime shift. Our results suggest two necessary conditions for supporting a sustained warm inflow into the Filchner Ice Shelf cavity: (i) an extreme relaxation of the Antarctic Slope Front density gradient and (ii) substantial freshening of the dense shelf water. We also find that the on-shelf transport over the western Weddell Sea shelf is sensitive to the Filchner Trough overflow characteristics. Plain Language Summary The Weddell Sea continental shelf is presently filled with water masses that are too cold to melt the Filchner-Ronne Ice Shelf from below. If warmer offshore water masses gain access to the Weddell Sea continental shelf and flow into the ice shelf cavity, the ocean-driven melting would increase rapidly and cause ice shelf thinning. Increased ice shelf melting would supply the continental shelf with freshwater that influence sea ice production and generation of dense water masses and cause an increased discharge of grounded ice, which would contribute to global sea level rise. Two main factors currently prevent warm water from accessing the Weddell Sea continental shelf. First, the warm water is located deeper than the continental shelf and does not have direct access. Second, the Weddell Sea continental shelf is filled with dense water masses that block an inflow of warmer and lighter water. We use a regional ocean model to investigate what would happen if the warm offshore water is lifted higher up or if the dense water masses become fresher and lighter. We find that the Weddell Sea system is robust, and we need to make extreme changes to both factors to allow warm water access to the continental shelf.

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Section: Resultssupporting

confidence: 92%

Section: Introductionsupporting

confidence: 74%

Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea

Daae

Hattermann

Darelius

et al. 2020

Geophysical Research Letters

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“…Using an ice-ocean model forced with a climate change projection, Warm Deep Water (WDW) from offshore was simulated to enter the cavity through the Filchner Trough, dramatically increasing basal melt rates. A similar circulation change has been triggered in other ocean models by manually varying the cavity salinity or atmospheric forcing 11 , 12 . However, it remains unclear how easily this circulation change could occur in reality, and over what timescales.…”

Section: Introductionmentioning

confidence: 79%

Two-timescale response of a large Antarctic ice shelf to climate change

et al. 2021

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A potentially irreversible threshold in Antarctic ice shelf melting would be crossed if the ocean cavity beneath the large Filchner–Ronne Ice Shelf were to become flooded with warm water from the deep ocean. Previous studies have identified this possibility, but there is great uncertainty as to how easily it could occur. Here, we show, using a coupled ice sheet-ocean model forced by climate change scenarios, that any increase in ice shelf melting is likely to be preceded by an extended period of reduced melting. Climate change weakens the circulation beneath the ice shelf, leading to colder water and reduced melting. Warm water begins to intrude into the cavity when global mean surface temperatures rise by approximately 7 °C above pre-industrial, which is unlikely to occur this century. However, this result should not be considered evidence that the region is unconditionally stable. Unless global temperatures plateau, increased melting will eventually prevail.

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“…Our results suggest that ice‐shelf/ocean modelers should carefully consider their choice of boundary conditions when running limited area models of the region. In some idealized cases, it has been past practice to use climatological boundary conditions for regional modeling studies (e.g., Hazel & Stewart, 2020; Naughten et al., 2019) but consistency between the boundary conditions and the local forcing is important for realistic representation of inter‐annual variability in re‐analysis focused studies (e.g., Hausmann et al., 2020). More generally, Figures 1a–1f show differences in the observed and simulated temperature and salinity structure of the ASC across different products/time periods.…”

Section: Summary and Further Workmentioning

confidence: 99%

“…(2019) showed that offshore polynyas in the Weddell Sea can increase the transport of WDW across the shelf through density changes above the shelf break. Hazel and Stewart (2020) suggest that decreasing the meridional winds by 50% can switch FRIS from a cold to warm state. In the broader context, several modeling studies in the Amundsen Sea have reported changes in far‐field forcing as a contributing factor to Circumpolar Deep Water crossing the shelf (Donat‐Magnin et al., 2017; Nakayama et al., 2018; Spence et al., 2017; Webb et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Remote Control of Filchner‐Ronne Ice Shelf Melt Rates by the Antarctic Slope Current

et al. 2021

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The Filchner-Ronne Ice Shelf (FRIS), located at the southern boundary of the Weddell Sea, is the largest volume of floating ice in the world (Nicholls et al., 2009). Its tributary ice streams have a combined discharge of over 254 Gigatons yr −1 , draining ∼15% of the Antarctic ice sheet by mass (Rignot et al., 2013). Several factors influence the environment that determines an ice shelf's basal melt rate, including: ice draft and bathymetry (Wei et al., 2019), sea ice growth (Markus et al., 1998), katabatic and large-scale wind patterns (Holland et al., 2019), and proximity to the shelf break of: Warm Deep Water (WDW), High Salinity Shelf Water (HSSW), Modified WDW (MWDW), and the Antarctic Circumpolar Current. With these factors in mind, the ice shelf's environment can be dynamically categorized in terms of a "cold" or "warm" regime (modes 1 and 2 in Jacobs et al., 1992, respectively), where FRIS is historically a cold regime ice shelf. For additional background, see Nicholls et al. (2009) for FRIS melt rates and relevant water masses on the surrounding continental shelf, Vernet et al. (2019) for a summary of present knowledge on the regional circulation and Dinniman et al. (2016) for a modern modeling perspective on ice shelf regimes. Future projections by Hellmer et al. (2012, 2017) suggest that the intrusion of warm water could lead to a tipping point where FRIS

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Bistability of the Filchner‐Ronne Ice Shelf Cavity Circulation and Basal Melt

Cited by 32 publications

References 84 publications

Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea

Necessary Conditions for Warm Inflow Toward the Filchner Ice Shelf, Weddell Sea

Two-timescale response of a large Antarctic ice shelf to climate change

Remote Control of Filchner‐Ronne Ice Shelf Melt Rates by the Antarctic Slope Current

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