Thongchai Thailand

Pine Island Glacier Tipping Point

Posted on: April 4, 2021

Geological 'Hotspot' Melting Pine Island and Thwaites Glaciers, Not Global  Warming — Plate climatology

THIS POST IS A CRITICAL EVALUATION OF RESEARCH FINDINGS THAT THE PINE ISLAND GLACIER IS UNSTABLE AND HAS REACHED A TIPPING POINT SUCH THAT ITS IMMINENT DEMISE BY CLIMATE CHANGE IMPLIES SEA LEVEL RISE THAT COULD CAUSE CATASTROPHIC CHANGES TO COASTAL REGIONS WORLDWIDE.

PART-1: WHAT THE RESEARCH PAPER SAYS

Rosier, Sebastian HR, et al. “The tipping points and early warning indicators for Pine Island Glacier, West Antarctica.” The Cryosphere 15.3 (2021): 1501-1516. Abstract: Mass loss from the West Antarctic Ice Sheet is the main source of uncertainty in projections of future sea-level rise, with important implications for coastal regions worldwide. Central to ongoing and future changes is the marine ice sheet instability: Once a critical threshold, or tipping point, is crossed, ice internal dynamics can drive a self-sustaining retreat committing a glacier to irreversible, rapid and substantial ice loss. This process might have already been triggered in the Amundsen Sea region, where Pine Island and Thwaites glaciers dominate the current mass loss from Antarctica, but modelling and observational techniques have not been able to establish this rigorously, leading to divergent views on the future mass loss of the West Antarctic Ice Sheet. Here, we aim at closing this knowledge gap by conducting a systematic investigation of the stability regime of Pine Island Glacier. To this end we show that early warning indicators in model simulations robustly detect the onset of the marine ice sheet instability. We are thereby able to identify three distinct tipping points in response to increases in ocean-induced melt. The third and final event, triggered by an ocean warming of approximately 1.2 C from the steady-state model configuration, leads to a retreat of the entire glacier that could initiate a collapse of the West Antarctic Ice Sheet.

PART-2: CRITICAL COMMENTRY

(1) THE EEMIAN CONNECTION: In a related post LINK: https://tambonthongchai.com/2018/12/21/eemian/ we descirbe the prior interglacial called the Eemian where we note that the Eemian was much warmer than the current interglacial the Holocene. A significant feature of the Eemian Interglacial was that the West Antarctic Ice Sheet had collapsed with a horrific sea level rise consequence. This historical background in the paleo record has inspired climate science to anticipate a similar event in the Holocene as a kind of horrific fear of climate change and a dramatic motivation for climate action that the climate movement needs to push its agenda against fossil fuels and to motivate the change to renewable energy. However, the Eemian passion has not subsided and the continued passion for an Eemian like WAIS event in the Holocene yields research of the kind described above.

(2) WEST ANTARCTICA IS GEOLOGICALLY ACTIVE: In another related post LINK: https://tambonthongchai.com/2019/06/27/antarctica/ we describe the relevant geological features of West Antarctica that make it impossible to undrstand ice melt events there purely as atmospheric phenomena. These include the West Antarctic Rift system and its many volcanoes as well as the Marie Byrd Mantle Plume. Both the Thwaites Glacier and the glacier discussed here, the Pine Island Glacier are located in this geological and volcanism hotspot. A detailed description of these geological hotspots is found in the related post linked above and their role in our understanding of ice melt events in the Pine Island glacier is described in the bibliography provided below with the title PART-3B: THE RELEVANT BIBLIOGRAPHY PART 2: PINE ISLAND GLACIER.

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IN VIEW OF THESE RELEVANT GEOLOGICAL FEATURES AND KNOWN GEOTHERMAL FLUX AND ACTIVE VOLCANOES UNDERNEATH THE PINE ISLAND GLACIER, WE PROPOSE THAT IT IS NOT POSSIBLE TO UNDERSTAND ICE MELT EVENTS THERE AS ANTHROPOGENIC GOBAL WARMING PHENOMENA. QED.

PART-3A: THE RELEVANT BIBLIOGRAPHY: PART-1: ANTARCTICA

  1. Scambos, Ted A., et al. “The link between climate warming and break-up of ice shelves in the Antarctic Peninsula.” Journal of Glaciology 46.154 (2000): 516-530.  A review of in situ and remote-sensing data covering the ice shelves of the Antarctic Peninsula provides a series of characteristics closely associated with rapid shelf retreat: deeply embayed ice fronts; calving of myriad small elongate bergs in punctuated events; increasing flow speed; and the presence of melt ponds on the ice-shelf surface in the vicinity of the break-ups. As climate has warmed in the Antarctic Peninsula region, melt-season duration and the extent of ponding have increased. Most break-up events have occurred during longer melt seasons, suggesting that meltwater itself, not just warming, is responsible. Regions that show melting without pond formation are relatively unchanged. Melt ponds thus appear to be a robust harbinger of ice-shelf retreat. We use these observations to guide a model of ice-shelf flow and the effects of meltwater. Crevasses present in a region of surface ponding will likely fill to the brim with water. We hypothesize (building on Weertman (1973), Hughes (1983) and Van der Veen (1998)) that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat. A thermodynamic finite-element model is used to evaluate ice flow and the strain field, and simple extensions of this model are used to investigate crack propagation by meltwater. The model results support the hypothesis.
  2. Convey, P., et al. “The flora of the South Sandwich Islands, with particular reference to the influence of geothermal heating.” Journal of Biogeography 27.6 (2000): 1279-1295.  Data obtained in 1997 are combined with updated records from the only previous survey (in 1964) to provide a baseline description of the flora of the archipelago, which currently includes 1 phanerogam, 38 mosses, 11 liverworts, 5 basidiomycete fungi, 41 lichenised fungi and 16 diatoms with, additionally, several taxa identified only to genus. Major elements of the moss and liverwort floras are composed of South American taxa (32% and 73%, respectively), with a further 45% of mosses having bipolar or cosmopolitan distributions. These two groups show low levels of Antarctic endemicity (11% and 18%, respectively). In contrast, 52% of lichens and 80% of basidiomycete fungi are endemic to the Antarctic. A further 36% of lichens are bipolar/cosmopolitan, with only 5% of South American origin. The flora of the South Sandwich Islands is clearly derived from those of other Antarctic zones. The flora of unheated ground is closely related to that of the maritime Antarctic, although with a very limited number of species represented. That of heated ground contains both maritime and sub‐Antarctic elements, confirming the importance of geothermal heating for successful colonisation of the latter group. The occurrence of several maritime Antarctic species only on heated ground confirms the extreme severity of the archipelago’s climate in comparison with well‐studied sites much further south in this biogeographical zone.
  3. Smith, RI Lewis. “The bryophyte flora of geothermal habitats on Deception Island, Antarctica.” The Journal of the Hattori Botanical Laboratory 97 (2005): 233-248.  Deception Island is one of the most volcanically active sites south of 60°S. Between 1967 and 1970 three major eruptions devastated large expanses of the landscape and its predominantly cryptogamic vegetation. Since 1970 extensive recolonisation has occurred on the more stable surfaces. Unheated ground supports several bryophyte and lichen communities typical of much of the maritime Antarctic, but geothermal habitats possess remarkable associations of bryophytes, many of the species being unknown or very rare elsewhere in the Antarctic. Nine geothermal sites were located and their vegetation investigated in detail. Communities associated with more transient sites have disappeared when the geothermal activity ceased. Mosses and liverworts occur to within a few centimetres of fumarole vents where temperatures reach 90-95℃, while temperatures within adjacent moss turf can reach 35-50℃ or more and remain consistently between 25 and 45℃. Most of the bryoflora has a Patagonian-Fuegian provenance and it is presumed that, unlike most species, the thermophiles are not pre-adapted to the Antarctic environment, being able to colonise only where the warm and humid conditions prevail.
  4. Vieira, Gonçalo, et al. “Geomorphological observations of permafrost and ground-ice degradation on Deception and Livingston Islands, Maritime Antarctica.” (2008): 1939-1844. The Antarctic Peninsula is experiencing one of the fastest increases in mean annual air temperatures (ca. 2.5oC in the last 50 years) on Earth. If the observed warming trend continues as indicated by climate models, the region could suffer widespread permafrost degradation. This paper presents field observations of geomorphological features linked to permafrost and ground-ice degradation at two study areas: northwest Hurd Peninsula (Livingston Island) and Deception Island along the Antarctic Peninsula. These observations include thermokarst features, debris flows, active-layer detachment slides, and rockfalls. The processes observed may be linked not only to an increase in temperature, but also to increased rainfall, which can trigger debris flows and other processes. On Deception Island some thermokarst (holes in the ground produced by the selective melting of permafrost)  features may be related to anomalous geothermal heat flux from volcanic activity.
  5. Mulvaney, Robert, et al. “Recent Antarctic Peninsula warming relative to Holocene climate and ice-shelf history.” Nature 489.7414 (2012): 141-144.  Rapid warming over the past 50 years on the Antarctic Peninsula is associated with the collapse of a number of ice shelves and accelerating glacier mass loss1,2,3,4,5,6,7. In contrast, warming has been comparatively modest over West Antarctica and significant changes have not been observed over most of East Antarctica8,9, suggesting that the ice-core palaeoclimate records available from these areas may not be representative of the climate history of the Antarctic Peninsula. Here we show that the Antarctic Peninsula experienced an early-Holocene warm period followed by stable temperatures, from about 9,200 to 2,500 years ago, that were similar to modern-day levels. Our temperature estimates are based on an ice-core record of deuterium variations from James Ross Island, off the northeastern tip of the Antarctic Peninsula. We find that the late-Holocene development of ice shelves near James Ross Island was coincident with pronounced cooling from 2,500 to 600 years ago. This cooling was part of a millennial-scale climate excursion with opposing anomalies on the eastern and western sides of the Antarctic Peninsula. Although warming of the northeastern Antarctic Peninsula began around 600 years ago, the high rate of warming over the past century is unusual (but not unprecedented) in the context of natural climate variability over the past two millennia. The connection shown here between past temperature and ice-shelf stability suggests that warming for several centuries rendered ice shelves on the northeastern Antarctic Peninsula vulnerable to collapse. Continued warming to temperatures that now exceed the stable conditions of most of the Holocene epoch is likely to cause ice-shelf instability to encroach farther southward along the Antarctic Peninsula.
  6. Fraser, Ceridwen I., et al. “Geothermal activity helps life survive glacial cycles.” Proceedings of the National Academy of Sciences 111.15 (2014): 5634-5639.  The evolution and maintenance of diversity through cycles of past climate change have hinged largely on the availability of refugia (places where life can survive through a period of unfavorable conditions such as glaciation). Geothermal refugia may have been particularly important for survival through past glaciations. Our spatial modeling of Antarctic biodiversity indicates that some terrestrial groups likely survived throughout intense glacial cycles on ice-free land or in sub-ice caves associated with areas of geothermal activity, from which recolonization of the rest of the continent took place. These results provide unexpected insights into the responses of various species to past climate change and the importance of geothermal regions in promoting biodiversity. Furthermore, they indicate the likely locations of biodiversity “hotspots” in Antarctica, suggesting a critical focus for future conservation efforts.
  7. An, Meijian, et al. “Temperature, lithosphere‐asthenosphere boundary, and heat flux beneath the Antarctic Plate inferred from seismic velocities.” Journal of Geophysical Research: Solid Earth 120.12 (2015): 8720-8742.  We estimate the upper mantle temperature of the Antarctic Plate based on the thermoelastic properties of mantle minerals and S velocities using a new 3‐D shear velocity model, AN1‐S. Crustal temperatures and surface heat fluxes are then calculated from the upper mantle temperature assuming steady state thermal conduction. The temperature at the top of the asthenosphere beneath the oceanic region and West Antarctica is higher than the dry mantle solidus, indicating the presence of melt. From the temperature values, we generate depth maps of the lithosphere‐asthenosphere boundary and the Curie temperature isotherm. The maps show that East Antarctica has a thick lithosphere similar to that of other stable cratons, with the thickest lithosphere (~250 km) between Domes A and C. The thin crust and lithosphere beneath West Antarctica are similar to those of modern subduction‐related rift systems in East Asia. A cold region beneath the Antarctic Peninsula is similar in spatial extent to that of a flat‐subducted slab beneath the southern Andes, indicating a possible remnant of the Phoenix Plate, which was subducted prior to 10 Ma. The oceanic lithosphere generally thickens with increasing age, and the age‐thickness correlation depends on the spreading rate of the ridge that formed the lithosphere. Significant flattening of the age‐thickness curves is not observed for the mature oceanic lithosphere of the Antarctic Plate.
  8. Dziadek, Ricarda, et al. “Geothermal heat flux in the Amundsen Sea sector of West Antarctica: New insights from temperature measurements, depth to the bottom of the magnetic source estimation, and thermal modeling.” Geochemistry, Geophysics, Geosystems 18.7 (2017): 2657-2672[FULL TEXT]  Focused research on the Pine Island and Thwaites glaciers, which drain the West Antarctic Ice Shelf (WAIS) into the Amundsen Sea Embayment (ASE), revealed strong signs of instability in recent decades that result from variety of reasons, such as inflow of warmer ocean currents and reverse bedrock topography, and has been established as the Marine Ice Sheet Instability hypothesis. Geothermal heat flux (GHF) is a poorly constrained parameter in Antarctica and suspected to affect basal conditions of ice sheets, i.e., basal melting and subglacial hydrology. Thermomechanical models demonstrate the influential boundary condition of geothermal heat flux for (paleo) ice sheet stability. Due to a complex tectonic and magmatic history of West Antarctica, the region is suspected to exhibit strong heterogeneous geothermal heat flux variations. We present an approach to investigate ranges of realistic heat fluxes in the ASE by different methods, discuss direct observations, and 3‐D numerical models that incorporate boundary conditions derived from various geophysical studies, including our new Depth to the Bottom of the Magnetic Source (DBMS) estimates. Our in situ temperature measurements at 26 sites in the ASE more than triples the number of direct GHF observations in West Antarctica. We demonstrate by our numerical 3‐D models that GHF spatially varies from 68 up to 110 mW m−2.
  9. Martos, Yasmina M., et al. “Heat flux distribution of Antarctica unveiled.” Geophysical Research Letters 44.22 (2017): 11-417.  [FULL TEXT]  Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent‐wide heat flux maps have only been derived from low‐resolution satellite magnetic and seismological data. We present a high‐resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small‐scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high‐resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.
  10. Burton‐Johnson, Alex, et al. “A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production.” Geophysical Research Letters 44.11 (2017): 5436-5446.  A new method for modeling heat flux shows that the upper crust contributes up to 70% of the Antarctic Peninsula’s subglacial heat flux and that heat flux values are more variable at smaller spatial resolutions than geophysical methods can resolve. Results indicate a higher heat flux on the east and south of the Peninsula (mean 81 mW m−2) where silicic rocks predominate, than on the west and north (mean 67 mW m−2) where volcanic arc and quartzose sediments are dominant. While the data supports the contribution of heat‐producing element‐enriched granitic rocks to high heat flux values, sedimentary rocks can be of comparative importance dependent on their provenance and petrography. Models of subglacial heat flux must utilize a heterogeneous upper crust with variable radioactive heat production if they are to accurately predict basal conditions of the ice sheet. Our new methodology and data set facilitate improved numerical model simulations of ice sheet dynamics.  
  11. Schroeder, Dustin M., et al. “Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet.” Proceedings of the National Academy of Sciences 111.25 (2014): 9070-9072.  SIGNIFICANCE: Thwaites Glacier is one of the West Antarctica’s most prominent, rapidly evolving, and potentially unstable contributors to global sea level rise. Uncertainty in the amount and spatial pattern of geothermal flux and melting beneath this glacier is a major limitation in predicting its future behavior and sea level contribution. In this paper, a combination of radar sounding and subglacial water routing is used to show that large areas at the base of Thwaites Glacier are actively melting in response to geothermal flux consistent with rift-associated magma migration and volcanism. This supports the hypothesis that heterogeneous geothermal flux and local magmatic processes could be critical factors in determining the future behavior of the West Antarctic Ice SheetABSTRACT: Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼114 ± 10 mW/m2 with areas of high flux exceeding 200 mW/m2 consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site.  [LINK TO FULL TEXT] 

LEFT: Bed topography of the West Antarctic Ice Sheet and Amundsen Sea Embayment. MIDDLE: Subglacial hydrologic potential (13) for a distributed water system in the upstream region of the Thwaites Glacier catchment (black boundary). RIGHT:  Collection of subglacial water routing models that best fit the observed radar bed echo strength distribution

Fig. 3.

Minimum geothermal flux and basal melt values required to reproduce the observed relative bed echo strengths (Fig. 2A) with subglacial water routing models (1327) (Fig. 1C) using the total melt water from an ice sheet model for the upstream portion of the Thwaites Glacier catchment (9). The minimum average inferred flux is ∼114 ± 10 mW/m2. High-flux areas exceed 200 mW/m2. A indicates the Mount Takahe volcano. B indicates the WAIS Divide ice core drilling site. High-melt areas are indicated by C in the westernmost tributary, D adjacent to the Crary mountains, and E in the upper portion of the central tributaries (8). Triangles show areas where radar-inferred melt anomalies exceed those generated by ice dynamics (friction and advection) (9) and inferred geothermal flux exceeds 150 mW/m2 (dark magenta) and 200 mW/m2 (light magenta). Bed topography (12) contour interval for Antarctica is 180 m. The upstream region of the Thwaites Glacier catchment contains several areas of strong relative bed echoes indicating larger quantities of subglacial water. The distribution of melt and geothermal flux includes several regions with high melt that are closely related to rift structure and associated volcanism.  These include the entire westernmost tributary (Fig. 3, location C) that flanks Mount Takahe (Fig. 3, location A), a subaerial volcano active in the Quaternary (2829), and several high-flux areas across the catchment adjacent to topographic features that are hypothesized to be volcanic in origin as seen in the image above and as described in Bahrendt 1998 and Bahrendt 2013, and Joughin 2009. We also observe high geothermal flux in the upper reaches of the central tributaries that are relatively close to the site of the WAIS Divide ice core where unexpectedly high melt and geothermal flux have been estimated. We estimate a minimum average geothermal flux value of about 114 mW/m2 with a notional uncertainty of about 10 mW/m2 for the Thwaites Glacier catchment with areas exceeding 200 mW/m2. These values are likely underestimates due to the low uniform geothermal flux value used in the ice sheet model and the compensating effect of enhanced vertical advection of cold shallow ice in high-melt areas. Note that this latter effect also predicts a subtle gradient of underestimated flux from the interior to the trunk as fast flow and associated frictional melting increases.

12. Behrendt, John C., et al. “Aeromagnetic evidence for a volcanic caldera  complex beneath the divide of the West Antarctic Ice Sheet.” Geophysical Research Letters 25.23 (1998): 4385-4388. A 1995–96 aeromagnetic survey over part of the Sinuous Ridge (SR) beneath the West Antarctic Ice Sheet (WAIS) divide shows a 70‐km diameter circular pattern of 400–1200‐nT anomalies suggesting one of the largest volcanic caldera complexes on earth. Radar‐ice‐sounding (RIS) shows the northern part of this pattern overlies the SR, and extends south over the Bentley Subglacial Trench (BST). Modeled sources of all but one the caldera anomalies are at the base of <1–2‐km thick ice and their volcanic edifices have been glacially removed. The exception is a 700‐m high, 15‐km wide volcano” producing an 800‐nT anomaly over the BST. Intrusion of this volcano beneath 3 km of ice probably resulted in pillow basalt rather than easily removed hyaloclastite erupted beneath thinner ice. The background area (−300 to −500‐nT) surrounding the caldera is possibly caused by a shallow Curie isotherm. We suggest uplift of the SR forced the advance of the WAIS

13. Behrendt, John C. “The aeromagnetic method as a tool to identify Cenozoic magmatism in the West Antarctic Rift System beneath the West Antarctic Ice Sheet—A review; Thiel subglacial volcano as possible source of the ash layer in the WAISCORE.” Tectonophysics 585 (2013): 124-136.  The West Antarctic Ice Sheet (WAIS) sits on the volcanically active West Antarctic Rift System (WARS). The aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks, since 1959–64 surveys, particularly combined with 1978 radar ice-sounding. The unique 1991–97 Central West Antarctica (CWA) aerogeophysical survey covering 354,000 km2 over the WAIS, (5-km line-spaced, orthogonal lines of aeromagnetic, radar ice-sounding, and aerogravity measurements), still provides invaluable information on subglacial volcanic rocks, particularly combined with the older aeromagnetic profiles. These data indicate numerous 100–>1000 nT, 5–50-km width, shallow-source, magnetic anomalies over an area greater than 1.2 × 106 km2, mostly from subglacial volcanic sources. I interpreted the CWA anomalies as defining about 1000 “volcanic centers” requiring high remanent normal magnetizations in the present field direction. About 400 anomaly sources correlate with bed topography. At least 80% of these sources have less than 200 m relief at the WAIS bed. They appear modified by moving ice, requiring a younger age than the WAIS (about 25 Ma). Exposed volcanoes in the WARS are < 34 Ma, but at least four are active. If a few buried volcanic centers are active, subglacial volcanism may well affect the WAIS regime. Aero-geo-physical data (Blankenship et al., 1993, Mt. Casertz; Corr and Vaughan, 2008, near Hudson Mts.) indicated active subglacial volcanism. Magnetic data indicate a caldera and a surrounding “low” in the WAISCORE vicinity possibly the result of a shallow Curie isotherm. High heat flow reported from temperature logging in the WAISCORE (Conway et al., 2011; Clow, personal communication.) and a volcanic ash layer (Dunbar, 2012) are consistent with this interpretation. A subaerially erupted subglacial volcano, (Mt Thiel), about 100 km distant, may be the ash source. Aeromagnetic method most useful to study subglacial volcanic rocks beneath WAIS.  The Central West Antarctica aerogeophysical survey is a unique Antarctic data set.  Data indicate ~ 1000 magnetic anomalies mostly from subglacial volcanic eruptions. 

14. Joughin, Ian, et al. “Basal conditions for Pine Island and Thwaites Glaciers, West Antarctica, determined using satellite and airborne data.” Journal of Glaciology 55.190 (2009): 245-257.  We use models constrained by remotely sensed data from Pine Island and Thwaites Glaciers, West Antarctica, to infer basal properties that are difficult to observe directly. The results indicate strong basal melting in areas upstream of the grounding lines of both glaciers, where the ice flow is fast and the basal shear stress is large. Farther inland, we find that both glaciers have ‘mixed’ bed conditions, with extensive areas of both bedrock and weak till. In particular, there are weak areas along much of Pine Island Glacier’s main trunk that could prove unstable if it retreats past the band of strong bed just above its current grounding line. In agreement with earlier studies, our forward ice-stream model shows a strong sensitivity to small perturbations in the grounding line position. These results also reveal a large sensitivity to the assumed bed (sliding or deforming) model, with non-linear sliding laws producing substantially greater dynamic response than earlier simulations that assume a linear-viscous till rheology. Finally, comparison indicates that our results using a plastic bed are compatible with the limited observational constraints and theoretical work that suggests an upper bound exists on maximum basal shear stress.

PART-3B: THE RELEVANT BIBLIOGRAPHY PART 2: PINE ISLAND GLACIER

Loose, Brice, et al. “Evidence of an active volcanic heat source beneath the Pine Island Glacier.” Nature communications 9.1 (2018): 1-9.

Tectonic landforms reveal that the West Antarctic Ice Sheet (WAIS) lies atop a major volcanic rift system. However, identifying subglacial volcanism is challenging. Here we show geochemical evidence of a volcanic heat source upstream of the fast-melting Pine Island Ice Shelf, documented by seawater helium isotope ratios at the front of the Ice Shelf cavity. The localization of mantle helium to glacial meltwater reveals that volcanic heat induces melt beneath the grounded glacier and feeds the subglacial hydrological network crossing the grounding line. The observed transport of mantle helium out of the Ice Shelf cavity indicates that volcanic heat is supplied to the grounded glacier at a rate of ~ 2500 ± 1700 MW, which is ca. half as large as the active Grimsvötn volcano on Iceland. Our finding of a substantial volcanic heat source beneath a major WAIS glacier highlights the need to understand subglacial volcanism, its hydrologic interaction with the marine margins, and its potential role in the future stability of the WAIS.

Iverson, Nels A., et al. “The first physical evidence of subglacial volcanism under the West Antarctic Ice Sheet.” Scientific reports 7.1 (2017): 1-8. The West Antarctic ice sheet (WAIS) is highly vulnerable to collapsing because of increased ocean and surface temperatures. New evidence from ice core tephra shows that subglacial volcanism can breach the surface of the ice sheet and may pose a great threat to WAIS stability. Micro-CT analyses on englacial ice core tephra along with detailed shard morphology characterization and geochemical analysis suggest that two tephra layers were derived from subglacial to emergent volcanism that erupted through the WAIS. These tephra were erupted though the center of the ice sheet, deposited near WAIS Divide and preserved in the WDC06A ice core. The sources of these tephra layers were likely to be nearby subglacial volcanoes, Mt. Resnik, Mt. Thiel, and/or Mt. Casertz. A widespread increase in ice loss from WAIS could trigger positive feedback by decreasing ice mass and increasing decompression melting under the WAIS, increasing volcanism. Both tephra were erupted during the last glacial period and a widespread increase in subglacial volcanism in the future could have a considerable effect on the stability of the WAIS and resulting sea level rise.

Dziadek, Ricarda, Karsten Gohl, and Norbert Kaul. “Elevated geothermal surface heat flow in the Amundsen Sea Embayment, West Antarctica.” Earth and Planetary Science Letters 506 (2019): 530-539.

The thermal state of polar continental crust plays a crucial role for understanding the stability and thickness of large ice sheets, the visco-elastic response of the solid Earth due to unloading when large ice caps melt and, in turn, the accuracy of future sea-level rise prediction. Various studies demonstrate the need for precise measurements and estimation of geothermal heat flow (GHF) in Antarctica for better constrained boundary conditions to enhance the ice sheet model performance. This study provides ground-truth for regional indirect GHF estimates in the Amundsen Sea Embayment, which is part of the West Antarctic Rift System, by presenting in situ temperature measurements in continental shelf sediments. Our results show regionally elevated and heterogeneous GHF (mean of 65 mW m−2) in the Amundsen Sea Embayment. Considering thermal blanketing effects, induced by inflow of warmer water and sedimentary processes, the estimated GHF ranges between 65 mW m−2 and 95 mW m−2.

Seroussi, Helene, et al. “Influence of a West Antarctic mantle plume on ice sheet basal conditions.” Journal of Geophysical Research: Solid Earth 122.9 (2017): 7127-7155.

The possibility that a deep mantle plume manifests Pliocene and Quaternary volcanism and potential elevated heat flux in West Antarctica has been studied for more than 30 years. Recent seismic images support the plume hypothesis as the cause of Marie Byrd Land (MBL) volcanism and geophysical structure. Mantle plumes may more than double the geothermal heat flux above nominal continental values. A dearth of in situ ice sheet basal data exists that samples the heat flux. Consequently, we examine a realistic distribution of heat flux associated with a possible late Cenozoic mantle plume in West Antarctica and explore its impact on thermal and melt conditions at the ice sheet base. We use a simple analytical mantle plume parameterization to produce geothermal heat flux at the base of the ice sheet. The three‐dimensional ice flow model includes an enthalpy framework and full‐Stokes stress balance. As both the putative plume location and extent are uncertain, we perform broadly scoped experiments to characterize the impact of the plume on geothermal heat flux and ice sheet basal conditions. The experiments show that mantle plumes have an important local impact on the ice sheet, with basal melting rates reaching several centimeters per year directly above the hotspot. In order to be consistent with observations of basal hydrology in MBL, the upper bound on the plume‐derived geothermal heat flux is 150 mW/m2. In contrast, the active lake system of the lower part of Whillans Ice Stream suggests a widespread anomalous mantle heat flux, linked to a rift source.

Volcano climate SHOCK: Heat source under Antarctica could be melting giant  ice caps | Science | News | Express.co.uk

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