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Posted on: February 9, 2020

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THWAITES-3

 

THIS POST IS A CRITICAL REVIEW OF A YOUTUBE LECTURE ABOUT THE POTENTIAL AGW SEA LEVEL RISE CATASTROPHE OF THE THWAITES GLACIER IN WEST ANTARCTICA  [LINK TO YOUTUBE VIDEO] . IT IS PRESENTED IN THREE PARTS. PART-1 IS A TRANSCRIPT OF THE VIDEO. PART-2 IS A CRITICAL EVALUATION OF THE CLAIMS MADE IN THE VIDEO. PART-3 IS A RELEVANT BIBLIOGRAPHY ON THE SUBJECT.

 

PART-1: TRANSCRIPT OF THE YOUTUBE LECTURE

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  1. Kiya Riverman, University of Oregon glaciologist: If we’re thinking about what sea level is going to look like in 10 years, whether you’re building a dyke around your town or anticipating how far inland to move coastal cities in Florida, this glacier is a big piece of that question (The Thwaites Glacier in West Antarctica).  bandicam 2020-02-09 18-11-08-742
  2. Justin Rowlatt, BBC Environment Correspondent: This is a historic moment. The first  time anyone has tried to drill down through this glacier. Beneath the 600 meters of ice below me is the most important point of all – the point at which the ice meets the ocean water. bandicam 2020-02-09 18-29-59-895
  3. This is ICE-FIN, a NASA funded robot submarine. This is the first time any measurement has been taken beneath what they call the doomsday glacier. Its the first time anyone has seen this – this is the point where the ice meets the warmer ocean water. It’s a place where this huge glacier is rapidly melting. bandicam 2020-02-09 18-42-35-267
  4. Kiya Riverman, University of Oregon glaciologist: So this is very significant because it is huge. And it’s deep! It’s thick. There’s a giant volume of ice here. The bottom of the ice is below sea level. And so that means that it’s very sensitive to change, so the ocean can very easily melt and thin this glacier. bandicam 2020-02-09 18-52-59-600
  5. Justin Rowlatt, BBC Environment Correspondent: So Thwaites Glacier is really remote. It’s right at the heart of the vast basin of ice that’s West Antarctica. The glacier is the size of the UK, it’s the stormiest part of the stormiest continent in the world – and more than a thousand miles from the nearest research station. bandicam 2020-02-09 19-53-19-379
  6. Justin Rowlatt, BBC Environment Correspondent: All this broken ice is more than a hundred miles long. The ice rises almost a mile from the seabed and it’s collapsing into the sea at 2 miles a year. If Thwaites melts it will increase sea levels worldwide by half a meter. But it sits in the middle of the West Antarctic ice sheet and there’s 3 meters more of sea level rise locked up in that. bandicam 2020-02-09 19-59-14-300
  7. Kiya Riverman, University of Oregon glaciologist:  We have just detonated a shot and recorded the energy, the echo from the explosion in order to map the grounding zone to the point where the glacier goes afloat on the ocean. It is changing. It is migrating inland. So this huge reservoir of ice behind us is becoming vulnerable to the ocean melting. What’s happening out there. bandicam 2020-02-09 20-05-16-036
  8. Justin Rowlatt, BBC Environment Correspondent: Let’s be clear. The ice here isn’t going to vanish overnight. It’ll take decades, maybe even centuries for the Thwaites to go, but as the work here has confirmed it is melting increasingly rapidly and that will mean huge changes for us all.

 

 

PART-2: CRITICAL COMMENTARY ON THE YOUTUBE LECTURE

  1. The assessment of the Thwaites Glacier, and the West Antarctic Ice Sheet in general, presented above is the usual AGW climate change interpretation of the observed conditions as described for example in Scambos etal (2017) in the bibliography below. It derives from the observation that the bottom of the Thwaites Glacier is below sea level.
  2. The climate science assessment is that an ongoing rapid loss of ice is observed in this region. This ice loss is a response to changing atmospheric and oceanic conditions brought about by AGW climate change where AGW driven increase in ocean heat content is responsible for the warm water beneath the glacier that’s melting the ice. Models of the ice sheet’s dynamic indicate a potential for accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments“.
  3. The time scale for these events is estimated to be “a few centuries” with a more alarming possibility that faster ice loss could occur through hydrofracture and ice cliff failure, in which case a cataclysmic collapse and sea level rise could happen in a few decades.
  4. This assessment of the observed ice loss from the Thwaites does not take into account known geological features of West Antarctica with significant geothermal heat potential described in a related post [LINK].
  5. The principal geological feature of West Antarctica is the West Antarctic Rift (WAR) and its major fault lines shown in the graphic below. The rift is 700 miles wide and 4,000 miles long with 149 known active volcanoes. A rift is an area where the lithosphere is being pulled apart by plate tectonics. In the diagram below, the black cross hatched area shows the location of the West Antarctic Rift. Red outlines identify regions of volcanic activity with red dots within them showing locations of the volcanoes. Two such red circles that are particularly significant in terms of geological activity and geothermal heat are Deception Island and the Marie Byrd Mantle Plume area. bandicam 2020-02-10 11-51-04-994
  6. As the lithosphere is pulled apart, its middle thins and brings hot mantle rocks closer to the ocean waters and aids in heat transfer from the mantle to the ocean. See graphic below provided by the University of Sydney [LINK]. Here, the color red indicates intensity of geothermal heat. The WAR contains 149 active volcanoes.bandicam 2020-02-10 12-03-35-146
  7. Within this giant rift structure are specific regions of intense geological activity and geothermal heat. The Northwest extension of the WAR, with a string of active volcanoes, goes into the Antarctic Peninsula and out into the ocean. The West Antarctic Rift (WAR) consists of a number of rift valleys between East and West Antarctica. A rift valley is a lowland region that forms in the middle where a rift occurs. They tend to be long, narrow, and deep. The WAR includes the Byrd area of West Antarctica. The Byrd area is the main portion of the WAR.
  8. The Marie Byrd Mantle Plume Hotspot is shown below. It includes the Thwaites Glacier and the Pine Island Glacier. A mantle plume hotspot is a large area where magma comes up from the mantle of the inner earth, goes up through layers of rock until obstructed when it spreads out into a mushroom shape over a widespread area. If it is under a sufficient pressure, the magma can break through to the atmosphere as a volcanic eruption. The shaded red areas on the map are graphical representations of NASA ice melt data from 1992-2019. Red shaded areas identify locations of melting and the darker the red color, the more intense the melting. These red areas are found close to the edge of the Marie Byrd Mantle Plume. These data suggest that the mantle plume is the cause of the observed ice melt. marie-byrd-mantle-plume
  9. A rise in elevation has been observed in the Marie Byrd Mantle Plume area It could be that the bedrock is being pushed up by the underlying magma although some of the elevation rise is likely due to “glacial rebound” –  (when ice melts and meltwater runs off it reduces the pressure on the underlying structure and causes it to rise). We note here that the Thwaites Glacier is located within Marie Byrd Mantle Plume Hotspot area in a region of extensive ice melt during 1992-2019.
  10. The image below shows the the Pine Island Glacier and the much larger Thwaites Glacier areas cross hatched in blue lines. Red circles show locations of known active volcanoes underneath the glacier. It is claimed in this video – and in the media in general, that they have discovered a huge air cavity beneath the ice and above the bedrock surface in the Thwaites Glacier that is evidence of the impact of AGW on the Thwaites Glacier. However, the more likely creator of that cavity is an eruption of any of the 40 active volcanoes known to exist underneath the Thwaites Glacier.

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THE RELEVANT BIBLIOGRAPHY

A bibliography of research papers 1993-2019 on the subject of the Thwaites Glacier is included below. Many of the papers support the climate change theory of mass loss from the Thwaites glacier by way of a warm ocean (warmed by AGW) eating away at the bottom of the volcano that dips into the ocean. Scambos (2017) is an example. There are a few others. However, the ability of the atmosphere through AGW to warm the deep ocean contains inconsistencies noted by several authors in the bibliography and also in a related post [LINK] . In the bibliography we find many of the authors have acknowledged these difficulties and have presented evidence of geothermal heat as the source of energy that warms the water that melts the glacier. (dVries 2018), (Fisher 2015), (Damiani 2014), (Schroeder 2014), (Maule 2005), and (Corr 2008) are examples.

 

CONCLUSION: We find that the presentation of the geological features of West Antarctica in terms of the West Antarctic Rift, the Marie Byrd Mantle Plume, and evidence of active volcanism underneath the Thwaites Glacier provide evidence that the role of geothermal heat in the evaluation of the ice melt dynamics of the Thwaites Glacier cannot be ignored. The geothermal heat flux data and their analysis in terms of the Thwaites glacier dynamics in the literature is generally supportive of that view. In consideration of the above we find it unlikely that ice melt at the bottom of the Thwaites Glacier can be understood in terms of AGW climate change as claimed in the video lecture presented above.

 

 

 

THWAITES GLACIER BIBLIOGRAPHY 1993-2018

  1. Blankenship, Donald et al. “Active volcanism beneath the West Antarctic ice sheet & implications for ice-sheet stability.” Nature 361.6412 (1993): It is widely understood that the collapse of the West Antarctic ice sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this ice sheet to climate change. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide4,5. Ice streams act to protect the reservoir of slowly moving inland ice from exposure to oceanic degradation, thus enhancing ice-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins. If this heat flow is indeed controlling ice-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West Antarctic rift system could lead to the disappearance of ice streams, and possibly trigger a collapse of the inland ice reservoir.
  2. 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.
  3. Dalziel, I. W. D., and L. A. Lawver. “The lithospheric setting of the West Antarctic ice sheet.” The West Antarctic Ice Sheet: Behavior and Environment, Antarct. Res. Ser 77 (2001): 29-44[FULL TEXT PDF]bandicam 2020-02-10 11-08-44-341
  4. Rignot, Eric, et al. “Acceleration of Pine island and Thwaites glaciers, west Antarctica.” Annals of Glaciology 34 (2002): 189-194.  Recent satellite investigations revealed that in the 1990s the grounding line of Pine Island and Thwaites Glaciers, West Antarctica, retreated several km, the ice surface on the interior of the basins lowered 10 cm a–1, and Pine Island Glacier thinned 1.6 ma–1. These observations, however, were not sufficient to determine the cause of the changes. Here, we present satellite radar interferometry data that show the thinning and retreat of Pine Island Glacier are caused by an acceleration of ice flow of about 18 ± 2% in 8 years. Thwaites Glacier maintained a nearly constant flow regime at its center, but widened along the sides, and increased its 30 ± 15% mass deficit by another 4% in 4 years. The combined mass loss from both glaciers, if correct, contributes an estimated 0.08 ± 0.03 mma–1 global sea-level rise in 2000.
  5. Engelhardt, Hermann. “Ice temperature and high geothermal flux at Siple Dome, West Antarctica, from borehole measurements.” Journal of Glaciology 50.169 (2004): 251-256A vertical temperature profile through the West Antarctic ice sheet (WAIS) at the summit of Siple Dome reveals an elevated geothermal flux. This could be the root cause for the existence of a dynamic ice-stream system in the WAIS. Siple Dome is still frozen on its bed, but adjacent ice streams have bed temperatures at the pressure-melting point of ice. Although present-day temperature increases due to climatic change do not have an immediate effect on the basal conditions that control the velocity of the ice, indirect effects like a rapid disintegration of the floating ice shelves or additional melt-water input at the surface could give rise to speed-up of the ice streams with an ensuing rise in sea level. Ongoing melt at the base of the ice and changes at the margins will allow continued rapid flow of the ice streams with a possibility of disintegration, within a relatively short period of time, of at least part of the WAIS.
  6. Maule, Cathrine Fox, et al. “Heat flux anomalies in Antarctica revealed by satellite magnetic data.” Science 309.5733 (2005): 464-467The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a method that uses satellite magnetic data to estimate the heat flux underneath the Antarctic ice sheet. We found that the heat flux underneath the ice sheet varies from 40 to 185 megawatts per square meter and that areas of high heat flux coincide with known current volcanism and some areas known to have ice streams.
  7. Vaughan, David G., et al. “New boundary conditions for the West Antarctic ice sheet: Subglacial topography beneath Pine Island Glacier.” Geophysical Research Letters 33.9 (2006).  Predictions about future changes in the Amundsen Sea sector of the West Antarctic ice sheet (WAIS) have been hampered by poorly known subglacial topography. Extensive airborne survey has allowed us to derive improved subglacial topography for the Pine Island Glacier basin. The trunk of this glacier lies in a narrow, 250‐km long, 500‐m deep sub‐glacial trough, suggesting a long‐lived and constrained ice stream. Two tributaries lie in similar troughs, others lie in less defined, shallower troughs. The lower basin of the glacier is surrounded by bedrock, which, after deglaciation and isostatic rebound, could rise above sea level. This feature would impede ice‐sheet collapse initiated near the grounding line of this glacier, and prevent its progress into the deepest portions of WAIS. The inland‐slope of the bed beneath the trunk of the glacier, however, confirms potential instability of the lower basin, containing sufficient ice to raise global sea by ∼24 cm.
  8. Holt, John W., et al. “New boundary conditions for the West Antarctic Ice Sheet: Subglacial topography of the Thwaites and Smith glacier catchments.” Geophysical Research Letters 33.9 (2006)Airborne radar sounding over the Thwaites Glacier (TG) catchment and its surroundings provides the first comprehensive view of subglacial topography in this dynamic part of the West Antarctic Ice Sheet (WAIS) and reveals that TG is underlain by a single, broad basin fed by a dendritic pattern of valleys, while Smith Glacier lies within an extremely deep, narrow trench. Subglacial topography in the TG catchment slopes inland from a broad, low‐relief coastal sill to the thickest ice of the WAIS and makes deep connections to both Pine Island Glacier and the Ross Sea Embayment enabling dynamic interactions across the WAIS during deglaciation. Simple isostatic rebound modeling shows that most of this landscape would be submarine after deglaciation, aside from an island chain near the present‐day Ross‐Amundsen ice divide. The lack of topographic confinement along TG’s eastern margin implies that it may continue to widen in response to grounding line retreat.
  9. Vogel, Stefan W., and Slawek Tulaczyk. “Ice‐dynamical constraints on the existence and impact of subglacial volcanism on West Antarctic Ice Sheet stability.” Geophysical Research Letters 33.23 (2006)Subglacial volcanism in West Antarctica may play a crucial role in the dynamics and stability of the West Antarctic Ice Sheet (WAIS). Evidence supporting the existence of an individual subglacial volcanic center (Mt. Casertz) in the upper catchments of Whillans and Kamb Ice Stream (WIS and KIS), comes from a comparison of ice sheet modeling results with measured ice velocities. Lubrication of an area, which otherwise should be frozen to its bed, is best explained by basal melt water generated in the vicinity of Mt. Casertz. The estimated melt water production of Mt. Casertz corresponds to ∼8 % of the total melt water production in the two catchments. This would be sufficient to offset basal freezing in the dormant KIS, relubricating its bed and potentially causing a restart. Near future volcanic activity changes are speculative, but would have far reaching implications on the dynamics and stability of the WAIS requiring further investigation.
  10. Banta, J. Ryan, et al. “Spatial and temporal variability in snow accumulation at the West Antarctic Ice Sheet Divide over recent centuries.” Journal of Geophysical Research: Atmospheres 113.D23 (2008).  Ice cores collected in 2000 (ITASE 00‐1) and 2005 (WDC05A, WDC05Q) from the West Antarctic Ice Sheet Divide (WAIS Divide) project site were used to investigate the spatial and temporal variability in accumulation. The ice cores were dated based on annual layer counting of multiple glaciochemical measurements resulting in bottom depth ages for WDC05A, WDC05Q, and ITASE 00‐1 of 1775, 1521, and 1653 A.D., with mean annual accumulation rates of 0.200, 0.204, and 0.221 mweq a−1, respectively. Small‐scale spatial variability (SSV) was determined using an analysis of variance of accumulation in the ice core array, thereby quantifying the uncertainty in individual accumulation records. Results indicate that the spatial variability was 0.030 mweq a−1, or approximately 15% of the average annual accumulation. An accumulation record representative of the WAIS Divide local area over recent centuries was developed using a principal component analysis to identify the coherent accumulation signal. The WAIS Divide local record exhibited 14% interannual variability (1 standard deviation of the mean) with the SSV reduced to 0.017 mweq a−1. Correlations of the WAIS Divide local accumulation record with atmospheric indices (e.g., Antarctic Oscillation) exhibited periods when the records oscillate in and out of phase. Thus, reconstructing local and global atmospheric indices from WAIS Divide accumulation records over recent centuries may prove problematic.
  11. Corr, Hugh FJ, and David G. Vaughan. “A recent volcanic eruption beneath the West Antarctic ice sheet.” Nature Geoscience 1.2 (2008): 122-125.  Indirect evidence suggests that volcanic activity occurring beneath the West Antarctic ice sheet influences ice flow and sheet stability1,2,3. However, only volcanoes that protrude through the ice sheet4 and those inferred from geophysical techniques1,2 have been mapped so far. Here we analyse radar data from the Hudson Mountains, West Antarctica5, that contain reflections from within the ice that had previously been interpreted erroneously as the ice-sheet bed. We show that the reflections are present within an elliptical area of about 23,000 km2 that contains tephra (solid rock pieces in volcanic ejections) from an explosive volcanic eruption. The tephra layer is thickest at a subglacial topographic high, which we term the Hudson Mountains Subglacial Volcano. The layer depth dates the eruption at 207 BC±240 years, which matches exceptionally strong but previously unattributed conductivity signals in nearby ice cores. The layer contains 0.019–0.31 km3 of tephra, which implies a volcanic explosive index of 3–4. Production and episodic release of water from the volcano probably affected ice flow at the time of the eruption. Ongoing volcanic heat production may have implications for contemporary ice dynamics in this glacial system.
  12. 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.
  13. Tinto, K. J., and Robin E. Bell. “Progressive unpinning of Thwaites Glacier from newly identified offshore ridge: Constraints from aerogravity.” Geophysical Research Letters 38.20 (2011) A new bathymetric model from the Thwaites Glacier region based on IceBridge airborne gravity data defines morphologic features that exert key controls on the evolution of the ice flow. A prominent ridge with two distinct peaks has been identified 40 km in front of the present‐day grounding line, undulating between 300–700 m below sea level with an average relief of 700 m. Presently, the Thwaites ice shelf is pinned on the eastern peak. More extensive pinning in the past would have restricted flow of floating ice across the full width of the Thwaites Glacier system. At present thinning rates, ice would have lost contact with the western part of the ridge between 55–150 years ago, allowing unconfined flow of floating ice and contributing to the present‐day mass imbalance of Thwaites Glacier. The bathymetric model also reveals a 1200 m deep trough beneath a bight in the grounding line where the glacier is moving the fastest. This newly defined trough marks the lowest topographic pathway to the Byrd Subglacial Basin, and the most likely path for future grounding line retreat.
  14. Larour, E., et al. “Ice flow sensitivity to geothermal heat flux of Pine Island Glacier, Antarctica.” Journal of Geophysical Research: Earth Surface 117.F4 (2012)Model projections of ice flow in a changing climate are dependent on model inputs such as surface elevation, bedrock position or surface temperatures, among others. Of all these inputs, geothermal heat flux is the one for which uncertainty is greatest. In the area of Pine Island Glacier, Antarctica, available data sets differ by up to a factor of 2.5. Here, we evaluate the impact of such uncertainty on ice flow, using sampling analyses based on the Latin‐Hypercube method. First, we quantify the impact of geothermal heat flux errors on ice hardness, a thermal parameter that critically controls the magnitude of ice flow. Second, we quantify the impact of the same errors on mass balance, specifically on the mass flux advecting through thirteen fluxgates distributed across Pine Island Glacier. We contrast our results with similar uncertainties generated by errors in the specification of ice thickness. Model outputs indicate that geothermal heat flux errors yield uncertainties on ice hardness on the order of 5–7%, with maximum uncertainty reaching 15%. Resulting uncertainties in mass balance remain however below 1%. We discuss the uncertainty distribution and its relationship to the amount of heat available at the base of the ice sheet from friction, viscous and geothermal heating. We also show that comparatively, errors in ice thickness contribute more to model uncertainty than errors in geothermal heat flux for fast‐flowing ice streams. [FULL TEXT]
  15. Schroeder, Dustin M., et al. “Estimating subglacial water geometry using radar bed echo specularity: application to Thwaites Glacier, West Antarctica.” IEEE Geoscience and Remote Sensing Letters 12.3 (2014A): 443-447.  Airborne radar sounding is an established tool for observing the bed conditions and subglacial hydrology of ice sheets and glaciers. The specularity content of radar bed echoes has also been used to detect the hydrologic transition of a subglacial water system from a network of distributed canals to a network of concentrated channels beneath the Thwaites Glacier. However, the physical dimensions of the distributed water bodies in these networks have not been constrained by observations. In this letter, we use a variety of simple radar scattering, attenuation, and cross-sectional models to provide a first estimate of the subglacial water body geometries capable of producing the observed anisotropic specularity of the Thwaites Glacier catchment. This approach leads to estimates of ice/water interface root mean square roughnesses less than about 15 cm, thicknesses of more than about 5 cm, lengths of more than about 15 m, and widths between about 0.5 and 5 m.
  16. 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 (2014B): 9070-9072.  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.
  17. Damiani, Theresa M., et al. “Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica.” Earth and Planetary Science Letters 407 (2014): 109-122Thwaites Glacier has one of the largest glacial catchments in West Antarctica. The future stability of Thwaites Glacier’s catchment is of great concern, as this part of the West Antarctic Ice Sheet has recently been hypothesized to already be en route towards collapse. Although an oceanic trigger is thought to be responsible for current change at the grounding line of Thwaites Glacier, in order to determine the effects of this coastal change further in the interior of the West Antarctic Ice Sheet it is essential to also better constrain basal conditions that control the dynamics of fast glacial flow within the catchment itself. One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. The primary goal of our study is to investigate the crustal thickness beneath Thwaites Glacier, which is an important contributor to regional-scale geothermal heat flux patterns. Crustal structure is an indicator of past tectonic events and hence provides a geophysical proxy for the thermal status of the crust and mantle. Terrain-corrected Bouguer gravity disturbances are used here to estimate depths to the Moho and mid-crustal boundary. The thin continental crust we reveal beneath Thwaites Glacier supports the hypothesis that the West Antarctic Rift System underlies the region and is expressed topographically as the Byrd Subglacial Basin. This rifted crust is of similar thickness to that calculated from airborne gravity data beneath neighboring Pine Island Glacier, and is more extended than crust in the adjacent Siple Coast sector of the Ross Sea Embayment. A zone of thinner crust is also identified near the area’s subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. Near-zero Bouguer gravity disturbances for the subglacial highlands and subaerial volcanoes indicate the absence of supporting crustal roots, suggesting either (1) thermal support from a warm lithosphere or alternatively, and arguably less likely; (2) flexural support of the topography by a cool and rigid lithosphere, or (3) Pratt-like compensation. Although forward modeling of gravity data is non-unique in respect to these alternative possibilities, we prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself. Our new crustal thickness estimates and geothermal heat flux inferences in the Thwaites Glacier region are significant both for studies of the structure of the broader West Antarctic Rift System and for assessments of geological influences on West Antarctic Ice Sheet dynamics and glacial isostatic adjustment models.
  18. Fisher, Andrew T., et al. “High geothermal heat flux measured below the West Antarctic Ice Sheet.” Science advances 1.6 (2015): e1500093.  The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m2, significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2. The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.
  19. Scambos, Ted A., et al. “How much, how fast?: A science review and outlook for research on the instability of Antarctica’s Thwaites Glacier in the 21st century.” Global and Planetary Change 153 (2017): 16-34.  Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo near-term significant change: Thwaites Glacier and the adjacent Amundsen Sea. Multiple lines of evidence point to an ongoing rapid loss of ice in this region in response to changing atmospheric and oceanic conditions. Models of the ice sheet’s dynamic behavior indicate a potential for greatly accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone and nearby areas leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments. This scenario could occur over the next few centuries, and faster ice loss could occur through processes omitted from most ice flow models such as hydrofracture and ice cliff failure, which have been observed in recent rapid ice retreats elsewhere. Increased basal melt at the grounding zone and increased potential for hydrofracture due to enhanced surface melt could initiate a more rapid collapse of Thwaites Glacier within the next few decades. 
  20. de Vries, Maximillian van Wyk, Robert G. Bingham, and Andrew S. Hein. “A new volcanic province: an inventory of subglacial volcanoes in West Antarctica.” Geological Society, London, Special Publications 461.1 (2018): 231-248[FULL TEXT]  The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity and its extent. Improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice-sheet growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial volcanoes. We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volcanoes to support this interpretation. The overall result presented here constitutes a first inventory of West Antarctica’s subglacial volcanism. We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the >3000 km central axis of the West Antarctic Rift System.

 

4 Responses to "ANTARCTICA THREATENS FLORIDA"

Reblogged this on Climate- Science.press.

Thank you uwe. Fixed a couple of typos in the meantime.

Welcome. Have a great week.

Thanks for following my site, and for liking my posts; you are very kind.

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  • jamesmatkinwritings: Here is a reference about your fake carbon footprint -Caring about sound science: Carbon is not carbon dioxide Wiki Commons photo October 25,
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