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CLIMATE CHANGE THREATENS POLAR ICE

Posted on: November 7, 2020

PPT - NASA Earth Science Applications PowerPoint Presentation, free  download - ID:4071852
NASA GLACIAL MELT VIDEO

THIS POST IS A CRITIAL REVIEW OF A NASA PUBLICATION ON POLAR ICE MELT BY ANTHROPOGENC GLOBAL WARMING AND CLIMATE CHANGE. LINK TO SOURCE: https://climate.nasa.gov/news/3038/the-anatomy-of-glacial-ice-loss/

Greenland's ice sheet melting seven times faster than in 1990s |  Environment | The Guardian

ABSTRACTThe attribution of observed polar ice melt events to anthropogenic global warming along with the proposal that such melt events can be attenuated by taking climate action and moving the global energy infrastructure away from fossil fuels to renewables, is not possible in light of the complex episodic and localized nature of these ice melt events and their locations restricted to known geologically active areas. The attribution to anthropogenic global warming requires an explanation of these anomalies. If polar ice melt were driven by global warming it would be more uniform and more of a trend and not isolated, episodic, and not restricted to known geologically active locations. Glacial and ice shelf melt events that are episodic and restricted to geologically active locations cannot be understood as the impacts of fossil fuel emissions that can be moderated or prevented by taking climate action. For that, significant additional evidence must be provided that relates the melt events to atmospheric temperature data. No such evidence has been provided in this study where, as in all such studies, an atmosphere bias in the research methodology assumes that ice melt can only be explained in terms of anthropogenic global warming. Such findings are more likely to be the product of confirmation bias than unbiased and objective scientific inquiry. 

Bias in Science: Further Thoughts from Skeptech – Skepchick

LINK: https://tambonthongchai.com/2018/08/03/confirmationbias/

PART-1: WHAT THE NASA PUBLICATION SAYS

  1. When an ice cube is exposed to a heat source, like warm water or air, it melts. So, it’s no surprise that a warming climate is causing our glaciers and ice sheets to melt. However, predicting just how much the glaciers and ice sheets will melt and how quickly – key components of sea level rise – is not nearly as straightforward.
  2. Glaciers and ice sheets are more complex structures than ice cubes. They form when snow accumulates and is compressed into ice by new snow over many years. As they grow, they begin to move slowly under the pressure of their own weight, dragging smaller rocks and debris across the land with them. Glacial ice that extends to cover large landmasses, as it does in Antarctica and Greenland, is considered an ice sheet.
  3. The processes that cause glaciers and ice sheets to lose mass are also more complex. While warm air certainly melts the surface of glaciers and ice sheets, they’re also significantly affected by other factors including the ocean water that surrounds them, the terrain over which they move, and even their own meltwater.
  4. Greenland and Antarctica are home to most of the world’s glacial ice, including its only two ice sheets. These thick slabs of ice – some 10,000 feet (3,000 meters) and 15,000 feet (4,500 meters) thick, respectively – contain most of the freshwater stored on Earth, making them of particular interest to scientists. Combined, the two regions also contain enough ice that, if it were to melt all at once, would raise sea levels by nearly 65 meters – making the study and understanding of them not just interesting, but crucial to our near-term adaptability and our long-term survival in a changing world.
  5. Ice Loss in Greenland: A glacier is considered “in balance” when the amount of snow that falls and accumulates at its surface (the accumulation zone) is equal to the amount of ice lost through melting, evaporation, calving and other processes. But with annual air temperatures in the Arctic increasing faster than anywhere else in the world, that balance is no longer achievable in Greenland. Warmer ocean waters surrounding the island’s tidewater glaciers are also problematic. It’s like pointing a hairdryer at an ice cube, while the ice cube is also sitting in a warm pot of water, according to NASA’s Oceans Melting Greenland OMG project that is investigating the effects of ocean water temperature on melting ice in the region. The glaciers are being melted by heat from above and below simultaneously.
  6. Although the warm air and the warm water contribute to melting individually, the interplay between the meltwater from the glacier and the warm ocean water also plays a significant role. When warm summer air melts the surface of a glacier, the meltwater bores holes down through the ice. It makes its way all the way down to the bottom of the glacier where it runs between the ice and the glacier bed, and eventually shoots out in a plume at the glacier base and into the surrounding ocean. The meltwater plume is lighter than the surrounding ocean water because it doesn’t contain salt. So it rises toward the surface, mixing the warm ocean water upward in the process. The warm water then rubs up against the bottom of the glacier, causing even more of the glacier to melt. This often leads to calving, ice cracking and breaking off into large ice chunks (icebergs) – at the front end, or terminus of the glacier.
  7. When warm summer air melts the surface of a glacier, the meltwater bores holes down through the ice. It makes its way all the way down to the bottom of the glacier where it runs between the ice and the glacier bed, and eventually shoots out in a plume at the glacier base and into the surrounding ocean.
  8. The complicated shape of the sea floor surrounding Greenland influences how readily this warm water melt can occur. It provides a barrier in some areas – preventing the deep, warmer water from the Atlantic Ocean from reaching glacier fronts. However, the underwater terrain, much like the terrain above water, includes other features like deep canyons. The canyons cut into the continental shelf, allowing the Atlantic waters in. Glaciers sitting in these waters will melt faster than those where the warm water is blocked by underwater ridges or sills.
  9. Ice Loss in Antarctica: In Antarctica, where similar surface and ocean melting processes occur, the topography and bedrock on which the ice sheet sits significantly influence the ice sheet’s stability and its contribution to sea level rise. Researchers separate Antarctica into two regions based on the relationship between the ice and the bedrock beneath it. East Antarctica, the area east of the Transantarctic Mountains, is extremely high in elevation and has the thickest ice on the planet. The bedrock underneath the ice sheet is also mostly above sea level. These features help to keep the east side relatively stable. West Antarctica, on the other hand, is lower in elevation and most of the ice sheet there is thinner. Unlike the east, the ice sheet in West Antarctica sits on bedrock that is below sea level.
  10. In West Antarctica, we have these glaciers resting on bedrock that is under water. Like in Greenland, there is a layer of warmer ocean water below the cold surface layer. So this warm water is able to flow onto the continental shelf, and then all the way underneath the ice shelves – the floating ice that extends from glaciers and the ice sheet, according to Jet Propulsion scientists. The water melts the ice shelves from below, which can cause them to thin and break off.
  11. Ocean currents flow around and under the Pine Island Glacier. As the water makes its way underneath the ice shelf, it erodes the ice shelf from the bottom causing it to become thinner.
  12. The ice shelves act like corks. They hold back the ice that is flowing from upstream, slowing its approach to the ocean where it raises sea level. When the ice shelves calve, the cork is essentially removed, allowing more inland ice to flow freely into the ocean. Furthermore, this leads to retreat of the grounding zone – the area where the ice separates from the bedrock and begins to float.
  13. The grounding zone delineates floating ice, which is already accounted for in the sea level budget from grounded ice which is not accounted for in the budget according to Goddard Space Flight Center scientists. Floating ice is like an ice cube floating in a glass. It doesn’t overflow the glass when it melts. But when non-floating ice is added to the ocean, it’s like adding more ice cubes to the glass which will cause the water level to rise.
  14. The bedrock in West Antarctica is reverse sloping – meaning it is higher at the edges and gradually becomes deeper further inland. When the grounding zone retreats inland, thicker ice is exposed to the ocean water and the glacier or ice sheet becomes grounded in deeper water. This allows even more ice to flow from upstream into the ocean. It’s concerning in West Antarctica because as we push the grounding zones back, the downward, reverse slope means that there’s really no backstop, nothing to interrupt this cycle of melting and retreat. Our maps of the bedrock under the ice sheet are not comprehensive and so we really don’t know if there are any little bumps or peaks down there that might help to slow the retreat.
  15. West Antarctic glaciers like Thwaites and Pine Island are already retreating faster than they were in the past. This is problematic because they provide a main pathway for ice from the West Antarctic Ice Sheet to enter the Amundsen Sea and raise sea levels.
  16. Melting and ice loss have accelerated at both poles in recent years. The more we learn about the processes and interactions that cause it the better we’ll be able to accurately and precisely predict sea level rise far into the future.

Geological 'Hotspot' Melting Pine Island and Thwaites Glaciers, Not Global  Warming — Plate climatology
SOME GEOLOGICAL FEATURES OF ANTARCTICA

PART-2: CRITICAL COMMENTARY

Although NASA has determined that fossil fuel driven global warming is causing polar ice sheets to melt thus causing sea level rise, and that we can and must attenuate this process with climate action to save the world from sea level rise, it is worth taking a detailed look at the dynamics and locations of these ice melt events and the geological features of these specific locations to make a critical assessment of the rocket science that climate action in the form of moving the world’s energy infrastructure from fossil fuels to renewables will slow down and stop these ice melt processes and save the world from sea level rise.

bandicam 2019-07-01 16-29-44-526
SOME GEOLOGICAL FEATURES OF THE ARCTIC

In the context of ice melt events in the polar regions, here we note that both the polar regions are geologically active with substantial empirical evidence of significant geothermal flux in the locations where polar ice melt is found. Details of the relevant geological features are described in related posts on this site for both the Arctic region and for Antarctica at the links below.

Related post on the relevant geological features of the Arctic: LINK: https://tambonthongchai.com/2019/07/01/arctic/

arctic-sea-ice2

Related post on the relevant geological features of Antarctica: LINK: https://tambonthongchai.com/2019/06/27/antarctica/

kamis-erebus

A relevant bibliography is provided below where empirical evidence of these location specific geothermal activity is presented. Principal investigators in this area are Yasmina Martos, a NASA scientist, and Ralf Greve, Glaciologist, Hokkaido University.

Bio - Yasmina M Martos Martin
DR. YASMINA MARTOS: NASA SCIENTIST

New estimates for the rise in sea levels due to ice sheet mass loss under  future climate change | Hokkaido University
RALF GREVE (RIGHT) HOKKAIDO UNI VERSITY GLACIOLOGIST

THE RELEVANT BIBLIOGRAPHY: PART-1: THE ARCTIC

  1. Fahnestock, Mark, et al. “High geothermal heat flow, basal melt, and the origin of rapid ice flow in central Greenland.” Science 294.5550 (2001): 2338-2342. Age-depth relations from internal layering reveal a large region of rapid basal melting in Greenland. Melt is localized at the onset of rapid ice flow in the large ice stream that drains north off the summit dome and other areas in the northeast quadrant of the ice sheet. Locally, high melt rates indicate geothermal fluxes 15 to 30 times continental background. The southern limit of melt coincides with magnetic anomalies and topography that suggest a volcanic origin.
  2. Rezvanbehbahani, Soroush, et al. “Predicting the geothermal heat flux in Greenland: A machine learning approach.” Geophysical Research Letters 44.24 (2017): 12-271. Geothermal heat flux (GHF) is a crucial boundary condition for making accurate predictions of ice sheet mass loss, yet it is poorly known in Greenland due to inaccessibility of the bedrock. Here we use a machine learning algorithm on a large collection of relevant geologic features and global GHF measurements and produce a GHF map of Greenland that we argue is within ∼15% accuracy. The main features of our predicted GHF map include a large region with high GHF in central‐north Greenland surrounding the NorthGRIP ice core site, and hot spots in the Jakobshavn Isbræ catchment, upstream of Petermann Gletscher, and near the terminus of Nioghalvfjerdsfjorden glacier. Our model also captures the trajectory of Greenland movement over the Icelandic plume by predicting a stripe of elevated GHF in central‐east Greenland. Finally, we show that our model can produce substantially more accurate predictions if additional measurements of GHF in Greenland are provided. FULL TEXT: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL075661
  3. van der Veen, Cornelis J., et al. “Subglacial topography and geothermal heat flux: Potential interactions with drainage of the Greenland ice sheet.” Geophysical research letters 34.12 (2007). Many of the outlet glaciers in Greenland overlie deep and narrow trenches cut into the bedrock. It is well known that pronounced topography intensifies the geothermal heat flux in deep valleys and attenuates this flux on mountains. Here we investigate the magnitude of this effect for two subglacial trenches in Greenland. Heat flux variations are estimated for idealized geometries using solutions for plane slopes derived by Lachenbruch (1968). It is found that for channels such as the one under Jakobshavn Isbræ, topographic effects may increase the local geothermal heat flux by as much as 100%.
  4. Greve, Ralf. “Relation of measured basal temperatures and the spatial distribution of the geothermal heat flux for the Greenland ice sheet.” Annals of Glaciology 42 (2005): 424-432. The thermomechanical, three-dimensional ice-sheet model SICOPOLIS is applied to the Greenland ice sheet. Simulations over two glacial–interglacial cycles are carried out, driven by a climatic forcing interpolated between present conditions and Last Glacial Maximum anomalies. Based on the global heat-flow representation by Pollack and others (1993), we attempt to constrain the spatial pattern of the geothermal heat flux by comparing simulation results to direct measurements of basal temperatures at the GRIP, NorthGRIP, Camp Century and Dye 3 ice-core locations. The heat-flux map shows an increasing trend from west to east, a high-heat-flux anomaly around NorthGRIP with values up to 135 mWm–2 and a low-heat-flux anomaly around Dye 3 with values down to 20 mW m–2. Validation is provided by the generally good fit between observed and measured ice thicknesses. Residual discrepancies are most likely due to deficiencies of the input precipitation rate and further variability of the geothermal heat flux not captured here.
  5. Smith‐Johnsen, Silje, et al. “Sensitivity of the Northeast Greenland Ice Stream to geothermal heat.” Journal of Geophysical Research: Earth Surface 125.1 (2020): e2019JF005252. Recent observations of ice flow surface velocities have helped improve our understanding of basal processes on Greenland and Antarctica, though these processes still constitute some of the largest uncertainties driving ice flow change today. The Northeast Greenland Ice Stream is driven largely by basal sliding, believed to be related to subglacial hydrology and the availability of heat. Characterization of the uncertainties associated with Northeast Greenland Ice Stream is crucial for constraining Greenland’s potential contribution to sea level rise in the upcoming centuries. Here, we expand upon past work using the Ice Sheet System Model to quantify the uncertainties in models of the ice flow in the Northeast Greenland Ice Stream by perturbing the geothermal heat flux. Utilizing a subglacial hydrology model simulating sliding beneath the Greenland Ice Sheet, we investigate the sensitivity of the Northeast Greenland Ice Stream ice flow to various estimates of geothermal heat flux, and implications of basal heat flux uncertainties on modeling the hydrological processes beneath Greenland’s major ice stream. We find that the uncertainty due to sliding at the bed is 10 times greater than the uncertainty associated with internal ice viscosity. Geothermal heat flux dictates the size of the area of the subglacial drainage system and its efficiency. The uncertainty of ice discharge from the Northeast Greenland Ice Stream to the ocean due to uncertainties in the geothermal heat flux is estimated at 2.10 Gt/yr. This highlights the urgency in obtaining better constraints on the highly uncertain subglacial hydrology parameters.
  6. Martos, Yasmina M., et al. “Geothermal heat flux reveals the Iceland hotspot track underneath Greenland.” Geophysical research letters 45.16 (2018): 8214-8222. Curie depths beneath Greenland are revealed by spectral analysis of data from the World Digital Magnetic Anomaly Map 2. A thermal model of the lithosphere then provides a corresponding geothermal heat flux map. This new map exhibits significantly higher frequency but lower amplitude variation than earlier heat flux maps and provides an important boundary condition for numerical ice‐sheet models and interpretation of borehole temperature profiles. In addition, it reveals new geologically significant features. Notably, we identify a prominent quasi‐linear elevated geothermal heat flux anomaly running northwest–southeast across Greenland. We interpret this feature to be the relic of the passage of the Iceland hotspot from 80 to 50 Ma. The expected partial melting of the lithosphere and magmatic underplating or intrusion into the lower crust is compatible with models of observed satellite gravity data and recent seismic observations. Our geological interpretation has implications for the geodynamic evolution of Greenland https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL078289
  7. Artemieva, Irina M. “Lithosphere thermal thickness and geothermal heat flux in Greenland from a new thermal isostasy method.” Earth-Science Reviews 188 (2019): 469-481. Lithosphere thermal structure in Greenland is poorly known and models based on seismic and magnetic data are inconsistent, while growing awareness in the fate of the ice sheet in Greenland requires reliable constraints on geothermal heat flux (GHF) from the Earth’s interior in the region where conventional heat flux measurements are nearly absent. The lithosphere structure of Greenland remains controversial, while its geological evolution is constrained by direct observations in the narrow ice-free zone along the coasts. The effect of the Iceland hotspot on the lithosphere structure is also debated. Here I describe a new thermal isostasy method which I use to calculate upper mantle temperature anomalies, lithosphere thickness, and GHF in Greenland from seismic data on the Moho depth, topography and ice thickness. To verify the model results, the predicted GHF values are compared to available measurements and show a good agreement. Thick (200–270 km) cratonic lithosphere of SW Greenland with GHF of ca. 40 mW/m2 thins to 180–190 km towards central Greenland without a clear boundary between the Archean and Proterozoic blocks, and the deepest lithosphere keel is observed beneath the largest kimberlite province in West Greenland. The NW-SE belt with an anomalously thin (100–120 km) lithosphere and GHF of 60–70 mW/m2 crosses north-central Greenland from coast to coast and it may mark the Iceland hotspot track. In East Greenland this anomalous belt merges with a strong GHF anomaly of >100 mW/m2 in the Fjordland region. The anomaly is associated with a strong lithosphere thinning, possibly to the Moho, that requires advective heat transfer such as above active magma chambers, which would accelerate ice basal melting. The anomaly may extend 500 km inland with possibly a significant contribution of ice melt to the ice-drainage system of Greenland.
  8. Greve, Ralf, and Kolumban Hutter. “Polythermal three-dimensional modelling of the Greenland ice sheet with varied geothermal heat flux.” Annals of Glaciology 21 (1995): 8-12. Computations over 50 000 years into steady state with Greve’s polythermal ice-sheet model and its numerical code are performed for the Greenland ice sheet with today’s climatological input (surface temperature and accumulation function) and three values of the geothermal heat flux: (42, 54.6, 29.4) mW m−2. It is shown that through the thermomechanical coupling the geometry as well as the thermal regime, in particular that close to the bed, respond surprisingly strongly to the basal thermal heat input. The most sensitive variable is the basal temperature field, but the maximum height of the summit also varies by more than ±100m. Furthermore, some intercomparison of the model outputs with the real ice sheet is carried out, showing that the model provides reasonable results for the ice-sheet geometry as well as for the englacial temperatures.
Active Volcano Found Under Antarctic Ice: Eruption Could Raise Sea Levels

CONCLUSIONThe attribution of observed polar ice melt events to anthropogenic global warming along with the proposal that such melt events can be attenuated by taking climate action and moving the global energy infrastructure away from fossil fuels to renewables, is not possible in light of the complex episodic and localized nature of these ice melt events and their locations restricted to known geologically active areas. The attribution to anthropogenic global warming requires an explanation of these anomalies. If polar ice melt were driven by global warming it would be more uniform and more of a trend and not isolated, episodic, and not restricted to known geologically active locations. Glacial and ice shelf melt events that are episodic and restricted to geologically active locations cannot be understood as the impacts of fossil fuel emissions that can be moderated or prevented by taking climate action. For that, significant additional evidence must be provided that relates the melt events to atmospheric temperature data. No such evidence has been provided in this study where, as in all such studies, an atmosphere bias in the research methodology assumes that ice melt can only be explained in terms of anthropogenic global warming. Such findings are more likely to be the product of confirmation bias than unbiased and objective scientific inquiry. 

LINK: https://tambonthongchai.com/2018/08/03/confirmationbias/

Bias in Science: Further Thoughts from Skeptech – Skepchick

YASMINA-1
YASMINA-2
dziadek2017

THE RELEVANT BIBLIOGRAPHY: PART-2: 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.

Bias in Science: Further Thoughts from Skeptech – Skepchick

CONCLUSIONThe attribution of observed polar ice melt events to anthropogenic global warming along with the proposal that such melt events can be attenuated by taking climate action and moving the global energy infrastructure away from fossil fuels to renewables, is not possible in light of the complex episodic and localized nature of these ice melt events and their locations restricted to known geologically active areas. The attribution to anthropogenic global warming requires an explanation of these anomalies. If polar ice melt were driven by global warming it would be more uniform and more of a trend and not isolated, episodic, and not restricted to known geologically active locations. Glacial and ice shelf melt events that are episodic and restricted to geologically active locations cannot be understood as the impacts of fossil fuel emissions that can be moderated or prevented by taking climate action. For that, significant additional evidence must be provided that relates the melt events to atmospheric temperature data. No such evidence has been provided in this study where, as in all such studies, an atmosphere bias in the research methodology assumes that ice melt can only be explained in terms of anthropogenic global warming. Such findings are more likely to be the product of confirmation bias than unbiased and objective scientific inquiry. 

LINK: https://tambonthongchai.com/2018/08/03/confirmationbias/

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