IMAGE#1: ARCTIC OCEAN

IMAGE#2: THE ULTRASLOW SPREADING MOHNS RIDGE

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RELATED POSTS ON GEOLOGY OF THE ARCTIC SEA [LINK] [LINK] [LINK] 

THIS POST IS A CRITICAL REVIEW OF FINDINGS BY CLIMATE SCIENCE OF GREENLAND ICE MELT FROM UNDER BY WARM WATERS ATTRIBUTED TO CLIMATE CHANGE BY WAY OF WARM WATER CURRENTS FROM THE GULF OF MEXICO. IT IS PRESENTED IN THREE PARTS. PART-1 IS A STATEMENT OF THE FINDINGS AS REPORTED IN NATURE GEOSCIENCE. PART-2 IS A PRESENTATION OF THE RELEVANT HYDROTHERMAL FEATURES OF THE ARCTIC SEA IN THAT REGION, AND PART-3 IS A CRITICAL EVALUATION OF THE ATTRIBUTION OF UNDERWATER ICE MELT IN GREENLAND TO CLIMATE CHANGE IN TERMS OF THE DATA IN PART-2. 

LINKS TO THE SOURCES OF THESE CLAIMS:

1. INTERVIEW OF CLIMATE SCIENTISTS: POPULAR SCIENCE MAGAZINE [LINK]
2. YOUTUBE VIDEO: NASA RESEARCH POSTED BY CNN [LINK] 

PART-1: THE FINDINGS OF ICE MELT BY WARM OCEAN WATERS ATTRIBUTED TO CLIMATE CHANGE AS DESCRIBED BY THE POPULAR SCIENCE ARTICLE

The Greenland ice sheet, a 656,000-square-mile mass of ice covering most of Greenland, is melting at a rapid pace losing ice seven times faster than in the 1990s, and rising air temperatures due to climate change are largely to blame except that glacial ice shelves in the ocean are melting from the bottom up. A new study in Nature Geoscience found that a previously unknown seafloor landscape is bringing warm water to the 79º North glacier, located in the northeastern part of the country, and eroding a 50-mile-long lobe of ice hanging off the glacier. And that could have serious repercussions for the entire ice sheet. What was known is that these ice tongues melt from underneath but what was not known is how this warm water makes it to the glacier. These relatively thin tongues of ice extending from the main ice sheet are most vulnerable to melting from below. Blasts of warm water from the deep can chip away at these slabs, which are basically attached icebergs. At the surface, the water is brisk and hovering below zero Celsuis so that is not what’s melting the ice. Below the ice tongue, they found a deep, mile-wide channel that was funneling warm water toward the glacier. The water down there reached around 34ºF, much warmer than Arctic waters above. The heat emitted by this warm water blast is equivalent to the heat produced by 60 to 70 nuclear power plants. The water was melting about 34 feet of ice below the glacier every year (but a smaller amount of ice is added to the top every year, too). The warm water is part of a current moving from the Gulf of Mexico, along the Gulf Stream, and then flowing along the west coast of Norway. As it hits the Arctic, the water ducks below the polar waters because it’s more dense. The seafloor topography then moves the water along deep channels. This layer of relatively warm water is normal to find here but this warm water has gotten a little bit warmer. However,  melting at the surface still drives most of Greenland ice sheet loss, but underwater melting is also important. It is necessary to understand a lot of these local details in order to understand what is happening on an ice sheet as a whole. Although the 79º North glacier is just one fragment of a massive icy expanse, it is located at the mouth of a river of ice that drains a fifth of the ice sheet. When the ice tongue is gone, this ice river will flow faster, ejecting its contents into the ocean. All that extra ice loss would contribute to sea level rise. This information on the glacier can now be incorporated into models to simulate how climate change will further erode the ice sheet. The findings may also help illuminate melting processes at the Antarctic ice sheet, which also has many large ice tongues extending from it. Being able to project how fast these two ice sheets are melting is crucial for coastal cities, where a difference of a couple feet is the difference between submerging and staying dry. “Ice loss from Greenland and Antarctica is one of the largest contributors to sea level rise. “Being able to understand what drives the pace of ice loss and the quantity of ice loss over multiple years is very valuable for us getting a better handle on what those sea level rise numbers are going to be in the future.

PART-2: HYDROTHERMAL ACTIVITY IN THE REGION 

A 2019 AGU research paper on the ULTRASLOW SPREADING MOHNS RIDGE [LINK]  describes the hydrothermal features of the sea adjacent to the part of Greenland where the underwater ice melt is reported. CITATION: Hydrothermal Activity at the Ultraslow‐Spreading Mohns Ridge: New Insights From Near‐Seafloor Magnetics, Anna Lim Marco Brönner Ståle Emil Johansen Marie‐Andrée Dumais, 19 November 2019, AGU https://doi.org/10.1029/2019GC008439 : ABSTRACT: Hydrothermal circulation is a process fundamental to all types of mid‐ocean ridges that largely impacts the chemical and physical balance of the World Ocean. However, diversity of geological settings hosting hydrothermal fields complicates the exploration and requires thorough investigation of each individual case study before effective criteria can be established. Analysis of high‐resolution bathymetric and magnetic data, coupled with video and rock samples material, furthers our knowledge about mid‐ocean‐ridge‐hosted venting sites and aid in the interpretation of the interplay between magmatic and tectonic processes along the axial volcanic ridges. The rock‐magnetic data provide constraints on the interpretation of the observed contrasts in crustal magnetization. We map the areal extent of the previously discovered active basalt‐hosted Loki’s Castle and inactive sediment‐hosted Mohn’s Treasure massive sulfide deposits and infer their subsurface extent. Remarkably, extinct hydrothermal sites have enhanced magnetizations and display clear magnetic signatures allowing their confident identification and delineation. Identified magnetic signatures exert two new fossil hydrothermal deposits, MT‐2 and MT‐3. The Loki’s Castle site coincides with negative magnetic anomaly observed in the 2‐D magnetic profile data crossing the deposit. First geophysical investigations in this area reveal the complexity of the geological setting and the variation of the physical properties in the subsurface.

GEOLOGICAL SETTING: The various intense geological properties of the Mohns Ridge  (Image#2) derive from major plate boundariy reorganization involving a 30° shift in the plate motion, followed by the initiation of oblique spreading of the Mohns Ridge and the inception of the Knipovich Ridge. The Mohns Ridge is an ultraslow and obliquely spreading ridge with a full rate estimated at ~15.6 mm/year for the last 10 Ma. The topography is rough with a complex spreading history of the Greenland basin. Both flanks of the rift valley and the valley floor are covered by sediments. The MOR is characterized by linked magmatic (volcanic) and amagmatic (tectonic) segments. Topographic highs are volcanic in origin. Abundant volcanic features such as prominent cones, flat‐topped volcanoes, and volcanic ridges, are observed consistent with the hypothesis that the two domed elongated edifices are newly formed volcanic axial volcanic ridges. The life cycle of axial volcanic ridges alternates between magmatic and tectonic. The area is seismically active—earthquake epicenters located within the ridge valley closely correlates with the major faults and volcanoes at the graben floor. The interplay between these processes is of major importance for hydrothermal circulation along the ridges. Loki’s Castle is an active high‐temperature hydrothermal venting field . It occurs at the northernmost AVR of the Mohns Ridge that rises approximately 1,300 m above the rift valley floor at 2,000‐m depth. En echelon faults can be traced along the entire ridge, which is locally covered by fresh lava flows. Volcanic cones, smaller ridges, flat‐topped volcanoes are common features. The hydrothermal fluid collected from the black smokers indicate significant magmatic influence.

FINDINGS: Near‐seafloor magnetic data from the ultraslow‐spreading Mohns Ridge indicates hydrothermal deposits associated with both active and inactive hydrothermal venting sites and imply magmatic and tectonic processes along the axial volcanic ridges. Loki’s Castle is an active hydrothermal venting field. Two strong positive magnetic anomalies near the Mohn’s Treasure reveal newly extinct hydrothermal venting sites with the same magnetic signature as the Mohn’s Treasure. The increasing prevalence of faulting and its complexity has positive implications for hydrothermal discharge and potentially controls the occurrence of active hydrothermal venting field in the northern AVR1, currently undergoing a destructive tectonic stage.

PART-3: CRITICAL COMMENTARY ON THE ATTRIBUTION OF WARM WATER ICE MELT OF GREENLAND ICE SHEET GLACIAL TONGUES TO CLIMATE CHANGE

It is reported in the Nature Geoscience paper described above in PART-1 that glacial ice  immersed in the Greenland Sea are melting from the bottom by warm water. Climate scientists who studied this phenomenon argue for human cause in these cases by attributing the warmth of the water to ocean currents that bring warm water from the Gulf of Mexico to the Arctic in a journey of about 5,000 km while retaining the heat. It is thus that AGW atmospheric heat can be trapped by the Gulf of Mexico and delivered to the Arctic to melt glacial ice dipped into the Arctic Sea. This line of reasoning and causation sequence maintains the human cause of ice melt in Greenland and the COP26 climate action rationale that climate action can and must stop the ice melt in Greenland. We argue here that geological activity is the more likely source of energy that is melting ice in Greenland. It is more likely that the warm water was made warm by geothermal heat. As seen in the AGU research paper in PART-2 and in a related post on the geology of the Arctic [LINK] , the Arctic sea floor is very geologically active. 

Image#3 below shows the 6,000 km long Mid Arctic Rift depicted as a long and curvy red hashed area in close proximity to Greenland with red triangles marking known active submarine volcanoes on the ocean floor. Also shown on this slide is the Greenland/Iceland mantle plume hotspot. A mantle plume hotspot is a large area of magma that 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. Under a sufficient pressure the magma can break through to the atmosphere as a volcanic eruption.

On the left of Greenland is the Baffin Bay Labrador rift system marked as BBLR. In the left upper corner on the image active submarine volcanoes are marked with red triangles. It is the Aleutian Island convergent plate boundary where two giant plates collide and one dives under the other and creates a tremendous amount of geological energy that becomes evident as geothermal heat.

IMAGE#3

CONCLUSION

In the context of these intense geological features of the Arctic region in an around Greenland, it requires a strong sense of the atmosphere bias to claim an atmospheric anthropogenic global warming source of the warmth in the water that is melting the “tongues” of Greenland’s glaciers immersed in the sea. We propose on the basis of the geological features of the Arctic cited here, that nature’s geothermal heat from the bottom of the Arctic Ocean is the likely source of energy that warms the water and melts the tongues of Greenland’s glaciers. To quote Carmack (2012), “The Arctic Ocean warms from below”. 

RELEVANT BIBLIOGRAPHY

1. Taylor, A., A. Judge, and V. Allen. “Terrestrial heat flow from project CESAR, Alpha Ridge, Arctic Ocean.” Journal of geodynamics 6.1-4 (1986): 137-176. During two months in spring, 1983, a multidisciplinary study, project CESAR, was undertaken from the sea ice across the eastern Alpha Ridge, Arctic Ocean. In the geothermal program, 10 gradiometer profiles were obtained; 63 determinations of in situ sediment thermal conductivity were obtained with the same probe, and 714 measurements of conductivity using the needle probe method were obtained on nearby core. Weighted means of the thermal conductivity of the sediment are 1.26 W/mK (in situ) and 1.34 W/mK (core), consistent with the compacted sediment encountered across the ridge and with the lithology. Calculated terrestrial heat flow values, corrected for the regional topography, range from 37 to 72 mWm−2; the average is 56+/−8 mWm−2. Some temperature and heat flow versus depth profiles exhibit non-linearities that can be explained by variations in bottom water temperatures preceding the measurements; models are hypothesized that reduce the curvatures. Two heat flow values considerably higher than others in the area may be explained by higher bottom water temperature over several years, while the low value is consistent with a recent deposition from a slump. This hypothetical modelling reduces the scatter of heat flows and reduces the average to 53+/−6 mWm−2. The CESAR heat flow is somewhat greater than expected for a purely continental fragment but is consistent with crust of oceanic origin. The heat flow is similar to values obtained in Cretaceous back-arc basins. Based on the oceanic heat flow-age relationship, the heat flow constrains the age of the ridge to 60–120 million years.
2. Carmack, Eddy C., et al. “The Arctic Ocean warms from below.” Geophysical research letters 39.7 (2012).  The old (∼450‐year isolation age) and near‐homogenous deep waters of the Canada Basin (CBDW), that are found below ∼2700 m, warmed at a rate of ∼0.0004°C yr⁻¹ between 1993 and 2010. This rate is slightly less than expected from the reported geothermal heat flux (F_g ∼ 50 mW m⁻²). A deep temperature minimum T_min layer overlies CBDW within the basin and is also warming at approximately the same rate, suggesting that some geothermal heat escapes vertically through a multi‐stepped, ∼300‐m‐thick deep transitional layer. Double diffusive convection and thermobaric instabilities are identified as possible mechanisms governing this vertical heat transfer. The CBDW found above the lower continental slope of the deep basin maintains higher temperatures than those in the basin interior, consistent with geothermal heat being distributed through a shallower water column, and suggests that heat from the basin interior does not diffuse laterally and escape at the edges.
3. Björk, Göran, and Peter Winsor. “The deep waters of the Eurasian Basin, Arctic Ocean: Geothermal heat flow, mixing and renewal.” Deep Sea Research Part I: Oceanographic Research Papers 53.7 (2006): 1253-1271.  Hydrographic observations from four separate expeditions to the Eurasian Basin of the Arctic Ocean between 1991 and 2001 show a 300–700 m thick homogenous bottom layer. The layer is characterized by slightly warmer temperature compared to ambient, overlying water masses, with a mean layer thickness of 500±100 m and a temperature surplus of 7.0±2×10⁻³ °C. The layer is present in the deep central parts of the Nansen and Amundsen Basins away from continental slopes and ocean ridges and is spatially coherent across the interior parts of the deep basins. Here we show that the layer is most likely formed by convection induced by geothermal heat supplied from Earth’s interior. Data from 1991 to 1996 indicate that the layer was in a quasi steady state where the geothermal heat supply was balanced by heat exchange with a colder boundary. After 1996 there is evidence of a reformation of the layer in the Amundsen Basin after a water exchange. Simple numerical calculations show that it is possible to generate a layer similar to the one observed in 2001 in 4–5 years, starting from initial profiles with no warm homogeneous bottom layer. Limited hydrographic observations from 2001 indicate that the entire deep-water column in the Amundsen Basin is warmer compared to earlier years. We argue that this is due to a major deep-water renewal that occurred between 1996 and 2001.
4. Edmonds, H. N., et al. “Discovery of abundant hydrothermal venting on the ultraslow-spreading Gakkel ridge in the Arctic Ocean.” Nature 421.6920 (2003): 252-256.  Submarine hydrothermal venting along mid-ocean ridges is an important contributor to ridge thermal structure¹, and the global distribution of such vents has implications for heat and mass fluxes² from the Earth’s crust and mantle and for the biogeography of vent-endemic organisms.³ Previous studies have predicted that the incidence of hydrothermal venting would be extremely low on ultraslow-spreading ridges (ridges with full spreading rates <2 cm yr^-1—which make up 25 per cent of the global ridge length), and that such vent systems would be hosted in ultramafic in addition to volcanic rocks^4,5. Here we present evidence for active hydrothermal venting on the Gakkel ridge, which is the slowest spreading (0.6–1.3 cm yr^-1) and least explored mid-ocean ridge. On the basis of water column profiles of light scattering, temperature and manganese concentration along 1,100 km of the rift valley, we identify hydrothermal plumes dispersing from at least nine to twelve discrete vent sites. Our discovery of such abundant venting, and its apparent localization near volcanic centres, requires a reassessment of the geologic conditions that control hydrothermal circulation on ultraslow-spreading ridges.
5. Sohn, Robert A., et al. “Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean.” Nature 453.7199 (2008):  Roughly 60% of the Earth’s outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m)¹. A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85° E, to acquire photographic and video images of ‘zero-age’ volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele)², covering a large (>10 km²) area. At least 13.5 wt% CO₂ is necessary to fragment magma at these depths³, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt⁴. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge⁵ and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.
6. Piskarev, A., Elkina, D. Giant caldera in the Arctic Ocean: Evidence of the catastrophic eruptive event. Sci Rep 7, 46248 (2017). https://doi.org/10.1038/srep46248:  A giant caldera located in the eastern segment of the Gakkel Ridge could be firstly seen on the bathymetric map of the Arctic Ocean published in 1999. In 2014, seismic and multibeam echosounding data were acquired at the location. The caldera is 80 km long, 40 km wide and 1.2 km deep. The total volume of ejected volcanic material is estimated as no less than 3000 km³ placing it into the same category with the largest Quaternary calderas (Yellowstone and Toba). Time of the eruption is estimated as ~1.1 Ma. Thin layers of the volcanic material related to the eruption had been identified in sedimentary cores located about 1000 km away from the Gakkel Ridge. The Gakkel Ridge Caldera is the single example of a supervolcano in the rift zone of the Mid-Oceanic Ridge System.
7. NATURE 2006, LIVESCIENCE 2008: Volcanoes Erupt Beneath Arctic Ice:  New evidence deep beneath the Arctic ice suggests a series of underwater volcanoes have erupted in violent explosions in the past decade. Hidden 2.5 miles beneath the Arctic surface, the volcanoes are up to a mile in diameter and a few hundred yards tall. They formed along the Gakkel Ridge, a rift system where the lithosphere is being pulled apart.  The extreme pressure from the overlying water makes it difficult for gas and magma to blast outward. The finding of jagged, glassy fragments of rock scattered around the volcanoes, suggest explosive eruptions occurred between 1999 and 2001. When the gas pressure gets high in the rift system it pops like a champagne bottle. The volcanoes have a major impact on the overlying water column. The eruptions discharge large amounts of carbon dioxide, helium, trace metals and geothermal heat into the water over long distances.
8. 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 thermo-mechanical, 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 obtained 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.
9. 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.