There was an 8 Million Year Warm Period Between Cryogenian Glaciations

The Late Cryogenian Warm Interval, NE Svalbard: Chemostratigraphy and genesis

Authors:

Fairchild et al

Abstract:

The Late Cryogenian Warm Interval (LCWI) refers to a non-glacial interval that separates presumed representatives of the Sturtian and Marinoan panglaciations. Its duration is poorly constrained radiometrically and its deposits are relatively poorly known in most geographic regions. This paper aims to constrain the duration, palaeoenvironments and petrogenesis of such deposits in the classic region of NE Spitsbergen, Svalbard. The succession comprises a 200–205 m dolomitic shale (Macdonaldryggen Member, known as E3, of the Elbobreen Formation) overlain by oolitic dolomite Slangen Member (E4), 15–25 m thick, with limestone developed at top and base of E3 in the south of the area. The assumed age context of the succession has been confirmed by the presence of a typical Sturtian cap carbonate profile of negative to positive δ13C, and primary Sr isotope compositions of basal E3 limestones  <0 .7072="" 0.7076.="" and="" br="" e3="" limestones="" of="" upper="">

<0 .7072="" 0.7076.="" and="" br="" e3="" limestones="" of="" upper=""> At the base of E3, interstratification of cap carbonate with ice-rafted and redeposited glacial sediments occurs. Early diagenetic stabilization of carbonate mineralogy from a precursor, possibly ikaite, to calcite or dolomite is inferred. E3 is predominantly dolomitic silt-shale, with sub-millimetre lamination, lacking sand or current-related sedimentary structures. Thin fine laminae are partly pyritized and interpreted as microbial mats. Dolomite content is 25–50%, with δ13C values consistently around +4‰, a value attributed to buffering by dissolution of a precursor metastable carbonate phase. Local calcite cement associates with low δ13C values. The carbonates form silt-sized, chemically zoned rhombic crystals from an environment with dynamically changing Fe and Mn. Three-dimensional reconstructions of cm-scale disturbance structures indicate that they represent horizontally directed sock-like folds, developed by release of overpressure into thin surficial sediment overlying an early-cemented layer.

A shoaling upwards unit near the top of E3 displays calcium sulphate pseudomorphs in dolomite in the north, but storm-dominated limestones in the south, both being overlain by peritidal oolitic dolomites, exposed under the succeeding Wilsonbreen glacial deposits. There is no Trezona δ13C anomaly, possibly implying top-truncation of the succession.

Regular 0.5 m-scale sedimentary rhythms, reflecting subtle variations in sediment texture or composition occur throughout E3 and are interpreted as allocyclic. They are thought to be mainly primary in origin, locally modified slightly during early diagenetic cementation. Rhythms are proposed to represent ca. 18 kyr precession cycles, implying 6–8 Myr deposition between glaciations.

Antarctic coastline images reveal 4 decades of ice loss to ocean

Part of Antarctica has been losing ice to the ocean for far longer than had been expected, satellite pictures reveal.

A study of images along 2000km of West Antarctica's coastline has shown the loss of about 1000km2 of ice - an area equivalent to the city of Berlin - over the past 40 years.

Researchers were surprised to find that the region has been losing ice for such a length of time. Their findings will help improve estimates of global sea level rise caused by ice melt.

A research team from the University of Edinburgh analysed hundreds of satellite photographs of the ice margin captured by NASA, the United States Geological Survey (USGS) and the European Space Agency (ESA).

They found that ice has been retreating consistently along almost the entire coastline of Antarctica's Bellingshausen Sea since satellite records began.

The team also monitored ice thickness and thinning rates using data taken from satellites and the air. This showed that some of the largest changes, where ice has rapidly thinned and retreated several miles since 1975, correspond to where the ice front is deepest.

Scientists suggest the loss of ice is probably caused by warmer ocean waters reaching Antarctica's coast, rather than rising air temperatures. They say further satellite monitoring is needed to enable scientists to track progress of the ice sheet.

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Mars is Emerging From an Ice Age

Radar measurements of Mars' polar ice caps reveal that the mostly dry, dusty planet is emerging from an ice age, following multiple rounds of climate change. Understanding the Martian climate will help determine when the planet was habitable in the past, how that changed, and may inform studies of climate change on Earth. Models have suggested that Mars has undergone ice ages in the past, but empirical data to confirm this has been sparse. Here, Isaac Smith and colleagues used radar to analyze layers of ice within the planet's polar ice caps, using the Shallow Radar instrument onboard the Mars Reconnaissance Orbiter spacecraft. As ice erodes, wind can create spiral troughs and other distinct features. Tracing the layers of these features within the ice can reveal changes in ice accumulation and flow - and thus changes in climate - in the past. While the southern ice cap is relatively small and altered by meteorite impacts, the researchers were able to trace the layers within the northern ice cap. They found layers and migration paths that increase in slope abruptly, reverse direction, or are completely buried. Their analysis suggests that the planet is currently emerging from an ice age, in a retreat that began approximately 370,000 years ago.

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Are the Dorsa Argentea on Mars eskers?

Are the Dorsa Argentea on Mars eskers?

Authors:

Butcher et al

Abstract:

The Dorsa Argentea are an extensive assemblage of ridges in the southern high latitudes of Mars. They have previously been interpreted as eskers formed by deposition of sediment in subglacial meltwater conduits, implying a formerly more extensive south polar ice sheet. In this study, we undertake the first large-scale statistical analysis of aspects of the geometry and morphology of the Dorsa Argentea in comparison with terrestrial eskers in order to evaluate this hypothesis. The ridges are re-mapped using integrated topographic (MOLA) and image (CTX/HRSC) data, and their planar geometries compared to recent characterisations of terrestrial eskers. Quantitative tests for esker-like relationships between ridge height, crest morphology and topography are then completed for four major Dorsa Argentea ridges. The following key conclusions are reached: (1) Statistical distributions of lengths and sinuosities of the Dorsa Argentea are similar to those of terrestrial eskers in Canada. (2) Planar geometries across the Dorsa Argentea support formation of ridges in conduits extending towards the interior of an ice sheet that thinned towards its northern margin, perhaps terminating in a proglacial lake. (3) Variations in ridge crest morphology are consistent with observations of terrestrial eskers. (4) Statistical tests of previously observed relationships between ridge height and longitudinal bed slope, similar to those explained by the physics of meltwater flow through subglacial meltwater conduits for terrestrial eskers, confirm the strength of these relationships for three of four major Dorsa Argentea ridges. (5) The new quantitative characterisations of the Dorsa Argentea may provide useful constraints for parameters in modelling studies of a putative former ice sheet in the south polar regions of Mars, its hydrology, and mechanisms that drove its eventual retreat.

Trace Evidence of Alps-like Glaciers on Mars

Former extent of glacier-like forms on Mars

Authors:

Brough et al

Abstract:

Mars’ mid-latitude glacier-like forms (GLFs) have undergone substantial mass loss and recession since a hypothesised last martian glacial maximum (LMGM) stand. To date, there is a lack of knowledge of the nature and timing of the LMGM, the subsequent mass loss and whether this mass loss has been spatially variable. Here, we present the results of a population-scale inventory of recessional GLFs, derived from analysis of 1293 GLFs3 identified within Context Camera (CTX) imagery, to assess the distribution and controls on GLF recession. A total of 436 GLFs were identified showing strong evidence of recession: 197 in the northern hemisphere and 239 in the southern hemisphere. Relative to their parent populations, recessional GLFs are over-represented in the low latitude belts between 25 and 40° and in areas of high relief, suggesting that these zones exert some control over GLF sensitivity and response to forcing. This analysis is complemented by the reconstruction of the maximum extent and morphology of a specific GLF for which High Resolution Imaging Science Experiment (HiRISE) derived digital elevation data are available. Using Nye's (Nye, J.F. [1951] Proc. Roy. Soc. Lond, Ser. a—Mat. Phys. Sci., 207, 554–572) perfect plastic approximation of ice flow applied to multiple flow-lines under an optimum yield strength of 22 kPa, we calculate that the reconstructed GLF has lost an area of 6.86 km2 with a corresponding volume loss of 0.31 km3 since the LMGM. Assuming the loss reconstructed at this GLF occurred at all mid-latitude GLFs yields a total planetary ice loss from Mars’ GLFs of 135 km3, similar to the current ice volume in the European Alps on Earth.

The Importance of Atmospheric Carbon in the end of the Last Glaciation

As the Earth emerged from its last ice age several thousand years ago, atmospheric carbon dioxide increased and further warmed the planet. Scientists have long speculated that the primary source of this CO2 was from the deep ocean around Antarctica, though it has been difficult to prove.

A new study published this week in Proceedings of the National Academy of Sciences confirmed that the ocean played a significant role in the rise of atmospheric carbon dioxide, but also documents the signature of land-based carbon sources in Antarctic ice cores that contributed to abrupt increases in CO2.

"There wasn't a steady rate of rising carbon dioxide during the last deglaciation," said Edward Brook, an Oregon State University paleoclimatologist and co-author on the PNAS study. "It happened in fits and starts. With the new precise techniques we developed to fingerprint the sources, it is apparent that the early carbon largely came from the ocean, but we think the system got a jolt from an influx of land-based carbon a few times as the climate warmed."

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At the end of the Pleistocene Ice Age, Antarctica had a Massive Ice-Shelf Collapse

In a new study that provides clues about how Antarctica's nation-sized Ross Ice Shelf might respond to a warming climate, U.S. and Japanese oceanographers have shown that a 100,000-square-mile section of the ice shelf broke apart within 1,500 years during a warming period after the last ice age.

The Ross Ice Shelf is the world's largest ice shelf, a vast floating extension of the West Antarctic Ice Sheet that is about the size of France. But at the end of the last ice age, it extended much farther north and covered the entire Ross Sea.

A study in this week's Proceedings of the National Academy of Sciences details how the ice shelf shrank during a period of climate warming following the ice age. The paper was co-authored by Rice University oceanographer John Anderson, postdoctoral research associate Lauren Simkins, graduate student Lindsay Prothro and colleagues at the University of Tokyo.

"At the height of the last ice age, we know that the sheet of ice covering the Antarctic continent was larger and thicker than it is today," said Anderson, Rice's Maurice Ewing Professor of Oceanography and professor of Earth science. "This continent-enveloping ice sheet extended all the way to the continental shelf, and in western Antarctica it filled the entire Ross Sea basin."

While people typically think of continents as landmasses that rise above the sea, the margins of all continents, including Antarctica, extend well beyond their shores to include continental shelves, subsea aprons that are far more shallow than the deep ocean abysses that mark the continental boundary.

In western Antarctica, the Ross Sea is characterized by a continental shelf that extends nearly 1,000 miles from the coast and is as much as 3,500 feet deep. Anderson said the geologic record shows that as recently as 18,000 years ago the entire Ross basin was filled with ice that was so thick and heavy it was grounded on the seafloor all the way to the edge of the continental shelf.

"We found that about 10,000 years ago, this thick, grounded ice sheet broke apart in dramatic fashion," Anderson said. "The evidence shows that an armada of icebergs -- each at least twice as tall as the Empire State Building -- was pushed out en masse. We know this because this part of the Ross Sea is about 550 meters (1,804 feet) deep, and the icebergs were so large and so tightly packed that they gouged huge furrows into the seafloor as they moved north."

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Greenland's Glaciers are Retreating Quickly

Greenland's glaciers are retreating quickly, and a new study shows in historical terms just how quickly: over the past century, at least twice as fast as any other time in the past 9,500 years. The study also provides new evidence for just how sensitive glaciers are to temperature, showing that they responded to past abrupt cooling and warming periods, some of which might have lasted only decades.

To track how glaciers grew and shrank over time, the scientists extracted sediment cores from a glacier-fed lake that provided the first continuous observation of glacier change in southeastern Greenland. They then compared the results to similar rare cores from Iceland and Canada's Baffin Island for a regional view.

"Two things are happening," said study co-author William D'Andrea, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory. "One is you have a very gradual decrease in the amount of sunlight hitting high latitudes in the summer. If that were the only thing happening, we would expect these glaciers to very slowly be creeping forward, forward, forward. But then we come along and start burning fossil fuels and adding carbon dioxide to the atmosphere, and glaciers that would still be growing start to melt back because summer temperatures are warmer."

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An Early Permian Paleopolar, Postglacial, River-dominated Delta From Antarctica

An Early Permian, paleopolar, postglacial, river-dominated deltaic succession in the Mackellar–Fairchild formations at Turnabout Ridge, Central Transantarctic Mountains, Antarctica

Authors:

Flaig et al

Abstract:

Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Transantarctic Mountains, comprises subglacial–glaciomarine deposits of the Pagoda Formation (Fm) overlain by a postglacial deltaic succession of the Mackellar–Fairchild formations (fms). Four depositional environments were identified in the Mackellar–Fairchild fms: 1) prodelta to distal-delta-front deposits that record the initial filling of a newly formed intracratonic basin; 2) an interval dominated by subaqueous terminal distributary channels and levees that signal the advancement of a delta into the region; 3) mouth bars and associated subaqueous terminal distributaries representing the proximal delta front; and 4) an overlying sand-dominated braidplain.

A companion ichnologic study identified 30 ichnogenera in the Mackellar Fm that combine to form six ichnocoenoses. Twelve traces are known only from marine settings, 18 are found across marine, brackish, and freshwater systems, and none are known solely from freshwater systems. The ichnology refines paleoenvironmental and paleosalinity interpretations for the Mackellar Fm, and indicates a predominantly brackish water paleoenvironment.

Subaqueous terminal distributary channels record the highest energies, suspended sediment concentrations, and sediment loads, and are the conduits that delivered sediment to the delta front and prodelta. Abundant traction deposits (hyperpycnites) displaying only minor wave or tide modification suggest that the delta is best classified as river-flood dominated. The succession exhibits similarities to the Panther Tongue and Ferron Notom deltas of the Cretaceous Western Interior Seaway, USA, and a Late Ordovician proglacial delta from the Murzuq Basin in Libya.

The combined ichnologic and sedimentologic evidence suggests that sediment-laden glacial outburst floods produced freshets that recurrently prepped a shallow-marine basin, reducing salinities and allowing for abundant channelization and hyperpycnite deposition along the delta front. Turnabout Ridge likely occupied a proximal and axial position relative to an Antarctic freshwater- and sedimentation-stressed, river-dominated marine deltaic system along the shoreline of an epeiric seaway during the Early Permian.

What are the Upper Limits of Sea Level Rise Caused by the Antarctic Icesheet Melting

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations

Authors:

Ritz et al

Abstract:

Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions the centennial to millennial contribution could be several metres. Physically plausible projections are challenging9: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections11 rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B, although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments9 (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.

New, Contrarian Study Claims Antarctic Driven Sea Level Rise Will be Slower Than Expected

A new study by scientists in the UK and France has found that Antarctic ice sheet collapse will have serious consequences for sea level rise over the next two hundred years, though not as much as some have suggested.

This study, published today in the journal Nature, uses an ice-sheet model to predict the consequences of unstable retreat of the ice, which recent studies suggest has begun in West Antarctica. Scientists, led by Catherine Ritz from Université Grenoble Alpes in France and Tamsin Edwards from The Open University, predict that the contribution is most likely to be 10 cm of sea-level rise this century under a mid to high climate scenario, but is extremely unlikely to be higher than 30 cm. When combined with other contributions, that's a significant challenge for adapting to future sea level rise. But it's also far lower than some previous estimates, which were as high as one metre from Antarctica alone.

The study's central estimate raises the Intergovernmental Panel on Climate Change (IPCC) central prediction of 60 cm global sea-level rise by just a few centimetres under the mid to high scenario they used. But the UK and France team's method allowed them to assess the likelihood of sea-level rise from substantial parts of the ice sheet collapsing, which the IPCC could not due to a lack of evidence. They predict there is a one in twenty chance that Antarctic collapse could contribute more than 30 cm sea-level rise by the end of the century and more than 72 cm by 2200. This does not rule out larger contributions on longer time scales.

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How Much of the Antarctic Marine Ice Retreat in the Ross Sea at the end of the Pleistocene Quaternary Ice Age

Antarctic marine ice-sheet retreat in the Ross Sea during the early Holocene

Authors:

McKay et al

Abstract:

Geological constraints on the timing of retreat of the Last Glacial Maximum (LGM) Antarctic Ice Sheets provide critical insights into the processes controlling marine-based ice-sheet retreat. The over-deepened, landward-sloping bathymetry of Antarctica's continental shelves is an ideal configuration for marine ice-sheet instability, with the potential for past and future ice-sheet collapse and accelerated sea-level rise. However, the chronology of retreat of the LGM ice sheet in the Ross Sea is largely constrained by imprecise radiocarbon chronology of bulk marine sediments or by coastal records that offer more reliable dating techniques but which may be influenced by local piedmont glaciers derived from East Antarctic outlet glaciers. Consequently, these coastal records may be ambiguous in the broader context of retreat in the central regions of the Ross Sea. Here, we present a sedimentary facies succession and foraminifera-based radiocarbon chronology from within the Ross Sea embayment that indicates glacial retreat and open-marine conditions to the east of Ross Island before 8.6 cal. (calibrated) kyr B.P., at least 1 k.y. earlier than indicated by terrestrial records in McMurdo Sound. Comparing these data to new modeling experiments, we hypothesize that marine-based ice-sheet retreat was triggered by oceanic forcings along most of the Pacific Ocean coastline of Antarctica, but continued Holocene retreat into the inner shelf region of the Ross Sea occurred primarily as a consequence of bathymetric controls on marine ice-sheet instability.

What is REALLY Happening With Antarctica's Ice Sheet?

There have been quite few big media stories related to Antarctica recently, including a paper on the irreversible collapse of the marine portion of the West Antarctic Ice Sheet and a NASA-funded study that finds, contrary to numerous previous results, that the Antarctic ice sheet as a whole has been gaining mass between 1992 and 2008. This most recent study received a lot of media attention because it runs counter to what was said in the last IPCC Report. Certain parts of the media hailed this as another sign that the impacts of climate change had somehow been exaggerated a risk that the lead author Jay Zwally was concerned about before the research was published.

So what did Zwally and his colleagues do, what did they find, and why does it contradict a plethora of previous studies that suggest Antarctica has been losing mass over the same time period?

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A Small, Local Collapse of Antarctic Ice Sheet Could Cause Wider Spread Collapse

The huge West Antarctic ice sheet would collapse completely if the comparatively small Amundsen Basin is destabilized, scientists of the Potsdam Institute for Climate Impact Research find. A full discharge of ice into the ocean is calculated to yield about 3 meters of sea-level rise. Recent studies indicated that this area of the ice continent is already losing stability, making it the first element in the climate system about to tip. The new publication for the first time shows the inevitable consequence of such an event. According to the computer simulations, a few decades of ocean warming can start an ice loss that continues for centuries or even millennia.

"What we call the eternal ice of Antarctica unfortunately turns out not to be eternal at all," says Johannes Feldmann, lead author of the study to be published in the Proceedings of the National Academy of Sciences (PNAS). "Once the ice masses get perturbed, which is what is happening today, they respond in a non-linear way: there is a relatively sudden breakdown of stability after a long period during which little change can be found."

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Pleistocene Quaternary Giant Mammals Became Extra Vulernable to Extinction due to Habitat Fragmentation?

Life and extinction of megafauna in the ice-age Arctic

Authors:

Mann et al

Abstract:

Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes.

Global Warming Commits the World to Long Term Sea Level Rise Even if Held to 2 C

The multi-millennial Antarctic commitment to future sea-level rise

Authors:

Golledge et al

Abstract:

Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century1. If anthropogenic emissions continue unchecked, the warming increase may reach 8–10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change3. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6–3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.

Evidence of Periglacial Areological Artifacts From Late Amazonian Glaciations on Mars

Sorted (clastic) polygons in the Argyre region, Mars, and possible evidence of pre- and post-glacial periglaciation in the Late Amazonian Epoch

Authors:

Soare et al

Abstract:

The Argyre basin and associated rim-materials in the southern highlands of Mars are ancient, having been formed by the impact of a large body ∼3.9 Gya. Despite its age, the regional landscape exhibits a wide range of geological/geomorphological modifications and/or features, e.g. fluvial, lacustrine, aeolian, glacial and periglacial. Collectively, this bears witness to the dynamic evolution of the Argyre region from the deep past through to, perhaps, the present day.

Here, we present three principal findings that point to at least two distinct episodes of periglaciation, separated by a possible glacial-interval, during the very Late Amazonian Epoch in eastern Aonia Terra (AT), i.e. on the western flank of the Argyre basin. These findings are the product of our circum-Argyre study of all HiRISE images (∼35–65°S and ∼290–350°E).

(1)

(a) The first periglacial episode involves the development of small-sized (∼15–25 m in diam.) and clastically-“sorted polygons” (SPs). The SPs are observed at eighteen locations within eastern AT. Hitherto, the presence of SPs in this region has been reported at one location alone. No other observations of SPs in the southern hemisphere of Mars have been documented. Morphologically similar landforms develop in cold-climate (permafrost) landscapes on Earth by means of periglacial processes, i.e. freeze–thaw cycling, segregated-ice formation, cryoturbation and frost heave.

(b) We ascribe a periglacial origin to the SPs in eastern AT on the basis of this similarity of form and, no less importantly, on the close spatial-association of the SPs with blockfields (whose weathered “clastic” products are the building blocks of periglacial sorting on Earth), gelifluction-like lobes and possible “wet” gullies. Where similar assemblages occur in terrestrial permafrost-landscapes, the presence of liquid water and of boundary conditions tolerant of freeze–thaw cycling, are observed or inferred.

(c) Fifteen of the eighteen SP locations are clustered longitudinally (44.4–57.5°S; 289.9–302.4°E). This is inconsistent with the latitudinal- and (obliquity-driven) dependency of freeze–thaw cycling in the Late Amazonian Epoch hypothesised by many workers in the discipline.

(2) The second periglacial episode is highlighted by the development of small-sized and clastically non-sorted polygons (NSPs). These polygons could have formed by means of a “dry” cryotic process, i.e. thermal-contraction cracking.

(3) The NSPs incise (and thus postdate) a light-toned mantle, thought by numerous workers to comprise an “ice-dust” admixture. At some of the locations where the putatively icy-mantle has undergone apparent ablation, underlying SPs are observed. This suggests that the SPs predate the mantle and, derivatively, the NSPs as well.

The proposed geochronology of “wet-based SP – icy mantle – dry-based NSP” (periods and interval) is entirely new to the community. Moreover, it underlines the possibility that periglacial and glacial boundary-conditions, at least in our study area, may have oscillated much more substantially in the very Late Amazonian Epoch than many workers have thought possible.

Extensive Middle Amazonian Mantling of Debris Aprons and Plains in Deuteronilus Mensae, Mars

Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implications for the record of mid-latitude glaciation

Authors:

Baker et al

Abstract:

The mid-latitudes of Mars are host to a record of recent episodes of accumulations of ice-rich materials. The record includes debris aprons, interpreted to be debris-covered glaciers, that may represent the preserved remnants of a much more extensive ice sheet. We assessed the possibility of former glacial extents by examining debris aprons and the surrounding plains in Deuteronilus Mensae. Geomorphic units and stratigraphic relationships were mapped and documented from Mars Reconnaissance Orbiter (MRO) Context (CTX) and High Resolution Imaging Science Experiment (HiRISE) camera images, and crater retention ages were estimated from crater size–frequency distributions. Three major units are observed within the study area: debris aprons, lower plains, and upper plains. Debris aprons exhibit characteristics typical for these features documented elsewhere and in previous studies, including integrated flow lineations and patterns, convex-upward profiles, and knobby and brain terrain surface textures. A lower bound on the age for debris aprons is estimated to be 0.9 Ga. Debris aprons are superposed on a lower plains unit having a lower bound age of 3.3–3.5 Ga. A 50–100 m thick upper plains unit superposes both debris apron landforms and lower plains units and has a best-fit minimum age of 0.6 Ga. The upper plains unit exhibits characteristics of atmospherically-emplaced mantle material, including fine-grained nature, sublimation textures, cyclic layering, draping character, and widespread spatial distribution. Fracturing and subsequent sublimation/erosion of upper plains on debris aprons has contributed to many of the surface textures on debris aprons. The upper plains unit has also been eroded from the lower plains and plateaus, evidenced by isolated blocks of upper plains in the interiors of craters and on the walls and tops of plateaus. While no conclusive evidence diagnostic of former cold-based ice sheets are observed in the plains within the study region, such landforms and units may have been poorly developed or absent, as is often the case on Earth, and would have been covered and reworked by later mantling episodes. These observations suggest that emplacement of thick ice-rich mantle deposits extended at least to near the Early/Middle Amazonian boundary and overlapped with the waning stages of glaciation in Deuteronilus Mensae.

Mars is Still in an Ice Age? Remnant ice Found on Tropical Latitude Arsia Mons

on mars (left), on earth (right)

Remnant buried ice in the equatorial Regions of Mars: Morphological Indicators Associated with the Arsia Mons Tropical Mountain Glacier Deposits

Authors:

Scanlon et al

Abstract:

The fan-shaped deposit (FSD) on the western and northwestern flanks of Arsia Mons is the remnant of tropical mountain glaciers, deposited several tens to hundreds of millions of years ago during periods of high spin-axis obliquity. Previous workers have argued that the Smooth Facies in the FSD contains a core of ancient glacial ice. Here, we find evidence that additional glacial ice remains preserved within several other landforms in the Smooth Facies and Ridged Facies. These include landforms that we interpret as kame and kettle topography on the basis of their distribution, size, and morphologies ranging progressively from knobs to degraded knobs to pits. We argue that some moraines in the Ridged Facies are ice-cored on the basis of their interactions with lava flows and the axial troughs at the crests of some moraines. We also argue that dunes with axial troughs, found in and surrounding the FSD, are the remnants of sediment-covered snow dunes formed by reworking of snow or glacial ice, and that the axial troughs form as tension cracks in the sediment and deepen by sublimation of the underlying ice. Long-term preservation of water ice in equatorial environments is assisted by a meters- to decameters-thick debris cover (lag) formed from sublimation of dirty ice, as well as burial beneath volcanic tephra and eolian deposits. This ancient ice could contain preserved biosignatures, provide information on Martian climate and atmospheric history, and serve as a resource for human exploration.

Late Permian Glossopteris Flora From Deglaciating Antarctica

Glossopteris flora in the Permian Weller Formation of Allan Hills, South Victoria Land, Antarctica: Implications for paleogeography, paleoclimatology, and biostratigraphic correlation

Authors:

Tewari et al

Abstract:

The Permo-Triassic Victoria Group in South Victoria Land, Antarctica, is a heterogeneous sequence of glacial tillite beds, carbonaceous and non-carbonaceous fluvial deposits, and volcaniclastic strata. The carbonaceous beds are rich in plant fossils associated with coal seams. In Antarctica, the geological record of the Late Paleozoic Ice Age is restricted to the Early Permian. After deglaciation, the Glossopteris flora thrived in polar forests in Antarctica throughout the Permian but disappeared at the end-Permian extinction. Here we describe the first comprehensive record of the Glossopteris flora from the Permian Weller Formation of Allan Hills, South Victoria Land, Antarctica. The flora is well preserved and comprises pteridophytes and gymnosperms. The pteridophytes include the sphenopsid order Equisetales and the gymnosperms comprise Glossopteridales. Equisetales are represented by branched and unbranched axes, whereas, Glossopteridales are highly diverse encompassing Gangamopteris, Glossopteris, Surangephyllum, sterile scale leaves namely Scirroma sp., Nautiyalolepis sp., Utkaliolepis indica, Scale leaf A and scale leaf of male fructification Eretmonia. The flora of the Weller Formation shows close similarity with the Late Permian assemblages of India, South Africa and Australia. Gangamopteris, an index fossil of the Early Permian formations of different Gondwana continents, had extended stratigraphic range in the Late Permian Weller Formation of Allan Hills. Antarctica played a crucial role in the dispersal of Glossopteris flora because of its central position in Gondwana.