Subglacial Meltwater Channels Research Articles

Tracking coarse sediment in an Alpine subglacial channel using radio-tagged particles

Abstract We present a method for tracking radio-tagged pebbles and cobbles through subglacial meltwater channels under shallow temperate glaciers. Natural particles tagged with active radio transmitters were injected directly into a large subglacial channel 300 m up-glacier from the terminus of the Glacier d'Otemma, Switzerland. A roving antenna was developed to localise tagged particles planimetrically in subglacial and proglacial channel reaches (350 and 150 m long, respectively) using a probabilistic technique, delivering records of the change in particle location and transport distance over time with uncertainty. The roving antenna had a ±5−15 m planimetric precision, a 75% particle localisation rate and operated at a maximum ice depth of 47 m. Additionally, stationary supraglacial and proglacial antennas continuously monitored the passage of tagged particles through consecutive reaches of the channel, constraining the timing of particle transport events. The proglacial antenna system had a 98.1% detection rate and was operational to 0.89 m water depth during testing. Roving and stationary antenna records were combined to create a transport distance model for each particle, which may be used in conjunction with hydraulic data to investigate the kinematics of particle motion. When applied at scale in future studies, this method may be used to reveal the mechanisms and timescales of coarse sediment export from Alpine glaciers.

Stratigraphic and palaeo-geomorphological evidence for the glacial-deglacial history of the last British-Irish Ice Sheet in the north-western Irish Sea

During its maximum extent around 25–23 ka BP, the British-Irish Ice Sheet extended to near the present-day shelf break with a large ice stream, the Irish Sea Ice Stream, occupied much of the present-day Celtic and Irish Seas. The different episodes of advance and retreat of the ice sheet have been extensively constrained onshore, with models based on feature characterisation and dating helping to understand the retreat pattern of the ice sheet. Offshore, glacial geomorphologies in the Irish Sea have been mostly recognised on the United Kingdom side but remains poorly constrained on the Irish side. In this paper, based on the analysis of an extensive seismic dataset, an update of the stratigraphic model of the northern Irish Sea, with new sub-units, is proposed with a mapping of newly discovered buried geomorphology. Characterisation of the geomorphology, including megascale glacial lineations, subglacial meltwater channels, moraines, and iceberg scours, has been used to extend the constraints on ice sheet retreat offshore. The transition from late glacial to marine setting has been constrained based on the mapping of marine sediment subunits and their terminations. This paper brings new constraints offshore, in a previously understudied area, and synthesises all the results into an updated conceptual model highlighting stratigraphic units succession and associated processes linked to geomorphology, within the context of a rapidly retreating ice stream.

Ocean Variability at Greenland's Largest Glacier Tongue Linked to Continental Shelf Circulation

AbstractIncreased ocean‐to‐ice heat fluxes play a key role in the accelerated mass loss of Greenland’s marine‐terminating glaciers. Ocean current variability leads to variations in this heat flux. A year‐long time series of ocean currents at all gateways to the ocean cavity under Greenland’s largest remaining floating ice tongue at the Nioghalvfjerdsfjorden Glacier (79NG) was analyzed. The variability of the exchange flow at intra‐annual to near‐daily timescales was characterized. The currents exhibit considerable variability with standard deviations exceeding the time mean flow strength by a factor of 2. The inflow of warm Atlantic Intermediate Water into the cavity and the outflow via the northernmost calving front were directly coupled on intra‐annual timescales (periods, T > 30 days) with enhanced fluctuations in the winter months. A strong correlation between the variability of the deep inflow and currents in the subsurface boundary current on the continental shelf suggests a link between cavity and continental shelf circulation. Variability on higher frequencies (T < 30 days) in the outflow was only partly induced by the inflow variability. Two export branches of the cavity circulation were identified, which were potentially constrained by subglacial meltwater channels. The relative importance of the two export branches varies on monthly time scales. This research has provided evidence that the large intra‐annual ocean current variability at the 79NG is strongly influenced by the continental shelf circulation. Temporally varying preferred export routes increase the complexity of the cavity circulation.

Landforms indicative of regional warm based glaciation, Phlegra Montes, Mars

Viscous flow features (VFF) occur in the mid-latitudes of Mars and have characteristics consistent with being glaciers. Climate models suggest that martian glaciers are cold-based systems in which meltwater has never been widely produced. VFF are common in Phlegra Montes, a mountain range in the mid-latitudes of the northern hemisphere of Mars. However, in Phlegra Montes, the presence of an esker associated with an extant Amazonian Period VFF provides evidence that warm-based glacial processes did formerly operate. The problem at the centre of this paper is that the glacial meltwater responsible for this esker could have been produced as a consequence of its setting in a graben, with locally enhanced geothermal heating having been the driver of melt, not systemic heating associated with a regional warm-based regime. Given this uncertainty, this paper aims to determine if there are indicators of more widespread warm-based glacial processes in Phlegra Montes. The paper briefly describes the distribution and characteristics of VFF across the region, before focussing on the search for key landforms considered diagnostic of erosion by warm-based glaciers. From our observations, including discriminant morphometrics, we conclude that the landscape of Phlegra Montes is indicative of widespread warm-based glacial processes, including subglacial scour, linear abrasion and the incision of subglacial meltwater channels. Our findings have significance in constraining the contexts and process environments within which liquid water has been produced during the Amazonian Period on Mars and point to several lines of future research into martian glaciation, climate and landscape evolution.

Mapping Subglacial Meltwater Channels

Researchers find that past studies underestimate the friction meltwater channels exert on glaciers by orders of magnitude.

Subglacial drainage patterns of Devon Island, Canada: detailed comparison of rivers and subglacial meltwater channels

Abstract. Subglacial meltwater channels (N-channels) are attributed to erosion by meltwater in subglacial conduits. They exert a major control on meltwater accumulation at the base of ice sheets, serving as drainage pathways and modifying ice flow rates. The study of exposed relict subglacial channels offers a unique opportunity to characterize the geomorphologic fingerprint of subglacial erosion as well as study the structure and characteristics of ice sheet drainage systems. In this study we present detailed field and remote sensing observations of exposed subglacial meltwater channels in excellent preservation state on Devon Island (Canadian Arctic Archipelago). We characterize channel cross section, longitudinal profiles, and network morphologies and establish the spatial extent and distinctive characteristics of subglacial drainage systems. We use field-based GPS measurements of subglacial channel longitudinal profiles, along with stereo imagery-derived digital surface models (DSMs), and novel kinematic portable lidar data to establish a detailed characterization of subglacial channels in our field study area, including their distinction from rivers and other meltwater drainage systems. Subglacial channels typically cluster in groups of ∼10 channels and are oriented perpendicular to active or former ice margins. Although their overall direction generally follows topographic gradients, channels can be oblique to topographic gradients and have undulating longitudinal profiles. We also observe that the width of first-order tributaries is 1 to 2 orders of magnitude larger than in Devon Island river systems and approximately constant. Furthermore, our findings are consistent with theoretical expectations drawn from analyses of flow driven by gradients in effective water pressure related to variations in ice thickness. Our field and remote sensing observations represent the first high-resolution study of the subglacial geomorphology of the high Arctic, and provide quantitative and qualitative descriptions of subglacial channels that revisit well-established field identification guidelines. Distinguishing subglacial channels in topographic data is critical for understanding the emergence, geometry, and extent of channelized meltwater systems and their role in ice sheet drainage. The final aim of this study is to facilitate the identification of subglacial channel networks throughout the globe by using remote sensing techniques, which will improve the detection of these systems and help to build understanding of the underlying mechanics of subglacial channelized drainage.

The seafloor geomorphology of the Windmill Islands, Wilkes Land, East Antarctica: Evidence of Law Dome ice margin dynamics

A high-resolution multibeam sonar dataset covering an area of ca. 33km2 was collected in the vicinity of the Windmill Islands (67°S, 110°E), Wilkes Land, East Antarctica. The new data permit visualisation of the nearshore seafloor morphology in unprecedented detail, providing invaluable insight into the ice-sheet history of the region. A range of geomorphic features are evident, including prominent parallel northwest-trending linear fault sets affecting Mesoproterozoic metamorphic basement, which appear to control the regional coastal physiography. The fault systems probably formed during fragmentation of eastern Gondwana during the Mesozoic. Networks of sub-glacial meltwater channels, preserved on bedrock platforms and ridges, indicate grounding of a thick ice sheet over the continental shelf during previous glaciations. West-trending subtle glacial lineations and streamlined landforms record evidence of the westward expansion of the grounded Law Dome ice sheet margin, probably during the late Pleistocene. The direction of these features coincides with glacial striae on onshore crystalline bedrock outcrops. Perhaps the most striking glacial geomorphological features are sets of arcuate ridges confined mostly within glacially excavated U-shaped troughs formed by erosion of the northwest-trending bedrock fault sets. These ridge sets are interpreted as push moraines or grounding zone features, formed during episodic retreat of highly channelised, topographically-controlled ice-streams following ice surging of the Law Dome margin. This event was possibly triggered in response to local environmental forcing during the mid-late Holocene. Minor post-glacial marine sedimentation is preserved in several small (≤1km2) isolated basins with shallow seaward sills.

Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data

Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.

Subglacial meltwater channels in Marguerite Trough, western Antarctic Peninsula

Meltwater channels that have formed beneath glaciers and ice sheets have been observed on glaciated terrain, both terrestrial and submarine. Around Antarctica, channels incised into bedrock on the inner continental shelf have been found in several cross-shelf troughs that held major ice-streams during the last full-glacial (e.g. Pine Island Trough, Nitsche et al. 2014; Dotson-Getz Trough, Larter et al. 2009). The relatively widespread occurrence of meltwater channels has important implications for enhancing the flow of former ice streams over rough bedrock topography, yet questions remain regarding their timing and mode of formation. Meltwater channels from Marguerite Trough offshore of the western Antarctic Peninsula are described here (Fig. 1a). Fig. 1. Seafloor data from the subglacial meltwater channels in Marguerite Trough. ( a ) Location of study area (red box, map from IBCSO v. 1.0). MT , Marguerite Trough. ( b ) Multibeam-bathymetric imagery of the inner–middle continental shelf; isobath interval is 500 m. Acquisition system Kongsberg EM120. Frequency 12 kHz. Grid-cell size 40 m. ( c ) Anastomosing channel system on the inner shelf; overdeepened sections are arrowed. ( d ) Channels around streamlined terrain on the middle shelf. Small, NW–SE-aligned channels are arrowed in black; the long, sinuous channel is arrowed in white. ( e ) Seafloor-bathymetric profiles from Isis ROV …

Ice-sheet related landforms at the continental shelf edge, Albatross Bank, Alaska

Albatross Bank is a flat glaciated bedrock bank (Fig. 1a) located on the distal edge of the Alaskan continental shelf south of Kodiak Island (Fig. 1b). The bank illustrates the glacial geomorphology from an active ice edge during Marine Isotopic Stage (MIS) 2 ( c. 22–19 ka) sea-level regression (Briner & Kaufman 2008). The multibeam echo-sounder (MBES) images presented here provide the first detailed morphological evidence that the furthest extent of glacial advance in the late Pleistocene reached the shelf edge of the Gulf of Alaska. Other disparate areas of MBES imagery from the distal edge of the SE Alaska shelf to the western part of the Gulf of Alaska show evidence of glacial advance to the shelf break and support earlier depictions of Wisconsinan glaciation (Kaufman & Manley 2004; Briner & Kaufman 2008). Fig. 1. Multibeam swath bathymetry and bathymetric profiles of glacial features on Albatross Bank, Alaskan continental shelf. ( a ) Sun-illuminated multibeam-bathymetric image showing a band of seafloor iceberg ploughmarks (red inset, box f), bedrock outcrops and subglacial meltwater channels (red inset, box c). Acquisition system Reason SeaBat 8111. Frequency 100 kHz. Grid-cell size c. 10 m. ( b ) Location of study …

Assemblages of submarine landforms in the glacial troughs of the northern Barents Sea, east of Svalbard

The Barents Sea is a wide, relatively deep epicontinental sea consisting of shallower banks ( c. 50–100 m depth) separated by broad, flat-bottomed troughs ( c. 200–400 m depth) that radiate out towards its western and northern margins (Fig. 1a). These troughs have been excavated by grounded ice during multiple glaciations through the Plio-Pleistocene (Jakobsson et al. 2014). During the Last Glacial Maximum (LGM) the Barents Sea Ice Sheet (BSIS) extended across the entire northern Barents Sea to the shelf break (Svendsen et al. 2004; Jakobsson et al. 2014). Fast-flowing ice drained the ice sheet through these troughs and produced a suite of seafloor landforms that preserves both a record of former ice-flow patterns and of how the ice sheet retreated during deglaciation (Dowdeswell et al. 2010; Hogan et al. 2010 a ). Fig. 1. Bathymetric images and sub-bottom profiles of landforms in glacial troughs east of Svalbard. Acquisition system Kongsberg EM120. Frequency 12 kHz. Grid-cell size 10–20 m. Acquisition system for profiles Kongsberg TOPAS PS018 parametric sub-bottom profiler (secondary beam frequency 0.5–6 kHz). ( a ) Location of study area (red boxes; map from IBCAO v. 3.0). KT, Kvitoya Trough; OT, Olga Trough; E, eastern Erik Eriksen Trough; W, western Erik Eriksen Trough; KKL, Kong Karls Land; No, Nordaustlandet; FVT, Franz Victoria Trough. ( b ) Glacial lineations (long dashes) overprinted in part by a debris-flow deposit (dotted) in western Erik Eriksen Trough; recessional moraine orientations shown by solid lines. Large black arrow indicates former ice-flow direction. ( c ) Saw-tooth-shaped recessional moraines in Olga Trough. ( d ) Hill–hole pairs and glacial lineations in eastern Olga Trough; same depth scale as (c). ( e ) Streamlined crag-and-tail landforms in Kvitoya Trough. ( f ) Sub-bottom profile over the till sheet and recessional moraines shown in (c). ( g ) Acoustic facies on the upper slope north of Kvitoya Trough. ( h ) Subglacial meltwater channels …

Climatic and morphological controls on diachronous postglacial lake and river valley evolution in the area of Last Glaciation, northern Poland

The Wda River valley in northern Poland is a polygenetic valley located in a former subglacial meltwater channel that after ice sheet retreat hosted separate and then interconnected lake basins, subsequently replaced by a river. In one part of the river system an abandoned Lateglacial valley is found. This dry valley is a unique feature in the area located within the limit of the Scandinavian Ice Sheet during the Last Glaciation in the Central European Lowland. We investigated lacustrine and fluvial sediments and landforms in the valley and applied palynological analysis combined with radiocarbon dating to reconstruct the valley evolution from the early period of river inception in the Lateglacial through the formation of lakes during the Pleistocene/Holocene transition up to the establishment of a modern river system in the early Holocene. Three coeval processes were identified: (1) formation of lake basins in the subglacial channel connected by a river, (2) erosion of the river bed between the lakes, and (3) sediment deposition at the mouths of the channels in the lake basins first generating delta fans and eventually filling the lakes entirely. The valley formation was associated with diachronous melting of dead ice blocks buried in the subglacial channel controlled by the capacity of the hydrological system to evacuate the meltwater. Most of the lake basins in the study area were formed during the Bølling–Allerød period, but one section of the subglacial channel not affected by thermokarst processes survived protected by dead ice blocks throughout the entire Lateglacial. Accelerated dead-ice decay at the beginning of the Holocene triggered widespread lowering of the base level, which caused lake disappearance and the formation of the modern river system. The processes reconstructed in the central section of the Wda River indicate a highly dynamic and diachronous river valley development during the Lateglacial and early Holocene whereby the valley formation was interwoven with the formation of lake basins within the valley triggered by melting of dead ice blocks in the substratum.

A temperate former West Antarctic ice sheet suggested by an extensive zone of subglacial meltwater channels

Several recent studies predict that the West Antarctic Ice Sheet will become increasingly unstable under warmer conditions. Insights on such change can be assisted through investigations of the subglacial landscape, which contains imprints of former ice-sheet behavior. Here, we present radio-echo sounding data and satellite imagery revealing a series of ancient large sub-parallel subglacial bed channels preserved in the region between the Möller and Foundation Ice Streams, West Antarctica. We suggest that these newly recognized channels were formed by significant meltwater routed along the ice-sheet bed. The volume of water required is likely substantial and can most easily be explained by water generated at the ice surface. The Greenland Ice Sheet today exemplifies how significant seasonal surface melt can be transferred to the bed via englacial routing. For West Antarctica, the Pliocene (2.6–5.3 Ma) represents the most recent sustained period when temperatures could have been high enough to generate surface melt comparable to that of present-day Greenland. We propose, therefore, that a temperate ice sheet covered this location during Pliocene warm periods.

The dry channels at Ballyfoyle, Co. Kilkenny: a relict landscape of subglacial water

This paper examines the geomorphology of a suite of deep channels around the village of Ballyfoyle on the Castlecomer Plateau, Co. Kilkenny, and suggests a mechanism for their formation. The channels were mapped using a 10-m digital terrain model and ground truthed in the field. The channel locations were superimposed on a bedrock map of the area. Sediments within two passages of the nearby Dunmore Cave were also examined. While the cave sediments represent flow within a karstic system from a stream with its origin outside of the cave system itself, and possibly indicate subglacial flow, the adjacent channels are all eroded into bedrock that would have acted as a poor aquifer beneath the glacier. The channels are therefore interpreted as subglacial meltwater channels. The paper suggests that the aquifer characteristics were important in determining themethod of subglacial hydrology present during glaciation in this area.

Retreat of the West Antarctic Ice Sheet from the western Amundsen Sea shelf at a pre- or early LGM stage

Recent palaeoglaciological studies on the West Antarctic shelf have mainly focused on the wide embayments of the Ross and Amundsen seas in order to reconstruct the extent and subsequent retreat of the West Antarctic Ice Sheet (WAIS) since the Last Glacial Maximum (LGM). However, the narrower shelf sectors between these two major embayments have remained largely unstudied in previous geological investigations despite them covering extensive areas of the West Antarctic shelf. Here, we present the first systematic marine geological and geophysical survey of a shelf sector offshore from the Hobbs Coast. It is dominated by a large grounding zone wedge (GZW), which fills the base of a palaeo-ice stream trough on the inner shelf and marks a phase of stabilization of the grounding line during general WAIS retreat following the last maximum ice-sheet extent in this particular area (referred to as the Local Last Glacial Maximum, ‘LLGM’). Reliable age determination on calcareous microfossils from the infill of a subglacial meltwater channel eroded into the GZW reveals that grounded ice had retreated landward of the GZW before ∼20.88 cal. ka BP, with deglaciation of the innermost shelf occurring prior to ∼12.97 cal. ka BP. Geophysical sub-bottom information from the inner-, mid- and outer shelf indicates grounded ice extended to the shelf edge prior to the formation of the GZW. Assuming the wedge was deposited during deglaciation, we infer the timing of maximum grounded ice extent occurred before ∼20.88 cal. ka BP. This could suggest that the WAIS retreat from the outer shelf was already underway during or even prior to the global LGM (∼23–19 cal. ka BP). Our new findings give insights into the regional deglacial behaviour of this understudied part of the West Antarctic shelf and at the same time support early deglaciation ages recently presented for adjacent drainage sectors of the WAIS. If correct, these findings contrast with the hypothesis that initial deglaciation of Antarctic Ice Sheets occurred synchronously at ∼19 cal. ka BP.

Evidence from ice shelves for channelized meltwater flow beneath the Antarctic Ice Sheet

Subglacial meltwater channels beneath the Antarctic Ice Sheet have been reported, but the nature and distribution of these meltwater pathways are unclear. Remote sensing observations reveal persistent channelized features beneath the Filchner–Ronne Ice Shelf in West Antarctica, suggesting widespread channelized flow driven by melting.

Glacial geomorphology of Marguerite Bay Palaeo-Ice stream, western Antarctic Peninsula

This paper presents a glacial geomorphological map of over 17,000 landforms on the bed of a major palaeo-ice stream in Marguerite Bay, western Antarctic Peninsula. The map was compiled using various geophysical datasets from multiple marine research cruises. Eight glacial landform types are identified: mega-scale glacial lineations, crag-and-tails, whalebacks, gouged, grooved and streamlined bedrock, grounding-zone wedges, subglacial meltwater channels, gullies and channels, and iceberg scours. The map represents one of the most complete marine ice-stream signatures available for scrutiny, and these data hold much potential for reconstructing former ice sheet dynamics, testing numerical ice sheet models, and understanding the formation of subglacial bedforms beneath ice streams. In particular, they record a complex bedform signature of palaeo-ice stream flow and retreat since the last glacial maximum, characterised by considerable spatial variability and strongly influenced by the underlying geology. The map is presented at a scale of 1: 750,000, designed to be printed at A2 size, and encompasses an area of 128,420 km2.

A reexamination of Pleistocene tunnel valley distribution on the central Scotian Shelf

Tunnel valleys are an erosional channel characterized by anastomosing, steep-sided channel systems formed by subglacial, confined meltwater flow. Our study uses two-dimensional (2D) industry reflection seismic on the Scotian Shelf near Sable Island to better constrain the geometry of tunnel valleys in the area. Here, U- to V-shaped buried channels north and west of Sable Island extensively branch, reconnect, and meander. They average 2–5 km wide and 150–700 m deep (below sea level) and have a dominantly north–south orientation. Immediately to the south and southwest of Sable Island, the channels become narrower (1–1.5 km), shallower (300–400 m maximum) and more widely spaced. Multiple tunnel valley generations may be present, but could not be separately mapped. There is a notable gap of 20–30 km between the ends of the detectable tunnel valleys and the shelf edge south of Sable Island. An exception is erosive features at the shelf edge at the head of Logan Canyon, but these channels are disconnected from the tunnel valley network further north and may not be tunnel valleys. The reason for the gap south of Sable Island is not clear; however, we do not believe it is due to data coverage or resolution issues. If the tunnel valleys genuinely end south of Sable Island, then the gap between them and the shelf edge means that between The Gully and Logan Canyon these subglacial meltwater channels did not empty directly at the shelf edge. This implies direct meltwater and sediment delivery by tunnel valleys to the Scotian Slope during the Pleistocene may have been limited in this area.

The dry channels at Ballyfoyle, Co. Kilkenny: a relict landscape of subglacial water

This paper examines the geomorphology of a suite of deep channels around the village of Ballyfoyle on the Castlecomer Plateau, Co. Kilkenny, and suggests a mechanism for their formation. The channels were mapped using a 10-m digital terrain model and ground truthed in the field. The channel locations were superimposed on a bedrock map of the area. Sediments within two passages of the nearby Dunmore Cave were also examined. While the cave sediments represent flow within a karstic system from a stream with its origin outside of the cave system itself, and possibly indicate subglacial flow, the adjacent channels are all eroded into bedrock that would have acted as a poor aquifer beneath the glacier. The channels are therefore interpreted as subglacial meltwater channels. The paper suggests that the aquifer characteristics were important in determining the method of subglacial hydrology present during glaciation in this area.

Early Mars climate near the Noachian–Hesperian boundary: Independent evidence for cold conditions from basal melting of the south polar ice sheet (Dorsa Argentea Formation) and implications for valley network formation

Currently, and throughout much of the Amazonian, the mean annual surface temperatures of Mars are so cold that basal melting does not occur in ice sheets and glaciers and they are cold-based. The documented evidence for extensive and well-developed eskers (sediment-filled former sub-glacial meltwater channels) in the south circumpolar Dorsa Argentea Formation is an indication that basal melting and wet-based glaciation occurred at the South Pole near the Noachian–Hesperian boundary. We employ glacial accumulation and ice-flow models to distinguish between basal melting from bottom-up heat sources (elevated geothermal fluxes) and top-down induced basal melting (elevated atmospheric temperatures warming the ice). We show that under mean annual south polar atmospheric temperatures (−100°C) simulated in typical Amazonian climate experiments and typical Noachian–Hesperian geothermal heat fluxes (45–65mW/m2), south polar ice accumulations remain cold-based. In order to produce significant basal melting with these typical geothermal heat fluxes, the mean annual south polar atmospheric temperatures must be raised from today’s temperature at the surface (−100°C) to the range of −50 to −75°C. This mean annual polar surface atmospheric temperature range implies lower latitude mean annual temperatures that are likely to be below the melting point of water, and thus does not favor a “warm and wet” early Mars. Seasonal temperatures at lower latitudes, however, could range above the melting point of water, perhaps explaining the concurrent development of valley networks and open basin lakes in these areas. This treatment provides an independent estimate of the polar (and non-polar) surface temperatures near the Noachian–Hesperian boundary of Mars history and implies a cold and relatively dry Mars climate, similar to the Antarctic Dry Valleys, where seasonal melting forms transient streams and permanent ice-covered lakes in an otherwise hyperarid, hypothermal climate.