Coats Land Research Articles

State of polar climate in 2023

The year 2023 has become the warmest year on global record. As the Antarctic and Arctic are sensitive regions to global warming, the climate changes in 2023 in these regions have attracted widespread attention. In this study, using observations, reanalysis and remote sensing data, we reported detailed polar climate changes in 2023, including warming, sea ice, atmospheric composition and extreme events. Antarctic exhibited large east‒west regional differences and the coexistence of extreme warm and cold events. In Coats Land, Queen Maud Land and the Antarctic Peninsula, three and seven stations recorded the second and third highest autumn air temperatures in history, respectively. The Amundsen–Scott station experienced extreme warming event in July, with the temperature increasing by 40 °C in one day. Abnormal cooling was evident in the Ross Sea and neighboring regions which were predominantly winter (June–August) cold anomalies, with Marylin Station reaching the lowest winter temperature in history. The Arctic experienced the warmest summer after 1979, with an overall distribution of ‘warm land‒cold sea’ on annual average. Compared with the 1991–2020 average, the annual air temperature anomalies reached more than 2 °C in northern Canada and the Barents Sea–Kara Sea coast. Abnormal high summer temperature caused most severe wildfires in Canada on record and second largest daily cumulative melt area over the Greenland ice Sheet daily post-1979. Polar sea ice continued to decrease rapidly, with minimum sea ice extent in Antarctic and Arctic ranking the first and sixth lowest post-1979. For melt season, Arctic Ocean sea ice began to melt later in 2023 than the 2011–2023 average, and freeze onset was delayed due to high temperatures in summer and autumn. Additionally, the status of polar atmospheric greenhouse gases remains bleak, and major greenhouse gas concentrations continue to increase. The Antarctic ozone hole in 2023 formed approximately 10 d earlier and lasted longer than the 1979–2023 average, with a maximum daily area of 2.6 × 107 km2 on 21 September. This summary of polar climate changes in 2023 will help people better understand global climate change and draw attention to polar regions.

Current knowledge of the Ordovician System in Antarctica

Abstract Evidence of Early Ordovician deposition and intrusion in East Antarctica is best known from the Ross Orogen, postdating the 495–489 Ma Ross Orogeny. Here, c. 490–475 Ma granites (with related dykes and sills) of the Granite Harbour Intrusives represent roots of a continental margin arc. Detrital zircon grains in the upper Byrd Group (Central Transantarctic Mountains) are of comparable Early Ordovician age. Contemporaneous fossils are rare. In northern Victoria Land they include latest Cambrian to earliest Ordovician conodonts and microbrachiopods in allochthonous limestones of the Handler Formation (Robertson Bay Group) in the Robertson Bay Terrane, and probable Early Ordovician trace fossils in the Camp Ridge Quartzite of the Leap Year Group in the Bowers Terrane. In the Shackleton Range of Coats Land, West Antarctica, the Blaiklock Glacier Group contains a diverse ichnofossil fauna of probable Ordovician age associated with undescribed bivalved arthropods and segmented crustacea. The Swanson Formation of the Ross Province in Marie Byrd Land (correlated with the Robertson Bay Group of the Ross Orogen) is a turbiditic unit dominated by quartz-rich sandstones. Its Ordovician age is based on a post-depositional whole rock K–Ar metamorphic age of 448–444 Ma, with detrital zircon grains indicating a late Cambrian maximum depositional age.

ANTASed – An Updated Sediment Model for Antarctica

We compile existing seismic, gravity, radar and magnetic data, together with the subglacial bedrock relief from the BEDMACHINE project, to build the most detailed sediment model for Antarctica. We interpolate these data according to a tectonic map of Antarctica using a statistical kriging method. Our results reveal significant sediment accumulation in Antarctica with several types of sedimentary basins: parts of the Beacon Supergroup and more recent rifting basins. The basement relief closely resembles major geological and tectonic structures. The thickness of sediments has significant variations around the continent, and depends on the degree of crustal extension. West Antarctica has wide sedimentary basins: the Ross basin (thickness 2–6 km), the Filchner-Ronne basin (2–12 km) with continuations into East Antarctica, the Bentley Subglacial Trench and the Byrd basin (2–4 km). The deepest Filchner-Ronne basin has a complex structure with multi-layered sediments. East Antarctica is characterized by vast sedimentary basins such as the Pensacola-Pole (1–2 km), Coats Land (1–3 km), Dronning Maud Land (1–2 km), Vostok (2–7 km), Aurora (1–3 km), Astrolabe (2–4 km), Adventure (2–4 km), and Wilkes (1–4 km) basins, along with narrow deep rifts filled by sediments: JutulStraumen (1–2 km), Lambert (2–5 km), Scott, Denman, Vanderford and Totten (2–4 km) rifts. The average thickness of sediments for the whole continent is about 0.77 km. The new model, ANTASed, represents a significant improvement over CRUST 1.0 for Antarctica, and reveals new sedimentary basins. Differences between ANTASed and CRUST 1.0 reach +12/−3 km.

Antarctic Geothermal Heat Flow Model: Aq1

AbstractWe present a refined map of geothermal heat flow for Antarctica, Aq1, based on multiple observables. The map is generated using a similarity detection approach by attributing observables from geophysics and geology to a large number of high‐quality heat flow values (N = 5,792) from other continents. Observables from global, continental, and regional datasets for Antarctica are used with a weighting function that allows the degree of similarity to increase with proximity and how similar the observables are. The similarity detection parameters are optimized through cross correlation. For each grid cell in Antarctica, a weighted average heat flow value and uncertainty metrics are calculated. The Aq1 model provides higher spatial resolution in comparison to previous results. High heat flow is shown in the Thwaites Glacier region, with local values over 150 mW m−2. We also map elevated values over 80 mW m−2 in Palmer Land, Marie Byrd Land, Victoria Land and Queen Mary Land. Very low heat flow is shown in the interior of Wilkes Land and Coats Land, with values under 40 mW m−2. We anticipate that the new geothermal heat flow map, Aq1, and its uncertainty bounds will find extended use in providing boundary conditions for ice sheet modeling and understanding the interactions between the cryosphere and solid Earth. The computational framework and open architecture allow for the model to be reproduced, adapted and updated with additional data, or model subsets to be output at higher resolution for regional studies.

The visualization of geophysical and geomorphologic data from the area of Weddell Sea by the generic mapping tools

The paper concerns GMT application for studies of the geophysical and geomorphological settings of the Weddell Sea. Its western part is occupied by the back-arc basin developed during geologic evolution of the Antarctic. The mapping presents geophysical settings reflecting tectonic formation of the region, glaciomarine sediment distribution and the bathymetry. The GlobSed grid highlighted the abnormally large thickness of sedimentary strata resulted from the long lasting sedimentation and great subsidence ratio. The sediment thickness indicated significant influx (>13,000m) in the southern segment. Values of 6,000–7,000 m along the peninsula indicate stability of the sediments influx. The northern end of the Filchner Trough shows increased sediment supply. The topography shows variability -7,160–4,763 m. The ridges in the northern segment and gravity anomalies (>75 mGal) show parallel lines stretching NW-SE (10°–45°W, 60°–67°S) which points at the effects of regional topography. The basin is dominated by the slightly negative gravity >-30 mGal. The geoid model shows a SW-NE trend with the lowest values <18 m in the south, the highest values >20m in the NE and along the Coats Land. The ripples in the north follow the geometry of the submarine ridges and channels proving correlation with topography and gravitational equipotential surface.

U-Pb zircon geochronology from Haag Nunataks, Coats Land and Shackleton Range (Antarctica): Constraining the extent of juvenile Late Mesoproterozoic arc terranes

Understanding the accretionary stages of Rodinia evolution and the arrangement of cratons and arc terranes is dependent upon high-precision geochronology from key piercing points of Mesoproterozoic rocks. U-Pb zircon dating is presented here from the Mesoproterozoic Haag Nunataks gneiss complex of West Antarctica where the dominant granodiorite protolith was emplaced at 1238 ± 4 Ma, aplite/pegmatite sheets were intruded at 1064 ± 4 Ma and the final intrusive phase of microgranite sheets were emplaced at 1056 ± 8 Ma. A separate magmatic event at ~1170 Ma is recorded as inherited zircons in the later stage intrusions. Based on field relationships, the main phase of deformation at Haag Nunataks is thought to have developed prior to the emplacement of the microgranite sheet at ~1056 Ma but after the ~1064 Ma aplite/pegmatite intrusive phase. Potentially correlative units from the Shackleton Range and Coats Land of East Antarctica are also dated to test supposed correlations with arc terranes and crustal blocks at the margins of Laurentia and the proto-Kalahari craton. An ice-transported granite pegmatite sample recovered from the Brunt Ice Shelf is used as a partial proxy for unexposed rocks of the ice-covered Coats Land block and has been dated at ~1100 Ma. A diorite gneiss from the Shackleton Range was also analysed as it forms part of a magnetic domain shared with the Haag Nunataks crustal block. Core zircon ages of ~2470 Ma were determined, and the age of migmatisation is interpreted at ~1740 Ma and rules out any potential correlation with the Haag Nunataks gneiss complex. The magmatic precursors of the Haag Nunataks orthogneisses were emplaced in a juvenile arc setting. We argue that this arc was located in the Natal Embayment region, contiguous with the Namaqua-Natal-Maud belt of arc terranes typified by enhanced magmatism at ~1240 Ma and ~1170 Ma not associated with any significant deformation events. The later magmatic events at Haag Nunataks at ~1060 Ma are more closely associated with collision of Laurentia with the proto-Kalahari craton and the associated deformation is correlated with the Ottawan phase of the Grenville orogeny.

Clastos con calcimicrobios y arqueociatos procedentes de depósitos marinos del talud de la Formación cámbrica del Monte Wegener, Coats Land, Cordillera de Shackleton Antártida

Los clastos carbonatados de la Formación del Monte Wegener proporcionan evidencias sedimentológicas, diagenéticas y paleontológicas de la destrucción y resedimentación de un registro carbonatadoo cámbrico oculto/no conocido en aguas someras de la región de Coats Land en la Antártida. Este mosaico incompleto podría jugar un papel clave en las comparaciones y correlaciones bioestratigráficas entre el registro cámbrico de las Montañas Transantárticas, el bloque Ellsworth-Whitmore y la Península Antártica del continente antártico. Además, representa un registro clave en las futuras reconstrucciones paleobiogeográficas de Gondwana meridional basadas en asociaciones de arqueociatos.

First Precambrian palaeomagnetic data from the Mawson Craton (East Antarctica) and tectonic implications

A pilot palaeomagnetic study was conducted on the recently dated with in situ SHRIMP U-Pb method at 1134 ± 9 Ma (U-Pb, zircon and baddeleyite) Bunger Hills dykes of the Mawson Craton (East Antarctica). Of the six dykes sampled, three revealed meaningful results providing the first well-dated Mesoproterozoic palaeopole at 40.5°S, 150.1°E (A95 = 20°) for the Mawson Craton. Discordance between this new pole and two roughly coeval poles from Dronning Maud Land and Coats Land (East Antarctica) demonstrates that these two terranes were not rigidly connected to the Mawson Craton ca. 1134 Ma. Comparison between the new pole and that of the broadly coeval Lakeview dolerite from the North Australian Craton supports the putative ~40° late Neoproterozoic relative rotation between the North Australian Craton and the combined South and West Australian cratons. A mean ca. 1134 Ma pole for the Proto-Australia Craton is calculated by combining our new pole and that of the Lakeview dolerite after restoring the 40° intracontinental rotation. A comparison of this mean pole with the roughly coeval Abitibi dykes pole from Laurentia confirms that the SWEAT reconstruction of Australia and Laurentia was not viable for ca. 1134 Ma.

Investigating the distribution of magmatism at the onset of Gondwana breakup with novel strapdown gravity and aeromagnetic data

Massive volumes of mafic magmatism forming the Karoo-Ferrar Large Igneous Province (LIP) in Southern Africa and Antarctica preceded Jurassic breakup of the Gondwana Supercontinent. This widespread LIP magmatism is attributed to a major mantle plume, or plumes, impacting an area thousands of kilometres across. Magmas in lava flows and shallow sills, which flowed laterally hundreds to thousands of kilometres, form most of the exposed LIP. Hence, the distribution of shallow level mafic rocks may not reflect the location of mantle melting. In contrast, large deep-seated mafic intrusions such as gabbros likely more directly overlie areas of mantle melting. Antarctic exposures of such intrusions are limited to the Dufek Intrusion and outcrops >1000 km to the north, hence the true pattern of mantle melting is poorly constrained. Regional aeromagnetic and aerogravity data suggest other Jurassic mafic intrusions are present, but detailed analysis of these bodies is lacking. To define more precisely the distribution of mafic intrusions we use data from the first stand-alone strapdown gravity survey in Antarctica. This innovative technique allows collection of aerogravity data during draped flight, resolving anomalies with a wavelength of ∼6 km and a root-mean-square error of 1.8 mGal. Combining this new gravity data with coincident aeromagnetic data we investigate a ∼50 mGal gravity and associated >1000 nT magnetic high in Coats Land, East Antarctica. Our interpretation is that the so called ‘Halley High’ reflects a large gabbroic body ∼80 km long, 30 km wide and ∼6 km thick, equivalent to the inferred total size to the better known Stillwater layered mafic intrusion in the US. Our interpretation of a large mafic intrusion supports the suggestion from reconnaissance aeromagnetic data that this and other similar anomalies are Jurassic mafic intrusions. These large mafic intrusions, and hence underlying mantle melting, appear restricted to a linear band parallel to the continental margin. This structured pattern of mantle melting is consistent with shallow mantle convection and lithospheric extension playing a significant role in the later stages of the Karoo-Ferrar magmatism. An apparent 650 km gap in mafic intrusions adjacent to the continental Weddell Sea Rift System suggests different mantle processes were occurring here. Future joint magnetic and strapdown gravity surveying presents a key opportunity to fully constrain the location and extent of mantle melting during Gondwana breakup.

Deglaciation and future stability of the Coats Land ice margin, Antarctica

Abstract. The East Antarctic Ice Sheet discharges into the Weddell Sea via the Coats Land ice margin. We have used geophysical data to determine the changing ice-sheet configuration in this region through its last glacial advance and Holocene retreat and to identify constraints on its future stability. Methods included high-resolution multibeam bathymetry, sub-bottom profiles, seismic-reflection profiles, sediment core analysis and satellite altimetry. These provide evidence that Coats Land glaciers and ice streams merged with the palaeo-Filchner Ice Stream during the last glacial advance. Retreat of this ice stream from 12 848 to 8351 cal. yr BP resulted in its progressive southwards decoupling from Coats Land outlet glaciers. Moraines and grounding-zone wedges document the subsequent retreat and thinning of these glaciers, their loss of contact with the bed and the formation of ice shelves, which re-advanced to pinning points on topographic highs at the distal end of the troughs. Once fully detached from the bed, these ice shelves were predisposed to rapid retreat back to coastal grounding lines. This was due to reverse-bed slopes, the consequent absence of further pinning points in the troughs and potentially to the loss of structural integrity resulting from weaknesses inherited at the grounding line. These processes explain why there are no large ice shelves in the eastern Weddell Sea between 75.5 and 77∘ S.

Long-term coastal-polynya dynamics in the southern Weddell Sea from MODIS thermal-infrared imagery

Abstract. Based upon thermal-infrared satellite imagery in combination with ERA-Interim atmospheric reanalysis data, we derive long-term polynya characteristics such as polynya area, thin-ice thickness distribution, and ice-production rates for a 13-year investigation period (2002–2014) for the austral winter (1 April to 30 September) in the Antarctic southern Weddell Sea. All polynya parameters are derived from daily cloud-cover corrected thin-ice thickness composites. The focus lies on coastal polynyas which are important hot spots for new-ice formation, bottom-water formation, and heat/moisture release into the atmosphere. MODIS has the capability to resolve even very narrow coastal polynyas. Its major disadvantage is the sensor limitation due to cloud cover. We make use of a newly developed and adapted spatial feature reconstruction scheme to account for cloud-covered areas. We find the sea-ice areas in front of the Ronne and Brunt ice shelves to be the most active with an annual average polynya area of 3018 ± 1298 and 3516 ± 1420 km2 as well as an accumulated volume ice production of 31 ± 13 and 31 ± 12 km3, respectively. For the remaining four regions, estimates amount to 421 ± 294 km2 and 4 ± 3 km3 (Antarctic Peninsula), 1148 ± 432 km2 and 12 ± 5 km3 (iceberg A23A), 901 ± 703 km2 and 10 ± 8 km3 (Filchner Ice Shelf), as well as 499 ± 277 km2 and 5 ± 2 km3 (Coats Land). Our findings are discussed in comparison to recent studies based on coupled sea-ice/ocean models and passive-microwave satellite imagery, each investigating different parts of the southern Weddell Sea.

Katabatic winds and polynya dynamics at Coats Land, Antarctica

AbstractMesoscale model simulations were conducted for the Weddell Sea region for the autumn and winter periods of 2008 using a high-resolution, limited-area, non-hydrostatic atmospheric model. A sea ice–ocean model was run with enhanced horizontal resolution and high-resolution forcing data of the atmospheric model. Daily passive thermal and microwave satellite data was used to derive the polynya area in the Weddell Sea region. The focus of the study is on the formation of polynyas in the coastal region of Coats Land, which is strongly affected by katabatic flows. The polynya areas deduced from two independent remote sensing methods and data sources show good agreement, while the results of the sea ice simulation show some weaknesses. Linkages between the pressure gradient force composed of a katabatic and a synoptic component, offshore wind regimes and polynya area are identified. It is shown that the downslope surface offshore wind component of Coats Land is the main forcing factor for polynya dynamics, which is mainly steered by the offshore pressure gradient force, where the katabatic force is the dominant term. We find that the synoptic pressure gradient is opposed to the katabatic force during major katabatic wind events.

New aeromagnetic view of the geological fabric of southern Dronning Maud Land and Coats Land, East Antarctica

The ice shield of Antarctica, which measures several kilometers in thickness, presents a challenge when attempting to unravel the subglacial geology. Here, we report about systematic airborne magnetic surveys conducted over the last decade, which investigated a significant part of Dronning Maud Land (DML), imaging for the first time the crustal architecture of the interior of this sector of East Antarctica. High-resolution data reveal parallel, elongated magnetic anomalies in southeastern DML. These NW–SE trending anomalies can be traced farther east into sparser Russian magnetic data sets. Several high amplitude magnetic anomalies with values above 400nT have been observed in southwestern DML and Coats Land. They differ clearly in wavelength and amplitudes from the magnetic pattern found in the east and do not show any evidence of a Pan-African orogenic belt or suture zone connecting the Shackleton Range with eastern DML, as hypothesized in several studies. This leads to the assumption of the existence of a hitherto unrecognized large tectonic province in southeastern DML. Whereas an over 100km long magnetic lineament in the interior of the Dronning Maud Land may reflect a major shear zone akin to the Pan-African age Heimefrontfjella shear zone. Both findings bring new evidences to the still open question about the amalgation of East and West Gondwana. In addition, the magnetic data allow mapping the eastern extent of the presumable cratonic province of Coats Land, a region considered as a key piercing point for reconstructions of Rodinia. Furthermore, the Beattie Magnetic Anomaly in southern Africa is assumed to continue into East Antarctica. Two magnetic highs in western DML are identified as possible eastward continuation of this prominent anomaly.

Temporal changes in crevasses in the middle Slessor Glacier, Coats Land, East Antarctica through SAR data analysis

Mosaic processing of SAR images by ERS 1/2 AMI revealed the detailed topography within a large valley (middle Slessor Glacier) in Coats Land, East Antarctica, showing oval and feather-shaped features that correspond to precipitous cliffs and accumulated crevasses, respectively. Time-series analysis of SAR intensity images acquired on six dates within the period October 1991 to August 2000 revealed the following topographic changes over time: (1) the feather-shaped feature moved down the slope at a rate of about 100 m/year; and (2) the extent of crevasse areas increased with time, both at the northern end of the feather-shaped feature and at the northeastern tip of the oval feature, with the increasing rates being much larger in the case of the feather-shaped feature. High increase ratios were generally correlated with a rapid increase in wintertime temperature within a short period of about 2 weeks: the relationship was approximated by an exponential function. Furthermore, we interpreted that the occurrence of a fault in the subglacial topography may have led to the initiation of ice fractures and a subsequent concentration of crevasses at the end of the feather-shaped feature.

Air and shipborne magnetic surveys of the Antarctic into the 21st century

The Antarctic geomagnetics' community remains very active in crustal anomaly mapping. More than 1.5million line-km of new air- and shipborne data have been acquired over the past decade by the international community in Antarctica. These new data together with surveys that previously were not in the public domain significantly upgrade the ADMAP compilation. Aeromagnetic flights over East Antarctica have been concentrated in the Transantarctic Mountains, the Prince Charles Mountains – Lambert Glacier area, and western Dronning Maud Land (DML) — Coats Land. Additionally, surveys were conducted over Lake Vostok and the western part of Marie Byrd Land by the US Support Office for Aerogeophysical Research projects and over the Amundsen Sea Embayment during the austral summer of 2004/2005 by a collaborative US/UK aerogeophysical campaign. New aeromagnetic data over the Gamburtsev Subglacial Mountains (120,000line-km), acquired within the IPY Antarctica's Gamburtsev Province project reveal fundamental geologic features beneath the East Antarctic Ice sheet critical to understanding Precambrian continental growth processes. Roughly 100,000line-km of magnetic data obtained within the International Collaboration for Exploration of the Cryosphere through Aerogeophysical Profiling promises to shed light on subglacial lithology and identify crustal boundaries for the central Antarctic Plate. Since the 1996/97 season, the Alfred Wegener Institute has collected 90,000km of aeromagnetic data along a 1200km long segment of the East Antarctic coast over western DML. Recent cruises by Australian, German, Japanese, Russian, British, and American researchers have contributed to long-standing studies of the Antarctic continental margin. Along the continental margin of East Antarctica west of Maud Rise to the George V Coast of Victoria Land, the Russian Polar Marine Geological Research Expedition and Geoscience Australia obtained 80,000 and 20,000line-km, respectively, of integrated seismic, gravity and magnetic data. Additionally, US expeditions collected 128,000line-km of shipborne magnetic data in the Ross Sea sector.

Distinguishing East and West Antarctic sediment sources using the Pb isotope composition of detrital K-feldspar

New Pb analyses of K feldspars (Kfs) from Archaean–Mesozoic crystalline rocks from across the Weddell Sea region of Antarctica show Pb isotopic compositions that vary geographically. Five distinct basement provinces are defined, each with characteristic Kfs Pb compositions, and indicate that the comparison of the Pb isotopic composition of individual detrital Kfs can be used as a sedimentary provenance tool in this region. This tool is tested on Permian sandstones deposited in a retro-arc foreland basin because the potential source regions for these sandstones, the active Palaeopacific margin arc of West Antarctica and uplifted regions of now ice-covered East Antarctica, comprise rocks with markedly different Pb isotope compositions. Pb compositions of detrital Kfs from sandstone samples collected from Dronning Maud Land suggest that their provenance was entirely from within East Antarctica, while those collected from the Theron Mountains, Coats Land, were wholly derived from the active margin of West Antarctica. Kfs Pb composition of bedrock samples is largely dependent on age and because Kfs tends to only survive a single cycle of erosion, transport, deposition and diagenesis, its provenance when compared with that determined by detrital zircon geochronology, may qualify what proportion of the more robust mineral zircon has been recycled through several sedimentary cycles. Detrital zircon analyses from a Permian sandstone from the Theron Mountains suggest that 45% of its detrital zircon was recycled from pre-existing (meta)sedimentary rocks. The detrital feldspar data also indicate that Archaean and 2.1 Ga crust, with a very different Pb isotope composition to any exposed in the Weddell Sea region, is likely to exist beneath the East Antarctic Ice sheet.

Coats Land crustal block, East Antarctica: A tectonic tracer for Laurentia?

Undeformed rhyolite and granophyre in the Coats Land crustal block of East Antarctica, dated as 1112 ± 4 Ma, are identical in age to both the Umkondo large igneous province (LIP) of the Kalahari craton (southern Africa) and the early Keweenawan LIP of Laurentia (North America). Although marine and satellite data demonstrate that Coats Land was close to Kalahari within the Gondwana supercontinent, the Coats Land rocks yield Pb isotope compositions strikingly distinct from those of the Umkondo province, yet indistinguishable from rocks of the Keweenawan province. The anorogenic Red Bluff granitic suite, along the present-day southern Laurentian margin in the Franklin Mountains (Texas, USA), is of comparable age, general rock type, and Pb isotope composition to rocks of Coats Land and may provide a piercing point for a Coats Land–Laurentia link. Paleomagnetic poles permit the Coats Land block to be close to this part of Laurentia ca. 1100 Ma and allow juxtaposition of Kalahari and southern Laurentia ca. 1000 Ma. The Coats Land crustal block may therefore be a critical tectonic tracer for placing Laurentia within late Mesoproterozoic and Neoproterozoic paleogeographic reconstructions. If this hypothesis is correct, Laurentia collided with the Kalahari craton along Antarctica's Maud orogen, which would represent a continuation of the ca. 1000 Ma Grenville orogen of eastern and southern Laurentia.

A comparative modeling study of the Brunt Ice Shelf/ Stancomb-Wills Ice Tongue system, East Antarctica

AbstractTwo diagnostic, dynamic/thermodynamic ice-shelf models are applied to the Brunt Ice Shelf/Stancomb-Wills Ice Tongue system, located off Caird Coast, Coats Land, Antarctica. The Brunt Ice Shelf/Stancomb-Wills Ice Tongue system is characterized as a thin, unbounded ice shelf with an atypical and highly heterogeneous structure. In contrast to other ice shelves, a composite mass of icebergs that calved at the grounding line and were then locked within fast (sea) ice exists between the fast-moving Stancomb-Wills Ice Stream and the slow-moving Brunt Ice Shelf. We simulate the present flow regime of the ice shelf that results from the ice-thickness distribution and the inflow at the grounding line with two different models, and compare the model results with feature tracking and InSAR flow velocities. We then incorporate two observed features, a rift and a shear margin, into the models with two different approaches, and demonstrate the effects of variations in numerical values for the shear strength and viscosity in these zones on the simulated velocity field. A major result is that both kinds of implementation of the rifts lead to similar effects on the entire velocity field, while there are discrepancies in the vicinity of the rifts.

Switch‐off of a major enhanced ice flow unit in East Antarctica

The East Antarctic Ice Sheet (EAIS) is the largest reservoir of ice on the planet by an order of magnitude. Compared with the West Antarctic Ice Sheet (WAIS), it is traditionally considered to be relatively stable, with only minor adjustments to its configuration over glacial‐interglacial cycles. Here, we present the results of a radio‐echo sounding survey from Coats Land, East Antarctica, which suggests that parts of the EAIS outlet drainage system may have changed significantly since the Last Glacial Maximum. We have identified an enhanced flow unit from buckled internal layering and smooth bed morphology that is no longer active. We believe this feature to have shut down at some point since the Last Glacial Maximum, ∼20 ka BP.

Profiles of katabatic flow in summer and winter over Coats Land, Antarctica

AbstractObservations from a novel autonomous Doppler sodar wind profiling system are described and analysed. These include the first continuous wintertime soundings of katabatic winds over Antarctica—a continent with which they are synonymous. During 2002 and 2003 over 2600 wind profiles were taken during ‘case‐studies’ of high‐resolution sounding lasting hours to days. These case‐studies have been subjectively classified as: synoptically driven, katabatically influenced (28 days); primarily katabatically driven flows (a subset of 16 days); or other flow types. The Doppler sodar observations were augmented by automatic weather station observations at the field site and further up the slope, as well as synoptic and upper‐air observations at Halley Research Station, some 50 km distant on the Brunt Ice Shelf.In primarily katabatic flows there is a systematic change in the shape and depth of the low‐level katabatic jet with wind speed. Relatively strong katabatic flows (maximum winds of typically 8–10 m s−1) have a jet maximum between 20 and 60 m above the surface and are relatively deep (up to 200 m); while moderate katabatic flows (4–8 m s−1) typically have a jet maximum between 3 and 30 m and are shallower (∼100 m), although they can also be more diffuse in structure with a wind speed maximum at higher altitude. In all katabatic flows there is backing of wind direction with height, consistent with decreasing friction away from the surface. During summertime katabatic flows there is a clear diurnal signature at all heights, although this is less pronounced in the surface layer where there seems to be a persistent 2–4 m s−1 katabatic flow during all case‐studies. Where the diurnal forcing results in an abrupt katabatic flow deceleration, i.e. what may be a katabatic ‘jump’, there is a concurrent vertical acceleration. Wind profiles from a recent numerical weather prediction study of idealized katabatic flows at this site compare favourably with selected mean profiles; the only significant difference is that the model's wind speed is too low over the lowest ∼10 m. Copyright © 2006 Royal Meteorological Society.