Antarctica Ice Sheet Research Articles

Characterizing South Pole Firn Structure With Fiber Optic Sensing

AbstractThe firn layer covers 98% of Antarctica's ice sheets, protecting underlying glacial ice from the external environment. Accurate measurement of firn properties is essential for assessing cryosphere mass balance and climate change impacts. Characterizing firn structure through core sampling is expensive and logistically challenging. Seismic surveys, which translate seismic velocities into firn densities, offer an efficient alternative. This study employs Distributed Acoustic Sensing technology to transform an existing fiber‐optic cable near the South Pole into a multichannel, low‐maintenance, continuously interrogated seismic array. The data resolve 16 seismic wave propagation modes at frequencies up to 100 Hz that constrain P and S wave velocities as functions of depth. Using co‐located geophones for ambient noise interferometry, we resolve very weak radial anisotropy. Leveraging nearby SPICEcore firn density data, we find prior empirical density‐velocity relationships underestimate firn air content by over 15%. We present a new empirical relationship for the South Pole region.

A PPP kinematic application on historical GPS data: the reprocessing of the ITASE98-99 Antarctica mission height profiles

The analysis of altimetric profiles in Antarctica and their evolution over the years is a sensitive topic for the scientific community since it helps understand the effects of climate change that the continent undergoes. Different geomatic techniques, including the GNSS technology, can be employed to obtain altimetric profiles. However, the GNSS differenced approaches, such as the Post Processing Kinematic, are hardly usable to define long profiles in Antarctica because of the low number of CORS stations. In these conditions, the Precise Point Positioning (PPP) approach is a valid alternative to avoid processing very long baselines. The aim of this article is to define a standard procedure for the processing of historical GPS data, thanks to the availability of a dataset from the International Trans-Antarctic Scientific Expedition, which took place between 1998 and 1999 (ITASE98-99). This expedition focused on mapping the Antarctic territory, subdividing it by nations of influence, using geophysical and geodetic technologies, including GPS. The altimetric profiles had already been calculated in 2002 by the Geomatics group of the University of Bologna using the Gipsy-OASIS II software. In this work, the new version of the JPL software, GipsyX, is used to apply the newly implemented models and reprocessed products. The calibration of the processing parameters leading to the final PPP solution is described in the paper, including details on the implementation of a post-processing filtering procedure. The average a posteriori elevation error is 4.6 cm, while 99% of them are within 27 cm. The comparison of the new results to both the previous processing and the REMA elevation model shown that about double the number of solutions are now available, meter-level elevation spikes have been avoided, and a half meter bias is now reduced to a few centimeters. Given the almost 15 years difference between the 1999.0 expedition epoch and the REMA reference epoch, the obtained results can be used to study accumulation/erosion effects on the Antarctica ice sheet.

Interactions of Seasonal Earth Processes and Climate System

The cumulative effects of seasonal Earth processes in different places and times in the atmosphere, hydrosphere, and cryosphere essentially and inevitably shape global climate conditions. Therefore, the article investigates the possibilities for modelling the periodicity of the observable seasonal climate processes. The starting assumption of the study is that the seasonal climate processes are representable by two-phase linear periodic models based on observed data. A numerical algorithm elaborated in the sequel makes it possible to accumulate the seasonal effects of two successively progressive and regressive process phases of periodic climate changes in time. The model first tackles the reported seasonal growth of the atmospheric CO2 concentration. Next, it considers the observed seasonal cryospheric melting and freezing processes of the Antarctica and Greenland ice sheets and of the Arctic sea ice. It also elaborates on the reported seasonal sea level rise. Finally, the article summarises the interactions of periodic climate processes and the global climate conditions in time scale. The reports on global temperature rise are only on an annual basis. The article also emphasises the importance of control over the seasonal worsening and recovery scenarios for more appropriate projections of climate policies to 2100.

A 1,470-Year Astronomical Cycle and Its Effect on Earth’s Climate

Earth’s millennial climate warming cycle has been studied by scientists for decades, but its cause has been lacking. It warms the Earth for several hundred years and melts some of the ice sheets in Greenland and Antarctica. This analysis found that the cycle is caused by the astronomical conjunction of the planets Jupiter, Saturn and Neptune. The current cycle started warming the Earth in the year 1791 and will probably reach peak temperature in approximately year 2060 at the next Jupiter, Saturn and Neptune conjunction. Then it will cause cooling oscillations for the rest of the cycle when the heat from the cycle is reduced.

Glacial Isostatic Adjustment modelling of the mid-Holocene sea-level highstand of Singapore and Southeast Asia

The mid-Holocene sea-level highstand refers to higher-than-present relative sea levels (RSLs) in far-field regions between 7000 and 4000 years ago because of equatorial ocean syphoning and continental levering. But the timing, magnitude, and spatial variability of the highstand are uncertain and the highstand parameterization in Glacial Isostatic Adjustment (GIA) modelling is understudied. Here, we use the RSL records of Southeast Asia to investigate the sensitivity of the mid-Holocene highstand properties to Earth and ice model parameters, including lithospheric thickness, mantle viscosity (both 1D and 3D), and deglaciation history of Antarctica and global ice sheets. We found that the Earth model variation only affects the magnitude of the mid-Holocene highstand unless extraordinary low upper mantle viscosity is used. The timing of the highstand moves towards present and there is an absence of the highstand if upper mantle viscosity is < 4.0 × 1019 Pa s or ≤ 1.0 × 1019 Pa s, respectively. Ice model variation changes both the timing and magnitude of the mid-Holocene highstand. Delaying the ice-equivalent sea level will shift the timing of the highstand later and result in a lower highstand magnitude. We produced a mid-Holocene highstand “treasure map” that considers topography change and accommodation space to guide future RSL data collection efforts in Southeast Asia. The highstand “treasure map” indicates that the northeast and central west coast of Malay-Thai Peninsula, east coast of Sumatra, north coast of Java, and southwest coast of Borneo are very likely (90% probability) to preserve mid-Holocene highstand evidence.

Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines

Abstract. The warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences.

The response of rhythmically forming processes to the latitudinal position of the zones of their implementation

The problem of variability of the Milankovich scale and cyclic oscillations in the troposphere circulation mode depending on the geographical latitude of the area is investigated. Parallels in the dynamics of multi-thousand-year and intra-century climate cycles in different latitudinal zones and possible causes of this phenomenon are considered. New data on the influence of axial rotation and the shape of the Earth on the structure of rhythm-forming processes are presented. It is established that the zone with a high frequency of pulsations of climatic phases is confined to low latitudes with the highest energy potential. The dependence of the velocity of air currents on the length of geographical parallels is shown. Thus, during the formation of air currents near the equator – the longest parallel of the planet (Hadley circulation cell), their velocity, which is set by the axial rotation of the Earth, is higher than the speed of sound and twice as high as similar flows originating in the temperate latitudes (Ferell cell). Paleogeographic evidence confirming Milankovich’s calculations about the different duration of the solar cycle period in the low, temperate and polar latitudes is presented. Thus, the dating of the terraces of the island of Barbados in the Caribbean Sea (low latitudes) showed that the period of the Milankovich cycle here is close to 20 thousand years. While in the zone of temperate latitudes, the period of the same cycle, judging by the dating of the stadial moraines of the former glacial covers, is 41 thousand years, i. e. twice as long. Maximum – up to 100 thousand years – set for polar latitudes in the study of the ice sheets of Antarctica and Greenland. Different degrees of meteorological impacts on ecosystems and the level of natural hazards within different latitudinal corridors have been revealed. The most dynamic and dangerous are the low latitudes with their hurricanes, typhoons, floods and storms with high frequency. This should be taken into account when developing a strategy for the economic development of high-risk territories and preventive measures for the protection of engineering orientation.

Factors Contributing to the Long-Term Sea Level Trends in the Iberian Peninsula and the Balearic and Canary Islands

We present an attempt to estimate the long-term changes in Relative Sea Level (RSL), in addition to the different factors contributing to such trends on a local and regional scale, using a statistical linear model. The time series analysis corresponded to 17 tide-gauges, grouped in three different areas: the northern and western Atlantic coasts of the Iberian Peninsula, the Canary Islands, and the southern and eastern coasts of the Iberian Peninsula and Balearic Islands. The analysis was performed for two periods: 1948–2019, using tide-gauge data; and 1993–2019, using both tide-gauge and altimetry data for comparison. The trends for the period 1948–2019 ranged between 1.09 ± 0.14 (Canary Islands) and 2.05 ± 0.21 mm/yr for the northern and western Atlantic Iberian Peninsula. Altimetry data during the period 1993–2019 yielded quite homogeneous results for all the locations and regions, ranging between 2.7 ± 0.4 and 3.0 ± 0.3 mm/yr. In contrast, the results obtained from tide-gauge data for this recent period showed a large dispersion, very likely due to local effects, or perhaps even to levelling or instrumental errors. Nevertheless, when the results were averaged for each area, the observed trends were comparable to the altimetry results, with values of 2.3 ± 0.8, 2.7 ± 0.5, and 2.8 ± 0.8 mm/yr for the three regions of study. A stepwise forward linear regression was used to relate the observed RSL variability to the atmospheric forcing and the thermosteric and halosteric components of the sea level. Surprisingly, the thermosteric and halosteric contributions were not significantly correlated to the observed RSL in many cases; consequently, the steric, the total addition of mass, the mass of salt, and the freshwater contributions to the observed sea level trends could not be reliably estimated. This result seems to have been the consequence of the scarcity of temperature and salinity data; this hypothesis was confirmed, with the exception of the tide-gauge data for L’Estartit. This location is close to a well sampled region. In this case, the atmospheric variables and the thermosteric and halosteric terms accounted for 80% of the observed RSL variance, and the contributions of these terms could be estimated. The freshwater contribution for this location was between 1.3 and 1.4 mm/yr, consistent with recent estimations of the contributions of glaciers and Greenland and Antarctica Ice Sheets. These results highlight the importance of monitoring programs and routine sampling for the determination of the different factors contributing to the sea level variability.

Contrasting current and future surface melt rates on the ice sheets of Greenland and Antarctica: Lessons from in situ observations and climate models

Surface meltwater production impacts the mass balance of the Greenland and Antarctic ice sheets in several ways, both directly (e.g., through runoff in Greenland) and indirectly (e.g., through cryo-hydrologic warming and frontal melt of marine-terminating glaciers in Greenland and hydrofracturing of ice shelves in Antarctica). Despite its importance, the spatial and temporal patterns in melt rates on both ice sheets are still relatively poorly understood. In this contribution we review and contrast surface melt ‘weather ‘(i.e., short term, intra- and interdiurnal variability) and surface melt ‘climate’ (i.e., longer term, interannual variability and future melt) of both ice sheets. We find that in situ observations using suitably equipped (automatic or staffed) weather stations are invaluable for a complete understanding of the melt process, which represents the complex transport of energy by radiation, turbulence, and molecular conduction between the lower atmosphere, the ice/snow surface, and the subsurface ice/snow layers. We provide example time series of ice sheet melt ‘weather’ for the marginal Greenland ice sheet, where warm and humid air masses tend to increase surface melt rate, and for coastal East Antarctica, where the opposite happens. Apart from process understanding, these in situ observations, which especially in Antarctica are scarce in space and time, are also invaluable to validate, evaluate and calibrate satellite- and model-based estimates of ice sheet surface melt rate. We provide examples of modelled melt maps for both ice sheets, and melt projections for a high-warming, fossil-fuelled development scenario. Although important milestones in melt observations (both in-situ and remotely sensed) and melt models (both global and regional) have recently been reached, we identify multiple outstanding research questions pertaining to current and future ice sheet surface melt rates.

East Antarctica ice sheet in Schirmacher Oasis, Central Dronning Maud Land, during the past 158 ka

Varied geomorphic landforms along the coast of eastern Antarctica suggest that the most recent phase of ice retreat was spatially heterogeneous. Ice retreat here comprised; a thinning of the East Antarctic Ice Sheet (EAIS) by up to 500 m and the recession of the ice wall in kilometre. This retreat deposited moraines over the Schirmacher Oasis (SO) in central Dronning Maud Land with minimal reworking. The present study used optical dating of the recessional moraines to determine the timing of their final emplacement. Three phases of moraine deposition, during 158–125 ka; 76–50 ka and 22 ka to present, were inferred. It is suggested that decreased sea surface temperatures and increased sea ice cover of the surrounding oceans limited the moisture supply and led to the retreat of ice. By ~ 35 ka the SO became ice-free and has remained so, ever since. The inference that the ice sheet in this region was moisture limited, implies that in a global warming context, this region may not contribute to an increase in sea-level. Instead, a warming-induced increase in moisture supply may even add to ice cover in the region.

AMOC Stabilization Under the Interaction With Tipping Polar Ice Sheets

AbstractSeveral large‐scale components of the climate system may undergo a rapid transition as critical conditions are exceeded. These tipping elements are also dynamically coupled, allowing for a global domino effect under global warming. Here we focus on such cascading events involving the Greenland Ice Sheet (GIS), the West Antarctica Ice Sheet (WAIS) and the Atlantic Meridional Overturning Circulation (AMOC). Using a conceptual model, we study the combined tipping behavior due to three dominant feedbacks: the marine ice sheet instability for the WAIS, the height‐surface mass balance feedback for the GIS and the salt‐advection feedback for the AMOC. We show that, in a realistic parameter range of the model, a tipping of the WAIS can inhibit cascading events by preserving the AMOC stability.

Through an Ice Sheet, Darkly

Through an Ice Sheet, Darkly

Evidence for an extensive ice shelf in northern Baffin Bay during the Last Glacial Maximum

The glaciological significance of ice shelves is relatively well established for the stability of modern ice sheets of Antarctica. Past ice shelves of the Arctic, however, are poorly documented while their role for the stability of former ice sheets remains mostly unknown. Here we present swath bathymetry data and seismostratigraphic profiles that reveal a large moraine system extending along the continental slope off Baffin Island, demonstrating that a 500-m thick ice shelf covered northern Baffin Bay during the last glacial episode. We suggest that this ice shelf had a profound impact on the stability of a series of major ice streams that drained the interior of the Laurentide, Innuitian and Greenland ice sheets. Climate warming and global sea-level rise in the early stage of deglaciation possibly contributed to a large-scale break-up of the ice shelf, which led to the destabilisation and reorganisation of tributary ice streams from these three ice sheets.

Which glaciers are the largest in the world?

AbstractGlacier monitoring has been internationally coordinated for more than 125 years. Despite this long history, there is no authoritative answer to the popular question: ‘Which glaciers are the largest in the world?’ Here, we present the first systematic assessment of this question and identify the largest glaciers in the world – distinct from the two ice sheets in Greenland and Antarctica but including the glaciers on the Antarctic Peninsula. We identify the largest glaciers in two domains: on each of the seven geographical continents and in the 19 first-order glacier regions defined by the Global Terrestrial Network for Glaciers. Ranking glaciers by area is non-trivial. It depends on how a glacier is defined and mapped and also requires differentiating between a glacier and a glacier complex, i.e. glaciers that meet at ice divides such as ice caps and icefields. It also depends on the availability of a homogenized global glacier inventory. Using separate rankings for glaciers and glacier complexes, we find that the largest glacier complexes have areas on the order of tens of thousands of square kilometers whereas the largest glaciers are several thousands of square kilometers. The world's largest glaciers and glacier complexes are located in the Antarctic, Arctic and Patagonia.

Estimation of surface melt induced melt pond depths over Amery Ice Shelf, East Antarctica using Multispectral and ICESat-2 data

Surface melting is increasing over the Antarctica continent, with unknown impacts on glacier and ice sheet dynamics at the ice-bed interface. Surface meltwater drains to the bed of Antarctica ice sheets and outlet glaciers, causing accelerations in ice flow (up to 100% greater than the annual mean). Because melt occurrences are currently erratic (also Antarctica surface melt refreezes), effective subglacial drainage cannot be maintained, resulting in repeated short-lived ice flow disturbances and calving of ice shelves. Longterm exposure to strong surface melting promotes the formation of melt ponds and subsequently Supraglacial lakes and therefore there is possibility of hydrofracturing. The present study aims to estimate the volume of surface melt-induced melt ponds over the Amery Ice Shelf (AIS) using a physically-based radiative transfer model. The AIS, located on Antarctica's east coast, is one of the world's biggest glacier drainage basins. The ICESat-2 geolocated photon data were used to validate the depth estimates of melt ponds derived from Landsat-8 and Sentinel-2 multispectral datasets based on the model. The average depth estimated is around 1.9±0.6 m for the melt ponds adopted for the present study. The present study aims to quantify surface melt over the Antarctica continent (AIS region) in the context of India’s scientific credentials in polar science. We recommend monitoring extensive surface melt and subsurface refreezing which might result in more ponding above impermeable ice layers in the coming years.

Investigation of the Differences in Onset Times for Magnetically Conjugate Magnetometers

We have identified nearly 1,000 onsets using two pairs of hemispheric conjugate ground magnetometers where the onset is defined based on a sharp decline in the H component of the magnetic field at a ground magnetometer station. Specifically, we used the pair of stations at West Antarctica Ice Sheet Divide and Sanikiluaq, Canada; Syowa, Antarctica; and Tjörnes, Iceland. While the onset time in the southern hemisphere is identified by eye, the value of the differences in the onset time between the northern and southern hemispheres is determined using cross covariance. We observe differences in the onset time between the two hemispheres as large as several minutes, but 53% of the events show no difference in the onset time. Using statistics, we show that the largest differences in onset time are associated with the summer and winter seasons and when the IMF By value is limited between 0.5 and 2.5 nT, which is the IMF By range when the local time difference between the northern and southern hemisphere foot points is the smallest. The results indicate that ionospheric conductivity associated with solar illumination plays a role in the differences in onset time between the northern and southern hemisphere when only non-zero differences in onset time are considered. We validate these results with two other less robust methods. The median value of the differences in onset time indicates that the onsets occur ∼23 s earlier in the winter hemisphere than that in the summer hemisphere. It has been reported that the time difference between the start of the substorm in the magnetotail and the observed auroral break up (substorm auroral onset) in the ionosphere is 30 s to 2 min in the current disruption model and the near earth neutral line model, respectively. Our results may be of interest to those two models.

Enhanced aridification across the Eocene/Oligocene transition evidenced by geochemical record in the Tajik Basin, Central Asia

The Tajik Basin is an intermontane depression between the mountain ranges of Tian Shan, Pamir, and Hindukush, which is located in the northwestern part of the India-Asia collision zone. Due to the westward retreat of the Neotethys Sea, the paleoenvironment of the Tajik Basin has underwent change from a shallow-sea to a continental semiarid land during the Cenozoic era. This implies that the long-term climatic record in the Tajik Basin can potentially reflect the environmental effects of the changed land-sea distributions controlled by plate collision and global eustatic sea-level changes. In this paper, we present new results of stable oxygen and carbon isotopes of carbonates and chemical weathering indices of bulk samples from the Eocene-Oligocene terrestrial strata (ca. 39–30 Ma) in the center of the Tajik Basin. The temporal variations of oxygen and carbon isotopes of carbonates indicate an isotopic shift across the Eocene-Oligocene transition (~34 Ma), characterized by a relatively positive shift due to the isotopic enrichment in authigenic carbonates in an enhanced aridification episode in the Tajik Basin. This shift was also mirrored by the weakened chemical weathering indicated by the ratios of major oxides across the Eocene-Oligocene transition. Such a regional climatic shift was generally coincident with a remarkable global scale sea-level drop. We suggest that the isolated Paratethys Sea, which was mainly driven by global cooling due to the initial formation of the Antarctica Ice-sheet, together with the decreased seawater evaporation due to lower sea surface temperature, reduced water vapor transport by westerlies to the downwind region, and thus intensified the aridification in the Tajik Basin began at ~34 Ma. • Reconstructed paleoclimatic record between ~39 and 30 Ma in Central Tajik Basin. • Stable isotopes and chemical weathering indices reveal enhanced aridity at ~34 Ma. • Regression of the Paratethys played a major role in reducing moisture transport.

Detection of Surface Crevasses over Antarctic Ice Shelves Using SAR Imagery and Deep Learning Method

Crevasses are formed by glacier movement and the stresses within glacier ice. Knowledge of the crevasses’ distribution is critical for understanding the glacier and ice shelf stability. In this study, we propose an automated crevasse extraction framework based on Sentinel-1 SAR imagery and an improved U-Net network. The spatial distribution of crevasses on Antarctic ice shelves in 2020 was mapped with a spatial resolution of ~40 m, and the characteristics of crevasses on the Nickerson Ice Shelf, Jelbart Ice Shelf, Amery Ice Shelf, Thwaites Glacier, and Shackleton Ice Shelf were analyzed. The results indicated the extraction accuracy of our method was 84.2% and the F1 score was 72.5%. Compared with previous published studies, the identification of the crevasse areas had good visual consistency. However, in some scenes, the recall rate was relatively lower due to the quality of the SAR image, terrain surrounding the crevasses, and observation geometry. The crevasses on different ice shelves had different characteristics in terms of length, density, type, and spatial pattern, implying the different stress structures of ice shelves. The Thwaites Glacier and the Nickerson Ice Shelf in the West Antarctica Ice Sheet (WAIS) had shorter ice crevasses, whereas the lengths of ice crevasses on the Jelbart Ice Shelf and the Amery Ice Shelf in the East Antarctica Ice Sheet (EAIS) were relatively long. Nevertheless, there are more closely spaced crevasses on the ice shelf in WAIS compared to that in the EAIS. For the distribution of crevasse types, the Nickerson Ice Shelf and the Shackleton Ice Shelf had various forms of crevasses. There were mainly transverse crevasses developed on the Jelbart Ice Shelf and the Amery Ice Shelf. This study provides a helpful reference and guidance for automated crevasse extraction. The method proposed by this study manifests great application potential and the efficacy of producing a time-series crevasse data set with higher spatial resolution and larger coverage. In the future, more Sentinel-1 SAR imagery will be applied and the effect of temporal and spatial variations in crevasses on the stability of ice shelves will be investigated, which will contribute to project the ice shelf stability and explore the sea level rise implications of recent and future cryosphere changes.

The geoPebble System: Design and Implementation of a Wireless Sensor Network of GPS-Enabled Seismic Sensors for the Study of Glaciers and Ice Sheets

The geoPebble system is a network of wirelessly interconnected seismic and GPS sensor nodes with geophysical sensing capabilities for the study of ice sheets in Antarctica and Greenland, as well as mountain glaciers. We describe our design methodology, which has enabled us to develop these state-of-the art units using commercial-off-the-shelf hardware combined with custom-designed hardware and software. Each geoPebble node is a self-contained, wirelessly connected sensor for collecting seismic activity and position information. Each node is built around a three-component seismic recorder, which includes an amplifier, filter, and 24-bit analog-to-digital converter that can sample incoming seismic signals up to 10 kHz. The timing for each node is available from GPS measurements and a local precision oscillator that is conditioned by the GPS timing pulses. In addition, we record the carrier-phase measurement of the L1 GPS signal in order to determine location at sub-decimeter accuracy (relative to other geoPebble nodes within a radius of a few kilometers). Each geoPebble includes 32 GB of solid-state storage, wireless communications capability to a central supervisory unit, and auxiliary measurements capability (including tilt from accelerometers, absolute orientation from magnetometers, and temperature). The geoPebble system has been successfully validated in the field in Antarctica and Greenland.

Detrital geochronology and lithologic signatures of Weddell Sea Embayment ice streams, Antarctica—Implications for subglacial geology and ice sheet history

ABSTRACT Tills from moraines adjacent to major ice streams of the Weddell Sea Embayment contain distinct detrital zircon (n = 5304) and K-bearing mineral age populations (n = 323) that, when combined with pebble composition data, can be used to better understand Antarctica's subglacial geology and ice sheet history. Till representing the Institute, Foundation, Academy, Recovery and Slessor Ice Streams each have distinct detrital zircon age populations. Detrital Ar-Ar ages are mostly younger than zircon ages, and distinctive populations include 270–300 Ma (Institute), 170–190 Ma (Foundation), and 1200–1400 Ma (Recovery), which are not easily explained by known outcrops. Pebble fractions of the Foundation and Academy tills are most diverse with up to &amp;gt;40% exotic erratics. The southern side of the Recovery Glacier has fossiliferous limestone erratics. Mixing models created using a nonlinear squares curve-fitting approach were developed to evaluate contributors of zircons to Foundation Ice Stream till. These model results and pebble lithology data both indicate that unexposed (subglacial) bedrock is mixed with exposed rocks to produce the observed till. Notably, the model required limited local Patuxent Formation input to the Foundation till's zircon population. Our data suggest that sandstones underlie the Foundation Ice Stream and Recovery Glacier troughs, which has a bearing on basal ice flow conditions and results in geological controls on ice stream location. This geo- and thermo-chronological characterization of the ice streams will enable ice-rafted debris in Weddell Sea marine sediments to be traced back to its sources and interpreted in terms of ice stream dynamics.