The Northeast Greenland Ice Stream (NEGIS) is the sole interior Greenlandic ice stream. Fast flow initiates near the summit dome, and the ice stream terminates approximately 1000 km downstream in ...three large outlet glaciers that calve into the Greenland Sea. To better understand this important system, in the summer of 2012 we drilled a 67 m firn core and conducted ground-based radio-echo sounding (RES) and active-source seismic surveys at a site approximately 150 km downstream from the onset of streaming flow (NEGIS firn core, 75°37.61' N, 35°56.49' W). The site is representative of the upper part of the ice stream, while also being in a crevasse-free area for safe surface operations. Annual cycles were observed for insoluble dust, sodium and ammonium concentrations and for electrolytic conductivity, allowing a seasonally resolved chronology covering the past 400 yr. Annual layer thicknesses averaged 0.11 m ice equivalent (i.e.) for the period 1607–2011, although accumulation varied between 0.08 and 0.14 m i.e., likely due to flow-related changes in surface topography. Tracing of RES layers from the NGRIP (North Greenland Ice Core Project) ice core site shows that the ice at NEGIS preserves a climatic record of at least the past 51 kyr. We demonstrate that deep ice core drilling in this location can provide a reliable Holocene and late-glacial climate record, as well as helping to constrain the past dynamics and ice–lithosphere interactions of the Greenland Ice Sheet.
Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from far-field records
are interpreted to reflect the loss of virtually all East Antarctic ice during peak warmth
. ...This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene
. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72-17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution.
Early to Middle Miocene sea-level oscillations of approximately 40-60 m estimated from farfield records 1,2,3 are interpreted to reflect the loss of virtually all East Antarctic ice during peak ...warmth 2. This contrasts with ice-sheet model experiments suggesting most terrestrial ice in East Antarctica was retained even during the warmest intervals of the Middle Miocene 4,5. Data and model outputs can be reconciled if a large West Antarctic Ice Sheet (WAIS) existed and expanded across most of the outer continental shelf during the Early Miocene, accounting for maximum ice-sheet volumes. Here, we provide the earliest geological evidence proving large WAIS expansions occurred during the Early Miocene (~17.72-17.40 Ma). Geochemical and petrographic data show glacimarine sediments recovered at International Ocean Discovery Program (IODP) Site U1521 in the central Ross Sea derive from West Antarctica, requiring the presence of a WAIS covering most of the Ross Sea continental shelf. Seismic, lithological and palynological data reveal the intermittent proximity of grounded ice to Site U1521. The erosion rate calculated from this sediment package greatly exceeds the long-term mean, implying rapid erosion of West Antarctica. This interval therefore captures a key step in the genesis of a marine-based WAIS and a tipping point in Antarctic ice-sheet evolution.
Direct observations of the size of the Greenland Ice Sheet during Quaternary interglaciations are sparse yet valuable for testing numerical models of ice-sheet history and sea level contribution. ...Recent measurements of cosmogenic
nuclides in bedrock from beneath the Greenland Ice Sheet collected during
past deep-drilling campaigns reveal that the ice sheet was significantly
smaller, and perhaps largely absent, sometime during the past 1.1 million
years. These discoveries from decades-old basal samples motivate new,
targeted sampling for cosmogenic-nuclide analysis beneath the ice sheet.
Current drills available for retrieving bed material from the US Ice
Drilling Program require < 700 m ice thickness and a frozen bed,
while quartz-bearing bedrock lithologies are required for measuring a large
suite of cosmogenic nuclides. We find that these and other requirements
yield only ∼ 3.4 % of the Greenland Ice Sheet bed as a
suitable drilling target using presently available technology. Additional
factors related to scientific questions of interest are the following: which areas of the
present ice sheet are the most sensitive to warming, where would a retreating ice
sheet expose bare ground rather than leave a remnant ice cap, and
which areas are most likely to remain frozen bedded throughout glacial
cycles and thus best preserve cosmogenic nuclides? Here we identify
locations beneath the Greenland Ice Sheet that are best suited for potential
future drilling and analysis. These include sites bordering Inglefield Land
in northwestern Greenland, near Victoria Fjord and Mylius-Erichsen Land in
northern Greenland, and inland from the alpine topography along the ice
margin in eastern and northeastern Greenland. Results from cosmogenic-nuclide analysis in new sub-ice bedrock cores from these areas would help to constrain dimensions of the Greenland Ice Sheet in the past.
This study examined the relationship between the degree of sexist beliefs held toward women by male subjects and their perceptions of attractiveness of females described as possessing either ...masculine or feminine personality characteristics. One hundred twenty‐two undergraduate males were given the Macho Scale, the Auburn University Personal Behavior Summary, a biodata sheet, and were asked to judge previously rated photographs of women along a dimension of attractiveness. Results demonstrated that males perceived physically unattractive and average females described as affectionate and compassionate as more attractive than similarly rated females described as independent and assertive. High Macho subjects viewed females as less attractive than low Macho subjects. Physical attractiveness of the male subjects was largely unrelated to their ratings of the females.
We present radio-echo sounding (RES), global positioning system (GPS), and active-source seismic data across the central portion of the Northeast Greenland Ice Stream (NEGIS). NEGIS widens ...downglacier from a small region of high geothermal flux near the ice divide. Our data reveal high-porosity (40+%) water-saturated till lubricating the ice stream. Ice accelerates and thins as it flows into NEGIS, producing marginal troughs in surface topography. These troughs create steep gradients in the subglacial hydropotential that generate parallel “sticky” and “slippery” bands beneath the shear margins. The low-porosity “sticky” sediment bands limit ice entrainment across the margins and thus restrict further widening, producing the long, narrow, and relatively stable ice stream. However, the observed relations among surface elevation, basal water routing, broad sedimentary drape, and till dilatancy suggest that rapid shifts in ice dynamics are possible, including rapid transmission of ocean forcing inland. The source and routing of the subglacial till are unclear, but our data help constrain hypotheses.
•Dilatant till facilitates ice-stream flow in northeast Greenland.•Source and routing of subglacial till are unclear.•Dynamics of ice flow control ice-stream extent.•Rapid shifts in ice dynamics may be possible.
Based on modeling motivated by new GPS and radio‐echo sounding surveys, a few‐kilometers‐long zone of Whillans Ice Stream, West Antarctica, just inland of the grounding line has higher basal shear ...stress than the ice farther upstream or the freely slipping ice shelf downstream. Data from this zone show a few‐meter‐high upwarp of the surface overlying a large fold extending through all internal radar layers observed. Flowband modeling shows that the fold can be generated by decreased basal lubrication beneath the upwarp. Basal topography alone cannot create this fold. Physical modeling and available data suggest that low‐amplitude tidal flexure of the ice shelf extends a few kilometers inland. Downward flexing of this grounded ice from the rising tide would compact subglacial till, resulting in higher basal shear stress. This result suggests that important processes influencing grounding line stability are not included in modern whole‐ice‐sheet models.
Key Points
Radar data depict the grounding line and associated internal layer folding
Fold in radar internal layers can be explained by enhanced basal friction
Enhanced friction is likely due to till compaction from tidal flexure
Past interglacial climates with smaller ice sheets offer analogs for ice sheet response to future warming and contributions to sea level rise; however, well-dated geologic records from formerly ...ice-free areas are rare. Here we report that subglacial sediment from the Camp Century ice core preserves direct evidence that northwestern Greenland was ice free during the Marine Isotope Stage (MIS) 11 interglacial. Luminescence dating shows that sediment just beneath the ice sheet was deposited by flowing water in an ice-free environment 416 ± 38 thousand years ago. Provenance analyses and cosmogenic nuclide data and calculations suggest the sediment was reworked from local materials and exposed at the surface <16 thousand years before deposition. Ice sheet modeling indicates that ice-free conditions at Camp Century require at least 1.4 meters of sea level equivalent contribution from the Greenland Ice Sheet.
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