Recent thinning and migration of the Western Divide, central West Antarctica

Conway, H.; Rasmussen, L. A.

doi:10.1029/2009gl038072

Cited by 39 publications

(73 citation statements)

References 22 publications

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“…Steig and others (2001) also found only small changes at the ice divide for a variety of model initial conditions. Strong conclusions should not be drawn from these modeling results, but they support our extrapolation from the data of Conway and Rasmussen (2009) that at least half and probably most of the reconstructed cooling represents a climatic change rather than an ice-flow effect.…”

Section: Discussionmentioning

confidence: 59%

“…Conway and Rasmussen (2009;see also Neumann and others, 2008) reported the modern flow velocity at the site as $3 m a -1 , decreasing up-glacier. Thus 2400 year old ice has come from 6-7 km up-glacier where the modern surface elevation is $5 m higher than at the drill site.…”

Section: Discussionmentioning

confidence: 66%

“…Assuming a lapse rate of 18C (100 m) -1 or slightly less, modern ice flow will have introduced an apparent warming of <0.18C over the length of our climate record, small compared to the observed signal. The modern accumulation rate decreases along ice flow in response to regional gradients, so the accumulation for the oldest ice in our sample was almost 5% larger than for the youngest ice (Conway and Rasmussen, 2009). Thus, about one-third of the apparent accumulation-rate change over time may have arisen from flow through the spatial accumulation-rate pattern, with the other two-thirds representing climate change.…”

Section: Discussionmentioning

confidence: 77%

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Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: bubble number-density estimates

et al. 2011

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ABSTRACT. A surface cooling of $ $1.78 8C occurred over the $ $two millennia prior to $ $1700 CE at the West Antarctic ice sheet (WAIS) Divide site, based on trends in observed bubble number-density of samples from the WDC06A ice core, and on an independently constructed accumulation-rate history using annual-layer dating corrected for density variations and thinning from ice flow. Density increase and grain growth in polar firn are both controlled by temperature and accumulation rate, and the integrated effects are recorded in the number-density of bubbles as the firn changes to ice. Numberdensity is conserved in bubbly ice following pore close-off, allowing reconstruction of either paleotemperature or paleo-accumulation rate if the other is known. A quantitative late-Holocene paleoclimate reconstruction is presented for West Antarctica using data obtained from the WAIS Divide WDC06A ice core and a steady-state bubble number-density model. The resultant temperature history agrees closely with independent reconstructions based on stable-isotopic ratios of ice. The $ $1.78C cooling trend observed is consistent with a decrease in Antarctic summer duration from changing orbital obliquity, although it remains possible that elevation change at the site contributed part of the signal. Accumulation rate and temperature dropped together, broadly consistent with control by saturation vapor pressure.

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Section: Discussionmentioning

confidence: 59%

Section: Discussionmentioning

confidence: 66%

Section: Discussionmentioning

confidence: 77%

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Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: bubble number-density estimates

et al. 2011

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“…sites (including WAIS-D) exhibit a lock-in zone, where vertical air movement is largely impeded by low-permeability seasonal layers, yet air samples can still be extracted from the remaining open pores in the intervening layers laid down in the complementary season (Martinerie et al, 1992 (Conway and Rasmussen, 2009). This site was 2 km upwind of the main camp and deep core location, in a previously-undisturbed region.…”

Section: Air Movement In Firnmentioning

confidence: 99%

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

et al. 2011

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Abstract. We sampled interstitial air from the perennial snowpack (firn) at a site near the West Antarctic Ice Sheet Divide (WAIS-D) and analyzed the air samples for a wide variety of gas species and their isotopes. We find limited convective influence (1.4-5.2 m, depending on detection method) in the shallow firn, gravitational enrichment of heavy species throughout the diffusive column in general agreement with theoretical expectations, a ∼ 10 m thick lock-in zone beginning at ∼ 67 m, and a total firn thickness consistent with predictions of Kaspers et al. (2004). Our modeling work shows that the air has an age spread (spectral width) of 4.8 yr for CO 2 at the firn-ice transition. We also find that advection of firn air due to the 22 cm yr −1 ice-equivalent accumulation rate has a minor impact on firn air composition, causing changes that are comparable to other modeling uncertainties and intrinsic sample variability. Furthermore, estimates of age (the gas age/ice age difference) at WAIS-D appear to be largely unaffected by bubble closure above the lock-in zone. Within the lock-in zone, small gas species and their isotopes show evidence of size-dependent fractionation due to permeation through the ice lattice with a size threshold of 0.36 nm, as at other sites. We also see an unequivocal and unprecedented signal of oxygen isotope fractionation within the lock-in zone, which we interpret as the mass-dependent expression of a size-dependent fractionation process.

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“…The surrounding ice lies in a regime of laterally convergent flow -extending across the divide and compressing along it. The Divide is migrating at ∼10 m a -1 (Conway and Rasmussen, 2009), but the strain configuration and ice topography have not changed substantially in the last several thousand years (Matsuoka and others, 2012). Some properties for the borehole are listed in Table 2.…”

Section: Site Characteristicsmentioning

confidence: 99%

Sonic methods for measuring crystal orientation fabric in ice, and results from the West Antarctic ice sheet (WAIS) Divide

et al. 2017

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ABSTRACT. We describe methods for measuring crystal orientation fabric with sonic waves in an ice core borehole, with special attention paid to vertical-girdle fabrics that are prevalent at the WAIS Divide. The speed of vertically propagating compressional waves in ice is influenced by vertical clustering of the ice crystal c-axes. Shear-wave speeds -particularly the speed separation between fast and slow shear polarizations -are sensitive to azimuthal anisotropy. Sonic data from the WAIS Divide complement thin-section measurements of fabric. Thin sections show a steady transition to strong girdle fabrics in the upper 2000 m of ice, followed by a transition to vertical-pole fabrics below 2500 m depth. Compressional-wave sonic data are inconclusive in the upper ice, due to noise, as well as the method's inherent insensitivity to girdle fabrics. Compared with available thin sections, sonic data provide better resolution of the transition to pole fabrics below 2500 m, notably including an abrupt increase in vertical clustering near 3000 m. Our compressional-wave measurements resolve fabric changes occurring over depth ranges of a few meters that cannot be inferred from available thin sections, but are sensitive only to zenithal anisotropy. Future logging tools should be designed to measure shear waves in addition to compressional waves, especially for logging in regions where ice flow patterns favor the development of girdle fabrics.

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Recent thinning and migration of the Western Divide, central West Antarctica

Cited by 39 publications

References 22 publications

Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: bubble number-density estimates

Late-Holocene climate evolution at the WAIS Divide site, West Antarctica: bubble number-density estimates

Controls on the movement and composition of firn air at the West Antarctic Ice Sheet Divide

Sonic methods for measuring crystal orientation fabric in ice, and results from the West Antarctic ice sheet (WAIS) Divide

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