Snow Densification and Recent Accumulation Along the iSTAR Traverse, Pine Island Glacier, Antarctica

TY - JOUR

T1 - Snow Densification and Recent Accumulation Along the iSTAR Traverse, Pine Island Glacier, Antarctica

AU - Morris, Edward

AU - Mulvaney, R.

AU - Arthern, R.J.

AU - Davies, D.

AU - Gurney, Robert J.

AU - Lambert, Patricia

AU - De Rydt, J.

AU - Smith, A. M.

AU - Tuckwell, R.J.

AU - Winstrup, Mai

PY - 2017/12

Y1 - 2017/12

N2 - Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual layer identification routine. A mean density profile which can be used to convert radar two-way travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain-boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10–14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence.

AB - Neutron probe measurements of snow density from 22 sites in the Pine Island Glacier basin have been used to determine mean annual accumulation using an automatic annual layer identification routine. A mean density profile which can be used to convert radar two-way travel times to depth has been derived, and the effect of annual fluctuations in density on estimates of the depth of radar reflectors is shown to be insignificant, except very near the surface. Vertical densification rates have been derived from the neutron probe density profiles and from deeper firn core density profiles available at 9 of the sites. These rates are consistent with the rates predicted by the Herron and Langway model for stage 1 densification (by grain-boundary sliding, grain growth and intracrystalline deformation) and stage 2 densification (predominantly by sintering), except in a transition zone extending from ≈8 to ≈13 m from the surface in which 10–14% of the compaction occurs. Profiles of volumetric strain rate at each site show that in this transition zone the rates are consistent with the Arthern densification model. Comparison of the vertical densification rates and volumetric strain rates indicates that the expected relation to mean annual accumulation breaks down at high accumulation rates even when corrections are made for horizontal ice velocity divergence.

U2 - 10.1002/2017JF004357

DO - 10.1002/2017JF004357

M3 - Journal article

SN - 0148-0227

VL - 122

SP - 2284

EP - 2301

JO - Journal of Geophysical Research

JF - Journal of Geophysical Research

IS - 12

ER -