A link between microwave extinction length, firn thermal diffusivity, and accumulation rate in West Antarctica

Abstract. We present a 2700-year annually resolved timescale for the Roosevelt Island Climate Evolution (RICE) ice core, and reconstruct a past snow accumulation history for the coastal sector of the Ross Ice Shelf in West Antarctica. The timescale was constructed by identifying annual layers in multiple ice-core impurity records, employing both manual and automated counting approaches, and constitutes the top part of the Roosevelt Island Ice Core Chronology 2017 (RICE17). The maritime setting of Roosevelt Island results in high sulfate influx from sea salts and marine biogenic emissions, which prohibits a routine detection of volcanic eruptions in the ice-core records. This led to the use of non-traditional chronological techniques for validating the timescale: RICE was synchronized to the WAIS Divide ice core, on the WD2014 timescale, using volcanic attribution based on direct measurements of ice-core acidity, as well as records of globally-synchronous, centennial-scale variability in atmospheric methane concentrations. The RICE accumulation history suggests stable values of 0.25 m water equivalent (w.e.) per year until around 1260 CE. Uncertainties in the correction for ice flow thinning of annual layers with depth do not allow a firm conclusion about long-term trends in accumulation rates during this early period but from 1260 CE to the present, accumulation rate trends have been consistently negative. The decrease in accumulation rates has been increasingly rapid over the last centuries, with the decrease since 1950 CE being more than 7 times greater than the average over the last 300 years. The current accumulation rate of 0.22 ± 0.06 m w.e. yr−1 (average since 1950 CE, ±1σ) is 1.49 standard deviations (86th percentile) below the mean of 50-year average accumulation rates observed over the last 2700 years.

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Climate variability in West Antarctica derived from annual accumulation-rate records from ITASE firn/ice cores

Annals of Glaciology ◽

10.3189/172756404781814447 ◽

2004 ◽

Vol 39 ◽

pp. 585-594 ◽

Cited By ~ 69

Author(s):

Susan Kaspari ◽

Paul A. Mayewski ◽

Daniel A. Dixon ◽

Vandy Blue Spikes ◽

Sharon B. Sneed ◽

...

Keyword(s):

Climate Variability ◽

Moisture Transport ◽

Southern Oscillation ◽

Accumulation Rate ◽

Drainage System ◽

Ice Cores ◽

Cyclonic Activity ◽

West Antarctica ◽

Sea Level Pressure

AbstractThirteen annually resolved accumulation-rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean accumulation since 1970 at each site to the long-term mean indicates an increase in accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean accumulation at most sites. Correlations of the accumulation-rate records with sea-level pressure (SLP) and the SOI suggest that accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in accumulation coupled with strong SLP–accumulation-rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.

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Response times of ice-sheet surface heights to changes in the rate of Antarctic firn compaction caused by accumulation and temperature variations

Journal of Glaciology ◽

10.3189/2015jog14j182 ◽

2015 ◽

Vol 61 (230) ◽

pp. 1037-1047 ◽

Cited By ~ 7

Author(s):

Jun Li ◽

H. Jay Zwally

Keyword(s):

Response Times ◽

Accumulation Rate ◽

Meteorological Data ◽

Climate Data ◽

West Antarctica ◽

Temperature Variations ◽

Depth Profiles ◽

Rates Of Change ◽

Surface Weather ◽

History Of

AbstractVariations in accumulation rate As(t) and temperature Ts(t) at the surface of firn cause changes in the rate of firn compaction (FC) and surface height H(t) that do not involve changes in mass, and therefore need to be accounted for in deriving mass changes from measured H(t). As the effects of changes in As(t) and Ts(t) propagate into the firn, the FC rate is affected with a highly variable and complex response time. The H(t) during measurement periods depend on the history of As(t) and Ts(t) prior to the measurements. Consequently, knowledge of firn response times to climate perturbations is important to estimate the required length of the time series of As(t) and Ts(t) used in FC models. We use our numerical FC model, which is time-dependent on both temperature and accumulation rate, to examine the response times of both H(t) and the rates of change dH(t)/dt to variations in As(t) and Ts(t) using sample perturbations and climate data for selected sites in Antarctica. Our results show that the response times for dH(t)/dt, which are of particular interest, are much shorter than the responses of H(t). Typical response times of dH(t)/dt are from several years to <20 years. The response times are faster in warmer and higher-accumulation areas such as Byrd Station, West Antarctica (4 years), and slower in colder and lower-accumulation areas such as Vostok, East Antarctica (18 years). The response times to temperature are much faster (0.9 year at Byrd and 2.2 years at Vostok), but the corresponding height changes persist much longer. The associated variations in firn density are significantly preserved in the density–depth profiles. For typical fluctuations of surface weather, the Ts(t) from satellite observations since 1982 and As(t) from meteorological data since 1979 are essentially of sufficient length to correct for FC height changes for measurements beginning in 1992.

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Stratigraphic continuity in 400MHz short-pulse radar profiles of firn in West Antarctica

Annals of Glaciology ◽

10.3189/172756404781813925 ◽

2004 ◽

Vol 39 ◽

pp. 195-200 ◽

Cited By ~ 43

Author(s):

Steven A. Arcone ◽

Vandy B. Spikes ◽

Gordon S. Hamilton ◽

Paul A. Mayewski

Keyword(s):

Short Pulse ◽

Accumulation Rate ◽

High Density ◽

Thin Layers ◽

East Antarctica ◽

Relative Amplitude ◽

Accumulation Rates ◽

West Antarctica ◽

Constructive Interference ◽

Pulse Radar

AbstractWe track dated firn horizons within 400 MHz short-pulse radar profiles to find the continuous extent over which they can be used as historical benchmarks to study past accumulation rates in West Antarctica. The 30–40cm pulse resolution compares with the accumulation rates of most areas. We tracked a particular set that varied from 30 to 90 m in depth over a distance of 600 km. The main limitations to continuity are fading at depth, pinching associated with accumulation rate differences within hills and valleys, and artificial fading caused by stacking along dips. The latter two may be overcome through multi-kilometer distances by matching the relative amplitude and spacing of several close horizons, along with their pulse forms and phases. Modeling of reflections from thin layers suggests that the – 37 to – 50 dB range of reflectivity and the pulse waveforms we observed are caused by the numerous thin ice layers observed in core stratigraphy. Constructive interference between reflections from these close, high-density layers can explain the maintenance of reflective strength throughout the depth of the firn despite the effects of compaction. The continuity suggests that these layers formed throughout West Antarctica and possibly into East Antarctica as well.

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

Journal of Glaciology ◽

10.3189/002214311797409677 ◽

2011 ◽

Vol 57 (204) ◽

pp. 629-638 ◽

Cited By ~ 14

Author(s):

J.M. Fegyveresi ◽

R.B. Alley ◽

M.K. Spencer ◽

J.J. Fitzpatrick ◽

E.J. Steig ◽

...

Keyword(s):

Late Holocene ◽

Accumulation Rate ◽

Ice Core ◽

Temperature History ◽

Flow Density ◽

Number Density ◽

West Antarctica ◽

Surface Cooling ◽

Bubble Number ◽

Bubble Number Density

AbstractA surface cooling of ∼1.7°C 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. Number-density 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 ∼1.7°C 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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A time marker at 17.5 kyr BP detected throughout West Antarctica

Annals of Glaciology ◽

10.3189/172756405781813348 ◽

2005 ◽

Vol 41 ◽

pp. 47-51 ◽

Cited By ~ 24

Author(s):

Robert W. Jacobel ◽

Brian C. Welch

Keyword(s):

Accumulation Rate ◽

Ice Sheet ◽

Weddell Sea ◽

West Antarctica ◽

Layer Depth ◽

Time Marker ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Siple Dome

AbstractDeep radar soundings as part of the International Trans-Antarctic Scientific Expedition (US-ITASE) traverses in West Antarctica have revealed a bright internal reflector that we have imaged throughout widespread locations across the ice sheet. The layer is seen in traverses emanating from Byrd Station in four directions and has been traced continuously for distances of 535km toward the Weddell Sea drainage, 500km toward South Pole, 150km toward the Executive Committee Range and 160km toward Kamb Ice Stream (former Ice Stream C). The approximate area encompassed by the layer identified in these studies is 250 000km2. If the layer identification can also be extended to Siple Dome where we have additional radar soundings (Jacobel and others, 2000), the approximate area covered would increase by 50%. In many locations echo strength from the layer rivals the bed echo in amplitude even though it generally lies at a depth greater than half the ice thickness. At Byrd Station, where the layer depth is 1260 m, an age of ~17.5 kyr BP has been assigned based on the Blunier and Brook (2001) chronology. Hammer and others (1997) note that the acidity at this depth is >20 times the amplitude of any other part of the core. The depiction of this strong and widespread dated isochrone provides a unique time marker for much of the ice in West Antarctica. We apply a layer-tracing technique to infer the depth–time scale at the inland West Antarctic ice sheet divide and use this in a simple model to estimate the average accumulation rate.

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A 2700-year annual timescale and accumulation history for an ice core from Roosevelt Island, West Antarctica

Climate of the Past ◽

10.5194/cp-15-751-2019 ◽

2019 ◽

Vol 15 (2) ◽

pp. 751-779 ◽

Cited By ~ 9

Author(s):

Mai Winstrup ◽

Paul Vallelonga ◽

Helle A. Kjær ◽

Tyler J. Fudge ◽

James E. Lee ◽

...

Keyword(s):

Sea Ice ◽

Accumulation Rate ◽

Ice Core ◽

Snow Accumulation ◽

Accumulation Rates ◽

West Antarctica ◽

Sea Ice Extent ◽

Amundsen Sea ◽

The Core ◽

Accumulation History

Abstract. We present a 2700-year annually resolved chronology and snow accumulation history for the Roosevelt Island Climate Evolution (RICE) ice core, Ross Ice Shelf, West Antarctica. The core adds information on past accumulation changes in an otherwise poorly constrained sector of Antarctica. The timescale was constructed by identifying annual cycles in high-resolution impurity records, and it constitutes the top part of the Roosevelt Island Ice Core Chronology 2017 (RICE17). Validation by volcanic and methane matching to the WD2014 chronology from the WAIS Divide ice core shows that the two timescales are in excellent agreement. In a companion paper, gas matching to WAIS Divide is used to extend the timescale for the deeper part of the core in which annual layers cannot be identified. Based on the annually resolved timescale, we produced a record of past snow accumulation at Roosevelt Island. The accumulation history shows that Roosevelt Island experienced slightly increasing accumulation rates between 700 BCE and 1300 CE, with an average accumulation of 0.25±0.02 m water equivalent (w.e.) per year. Since 1300 CE, trends in the accumulation rate have been consistently negative, with an acceleration in the rate of decline after the mid-17th century. The current accumulation rate at Roosevelt Island is 0.210±0.002 m w.e. yr−1 (average since 1965 CE, ±2σ), and it is rapidly declining with a trend corresponding to 0.8 mm yr−2. The decline observed since the mid-1960s is 8 times faster than the long-term decreasing trend taking place over the previous centuries, with decadal mean accumulation rates consistently being below average. Previous research has shown a strong link between Roosevelt Island accumulation rates and the location and intensity of the Amundsen Sea Low, which has a significant impact on regional sea-ice extent. The decrease in accumulation rates at Roosevelt Island may therefore be explained in terms of a recent strengthening of the ASL and the expansion of sea ice in the eastern Ross Sea. The start of the rapid decrease in RICE accumulation rates observed in 1965 CE may thus mark the onset of significant increases in regional sea-ice extent.

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Crevasse ages on the northern margin of Ice Stream C, West Antarctica

Annals of Glaciology ◽

10.3189/172756402781817932 ◽

2002 ◽

Vol 34 ◽

pp. 209-216 ◽

Cited By ~ 25

Author(s):

B. E. Smith ◽

N. E. Lord ◽

C. R. Bentley

Keyword(s):

Accumulation Rate ◽

Austral Summer ◽

Radar Data ◽

Internal Layers ◽

West Antarctica ◽

Northern Margin ◽

Southern Margin ◽

Ice Stream ◽

Field Season ◽

Ground Penetrating

AbstractIn the 1997/98 austral summer field season, we conducted a ground-penetrating radar survey on the northern shear margin of Ice Stream C, West Antarctica. The radar data were used to identify features near the surface of the ice, including internal layers and buried crevasses. The survey was intended to determine the variation in the age of buried crevasses along the ice stream. A procedure was developed by which the accumulation rate and the age of buried crevasses can be estimated based on radar records, firn-core measurements and the assumption that the crevasses were once open to the surface. With this method we were able to determine the age of buried crevasses with a standard error of 15–20%. We discuss our new results in conjunction with those of Retzlaff and Bentley (1993) on the southern margin of the ice stream. Typical crevasse ages were found to range from 120 to 200 years, although crevasses in a few areas were significantly younger. The youngest crevasses are at the extreme upstream end of the survey, but the next youngest were found midway along the ice stream. Crevasses upstream and downstream are older, with ages 40–80 years greater than those in the middle. Crevasses on the northern shear margin of tributary C2 were 30–50 years older than those on the southern margin. These patterns of crevassing suggest that variability in shear margin response to changes in ice-stream flow played an essential role in determining the time at which crevassing became inactive.

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The impact of accumulation rate on anisotropy and air permeability of polar firn at a high-accumulation site

Journal of Glaciology ◽

10.3189/002214309789471021 ◽

2009 ◽

Vol 55 (192) ◽

pp. 625-630 ◽

Cited By ~ 21

Author(s):

Maria W. Hörhold ◽

Mary R. Albert ◽

Johannes Freitag

Keyword(s):

Accumulation Rate ◽

Three Dimensional ◽

Air Permeability ◽

West Antarctica ◽

Short Term ◽

Snow Layer ◽

High Accumulation ◽

X Ray ◽

Degree Of Anisotropy ◽

The Impact

AbstractThe first three-dimensional properties of polar firn obtained by X-ray microtomography are used to study the microstructure of snow on a 15 m deep firn core from West Antarctica. The snow is found to undergo coarsening down to approximately 2.5 m depth before grain growth and densification become the prevalent mechanisms of microstructure change. In contrast to previous assumptions, distinct anisotropy of the ice and pore geometry is observed throughout the profile, with a maximum at 2.5 m depth. The air permeability and the degree of anisotropy vary with depth and can be linked to short-term changes in accumulation rate via the residence time for which a certain snow layer stays in the uppermost 2.5 m. Patterns of the degree of anisotropy and air permeability of buried polar firn are relative indicators of past accumulation rates.

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Mass Balance of Ice Stream B, West Antarctica

Annals of Glaciology ◽

10.1017/s0260305500006534 ◽

1988 ◽

Vol 11 ◽

pp. 187-193 ◽

Cited By ~ 71

Author(s):

I. M. Whillans ◽

R. A. Bindschadler

Keyword(s):

Mass Balance ◽

Catchment Area ◽

Accumulation Rate ◽

Katabatic Wind ◽

Stream Velocity ◽

Beta Activity ◽

West Antarctica ◽

Gross Beta ◽

Ice Stream ◽

Ice Stream B

The mass balance of the drainage area of Ice Stream B, West Antarctica, is calculated from new measurements of both discharge and accumulation rate. The discharge is computed for a transverse section near the lower end of the ice stream. Velocities have been obtained for 787 sites, using repeated photogrammetry, with ground control by Transit (doppler) satellite tracking. Thicknesses have been obtained by radio echo-sounding. The uncertainties in the discharge calculations are only about 3%. Net accumulation is derived from profiles of gross beta activity and from identification of the 1954–55 and 1964–65 nuclear-bomb strata. The major uncertainties are associated with the identification of the catchment area and with the accumulation rate. Accumulation rate varies locally, probably due to the interaction of katabatic wind with local slope, and many spot measurements are needed to obtain a good regional mean. The integrated input is 21.4 ± 5.2 km3 a−1, and the output is 30.0 ± 1.0 km3 a−1. The deficit is thus 8.6 ± 6.2 km3 a−1, which corresponds to a mean thinning rate of 0.06 m a−1 ± 0.04 m a−1. The difference from earlier estimates is mainly due to the refined catchment area and accumulation. The imbalance is significant but smaller than previously calculated: for balance the accumulation rate or catchment area would need to be about 39% larger or the ice stream velocity would need to be 28% slower.

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