Ice core evidence for a recent increase in snow accumulation in coastal Dronning Maud Land, East Antarctica

Abstract. Ice cores provide temporal records of snow accumulation, a crucial component of Antarctic mass balance. Coastal areas are particularly under-represented in such records, despite their relatively high and sensitive accumulation rates. Here we present records from a 120 m ice core drilled on Derwael Ice Rise, coastal Dronning Maud Land (DML), East Antarctica in 2012. We date the ice core bottom back to 1745 ± 2 AD. δ18O and δD stratigraphy is supplemented by discontinuous major ion profiles, and verified independently by electrical conductivity measurements (ECM) to detect volcanic horizons. The resulting annual layer history is combined with the core density profile to calculate accumulation history, corrected for the influence of ice deformation. The mean long-term accumulation is 0.425 ± 0.035 m water equivalent (w.e.) a−1 (average corrected value). Reconstructed annual accumulation rates show an increase from 1955 onward to a mean value of 0.61 ± 0.02 m w.e. a−1 between 1955 and 2012. This trend is compared to other reported accumulation data in Antarctica, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model demonstrates that sea ice and atmospheric patterns largely explain the accumulation variability. This is the first and longest record from a coastal ice core in East Antarctica showing a steady increase during the 20th and 21st centuries, thereby supporting modelling predictions.

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Reconstructing Antarctic snow accumulation using nitrogen isotopes of nitrate

10.5194/egusphere-egu21-672 ◽

2021 ◽

Author(s):

Pete D. Akers ◽

Joël Savarino ◽

Nicolas Caillon ◽

Mark Curran ◽

Tas Van Ommen

Keyword(s):

Nitrogen Isotopes ◽

Full Range ◽

Ice Core ◽

Ice Cores ◽

Snow Accumulation ◽

East Antarctica ◽

Accumulation Rates ◽

Sea Levels ◽

Antarctic Snow ◽

Parallel Reconstruction

Precise Antarctic snow accumulation estimates are needed to understand past and future changes in global sea levels, but standard reconstructions using water isotopes suffer from competing isotopic effects external to accumulation. We present here an alternative accumulation proxy based on the post-depositional photolytic fractionation of nitrogen isotopes (d15N) in nitrate. On the high plateau of East Antarctica, sunlight penetrating the uppermost snow layers converts snow-borne nitrate into nitrogen oxide gas that can be lost to the atmosphere. This nitrate loss favors 14NO3- over 15NO3-, and thus the d15N of nitrate remaining in the snow will steadily increase until the nitrate is eventually buried beneath the reach of light. Because the duration of time until burial is dependent upon the rate of net snow accumulation, sites with lower accumulation rates have a longer burial wait and thus higher d15N values. A linear relationship (r2 = 0.86) between d15N and net accumulation-1 is calculated from over 120 samples representing 105 sites spanning East Antarctica. These sites largely encompass the full range of snow accumulation rates observed in East Antarctica, from 25 kg m-2 yr-1 at deep interior sites to >400 kg m-2 yr-1 at near coastal sites. We apply this relationship as a transfer function to an Aurora Basin ice core to produce a 700-year record of accumulation changes. Our nitrate-based estimate compares very well with a parallel reconstruction for Aurora Basin that uses volcanic horizons and ice-penetrating radar. Continued improvements to our database may enable precise independent estimates of millennial-scale accumulation changes using deep ice cores such as EPICA Dome C and Beyond EPICA-Oldest Ice.

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Spatial and temporal distributions of surface mass balance between Concordia and Vostok stations, Antarctica from combined radar and ice core data: First results and detailed error analysis

10.5194/tc-2017-104 ◽

2017 ◽

Author(s):

Emmanuel Le Meur ◽

Olivier Magand ◽

Laurent Arnaud ◽

Michel Fily ◽

Massimo Frezzotti ◽

...

Keyword(s):

Error Analysis ◽

Ice Core ◽

Temporal Trends ◽

Ice Cores ◽

Snow Accumulation ◽

Steady Increase ◽

Time Averaging ◽

Accumulation Rates ◽

Accumulation Pattern ◽

Antarctic Plateau

Abstract. Results from Ground Penetrating Radar (GPR) measurements and shallow ice cores carried out during a scientific traverse between Dome Concordia (DC) and Vostok stations are presented in order to infer both spatial and temporal characteristics of snow accumulation over the East Antarctic plateau. Spatially continuous accumulation rates along the traverse are computed from the identification of three equally spaced radar reflections spanning about the last 600 yr. Accurate dating of these Internal Reflection Horizons (IRHs) is obtained from a depth-age relationship derived from volcanic horizons and bomb testing fallout on a DC ice core and shows a very good consistency when tested against extra ice cores drilled along the radar profile. Accumulation rates are then inferred by accounting for density profiles down to each IRH. For this latter purpose, a careful error analysis showed that using a single and more accurate density profile along a DC core provided more reliable results than trying to include the potential spatial variability in density from extra (but less accurate) ice cores distributed along the profile. The most striking feature is an accumulation pattern that remains constant through time with persistent gradients such as a marked decrease from 26 mm w.e. yr−1 at DC to 20 mm w.e. yr−1 at the South West end of the profile over the last 234 yr average (with a similar decrease from 25 mm w.e. yr−1 to 19 mm w.e. yr−1 over the last 592 yr). Insights into the time-dependency reveal a steady increase of accumulation on the East Antarctic plateau during the last 600 yr and more particularly since about 200 yr as already suggested by previous studies relying on GPR and/or time markers in ice cores. Maximum margins of error are in the range 4 mm w.e. yr−1 (last 234 yr) to 2 mm w.e. yr−1 (last 592 yr), a decrease with depth mainly resulting from the time-averaging when computing accumulation rates. The gradients proposed in this study remain however significant since only the reduced non systematic component (with regard to space or time) of these error terms has to be considered when interpreting spatial or temporal trends.

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A novel high-resolution laser-melting sampler for discrete analyses of ion concentrations and stable water isotopic compositions in firn and ice cores

10.5194/egusphere-egu21-7935 ◽

2021 ◽

Author(s):

Yuko Motizuki ◽

Yoichi Nakai ◽

Kazuya Takahashi ◽

Junya Hirose ◽

Yu Vin Sahoo ◽

...

Keyword(s):

Ice Core ◽

Ice Cores ◽

Depth Resolution ◽

Climatic Changes ◽

Accumulation Rates ◽

Laser Melting ◽

Ion Concentrations ◽

Annual Layer ◽

Annual Resolution ◽

High Depth

Ice cores preserve past climatic changes and, in some cases, astronomical signals. Here we present a newly developed automated ice-core sampler that employs laser melting. A hole in an ice core approximately 3 mm in diameter is melted and heated well below the boiling point by laser irradiation, and the meltwater is simultaneously siphoned by a 2 mm diameter movable evacuation nozzle that also holds the laser fiber. The advantage of sampling by laser melting is that molecular ion concentrations and stable water isotope compositions in ice cores can be measured at high depth resolution, which is advantageous for ice cores with low accumulation rates. This device takes highly discrete samples from ice cores, attaining depth resolution as small as ~3 mm with negligible cross contamination; the resolution can also be set at longer lengths suitable for validating longer-term profiles of various ionic and water isotopic constituents in ice cores. This technique allows the detailed reconstruction of past climatic changes at annual resolution and the investigation of transient ionic and isotopic signals within single annual layers in low-accumulation cores, potentially by annual layer counting.

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Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability

10.5194/cp-2021-7 ◽

2021 ◽

Author(s):

Yuzhen Yan ◽

Nicole E. Spaulding ◽

Michael L. Bender ◽

Edward J. Brook ◽

John A. Higgins ◽

...

Keyword(s):

Accumulation Rate ◽

Ice Cores ◽

Snow Accumulation ◽

East Antarctica ◽

Ice Age ◽

Accumulation Rates ◽

Last Interglacial ◽

Ice Shelf ◽

Ross Ice Shelf ◽

Victoria Land

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in Southern Victoria Land ~80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 and 116 thousand years before present (ka) to infer moisture transport into the region. The accumulation rate is based on the ice age-gas age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields a six-fold increase in the accumulation rate in the LIG, whereas other Antarctic ice cores are typically characterized by a glacial-interglacial difference of a factor of two to three. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size, and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.

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On the occurrence of annual layers in Dome Fuji ice core early Holocene ice

Climate of the Past ◽

10.5194/cp-11-1127-2015 ◽

2015 ◽

Vol 11 (9) ◽

pp. 1127-1137 ◽

Cited By ~ 5

Author(s):

A. Svensson ◽

S. Fujita ◽

M. Bigler ◽

M. Braun ◽

R. Dallmayr ◽

...

Keyword(s):

Ice Core ◽

Flow Analysis ◽

Ice Cores ◽

Snow Accumulation ◽

Early Holocene ◽

High Temporal Resolution ◽

High Accumulation ◽

Data Set ◽

Antarctic Plateau ◽

Annual Layer

Abstract. Whereas ice cores from high-accumulation sites in coastal Antarctica clearly demonstrate annual layering, it is debated whether a seasonal signal is also preserved in ice cores from lower-accumulation sites further inland and particularly on the East Antarctic Plateau. In this study, we examine 5 m of early Holocene ice from the Dome Fuji (DF) ice core at a high temporal resolution by continuous flow analysis. The ice was continuously analysed for concentrations of dust, sodium, ammonium, liquid conductivity, and water isotopic composition. Furthermore, a dielectric profiling was performed on the solid ice. In most of the analysed ice, the multi-parameter impurity data set appears to resolve the seasonal variability although the identification of annual layers is not always unambiguous. The study thus provides information on the snow accumulation process in central East Antarctica. A layer counting based on the same principles as those previously applied to the NGRIP (North Greenland Ice core Project) and the Antarctic EPICA (European Project for Ice Coring in Antarctica) Dronning Maud Land (EDML) ice cores leads to a mean annual layer thickness for the DF ice of 3.0 ± 0.3 cm that compares well to existing estimates. The measured DF section is linked to the EDML ice core through a characteristic pattern of three significant acidity peaks that are present in both cores. The corresponding section of the EDML ice core has recently been dated by annual layer counting and the number of years identified independently in the two cores agree within error estimates. We therefore conclude that, to first order, the annual signal is preserved in this section of the DF core. This case study demonstrates the feasibility of determining annually deposited strata on the central East Antarctic Plateau. It also opens the possibility of resolving annual layers in the Eemian section of Antarctic ice cores where the accumulation is estimated to have been greater than in the Holocene.

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Atmospheric history of carbon monoxide since preindustrial times reconstructed from multiple Greenland ice cores

10.5194/egusphere-egu21-10171 ◽

2021 ◽

Author(s):

Xavier Faïn ◽

Rachael Rhodes ◽

Philip Place ◽

Vasilii Petrenko ◽

Kévin Fourteau ◽

...

Keyword(s):

Carbon Monoxide ◽

High Resolution ◽

Ice Core ◽

Ice Cores ◽

Snow Accumulation ◽

Absolute Calibration ◽

Chemical Compositions ◽

Accumulation Rates ◽

Mixing Ratios ◽

Enhanced Absorption

Carbon monoxide (CO) is a regulated pollutant and one of the key components determining the oxidizing capacity of the atmosphere. Obtaining a reliable record of atmospheric CO mixing ratios since pre-industrial times is necessary to evaluate climate-chemistry models in conditions different from today. We present high-resolution measurements of CO mixing ratios from ice cores drilled at five different sites on the Greenland ice sheet which experience a range of snow accumulation rates, mean surface temperatures, and different chemical compositions. An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) was coupled to continuous melter systems and operated during four analytical campaigns conducted between 2013 and 2019. The CFA-based CO measurements exhibit excellent external precision (ranging 3.3 - 6.6 ppbv, 1&#963;), and achieve consistently low blanks (ranging from 4.1&#177;1.2 to 12.6&#177;4.4 ppbv). Good accuracy and absolute calibration of CFA-based CO records enable paleo-atmospheric interpretations. The five CO records all exhibit variability in CO mixing ratios that is too large and rapid to reflect past atmospheric mixing ratio changes. Complementary tests conducted on discrete ice samples demonstrate that such patterns are not related to the analytical process (i.e., production of CO from organics in the ice during melting), but very likely are related to in situ CO production within the ice before analyses. Evaluation of signal resolution and co-investigation of high-resolution records of CO and TOC show that past atmospheric CO concentration can be extracted from the records&#8217; baselines at four sites with accumulation rates higher than 20 cm water equivalent per year (weq yr-1). However, such baselines should be taken as upper bounds of past atmospheric CO burden. CO records from four sites are combined to produce a multisite average ice core reconstruction of past atmospheric CO for the Northern Hemisphere high latitudes, covering the period from 1700 to 1957 CE. From 1700 to 1875 CE, this record reveals stable or slightly increasing values remaining in the 100-115 ppbv range. From 1875 to 1957 CE, the record indicates a monotonic increase from 114&#177;4 ppbv to 147&#177;6 ppbv. The ice-core multisite CO record exhibits an excellent overlap with the atmospheric CO record from Greenland firn air which span the 1950-2010 time period. The combined ice-core and firn air CO history, spanning 1700-2010 CE, largely exhibits patterns that are consistent with the recent anthropogenic and biomass burning CO emission inventories. This brand new time series will be compared with the most recent results from Earth System Models involved in the CMIP6-AerChemMIP multi-model exercise.

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Iron in ice cores from Law Dome, East Antarctica: implications for past deposition of aerosol iron

Annals of Glaciology ◽

10.3189/s0260305500017742 ◽

1998 ◽

Vol 27 ◽

pp. 365-370 ◽

Cited By ~ 24

Author(s):

R. Edwards ◽

P. N. Sedwick ◽

Vin Morgan ◽

C. F. Boutron ◽

S. Hong

Keyword(s):

Southern Ocean ◽

Late Holocene ◽

Ice Core ◽

Iron Concentration ◽

Ice Cores ◽

Snow Accumulation ◽

East Antarctica ◽

Iron Deposition ◽

Past Century ◽

Preliminary Estimate

Total-dissolvable iron has been measured in sections of three ice cores from Law Dome, East Antarctica, and the results used to calculate atmospheric iron deposition over this region during the late Holocene and to provide a preliminary estimate of aerosol iron deposition during the Last Glaciol Maximum I LGM). Ice-core sections dating from 56-2730 BP (late Holocene) and ~18000 BP (LGM) were decontaminated using trace-metal clean techniques, and total-dissolvable iron was determined in the acidified meltwatcrs by flow-injection analysis. Our results suggest that the atmospheric iron flux onto the Law Dome region has varied significantly over time-scales ranging from seasonal to Glaciol-interglaciol. The iron concentrations in ice-core sections from the past century suggest (1) a 2 4-fold variation in the atmospheric iron flux over a single annual cycle, with the highest flux occurring during the spring and summer, and (2) a nearly 7-fold variation in the annual maximum atmospheric iron flux over a 14 year period. The average estimated atmospheric iron flux calculated from our late-Holocene samples is 0.056-0.14 mg m a−1, which agrees well with Holocene flux estimates derived from aluminium measurements in inland Antarctic ice cores and a recent order-of-magnitude estimate of present-day atmospheric iron deposition over the Southern Ocean. The iron concentration of an ice-corc section dating from the LGM was more than 50 times higher than in the late-Holocene ice samples. Using a snow-accumulation rate estimate of 130 kg m −2 a−1 for this period, we calculate 0.87 mgm −2 a−1 as a preliminary estimate of atmospheric iron deposition during the LGM, which is 6-16 times greater than our average late-Holocene iron flux. Our data are consistent with the suggestion that there was a significantly greater flux of atmospheric iron onto the Southern Ocean during the LGM than during then Holocene.

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A 2000-year annual record of snow accumulation rates for Law Dome, East Antarctica

Climate of the Past ◽

10.5194/cp-11-697-2015 ◽

2015 ◽

Vol 11 (5) ◽

pp. 697-707 ◽

Cited By ~ 18

Author(s):

J. Roberts ◽

C. Plummer ◽

T. Vance ◽

T. van Ommen ◽

A. Moy ◽

...

Keyword(s):

Southern Oscillation ◽

Accumulation Rate ◽

Snow Accumulation ◽

East Antarctica ◽

Accumulation Rates ◽

Annual Layer ◽

Decadal Scale ◽

Ice Sheet Mass Balance ◽

The Law ◽

Rate Profile

Abstract. Accurate high-resolution records of snow accumulation rates in Antarctica are crucial for estimating ice sheet mass balance and subsequent sea level change. Snowfall rates at Law Dome, East Antarctica, have been linked with regional atmospheric circulation to the mid-latitudes as well as regional Antarctic snowfall. Here, we extend the length of the Law Dome accumulation record from 750 years to 2035 years, using recent annual layer dating that extends to 22 BCE. Accumulation rates were calculated as the ratio of measured to modelled layer thicknesses, multiplied by the long-term mean accumulation rate. The modelled layer thicknesses were based on a power-law vertical strain rate profile fitted to observed annual layer thickness. The periods 380–442, 727–783 and 1970–2009 CE have above-average snow accumulation rates, while 663–704, 933–975 and 1429–1468 CE were below average, and decadal-scale snow accumulation anomalies were found to be relatively common (74 events in the 2035-year record). The calculated snow accumulation rates show good correlation with atmospheric reanalysis estimates, and significant spatial correlation over a wide expanse of East Antarctica, demonstrating that the Law Dome record captures larger-scale variability across a large region of East Antarctica well beyond the immediate vicinity of the Law Dome summit. Spectral analysis reveals periodicities in the snow accumulation record which may be related to El Niño–Southern Oscillation (ENSO) and Interdecadal Pacific Oscillation (IPO) frequencies.

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Topographic control of regional accumulation rate variability at South Pole and implications for ice-core interpretation

Annals of Glaciology ◽

10.3189/172756404781814050 ◽

2004 ◽

Vol 39 ◽

pp. 214-218 ◽

Cited By ~ 23

Author(s):

Gordon S. Hamilton

Keyword(s):

Accumulation Rate ◽

Ice Core ◽

Ice Sheet ◽

Ice Cores ◽

Snow Accumulation ◽

Topographic Effects ◽

South Pole ◽

Accumulation Rates ◽

Surface Slope ◽

Ice Dynamics

AbstractSnow-accumulation rates are known to be sensitive to local changes in ice-sheet surface slope because of the effect of katabatic winds. These topographic effects can be preserved in ice cores that are collected at non-ice-divide locations. The trajectory of an ice-core site at South Pole is reconstructed using measurements of ice-sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years. Recent accumulation rates, derived from shallow firn cores, vary along this trajectory according to surface topography, so that on a relatively steep flank mean annual accumulation is ∼18% smaller than on a nearby topographic depression. These modern accumulation rates are used to reinterpret the cause of accumulation rate variability with time in the long ice-core record as an ice-dynamics effect and not a climate-change signal. The results highlight the importance of conducting ancillary ice-dynamics measurements as part of ice-coring programs so that topographic effects can be deconvolved from potential climate signals.

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Snow Accumulation and Oxygen-Isotope Records at the Law Dome Summit, Antarctica (Abstract)

Annals of Glaciology ◽

10.3189/s0260305500006844 ◽

1988 ◽

Vol 11 ◽

pp. 220-220

Author(s):

V. I. Morgan

Keyword(s):

Oxygen Isotope ◽

Isotope Ratio ◽

Meteorological Data ◽

Ice Core ◽

Surface Profile ◽

Correlation Coefficients ◽

Ice Cores ◽

Snow Accumulation ◽

Annual Layer ◽

The Law

At the summit of Law Dome (66°44′S, 112°50′E) the annual snow accumulation is equivalent to 0.7 m of water, and seasonal cycles of oxygen-isotope ratio are preserved clearly in the firn. Isotope-ratio measurements on three 28 m deep ice cores taken 15 m apart near the summit show that although annual layer thicknesses are well correlated between the cores, the actual isotope values (even when averaged over several years’ accumulation) are poorly correlated.Since the three sites must obviously receive the same precipitation, the differences in isotope ratio imply that the amounts of the precipitation retained as accumulation from individual snow-falls throughout the year must vary. The large seasonal variation in isotope ratio then easily accounts for the offsets.In the Law Dome region, precipitation occurs mainly as a result of cyclonic activity in spring, winter and autumn. The stronger winds experienced at these times cause the snow to be formed into large dunes, which are the stable (although moving) surface configuration under these conditions. The movement of dunes by erosion on one face and deposition on the other causes the snow in them to be well mixed. Isotope measurements on a 0.7 m high dune on the inland ice cap showed that it was composed of “winter” snow, with an average isotope value of −28.2% and a range of only 1%. The harder underlying snow had values which varied between −24.2 and −27.4%.During periods of relatively calm or warm conditions the dunes become consolidated and their movement is greatly reduced. Further snow-falls then do not add accumulation to the top and up-wind side of the dunes but tend to fill them in on the down-wind side. In particular it is observed that for Law Dome the surface profile is quite rough in winter and spring, but the more gentle winds and light snow-falls experienced in summer produce a very smooth surface at the beginning of autumn, with all the surface hollows filled in.The ice-core isotope profiles confirm the evenness of the summer accumulation, compared to that of winter. Correlation coefficients are typically 0.26 for the winter minima and 0.65 for the summer peak in isotope ratio. This means that somewhat shorter averaging times can be used when compiling “climatic” records from isotope profiles if only the “summer” isotope values are used. This is useful in comparison of isotopic and meteorological data when only a limited time span is available.Apart from the short-term effects, which can be reduced as desired by longer averaging periods, these core studies also demonstrate how any process which can modulate the precipitation or accumulation will also affect the isotopic composition of the accumulated snow.

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