Supplementary material to "Optimal site selection for a high resolution ice core record in East Antarctica (original) (raw)
Optimal site selection for a high-resolution ice core record in East Antarctica
Climate of the Past, 2016
Ice cores provide some of the best-dated and most comprehensive proxy records, as they yield a vast and growing array of proxy indicators. Selecting a site for ice core drilling is nonetheless challenging, as the assessment of potential new sites needs to consider a variety of factors. Here, we demonstrate a systematic approach to site selection for a new East Antarctic high-resolution ice core record. Specifically, seven criteria are considered: (1) 2000-year-old ice at 300 m depth; (2) above 1000 m elevation; (3) a minimum accumulation rate of 250 mm years<sup>−1</sup> IE (ice equivalent); (4) minimal surface reworking to preserve the deposited climate signal; (5) a site with minimal displacement or elevation change in ice at 300 m depth; (6) a strong teleconnection to midlatitude climate; and (7) an appropriately complementary relationship to the existing Law Dome record (a high-resolution record in East Antarctica). Once assessment of these physical characteris...
Holocene accumulation and ice flow near the West Antarctic Ice Sheet Divide ice-core site
Journal of Geophysical Research: Earth Surface, 2016
The West Antarctic Ice Sheet Divide Core (WDC) provided a high-resolution climate record from near the Ross-Amundsen Divide in Central West Antarctica. In addition, radar-detected internal layers in the vicinity of the WDC site have been dated directly from the ice core to provide spatial variations in the age structure of the region. Using these two data sets together, we first infer a high-resolution Holocene accumulation-rate history from 9.2 kyr of the ice-core timescale and then confirm that this climate history is consistent with internal layers upstream of the core site. Even though the WDC was drilled only 24 km from the modern ice divide, advection of ice from upstream must be taken into account. We evaluate histories of accumulation rate by using a flowband model to generate internal layers that we compare to observed layers. Results show that the centennially averaged accumulation rate was over 20% lower than modern at 9.2 kyr before present (B.P.), increased by 40% from 9.2 to 2.3 kyr B.P., and decreased by at least 10% over the past 2 kyr B.P. to the modern values; these Holocene accumulation-rate changes in Central West Antarctica are larger than changes inferred from East Antarctic ice-core records. Despite significant changes in accumulation rate, throughout the Holocene the regional accumulation pattern has likely remained similar to today, and the ice-divide position has likely remained on average within 5 km of its modern position. Continent-scale ice-sheet models used for reconstructions of West Antarctic ice volume should incorporate this accumulation history.
The Cryosphere, 2016
Ice cores provide temporal records of surface mass balance (SMB). Coastal areas of Antarctica have relatively high and variable SMB, but are under-represented in records spanning more than 100 years. Here we present SMB reconstruction from a 120 m-long ice core drilled in 2012 on the Derwael Ice Rise, coastal Dronning Maud Land, East Antarctica. Water stable isotope (δ 18 O and δD) stratigraphy is supplemented by discontinuous major ion profiles and continuous electrical conductivity measurements. The base of the ice core is dated to AD 1759 ± 16, providing a climate proxy for the past ∼ 250 years. The core's annual layer thickness history is combined with its gravimetric density profile to reconstruct the site's SMB history, corrected for the influence of ice deformation. The mean SMB for the core's entire history is 0.47 ± 0.02 m water equivalent (w.e.) a −1. The time series of reconstructed annual SMB shows high variability, but a general increase beginning in the 20th century. This increase is particularly marked during the last 50 years (1962-2011), which yields mean SMB of 0.61 ± 0.01 m w.e. a −1. This trend is compared with other reported SMB data in Antarctica, generally showing a high spatial variability. Output of the fully coupled Community Earth System Model (CESM) suggests that, although atmospheric circulation is the main factor influencing SMB, variability in sea surface temperatures and sea ice cover in the precipitation source region also explain part of the variability in SMB. Local snow redistribution can also influence interannual variability but is unlikely to influence long-term trends significantly. This is the first record from a coastal ice core in East Antarctica to show an increase in SMB beginning in the early 20th century and particularly marked during the last 50 years.
Glacial-interglacial variations in central East Antarctica ice accumulation rates
2015
Past rates of ice accumulation in central East Antarctica are defined poorly for the Last Glacial period. Ice cores, from which current estimates are based, are limited in number (there is one deep ice core at Vostok Station, one at Dome F and two others currently being extracted at Dome C and Dronning Maud Land), and are restricted spatially (they are one-dimensional). Here, spatial variations in ice accumulation rates during the Last Glacial are calculated from isochronous internal ice sheet layering, measured by airborne ice penetrating radar data. The layers are used to identify the stratigraphy around five East Antarctic ice domes. Isochrons are dated by linking them to the Vostok ice core and, in one case, the EPICA Dome C ice core. This chronostratigraphy allows the depth–age function to be identified across the ice sheet. A simple ice flow model, using the depth–age measurements as input, is then used to determine the spatial and temporal variation in East Antarctic ice accu...
A topographic hinge-zone divides coastal and inland ice dynamic regimes in East Antarctica
Communications Earth & Environment
The impact of late Cenozoic climate on the East Antarctic Ice Sheet is uncertain. Poorly constrained patterns of relative ice thinning and thickening impair the reconstruction of past ice-sheet dynamics and global sea-level budgets. Here we quantify long-term ice cover of mountains protruding the ice-sheet surface in western Dronning Maud Land, using cosmogenic Chlorine-36, Aluminium-26, Beryllium-10, and Neon-21 from bedrock in an inverse modeling approach. We find that near-coastal sites experienced ice burial up to 75–97% of time since 1 Ma, while interior sites only experienced brief periods of ice burial, generally <20% of time since 1 Ma. Based on these results, we suggest that the escarpment in Dronning Maud Land acts as a hinge-zone, where ice-dynamic changes driven by grounding-line migration are attenuated inland from the coastal portions of the East Antarctic Ice Sheet, and where precipitation-controlled ice-thickness variations on the polar plateau taper off towards t...
Geology, 2007
Past changes in East Antarctic Ice Sheet (EAIS) volume are poorly known and diffi cult to measure, yet are critical for predicting the response of the ice sheet to modern climate change. In particular, it is important to identify the sources of sea-level rise since the Last Glacial Maximum (LGM), and ascertain the present-day stability of the world's largest ice sheet. We present altitudinal transects of 10 Be and 26 Al exposure ages across the Framnes Mountains in Mac. Robertson Land that allow the magnitude and timing of EAIS retreat to be quantifi ed. Our data show that the coastal EAIS thinned by at most 350 m in this region during the past 13 k.y. This reduction in ice-sheet volume occurred over a ~5 k.y. period, and the present icesheet profi le was attained ca. 7 ka, in contrast to the West Antarctic Ice Sheet, which continues to retreat today. Combined with regional offshore and terrestrial geologic evidence, our data suggest that the reduction in EAIS volume since the LGM was smaller than that indicated by contemporary ice-sheet models and added little meltwater to the global oceans. Stability of the ice margin since the middle Holocene provides support for the hypothesis that EAIS volume changes are controlled by growth and decay of Northern Hemisphere ice sheets and associated global sea-level changes.
Annals of Glaciology, 2004
Thirteen 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 midlatitudes. 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.