25,277 research outputs found
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
Core handling and processing for the WAIS Divide ice-core project
On 1 December 2011 the West Antarctic Ice Sheet (WAIS) Divide ice-core project reached its final depth of 3405 m. The WAIS Divide ice core is not only the longest US ice core to date, but is also the highest-quality deep ice core, including ice from the brittle ice zone, that the US has ever recovered. The methods used at WAIS Divide to handle and log the drilled ice, the procedures used to safely retrograde the ice back to the US National Ice Core Laboratory (NICL) and the methods used to process and sample the ice at the NICL are described and discussed
A Comparison Of New Calculations Of The Yearly 10Be Production In The Earths Polar Atmosphere By Cosmic Rays With Yearly 10Be Measurements In Multiple Greenland Ice Cores Between 1939 And 1994 - A Troubling Lack Of Concordance Paper #2
We have compared the yearly production rates of 10Be by cosmic rays in the
Earths polar atmosphere over the last 50-70 years with 10Be measurements from
two separate ice cores in Greenland. These ice cores provide measurements of
the annual 10Be concentration and 10Be flux levels during this time. The
scatter in the ice core yearly data vs. the production data is larger than the
average solar 11 year production variations that are being measured. The cross
correlation coefficients between the yearly 10Be production and the ice core
10Be measurements for this time period are <0.4 in all comparisons between ice
core data and 10Be production, including 10Be concentrations, 10Be fluxes and
in comparing the two separate ice core measurements. In fact, the cross
correlation between the two ice core measurements, which should be measuring
the same source, is the lowest of all, only ~0.2. These values for the
correlation coefficient are all indicative of a "poor" correlation. The
regression line slopes for the best fit lines between the 10Be production and
the 10Be measurements used in the cross correlation analysis are all in the
range 0.4-0.6. This is a particular problem for historical projections of solar
activity based on ice core measurements which assume a 1:1 correspondence. We
have made other tests of the correspondence between the 10Be predictions and
the ice core measurements which lead to the same conclusion, namely that other
influences on the ice core measurements, as large as or larger than the
production changes themselves, are occurring. These influences could be
climatic or instrumentally based. We suggest new ice core measurements that
might help in defining more clearly what these influences are and-if
possible-to correct for them.Comment: 24 pages, 6 figure
A 100-year record of North Pacific volcanism in an ice core from Eclipse icefield, Yukon Territory, Canada
A record of regionally significant volcanic eruptions in the North Pacific over the last century has been developed using a glaciochemical record from Eclipse Icefield, Yukon Territory, Canada. Tephrochronology of the Eclipse ice core provides positive identification of the 1907 Ksudach, Kamchatka, the 1912 Katmai, Alaska, the 1947 Hekla, Iceland, and the 1989 Redoubt, Alaska, eruptions. Non-sea-salt SO42â residuals above a robust spline and empirical orthogonal function (EOF) analysis were used to identify volcanic SO42â signatures. Volcanic sulfate values are more conservatively identified by the EOF analysis as sulfate deposition from other sources is more robustly accounted for. Some eruptions are also recorded as peaks in non-sea-salt chloride. The volcanic signals in the Eclipse ice core are mostly attributable to Alaskan, Aleutian, or Kamchatkan eruptions. Conversely, the Eclipse ice core provides a poor record of globally significant tropical eruptions. These results are promising for the development of longer ice core based records of paleovolcanism in the North Pacific rim
Seasonal deuterium excess in a Tien Shan ice core: Influence of moisture transport and recycling in Central Asia
Stable water isotope (ÎŽ18O, ÎŽD) data from a high elevation (5100 masl) ice core recovered from the Tien Shan Mountains, Kyrgyzstan, display a seasonal cycle in deuterium excess (d = ÎŽD â 8*ÎŽ18O) related to changes in the regional hydrologic cycle during 1994â2000. While there is a strong correlation (r2 = 0.98) between ÎŽ18O and ÎŽD in the ice core samples, the regression slope (6.9) and mean d value (23.0) are significantly different than the global meteoric water line values. The resulting time-series ice core d profile contains distinct winter maxima and summer minima, with a yearly d amplitude of âŒ15â20â°. Local-scale processes that may affect d values preserved in the ice core are not consistent with the observed seasonal variability. Data from Central Asian monitoring sites in the Global Network of Isotopes in Precipitation (GNIP) have similar seasonal d changes. We suggest that regional-scale hydrological conditions, including seasonal changes in moisture source, transport, and recycling in the Caspian/Aral Sea region, are responsible for the observed spatial and temporal d variability
Automated ice-core layer-counting with strong univariate signals
We present an automated process for determining the annual layer chronology of an ice-core with a strong annual signal, utilising the hydrogen peroxide record from an Antarctic Peninsula ice-core as a test signal on which to count annual cycles and explain the methods. The signal is de-trended and normalised before being split into sections with a deterministic cycle count and those that need more attention. Possible reconstructions for the uncertain sections are determined which could be used as a visual aid for manual counting, and a simple method for assigning probability measures to each reconstruction is discussed. The robustness of this process is explored by applying it to versions of two different chemistry signals from the same stretch of the NGRIP (North Greenland Ice Core Project) ice-core, which shows more variation in annual layer thickness, with and without thinning to mimic poorer quality data. An adapted version of these methods is applied to the more challenging non-sea-salt sulphur signal from the same Antarctic Peninsula core from which the hydrogen peroxide signal was taken. These methods could readily be adapted for use on much longer datasets, thereby reducing manual effort and providing a robust automated layer-counting methodology
Anatomy of a Dansgaard-Oeschger warming transition: High-resolution analysis of the North Greenland Ice Core Project ice core
Large and abrupt temperature oscillations during the last glacial period, known as DansgaardâOeschger (DO) events, are clearly observed in the Greenland ice core record. Here we present a new highâresolution chemical (2 mm) and stable isotope (20 mm) record from the North Greenland Ice Core Project (NGRIP) ice core at the onset of one of the most prominent DO events of the last glacial, DOâ8, observed âŒ38,000 years ago. The unique, subannualâresolution NGRIP record provides a true sequence of change during a DO warming with detailed annual layer counting of very high depth resolution geochemical measurements used to determine the exact duration of the transition. The continental ions, indicative of longârange atmospheric loading and dustiness from East Asia, are the first to change, followed by the snow accumulation, the moisture source conditions, and finally the atmospheric temperature in Greenland. The sequence of events shows that atmospheric and oceanic source and circulation changes preceded the DO warming by several years
Depletion of atmospheric nitrate and chloride as a consequence of the Toba Volcanic Eruption
Continuous measurements of SO42â and electrical conductivity (ECM) along the GISP2 ice core record the Toba megaâeruption at a depth 2590.95 to 2091.25 m (71,000±5000 years ago). Major chemical species were analyzed at a resolution of 1 cm per sample for this section. An âŒ6âyear long period with extremely high volcanic SO42â coincident with a 94% depletion of nitrate and 63% depletion of chloride is observed at the depth of the Toba horizon. Such a reduction of chloride in a volcanic layer preserved in an ice core has not been observed in any previous studies. The nearly complete depletion of nitrate (to 5 ppb) encountered at the Toba level is the lowest value in the entire âŒ250,000 years of the GISP2 ice core record. We propose possible mechanisms to explain the depletion of nitrate and chloride resulting from this megaâeruption
Ice cores and SeaRISE: What we do (and don't) know
Ice core analyses are needed in SeaRISE to learn what the West Antarctic ice sheet and other marine ice sheets were like in the past, what climate changes led to their present states, and how they behave. The major results of interest to SeaRISE from previous ice core analyses in West Antarctic are that the end of the last ice age caused temperature and accumulation rate increases in inland regions, leading to ice sheet thickening followed by thinning to the present
Constraining recent lead pollution sources in the North Pacific using ice core stable lead isotopes
Trends and sources of lead (Pb) aerosol pollution in the North Pacific rim of North America from 1850 to 2001 are investigated using a high-resolution (subannual to annual) ice core record recovered from Eclipse Icefield (3017 masl; St. Elias Mountains, Canada). Beginning in the early 1940s, increasing Pb concentration at Eclipse Icefield occurs coevally with anthropogenic Pb deposition in central Greenland, suggesting that North American Pb pollution may have been in part or wholly responsible in both regions. Isotopic ratios (208Pb/207Pb and 206Pb/207Pb) from 1970 to 2001 confirm that a portion of the Pb deposited at Eclipse Icefield is anthropogenic, and that it represents a variable mixture of East Asian (Chinese and Japanese) emissions transported eastward across the Pacific Ocean and a North American component resulting from transient meridional atmospheric flow. Based on comparison with source material Pb isotope ratios, Chinese and North American coal combustion have likely been the primary sources of Eclipse Icefield Pb over the 1970â2001 time period. The Eclipse Icefield Pb isotope composition also implies that the North Pacific mid-troposphere is not directly impacted by transpolar atmospheric flow from Europe. Annually averaged Pb concentrations in the Eclipse Icefield ice core record show no long-term trend during 1970â2001; however, increasing 208Pb/207Pb and decreasing 206Pb/207Pb ratios reflect the progressive East Asian industrialization and increase in Asian pollutant outflow. The post-1970 decrease in North American Pb emissions is likely necessary to explain the Eclipse Icefield Pb concentration time series. When compared with low (lichen) and high (Mt. Logan ice core) elevation Pb data, the Eclipse ice core record suggests a gradual increase in pollutant deposition and stronger trans-Pacific Asian contribution with rising elevation in the mountains of the North Pacific rim
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