Centre for Ice and Climate's Unique Solution for Ice Cores

Centre for Ice and Climate's Unique Solution for Ice Cores

CFA Lab at NEEM
CFA Lab at NEEM

The Centre for Ice and Climate at the University of Copenhagen in Denmark is one of the birthplaces of ice core science.  In 1954 Willi Dansgaard [1] suggested the correlation between the oxygen isotope ratio and temperature at which the precipitation was formed and postulated that past climate changes could be discerned by such measurements. Ten years later, in 1964, Willi Dansgaard outlined the capabilities and limitations of the isotopic paleothermometer for glaciological uses in Greenland and Antarctica in a milestone publication in Tellus [2]. Since then stable water isotope ratios have been one of the main paleoclimate proxies used in ice core science, yielding scientific results of high impact [3], [4], [5]. 

The research grew over the years and in 2007 the Centre for Ice and Climate was established. Today the ice core archive at Copenhagen contains 15 kilometers of ice cores from Greenland and other sites.  The centre has developed a climate history tracing the temperature in Greenland and Antarctica back over 100,000 and 800,000 years respectively.  These records are invaluable insights into history and are a critical baseline against which to measure climate change.  One of the most recent research initiatives is the North Greenland Eemian Ice Drilling Project (NEEM) which aimed to reach ice from the Eemian interglacial period which ended nearly 115,000 years ago.  The Eemian period is of particular interest because of the expected similarity in temperature with future climate projections.  After 3 years of drilling the bedrock was reached at a depth of 2.5 kilometers.  Analyzing such quantities of ice poses significant challenges.

Traditionally ice cores have been segmented into sections a few centimeters in length and analyzed as discrete samples—a labor intensive approach with limited temporal resolution.  The amount of ice cores and the desire to fully exploit the temporal resolution of the ice cores make previously used technologies highly impractical.  To overcome these hurdles a new technique was developed by  the stable isotope group of the Center for Ice and Climate. The new technique allows to measure the entire ice core with high precision and temporal resolution by coupling the Picarro L1102-i isotopic water analyzer with the new sample preparation technique.

It takes advantage of the Picarro’s small cavity volume, continuous measurement design, and overall flexibility by coupling the output of a continuous-flow analysis (CFA, University of Bern) system into a vaporizer.  As the ice melts the location in the ice core sample is measured, the resulting liquid is vaporized continuously and sent directly to the Picarro analyzer along with the relative depth in the ice core sample.  In doing so d18O, dD and deuterium excess can be mapped as a function of ice depth (age).  This allows for reconstructing important historical climate information such as the temperature at the point of condensation and source of the water, dating back to over 100,000 years ago. 

While CFA has been used to measure chemical impurities trapped in ice cores, it had not been applied to isotopic analysis previously.  The extremely low sample volume required (~0.1 mL/min) allowed a minute amount of sample to be drawn off from the existing ice core melting apparatus used for other analyses.  This low flow volume is introduced into a simple continuous vaporizer, which instantaneously achieves 100% vaporization to deliver a steady vapor concentration to the Picarro analyzer.  In the recent publication [6], co-authored with the University of Bern Switzerland, an 11,000 year old section of ice core from the NEEM project was analyzed with newly developed technique.  In a period of less than 8 hours a span of 411 years of climate history was analyzed—about 450,000 times faster than it took for the ice sheet to be deposited. 

The combination of high precision and temporal resolution allowed this technique to achieve higher resolution when compared to conventional discrete sampling, a particularly important attribute when studying ice cores with small amplitude high frequency isotopic variations.  This innovative approach, which mathematically accounted for diffusion in the liquid and gas phase and included additional hardware for integrated standards delivery, resulted in an estimated uncertainty of 0.06, 0.2, and 0.5‰ for d18O, dD and deuterium excess, respectively.  This level of precision, coupled with extremely high temporal resolution, opens up new possibilities for ice core science especially for field measurements. 

The analysis took place in the field, in a state of the art laboratory deployed and operated at the NEEM camp in the middle of the Greenland ice sheet, in a science trench 8 meters under the snow surface (see photos above). Adjacent to the chemistry and stable water isotope measurements and in close collaboration, the Greenhouse Gases group of the Centre for Ice and Climate (Prof. T. Blunier) has developed and operated an online system for the measurement of the mixing ratios of the methane gas trapped in the ice core using a modified version of the Picarro G1301 CH4/CO2/H2O analyzer. The system delivers measurements of high precision and unprecedented temporal resolution. The results of this study have been submitted and are currently under review [6].

Vasileios Gkinis, a researcher at the Center for Ice and Climate will visit Picarro later this month as part of a collaborative research project between Picarro and the ice core scientific community.  Look for results from this research to be coming out by the middle of this year.

Learn more about the Centre for Ice and Climate and read their most recent publication.

[1] Dansgaard, W.: The O18-abundance in fresh water. Geochimica et Cosmochimica Acta, 6, 241 – 260, 1954

[2] Dansgaard, W.: Stable isotopes in precipitation. Tellus, 16, 436 – 468, 1964

[3] Dansgaard, W., Clausen, H.B., Gundestrup, N., Hammer, C.U., Johnsen, S.J. and Kristinsdottir, P.M., Reeh, N.: A new Greenland deep ice core. Science, 218, 1273 – 1277, 1982

[4] Johnsen, S. J., Clausen, HB, Dansgaard, W., Fuhrer, K., Gundestrup, N., Hammer, C.U., Iversen, P., Jouzel, J., Stauffer, B., Steffensen, J.P..: Irregular glacial interstadials recorded in a new Greenland ice core. Nature, 359, 311 – 313, 1992.

[5] EPICA community members. Eight glacial cycles from an Antarctic ice core. Nature, 429, 623 – 628, 2004

[6] Gkinis, V., Popp, T. J., Blunier, T., Bigler, M., Schüpbach, S., Kettner, E., Johnsen, S. J.: Water isotopic ratios from a continuously melted ice core sample. Atmospheric Measurement Techniques, 4, 2531 – 2542, 2011

[7] Stowasser, C., Buizert, C., Gkinis, V., Chappellaz, J., Schüpbach, S., Bigler, M., Faïn, X., Sperlich, P., Baumgartner, M., Schilt, A., Blunier, T.: Continuous measurements of methane mixing ratios from ice cores, Atmospheric Measurement Techniques Discussions, 5, 211 – 244, 2012