A new method for high-resolution methane measurements on polar ice cores using continuous flow analysis.

Methane (CH4) is the second most important anthropogenic greenhouse gas in the atmosphere. Rapid variations of the CH4 concentration, as frequently registered, for example, during the last ice age, have been used as reliable time markers for the definition of a common time scale of polar ice cores. In addition, these variations indicate changes in the sources of methane primarily associated with the presence of wetlands. In order to determine the exact time evolution of such fast concentration changes, CH4 measurements of the highest resolution in the ice core archive are required. Here, we present a new, semicontinuous and field-deployable CH4 detection method, which was incorporated in a continuous flow analysis (CFA) system. In CFA, samples cut along the axis of an ice core are melted at a melt speed of typically 3.5 cm/min. The air from bubbles in the ice core is extracted continuously from the meltwater and forwarded to a gas chromatograph (GC) for high-resolution CH4 measurements. The GC performs a measurement every 3.5 min, hence, a depth resolution of 15 cm is achieved atthe chosen melt rate. An even higher resolution is not necessary due to the low pass filtering of air in ice cores caused by the slow bubble enclosure process and the diffusion of air in firn. Reproducibility of the new method is 3%, thus, for a typical CH4 concentration of 500 ppb during an ice age, this corresponds to an absolute precision of 15 ppb, comparable to traditional analyses on discrete samples. Results of CFA-CH4 measurements on the ice core from Talos Dome (Antarctica) illustrate the much higher temporal resolution of our method compared with established melt-refreeze CH4 measurements and demonstrate the feasibility of the new method.

Continuous flow analysis of total organic carbon in polar ice cores.

Ice cores are a widely used archive to reconstruct past changes of the climate system. This is done by measuring the concentration of substances in the ice and in the air of bubbles enclosed in ice. Some species pertaining to the carbon cycle (e.g., CO2, CH4) are routinely measured. However, information about the organic fraction of the impurities in polar ice is still very limited. Therefore, we developed a new method to determine the content of total organic carbon (TOC) in ice cores using a continuous flow analysis (CFA) system. The method is based on photochemical oxidation of TOC and the electrolytic quantification of the CO2 produced during oxidation. The TOC instrument features a limit of detection of 2 ppbC and a response time of 60 s at a sample flow rate of 0.7 mL/min and a linear measurement range of 2-4000 ppbC. First measurements on the ice core from Talos Dome, Antarctica, reveal TOC concentrations varying between 80 and 360 ppbC in the 20 m section presented.

An improved continuous flow analysis system for high-resolution field measurements on ice cores.

Continuous flow analysis (CFA) is a well-established method to obtain information about impurity contents in ice cores as indicators of past changes in the climate system. A section of an ice core is continuously melted on a melter head supplying a sample water flow which is analyzed online. This provides high depth and time resolution of the ice core records and very efficient sample decontamination as only the inner part of the ice sample is analyzed. Here we present an improved CFA system which has been totally redesigned in view of a significantly enhanced overall efficiency and flexibility, signal quality, compactness, and ease of use. These are critical requirements especially for operations of CFA during field campaigns, e.g., in Antarctica or Greenland. Furthermore, a novel deviceto measure the total air content in the ice was developed. Subsequently, the air bubbles are now extracted continuously from the sample water flow for subsequent gas measurements.

Proxies and measurement techniques for mineral dust in Antarctic ice cores.

To improve quantitative interpretation of ice core aeolian dust records, a systematic methodological comparison was made. This involved methods for water-insoluble particle counting (Coulter counter and laser-sensing particle detector), soluble ion analysis (ion chromatography and continuous flow analysis), elemental analysis (inductively coupled plasma mass spectroscopy at pH 1 and after full acid digestion), and water-insoluble elemental analysis (proton induced X-ray emission). Antarctic ice core samples covering the last deglaciation from the EPICA Dome C (EDC) and the EPICA Dronning Maud Land (EDML) cores were used. All methods correlate very well among each other, but the ratios of glacial age to Holocene concentrations, which are typically a factor approximately 100, differ between the methods by up to a factor of 2 with insoluble particles showing the largest variability. The recovery of ICP-MS measurements depends on the digestion method and is differentfor different elements and during different climatic periods. EDC and EDML samples have similar dust composition, which suggests a common dust source or a common mixture of sources for the two sites. The analyzed samples further reveal a change of dust composition during the last deglaciation.

Eight glacial cycles from an Antarctic ice core.

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long--28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.