CO2 and O2/N2 variations in and just below the bubble–clathrate transformation zone of Antarctic ice cores (original) (raw)
Related papers
Journal of Glaciology, 2008
One common assumption in interpreting ice-core CO2 records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO2 diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO2 associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO2 diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca2+ ion concentrations to show that substantial CO2 diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO2 in ice is ∼4 × 10−21 mol m−1 s−1 Pa−1 at −23°C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO2 record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of ∼930–950 m (∼60–70 kyr) indicate that smoothing of the CO2...
Journal of Geophysical Research, 1996
A record of atmospheric CO 2 mixing ratios from 1006 A.D. to 1978 A.D. has been produced by analysing the air enclosed in three ice cores from Law Dome, Antarctica. The enclosed air has m•paralleled age resolution and extends into recent decades, because of the high rate of snow accumulation at the ice core sites. The CO 2 data overlap with the record from direct atmospheric measurements for up to 20 years. The effects of diffusion in the fun on the CO 2 mixing ratio and age of the ice core air were determined by analyzing air sampled from the surface down to the bubble close-off depth. The uncertainty of the ice core CO 2 mixing ratios is 1.2 ppm (1 o). Preindustrial CO 2 mixh•g ratios were in the range 275-284 ppm, with the lower levels during 1550-1800 A.D., probably as a result of colder global climate. Natural CO 2 variations of this magnitude make it inappropriate to refer to a single preindustrial CO 2 level. Major CO 2 growth occurred over the industrial period except during 1935-1945 A.D. when CO 2 mixing ratios stabilized or decreased slightly, probably as a result of natural variations of the carbon cycle on a decadal timescale. CO 2 levels is required to improve the understanding of the natural and human-perturbed carbon cycle and the climatic impact of CO 2 as a greenhouse gas. Measuring air extracted from polar ice is the most direct way of reconstructing past atmospheric CO 2 mixing ratios. Less direct techniques are based on measurement of the isotopic ratios of carbon preserved in organic matter. They suffer from larger measurement error, uncertainties caused by physiological influences on photosynthetic fractionation, and by the assumptions required to derive atmospheric mixing ratios from isotopic values in a carbon exchange model. Ice cores, in particular those from cold Antarctic sites, offer the following advantages: (1) whole air is enclosed in bubbles in the ice; (2) the ice is a relatively inert storage medium for CO 2 and many other atmospheric trace gases; (3) the enclosed air generally represents the "background" atmosphere, remote from biological or anthropogenic CO 2 sources or sinks; (4) timescales ranging from tens of years to hundreds of thousands of years can be investigated by selecting appropriate sites; and (5) other relevant physical and chemical i•fformation resides in the same stratigraphy, such as trace acids for dating [Hammer, 1980], or water isotopic ratios as climatic indicators (in the case of Law Dome, Morgan [1985]). There are several possible difficulties in the ice technique: (1) reactions involving CO 2 may occur if the ice approaches melting [Neftel et al., 1982], or if it contains high concentrations of impurities, conditions that may have affected the CO 2 in some sections of Greenland ice cores [Delmas, 1993; Staffelbach et al., 1991]; (2) cracks in cores may release air or allow contamination to enter; (3) ice core samples must be carefully refrigerated to avoid post coring melting (PCM) which may change the composition of the air bubbles [Pearman et al., 1986]; (4) the pressure in the ice at about 500 m and deeper may be sufficient (depending on temperature) for the bubbles to disappear and form clathrates 4115 4116 ETHEPdDGE ET AL.: CHANGES IN, CO 2 OVER THE LAST 1000 YEARS [Miller, 1969] which may complicate air extraction; (5) dating the ice by annual stratigraphy becomes difficult at sites with low-accumulation rate or where ice flow disturbs the layered sequence at depth; (6) the age resolution of the enclosed air can be limited by the progressive closure of the air bubbles and, to a lesser degree, diffusion of air from the ice sheet surface through the firn layer to the closure depth; and (7) associated with the diffusion are possible fractionation effects [Craig et al., 1988; Schwander, 1989] which are small for CO 2 mixing ratios but significant at the precision level of carbon isotope ratio measurements. Most of these difficulties can be avoided by appropriate selection of the drilling site and careful handling of the ice sample. Desirable characteristics of ice core sites for CO 2 studies are negligible melting of the ice sheet surface, low concentrations of impurities, regular stratigraphic layering which is undisturbed at the surface by wind or at depth by ice flow, and high snow accumulation rate.
CO2 measurements from polar ice cores: more data from different sites
Tellus B: Chemical and Physical Meteorology, 1991
Air in the bubbles of polar ice has in principal the same composition as the atmospheric air at the time of ice formation. Based on this relationship, an increase in atmospheric C0 2 since the beginning of industrialisation has been documented (Neftel et al., 1985, Pearman et al., 1986) in Antarctic ice cores. It has also been shown that the C0 2 concentration was much lower during the glacial period than in the preindustrial Holocene (Neftel et al., 1982, Barnola et al., 1987). These two results are well established. In this paper, we will discuss possible small deviations of the C0 2 concentration in air bubbles from that of the atmosphere at the time of enclosure. To do this, new results from Crete (Central Greenland) ice cores, covering the period since the beginning of industrialisation are presented, showing a good agreement with the data from Antarctic ice cores. In addition, the record of the atmospheric C0 2 concentration during the transition from the last glaciation to the Holocene and the fast variations in the concentration of atmospheric C0 2 during parts of the last glaciation, as suggested by Greenland ice core data, will be discussed.
CO2 record between 40 and 8 kyr B.P. from the Greenland Ice Core Project ice core
Journal of Geophysical Research, 1997
CO2 ice-core records show an increase in the atmospheric concentration of 80-100 parts per million by volume (ppmv) from the last glacial maximum (LGM) to the early Holocene. We present CO2 measurements performed on an ice core from central Greenland, drilled during the Greenland Ice Core Project (GRIP). This CO2 profile from GRIP confirms the most prominent CO2 increase from the LGM, with a mean concentration of 200 ppmv, to the early Holocene with concentrations between 290 and 310 ppmv. Some structures of the new CO2 record are similar to those previously obtained from the Dye 3 ice core (Greenland), which indicated • dilemm• between Greenland •nd Antarctic CO2 records [Oeschger et al., 1988]. Both Greenland cores show high CO2 values for rather mild climatic periods during the last glaciation, whereas CO2 records from Antarctica do not show such high CO2 variations during the glaciation and, furthermore, the CO2 values in the early Holocene are about 20-30 ppmv higher in the GRIP record than in Antarctic records. There is some evidence that the difference could be due to chemical reactions between impurities in the ice leading to an increase of the CO2 concentration under certain conditions. If in situ processes can change the CO2 concentration in the air bubbles, the question arises about how reliably do CO2 records from ice cores reflect the atmospheric composition at the time of ice formation. The discrepancies between the CO2 profiles from Greenland and Antarctica can be explained by in situ production of excess CO2 due to interactions between carbonate and acidic species. Since the carbonate concentration in Antarctic ice is much lower than in Greenland ice, CO2 records from Antarctica are much less affected by such in situ-produced CO2. ing the Holocene, pronounced differences occur between Antarctic and Greenland CO2 records during periods of the glaciation between 20 and 40 kyr B.P., where the CO2 profile from Dye 3 (Greenland) shows several fast variations of the order of 50 parts per million per volume (ppmv), while the Byrd and Vostok fluctuations of no more than 20 ppmv. If both profiles would reflect unadulterated atmospheric concentrations, then this implies an interhemispheric difference up to about 50 ppmv during certain periods. On the basis of the present knowledge of the atmospheric carbon cycle, such large interhemispheric concentration differences can be excluded. High CO2 values found in the Dye 3 core between 20 and 40 kyr B.P. are parallel with mild climatic periods, the so-called Dansgaard-Oeschger events. One possible explanation for the high CO2 concentration during the Dansgaard-Oeschger events in the Dye 3 core is melt layers, which contain air considerably enriched in CO2 [Neftel et el., 1982]. It was one of the important goals of the Greenland Ice Core Project (GRIP) to solve the CO2dilemma mentioned by Oeschger et el. [1988]. The above explanation is not very likely because the new drill site at Summit (central Greenland) was selected also due to its current low mean annual temperature 26,539 26,540
A high-precision method for measurement of paleoatmospheric CO2 in small polar ice samples
Journal of Glaciology, 2009
We describe a high-precision method, now in use in our laboratory, for measuring the CO2 mixing ratio of ancient air trapped in polar ice cores. Occluded air in ice samples weighing ∼8–15 g is liberated by crushing with steel pins at −35°C and trapped at −263°C in a cryogenic cold trap. CO2 in the extracted air is analyzed using gas chromatography. Replicate measurements for several samples of high-quality ice from the Siple Dome and Taylor Dome Antarctic ice cores have pooled standard deviations of <0.9 ppm. This high-precision technique is directly applicable to high-temporal-resolution studies for detection of small CO2 variations, for example CO2 variations of a few parts per million on millennial to decadal scales.
Impact of snow cover on CO<sub>2</sub> dynamics in Antarctic pack ice
2014
Temporal evolution of pCO 2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows that the CO 2 system in the ice was primarily controlled by physical and thermodynamic processes. During the survey, a succession of warming and cold events strongly influenced the physical, chemical and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We confirm that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (T CO 2), and in situ brine and bulk ice CO 2 partial pressures (pCO 2). Thicker snow covers muted these changes, suggesting that snow influences changes in the sea ice carbonate system through its impact on the temperature and salinity of the sea ice cover. During this survey, pCO 2 was undersaturated with respect to the atmosphere both in situ, in the bulk ice (from 10 to 193 µatm), and in the brine (from 65 to 293 µatm), and the ice acted as a sink for atmospheric CO 2 (up to 2.9 mmol m −2 d −1), despite the underlying supersaturated seawater (up to 462 µatm).
Tellus B, 2003
A deep ice core drilled at Dome Fuji, East Antarctica was analyzed for the CO 2 concentration using a wet extraction method in order to reconstruct its atmospheric variations over the past 320 kyr, which includes three full glacial-interglacial climatic cycles, with a mean time resolution of about 1.1 kyr. The CO 2 concentration values derived for the past 65 kyr are very close to those obtained from other Antarctic ice cores using dry extraction methods, although the wet extraction method is generally thought to be inappropriate for the determination of the CO 2 concentration. The comparison between the CO 2 and Ca 2+ concentrations deduced from the Dome Fuji core suggests that calcium carbonate emitted from lands was mostly neutralized in the atmosphere before reaching the central part of Antarctica, or that only a small part of calcium carbonate was involved in CO 2 production during the wet extraction process. The CO 2 concentration for the past 320 kyr deduced from the Dome Fuji core varies between 190 and 300 ppmv, showing clear glacial-interglacial variations similar to the result of the Vostok ice core. However, for some periods, the concentration values of the Dome Fuji core are higher by up to 20 ppmv than those of the Vostok core. There is no clear indication that such differences are related to variations of chemical components of Ca 2+ , microparticle and acidity of the Dome Fuji core.
The Cryosphere, 2014
Temporal evolution of pCO 2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO 2 system in the ice. During the survey, cyclical warming and cooling strongly influenced the physical, chemical, and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (T CO 2 ), and in situ brine and bulk ice CO 2 partial pressures (pCO 2 ). Thicker snow covers reduced the amplitude of these changes: snow cover influences the sea ice carbonate system by modulating the temperature and therefore the salinity of the sea ice cover. Results indicate that pCO 2 was undersaturated with respect to the atmosphere both in the in situ bulk ice (from 10 to 193 µatm) and brine (from 65 to 293 µatm), causing the sea ice to act as a sink for atmospheric CO 2 (up to 2.9 mmol m −2 d −1 ), despite supersaturation of the underlying seawater (up to 462 µatm).
The Cryosphere, 2014
Temporal evolution of pCO 2 profiles in sea ice in the Bellingshausen Sea, Antarctica, in October 2007 shows physical and thermodynamic processes controls the CO 2 system in the ice. During the survey, cyclical warming and cooling strongly influenced the physical, chemical, and thermodynamic properties of the ice cover. Two sampling sites with contrasting characteristics of ice and snow thickness were sampled: one had little snow accumulation (from 8 to 25 cm) and larger temperature and salinity variations than the second site, where the snow cover was up to 38 cm thick and therefore better insulated the underlying sea ice. We show that each cooling/warming event was associated with an increase/decrease in the brine salinity, total alkalinity (TA), total dissolved inorganic carbon (T CO 2), and in situ brine and bulk ice CO 2 partial pressures (pCO 2). Thicker snow covers reduced the amplitude of these changes: snow cover influences the sea ice carbonate system by modulating the temperature and therefore the salinity of the sea ice cover. Results indicate that pCO 2 was undersaturated with respect to the atmosphere both in the in situ bulk ice (from 10 to 193 µatm) and brine (from 65 to 293 µatm), causing the sea ice to act as a sink for atmospheric CO 2 (up to 2.9 mmol m −2 d −1), despite supersaturation of the underlying seawater (up to 462 µatm).
Atmospheric Chemistry and Physics Discussions, 2010
Response to Referee #2 Comments We thank referee #2 for many valuable comments and suggestions, many of which we have incorporated into a revised version of the manuscript. However, we also wish to note a bit of self-contradiction in this review. This is instructive because we believe it reflects confusion on this issue in the community as a whole and highlights some shortcomings in the text that contributed to the misinterpretation of our results. C1972 The review starts out by agreeing with our major findings, stating that the manuscript "provides evidence of the shallow sample problem in a more systematic and complete way than the scattering of evidence that exists in the literature" and that "it has been known for a while by ice core researchers that measurement of enclosed gases can be problematic near close off." The rest of the comments argue that it is well established that gas measurements near close-off are not problematic as implied by Law Dome ice core records. Resolving this conflict requires careful reading of the original literature, which we have attempted to do (see below). The major point of this manuscript is that there are challenges associated with trace gas measurements in shallow ice cores near the close-off region at most locations. We feel strongly that this information should be available to interested researchers from all disciplines, not only to ice core researchers. This does not pose a challenge to the integrity of the global ice core archive. In reality, it is quite the contrary. The present work puts ice cores from a variety of Antarctic sites to a highly stringent test, and outside of a narrow depth range near the close-off, we find no evidence of modern air contamination. One important implication of this manuscript is that, at many ice core sites, it may not be possible to confirm the integrity of the ice core air with respect to a trace gas by testing continuity through the firn-ice transition. This is particularly important for ongoing efforts to expand the suite of trace gases measured in ice cores.