Atmospheric CO2 Concentration During the Last Glaciation

Stauffer, B.; Hofer, Helene; Oeschger, H.; Schwander, Jakob; Siegenthaler, U.

doi:10.1017/s0260305500003670

Cited by 98 publications

(22 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Bonnefille et al 1990, Vincens et al 1993, however, do overlap with the upper limits of the CLIMAP (1981) temperature estimates, within the limits of uncertainty. Polar ice cores have, in addition, provided evidence of large changes in the concentrations of the atmospheric greenhouse gases CO 2 and CH 4 through geological time (Delmas et al 1980, Stauffer et al 1984, Barnola et al 1987, Chappellaz et al 1990, Jouzel et al 1993 extending back to 250 000 yr ago in the case of the Vostok ice core (Jouzel et al 1993). The gases vary in phase, and correlate well with temperature changes (Jouzel et al 1993).…”

Section: Summary: Temporal Profile Of Vegetation Change In Africamentioning

confidence: 99%

Vegetation changes over palaeo-time scales in Africa

Olago

2001

Clim. Res.

View full text Add to dashboard Cite

The record of palaeovegetation dynamics in Africa generally extends back to 30 000 yr BP, and longer records, where they do exist, tend to be characterised by hiatuses, giving a broken slide-show of vegetation dynamics in the past. A few specific sites on, for example, Mount Kenya and the Burundi Highlands in the equatorial tropics offer much longer and continuous records. Pollen analysis of lake, peat, swamp sediments and other materials have largely formed the basis of vegetation and climatic reconstruction on the continent. These pollen diagrams indicate depression of highland vegetation to lower altitudes relative to their positions today, fragmentation of lowland forests, and concomitant expansion of grassland prior to 14 000 yr BP, with maximum impact occurring between 22 000 and 14 000 yr BP. The period 14 000 to 10 000 yr BP was a time of transition, with vegetation recovering to present-day distributions by 10 000 yr BP. These are generalisations, and significant differences do occur from region to region; in particular, vegetation change in southern Africa has been largely asynchronous with the rest of the African continent, save for the peak of the last glacial maximum at 18 000 yr BP. Based on the changes in vegetation, the period prior to 14 000 yr BP is viewed as less humid (with exceptions in southern Africa) and cooler than present, with maximum aridity and temperature depressions (estimated to be between 4 and 7°C lower than today, occurring between 22 000 and 14 000 yr BP. A climatic amelioration followed thereafter, reaching optimal warm and humid conditions at about 10 000 yr BP in the equatorial regions, and about 2000 to 5000 yr later in the subtropical regions. Temperature has been generally viewed as being the major factor driving climate change. Following the recent discovery, from polar ice cores, that atmospheric CO 2 concentrations have also changed through time, current palaeovegetation studies have focused on both pollen and, to probe the physiological effect of changing atmospheric CO 2 on vegetation, on bulk and compound-specific stable carbon isotope analysis of organic sediments. These studies have yielded much valuable information on the relationship between the climatic drivers of vegetation change, namely, temperature, precipitation and atmospheric CO 2 changes. They suggest that CO 2 rather than temperature was the main driving force of vegetation change in the tropics during the glacial-interglacial period, and that vegetation may have responded much more sensitively to humidity changes based on physiological responses to lowered CO 2 concentrations. These conclusions are supported by modelling experiments, and indicate that previous estimates of temperature depression in the tropics are overestimated and need to be revised in light of these new discoveries. KEY WORDS: Palaeovegetation · Palaeoclimate · AfricaResale or republication not permitted without written consent of the publisher

show abstract

Section: Summary: Temporal Profile Of Vegetation Change In Africamentioning

confidence: 99%

Vegetation changes over palaeo-time scales in Africa

Olago

2001

Clim. Res.

View full text Add to dashboard Cite

show abstract

“…Several mechanisms have been proposed to account for this phenomenon. It has been speculated that CO 2 could originate from the acidification of carbonate [Delmas, 1993;Stauffer et al, 1998] or the oxidation of organic matter by coextensive oxidizers, such as H 2 O 2 [Tschumi and Stauffer, 2000].…”

Section: Introductionmentioning

confidence: 99%

Photolysis of pyruvic acid in ice: Possible relevance to CO and CO₂ ice core record anomalies

2007

View full text Add to dashboard Cite

The abnormal spikes detected in some CO and CO2 polar ice core records indicate persistent chemical activity in glacial ice. Since CO and CO2 spikes are correlated, and their amplitudes scale with reported CO/CO2 yields for the photolysis of dissolved natural organic matter, a common photochemical source is implicated. Given that sufficient actinic radiation is constantly generated throughout ice by cosmic muons (Colussi and Hoffmann, 2003), it remains to be shown that the photolyses of typical organic contaminants proceed by similar mechanisms in water and ice. Here we report that the photodecarboxylation of pyruvic acid (PA, an ubiquitous ice contaminant) indeed leads to the same products nearly as efficiently in both media. CO2 is promptly released from frozen PA/H2O films upon illumination and continues to evolve after photolysis. By analogy with our studies in water (Guzmán et al., 2006b), we infer that 3PA* reacts with PA in ice producing CH3C(O)C(O)O· and (CH3 (OH)C(O)OH) radicals. The barrierless decarboxylation, CH3C(O)C(O)O· → CH3C(O)· + CO2, accounts for prompt CO2 emissions down to ∼140 K. Bimolecular radical reactions subsequently ensue in fluid molecular environments, both in water and ice, leading to metastable intermediates that decarboxylate immediately in water, but protractedly in ice. The overall quantum yield of CO2 production in the λ ~313 nm photolysis of PA in ice at 250 K is ∼60% of that in water at 293 K. The in situ photolysis of natural organic matter is, therefore, a plausible explanation of CO and CO2 ice core record anomalies.

show abstract

“…Three of the numerous oscillations (in the depth interval 1975-1889 m) have been analyzed in great detail for chemical composition (Finkel and Langway, 1985), l0Be (Beer et al, 1984), C02 (Stauffer et al, 1984), 6l80 and dust content (Dansgaard et al, 1984;Hammer et al, 1985). All of these parameters change almost simultaneously, indicating drastic shifts in the entire environment.…”

Section: Introductionmentioning

confidence: 99%