Why are measurements of CO2 different in plant stomata than they are from ice cores?
Which is more reliable? Please provide a source of information.
- DavidLv 41 decade agoFavorite Answer
Ice core data provide a low-frequency estimate of atmospheric CO2 variations of the glacial/interglacial cycles of the Pleistocene. However, the ice cores seriously underestimate the variability of interglacial CO2 levels.
Plant stomata data show that ice cores do not resolve past decadal and century scale CO2 variations that were of comparable amplitude and frequency to the rise since 1860.
Stomata data are "noisier" and not all taxa are equally responsive to CO2 variations. Local variability can be very high.
Neither one is really more reliable to than the other. It's kind of like the difference between a woofer (ice cores) and a tweeter (stomata).
The advantage to the ice core method is that it provides a continuous record of relative CO2 changes going back in time 800,000 years, with a resolution ranging from annual in the shallow section to multi-decadal in the deeper section. Pleistocene-age ice core records seem to indicate a strong correlation between CO2 and temperature; although the delta-CO2 lags behind the delta-T by an average of 800 years.
Stomata are microscopic pores found in leaves and the stem epidermis of plants. They are used for gas exchange. The stomatal density in some C3 plants will vary inversely with the concentration of atmospheric CO2. Stomatal density can be empirically tested and calibrated to CO2 changes over the last 60 years in living plants. The advantage to the stomatal data is that the relationship of the Stomatal Index and atmospheric CO2 can be empirically demonstrated.
When stomata-derived CO2 is compared to ice core-derived CO2, the stomata generally show much more variability in the atmospheric CO2 level and often show levels much higher than the ice cores. Plant stomata suggest that the pre-industrial CO2 levels were commonly in the 360 to 390ppmv range.
Ice cores and GEOCARB provide continuous long-term records; while plant stomata records are discontinuous and limited to fossil stomata that can be accurately aged and calibrated to extant plant taxa. GEOCARB yields a very low frequency record, ice cores have better resolution and stomata can yield very high frequency data. Modern CO2 levels are unspectacular according to GEOCARB, unprecedented according to the ice cores and not anomalous according to plant stomata. So which method provides the most accurate reconstruction of past atmospheric CO2?
The problems with the ice core data are 1) the air-age vs. ice-age delta and 2) the effects of burial depth on gas concentrations.
The age of the layers of ice can be fairly easily and accurately determined. The age of the air trapped in the ice is not so easily or accurately determined. Currently the most common method for aging the air is through the use of “firn densification models” (FDM). Firn is more dense than snow; but less dense than ice. As the layers of snow and ice are buried, they are compressed into firn and then ice. The depth at which the pore space in the firn closes off and traps gas can vary greatly… So the delta between the age of the ice and the ago of the air can vary from as little as 30 years to more than 2,000 years.
I have a lot of doubts about the accuracy of the FDM method. I somehow doubt that the air at a depth of 99 meters is last year’s air. Gas doesn’t tend to migrate downward through sediment… Being less dense than rock and water, it migrates upward. That’s why oil and gas are almost always a lot older than the rock formations in which they are trapped. I do realize that the contemporaneous atmosphere will permeate down into the ice… But it seems to me that at depth, there would be a mixture of air permeating downward, in situ air, and older air that had migrated upward before the ice fully “lithified”.
A recent study (Van Hoof et al., 2005) demonstrated that the ice core CO2 data essentially represent a low-frequency, century to multi-century moving average of past atmospheric CO2 levels.
It appears that the ice core data represent a long-term, low-frequency moving average of the atmospheric CO2 concentration; while the stomata yield a high frequency component.
The stomata data routinely show that atmospheric CO2 levels were higher than the ice cores do. Plant stomata data from the previous interglacial (Eemian/Sangamonian) were higher than the ice cores indicate.
Kouwenberg et al., 2005 found that a “stomatal frequency record based on buried Tsuga heterophylla needles reveals significant centennial-scale atmospheric CO2 fluctuations during the last millennium.”
Plant stomata data show much greater variability of atmospheric CO2 over the last 1,000 years than the ice cores and that CO2 levels have often been between 300 and 340ppmv over the last millennium, including a 120ppmv rise from the late 12th Century through the mid 14th Century.Source(s): CO2: Ice Cores vs. Plant Stomata http://debunkhouse.wordpress.com/2010/03/28/co2-ic... Wagner et al., 1999. Century-Scale Shifts in Early Holocene Atmospheric CO2 Concentration. Science 18 June 1999: Vol. 284. no. 5422, pp. 1971 – 1973. Kouwenberg et al., 2004. APPLICATION OF CONIFER NEEDLES IN THE RECONSTRUCTION OF HOLOCENE CO2 LEVELS. PhD Thesis. Laboratory of Palaeobotany and Palynology, University of Utrecht. Kouwenberg et al., 2005. Atmospheric CO2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of Tsuga heterophylla needles. GEOLOGY, January 2005. Van Hoof et al., 2005. Atmospheric CO2 during the 13th century AD: reconciliation of data from ice core measurements and stomatal frequency analysis. Tellus (2005), 57B, 351–355.
- Facts MatterLv 71 decade ago
We have infrared atmospheric data gong back over 50 years, and it matches the ice cores. We have atmospheric chemical determinations from the 19th century, which cluster close to a trend line that matches the ice cores. We have mass balance and isotope distribution data that fit the ice cores. And we know that CO2 concentration is not the only thing that affects stomata.
David the answerer: you obviously don't know what Kouwenberg himself says about other factors affecting stomata:
Stomatal Frequency Change Over Altitudinal Gradients: Prospects for Paleoaltimetry
Lenny L.R. Kouwenberg et al
Reviews in Mineralogy and Geochemistry; October 2007; v. 66;1; p. 215-241; DOI: 10.2138/rmg.2007.66.9
"Recently, a novel paleoaltimetry method was presented using leaf stomatal frequency response to the decline in CO2 partial pressure with altitude, and tested on California black oak (Quercus kelloggii) (McElwain 2004). Here, we present new data detailing the influence of other climatic variables on leaf stomatal frequency change with altitude in the context of more fully characterizing how stomatal frequencies can be used to infer paleoelevations. A clear increase in stomatal density and stomatal index is observed with increasing elevation for Q. kelloggii (black oak) leaves, and Nothofagus solandri var. cliffortioides (mountain beech) growing over an altitudinal transect on the slope of Mt. Ruapehu (New Zealand). Modern leaves growing in full direct sunlight versus shaded diffuse light for both species show substantial differences in stomatal density and index, however, growth chamber experiments that vary light intensity have revealed that the magnitude of natural increase in radiation with altitude is likely insufficient to explain the overall increase in stomatal frequency (density and index) with elevation. Furthermore, temperature does not have a significant influence on black oak stomatal frequency in growth chamber experiments. Rather changes in stomatal density and index with altitude appear to reflect an adaptation to counteract the limited photosynthetic potential due to the CO2 partial pressure decrease, further limited by shorter growing seasons and/or increased UV radiation."
- Dana1981Lv 71 decade ago
Ice cores are a direct measurement of air trapped in bubbles. Plant stomata are an indirect measurement of atmospheric CO2, which isn't the only thing that can effect stomatal density. Experiments on stomata density have showed that "the stomatal response to increasing atmospheric CO2 was identical to that induced by removing water from the plant roots"
In other words, stomatal index data may not be the able to measure the atmospheric concentration as precisely as we would like.
Different ice cores are very consistent in terms of atmospheric CO2 measurements, but that's not the case with plant stomata. As mentioned before, the problem with plant stomata is that they're impacted by more than just atmospheric CO2, whereas ice cores provide direct measurements of trapped air bubbles. Thus ice cores are more reliable.
- john mLv 41 decade ago
CO2 has 2 negatively charged oxygen molecules and is dragged to the north by magnetics and at -78 degrees C it turns into dry ice and falls as dry ice snow and it turns back to gas at -60 that's why the ice is melting faster at the north pole .
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- Anonymous1 decade ago
Ice cores can contain air that was trapped in the ice thousands of years ago.