Increases in terrestrial carbon storage from the Last Glacial Maximum to the present

Adams, Jonathan M.; Faure, H.; Faure-Denard, L.; McGlade, Jacqueline; Woodward, F. I.

doi:10.1038/348711a0

Cited by 483 publications

(273 citation statements)

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“…More detailed reservoir age corrections are incorporated in the calibration curves of Figure 17. Although application of these curves minimizes coral/tree-ring differences (see Fig.1 As a first approximation, the model exchange parameters are constant during our 32,000-yr simulation, despite significant changes in atmosphere, ocean and terrestrial biosphere dynamics that occurred before 10,000 14C yr BP; these changes were associated with the glacial-interglacial climate transition (Adams et al 1990;Broecker & Denton 1989). Three lines of evidence suggest that the differences among glacial, deglaciation and interglacial conditions had secondary effects on atmospheric (and oceanic) 14C after 10,000 BC.…”

Section: The Global Carbon Modelmentioning

confidence: 93%

Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

1993

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INTRODUCTIONThe detailed radiocarbon age vs, calibrated (cal) age studies of tree rings reported in this Calibration Issue provide a unique data set for precise 14C age calibration of materials formed in isotopic equilibrium with atmospheric CO2. The situation is more complex for organisms formed in other reservoirs, such as lakes and oceans. Here the initial specific 14C activity may differ from that of the contemporaneous atmosphere. The measured remaining 14C activity of samples formed in such reservoirs not only reflects 14C decay (related to sample age) but also the reservoir '4C activity. As the measured sample 14C activity figures into the calculation of a conventional 14C age (Stuiver & Polach 1977), apparent 14C age differences occur when contemporaneously grown samples of different reservoirs are dated.A correction for the apparent age anomaly is possible when the reservoir-atmosphere offset in specific 14C activity is known. The offset (e.g.,14C age of marine sample -14C age of atmospheric sample) is expressed as a reservoir 14C age, R(t), which need not be constant with time. When constant, however, the reservoir sample 14C age, A, can be reconciled with the atmospheric one by deducting R(t) from A. Similar reservoir age corrections would be possible for a variable R(t), but complications arise because information on R time dependency usually is lacking. However, R(t) can be accounted for in the world oceans by using a marine calibration curve derived from carbon reservoir modeling (Stuiver, Pearson & Braziunas 1986). In these calculations, atmospheric 14C change is attributed to solar-and geomagnetic-induced 14C production change. Climate-induced changes in global carbon reservoirs, which may repartition 14C among reservoirs, are not accounted for in these calculations.Measuring a marine calibration curve is complicated because most marine samples lack the continuity and fine structure of tree rings. The 234U/23°Th dating of corals (Bard et al. 1993) provides a good cal age equivalent, but measuring errors in the 234U/230Th ratio and 14C accelerator mass spectrometry (AMS) determinations are such that the (bi)decadal chronological detail achieved for tree rings is not possible. Such detail, however, can be realized by calculating the response of the world oceans to tree-ring derived atmospheric 14C changes.The long-term trend of the 14C age vs. cal age curve for the world oceans parallels that of the atmosphere. Short-term (century) variations, however, are smoothed in the oceans. Thus, whereas a constant, R, could be used for long-term variations, the shorter-term variations cannot be accounted for in this manner. Use of constant, R, and the atmospheric calibration curve assumes that the features of the marine and atmospheric curves are identical. The consequences of the constant R approach are obvious when the cal ages of a marine and atmospheric sample with identical (reservoir-corrected) 14C age + standard deviation are evaluated. Calibration of both vs. the atmospheric curve yields identical re...

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Section: The Global Carbon Modelmentioning

confidence: 93%

Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

1993

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“…The fate of the subglacial reservoir of organic carbon (SOC) is uncertain. In models of global carbon cycling and calculations of the global carbon budget at the Last Glacial Maximum (LGM) through to the present-day, the carbon storage under ice sheets is effectively set to zero [Adams et al, 1990;Van Campo et al, 1993;François et al, 1999]. None of these consider that the buried OC is converted to greenhouse gases (methane and carbon dioxide) by subglacial microbial activity during storage in warm-based parts of the ice sheets, where liquid water was present.…”

Section: Introductionmentioning

confidence: 99%

Subglacial methanogenesis: A potential climatic amplifier?

Wadham

Tranter

Tulaczyk

et al. 2008

Global Biogeochemical Cycles

114

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[1] Subglacial environments are a previously neglected component of the Earth's global carbon cycle, a reflection of the view held until recently that they are dominated by abiotic and oxic conditions. Here we provide a realistic assessment of the theory that the basal regions of the ice sheets that formed over North America and Europe during glaciations were host to significant populations of anaerobic microorganisms, including methanogens, able to metabolize organic carbon sequestered during interglacials and overridden during Quaternary glacials. In doing so, we review the current evidence for subglacial methane release during deglaciation, estimate the size of the subglacial reservoir of organic carbon (SOC), and assess the amount of SOC available to subglacial microbes and the likely pathways and rates of carbon turnover. We then discuss the fate of subglacial methane and the potential impact of its release on atmospheric methane concentrations. We calculate that the SOC equates to 418-610 Pg C and includes carbon from terrestrial soils/vegetation, peatlands, lake, and marine sediments. The SOC that is potentially available for microbial conversion to methane is smaller than this estimate due to (1) glacial erosion, (2) accumulation of recalcitrant organic carbon compounds over time, (3) conversion to carbon dioxide by aerobic/anaerobic respiration, and (4) incomplete conversion of labile organic matter to methane. We estimate that the total SOC available for conversion to methane is 63 Pg C. Our estimates of methane production potentials span a wide range because of the current uncertainty surrounding subglacial metabolic rates. We believe, however, that there is a strong likelihood that subglacial microbes could convert 63 Pg of SOC to methane during a glacial cycle. If this were the case, release of this methane from the ice sheet margins during retreat would need to be episodic in order to significantly impact atmospheric methane concentrations. Our findings suggest that it may well be important to consider subglacial environments as active components of the Earth's carbon cycle. Conclusive determination of the potential impact of subglacial methane production on atmospheric methane concentrations during deglaciation, however, awaits more precise determination of the ability of subglacial microbes to degrade organic carbon components and their associated rates of metabolism under in situ conditions.

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“…In contrast, the direct palaeoevidence shows that in fact the opposite was the case (Adams et al, 1990). It now seems from the ecophysiological evidence presented here that the lower CO.^ levels prevailing during the LGM reduced the WUE of vegetation to such an extent that it could have resulted in the substantial decrease in rain forest areas and a major expansion of deserts observed by Adams et al (1990). This may account for some part of the discrepancy between the GCM predictions and the palaeoevidence (Adams & Woodward, 1992).…”

Section: Implications Of Increased Wue Since the Lgm For Plant Distrimentioning

confidence: 61%

“…GCM predictions of moisture balance for the LGM, translated into vegetation types, suggest moister conditions over large areas of the land surface, together with a 90 % reduction in deserts and a 20 % increase in the area of rain forests (Prentice, 1990). In contrast, the direct palaeoevidence shows that in fact the opposite was the case (Adams et al, 1990). It now seems from the ecophysiological evidence presented here that the lower CO.^ levels prevailing during the LGM reduced the WUE of vegetation to such an extent that it could have resulted in the substantial decrease in rain forest areas and a major expansion of deserts observed by Adams et al (1990).…”

Section: Implications Of Increased Wue Since the Lgm For Plant Distrimentioning

confidence: 99%

Ecophysiological responses of plants to global environmental change since the Last Glacial Maximum

Beerling

Woodward

1993

New Phytologist

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SUMMARYEcophysiological information on the responses of plants to past global environmental changes may be obtained from Quaternary fossil leaves by measurements of (i) stomatal density, (ii) stomatal dimensions and (iii) '•''C discrimination (A ^'C). The stomatal density and stomatal dimensions of leaves can be used to calculate stomatal conductance, while leaf A "C values provide independent infortnation on stomatal conductance and plant water use efficiency. In this paper, stomatal conductance is calculated for a sequence of radiocarbon dated fossil leaves of Salix herbacea L. which, together witb herbarium and fresb material, represents a time-series spanning from tbe Last Glacial Maximum (LGM) (16500 yrBP) to tbe present day. Tbe calculated values were tben tested against leaf A '''C values previously reported for tbe same material.Our calculations sbow tbat stomatal conductance is negatively correlated witb increases in atmospberic COĉ oncentration over tbe last 16500 yr. Tbis represents tbe first evidence of long-term response of stomatal conductance to increases in atmospberic COj concentration and confirms tbe response observed in experimental systems exposing plants to lower-tban-present CO.^ concentrations in controlled environments. The calculated decrease in conductance was positively correlated witb leaf A '''C values, supporting tbis interpretation. Tbe mean leaf A '-'C value for tbe 18tb and 19tb centuries was significantly (P < 0-05) lower tban tbe mean for tbe interval LGM-Holocene (10000 yr BP) implying an increase in plant water-use-efficiency over tbis time. Tbese two lines of evidence, together witb tbe stomatal density record from a glacial cycle, and experimental studies growing Cg plants in glacial-to-present CO^ concentrations, strongly imply tbat tbe water use efficiency of vegetation during tbe LGM was lower tban at present and tbat it bas increased since tbat time. Furtber evidence in support of tbis conclusion comes from tbe pattern of world vegetation types present during tbe LGM previously reconstructed using palaeoecological data. Tbis evidence demonstrates tbat tbe distribution of vegetation types during tbe LGM was significantly different from tbat of tbe present day and sbowed a contraction in tbe area of rain forest and a major expansion of desert areas.

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Increases in terrestrial carbon storage from the Last Glacial Maximum to the present

Cited by 483 publications

References 18 publications

Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

Subglacial methanogenesis: A potential climatic amplifier?

Ecophysiological responses of plants to global environmental change since the Last Glacial Maximum

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Increases in terrestrial carbon storage from the Last Glacial Maximum to the present

Cited by 483 publications

References 18 publications

Modeling Atmospheric 14C Influences and 14C Ages of Marine Samples to 10,000 BC

Modeling Atmospheric 14C Influences and 14C Ages of Marine Samples to 10,000 BC

Subglacial methanogenesis: A potential climatic amplifier?

Ecophysiological responses of plants to global environmental change since the Last Glacial Maximum

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Product

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Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC

Modeling Atmospheric ¹⁴C Influences and ¹⁴C Ages of Marine Samples to 10,000 BC