Changes in the atmospheric CH<sub>4</sub> gradient between Greenland and Antarctica during the Last Glacial and the transition to the Holocene

Dällenbach, A.; Blunier, Thomas; Flückiger, Jacqueline; Stauffer, B.; Chappellaz, J.; Raynaud, Dominique

doi:10.1029/1999gl010873

Cited by 194 publications

(160 citation statements)

References 12 publications

Supporting

Mentioning

141

Contrasting

Unclassified

Order By: Relevance

“…Summarising: Orbital parameters are taken from Berger and Loutre (1992) and set to 21 ka B.P. Greenhouse gas concentrations are set in accordance with reconstructed levels from icecore data (Fluckiger et al 1999;Dallenbach et al 2000;Monnin et al 2001), to 185 p.p.m.v., 350 and 200 p.p.b.v. for CO 2 , CH 4 and N 2 O respectively; The ice-sheet topography and ice-mask are based on Peltier's (2004) reconstruction, interpolated at T21 resolution.…”

Section: Experimental Designmentioning

confidence: 99%

Simulating Heinrich event 1 with interactive icebergs

2012

View full text Add to dashboard Cite

During the last glacial, major abrupt climate events known as Heinrich events left distinct fingerprints of ice rafted detritus, and are thus associated with iceberg armadas; the release of many icebergs into the North Atlantic Ocean. We simulated the impact of a large armada of icebergs on glacial climate in a coupled atmosphereocean model. In our model, dynamic-thermodynamic icebergs influence the climate through two direct effects. First, melting of the icebergs causes freshening of the upper ocean, and second, the latent heat used in the phase-transition of ice to water results in cooling of the iceberg surroundings. This cooling effect of icebergs is generally neglected in models. We investigated the role of the latent heat by performing a sensitivity experiment in which the cooling effect is switched off. At the peak of the simulated Heinrich event, icebergs lacking the latent heat flux are much less efficient in shutting down the meridional overturning circulation than icebergs that include both the freshening and the cooling effects. The cause of this intriguing result must be sought in the involvement of a secondary mechanism: facilitation of sea-ice formation, which can disturb deep water production at key convection sites, with consequences for the thermohaline circulation. We performed additional sensitivity experiments, designed to explore the effect of the more plausible distribution of the dynamic icebergs' melting fluxes compared to a classic hosing approach with homogeneous spreading of the melt fluxes over a section in the mid-latitude North Atlantic (NA) Ocean. The early response of the climate system is much stronger in the iceberg experiments than in the hosing experiments, which must be a distribution-effect: the dynamically distributed icebergs quickly affect western NADW formation, which synergizes with direct sea-ice facilitation, causing an earlier sea-ice expansion and climatic response. Furthermore, compared to dynamic-thermodynamic icebergs, a homogeneous hosing overestimates the fresh water flux in the Eastern Ruddiman belt, causing a fresh anomaly in the Eastern North Atlantic, leading to a delayed recovery of the circulation after the event.

show abstract

Section: Experimental Designmentioning

confidence: 99%

Simulating Heinrich event 1 with interactive icebergs

2012

View full text Add to dashboard Cite

show abstract

“…The same boundary conditions have been used to run the different models participating to PMIP2 (Braconnot et al 2007, http://pmip2.lsce.ipsl.fr/pmip2/). For its second phase and for the LGM, they consist of GHG concentrations equal to 185 ppm for the CO 2 (Monnin et al 2001), 350 ppb for CH 4 (Dallenbach et al 2000) and 200 ppb for N 2 O (Flückiger et al 1999). The ice-sheets are imposed and based on the reconstruction from Peltier (2004) ICE-5G.…”

Section: Models and Simulation Runsmentioning

confidence: 99%

Northern hemisphere storm tracks during the last glacial maximum in the PMIP2 ocean-atmosphere coupled models: energetic study, seasonal cycle, precipitation

et al. 2008

View full text Add to dashboard Cite

Mid-latitude eddies are an important component of the climatic system due to their role in transporting heat, moisture and momentum from the tropics to the poles, and also for the precipitation associated with their fronts, especially in winter. We study northern hemisphere stormtracks at the Last Glacial Maximum (LGM) and their influence on precipitation using ocean-atmosphere general circulation model (OAGCM) simulations from the second phase of the Paleoclimate Modelling Intercomparison Project (PMIP2). The difference with PMIP1 results in terms of sea-surface temperature forcing, fundamental for storm-track dynamics, is large, especially in the eastern North Atlantic where sea-ice extends less to the south in OAGCMs compared to atmospheric-only GCMs. Our analyses of the physics of the eddies are based on the equations of eddy energetics. All models simulate a consistent southeastward shift of the North Pacific storm-track in winter, related to a similar displacement of the jet stream, partly forced by the eddies themselves. Precipitation anomalies are consistent with storm-track changes, with a southeastward displacement of the North Pacific precipitation pattern. The common features of North Atlantic changes in the LGM simulations consist of a thinning of the storm-track in its western part and an amplification of synoptic activity to the southeast, in the region between the Azores Islands and the Iberian Peninsula, which reflects on precipitation. This southeastward extension is related to a similar displacement of the jet, partly forced by the eddies. In the western North Atlantic, the synoptic activity anomalies are at first order related to baroclinic generation term anomalies, but the mean-flow baroclinicity increase due to the presence of the Laurentide ice-sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow. Moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves, leading to less synopticscale latent heat release and hence less precipitation also. In terms of seasonality, the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered. This shift does not directly reflect on the first-order seasonal cycle of precipitation, which also depends on other mechanisms, especially in summer.

show abstract

“…This finding needs to be validated at other sites, and then its implications require further consideration. The differences between CH 4 concentrations in Greenland and Antarctica have been assessed in a number of papers (Brook et al 2000;Dällenbach et al 2000). It is of course important to use records from both hemispheres that have the same calibration and to align the time-scales very carefully: both factors impose some uncertainty on the interhemispheric differences.…”

Section: The Causes Of the Observed Glacial-interglacial And D-o Chmentioning

confidence: 99%

“…Estimated northern and tropical CH 4 source strengths for different time periods. This is based on a box model using the concentration and the interpolar gradient in concentration, with data from the ice cores at Taylor Dome and GISP2 (Brook et al 2000), or at Byrd, Vostok and GRIP (Dällenbach et al 2000). The emissions from the southern box are assumed steady at 15 Tg yr K1 (warm periods, and Younger Dryas in Brook et al (2000)) or 12 Tg yr K1 (LGM and D-O cold periods).…”

Section: The Causes Of the Observed Glacial-interglacial And D-o Chmentioning

confidence: 99%

Methane and nitrous oxide in the ice core record

Wolff

Spahni

2007

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

Polar ice cores contain, in trapped air bubbles, an archive of the concentrations of stable atmospheric gases. Of the major non-CO 2 greenhouse gases, methane is measured quite routinely, while nitrous oxide is more challenging, with some artefacts occurring in the ice and so far limited interpretation. In the recent past, the ice cores provide the only direct measure of the changes that have occurred during the industrial period; they show that the current concentration of methane in the atmosphere is far outside the range experienced in the last 650 000 years; nitrous oxide is also elevated above its natural levels. There is controversy about whether changes in the pre-industrial Holocene are natural or anthropogenic in origin. Changes in wetland emissions are generally cited as the main cause of the large glacial-interglacial change in methane. However, changing sinks must also be considered, and the impact of possible newly described sources evaluated. Recent isotopic data appear to finally rule out any major impact of clathrate releases on methane at these time-scales. Any explanation must take into account that, at the rapid Dansgaard-Oeschger warmings of the last glacial period, methane rose by around half its glacial-interglacial range in only a few decades. The recent EPICA Dome C (Antarctica) record shows that methane tracked climate over the last 650 000 years, with lower methane concentrations in glacials than interglacials, and lower concentrations in cooler interglacials than in warmer ones. Nitrous oxide also shows DansgaardOeschger and glacial-interglacial periodicity, but the pattern is less clear.

show abstract

Changes in the atmospheric CH₄ gradient between Greenland and Antarctica during the Last Glacial and the transition to the Holocene

Cited by 194 publications

References 12 publications

Simulating Heinrich event 1 with interactive icebergs

Simulating Heinrich event 1 with interactive icebergs

Northern hemisphere storm tracks during the last glacial maximum in the PMIP2 ocean-atmosphere coupled models: energetic study, seasonal cycle, precipitation

Methane and nitrous oxide in the ice core record

Contact Info

Product

Resources

About

Changes in the atmospheric CH4 gradient between Greenland and Antarctica during the Last Glacial and the transition to the Holocene

Cited by 194 publications

References 12 publications

Simulating Heinrich event 1 with interactive icebergs

Simulating Heinrich event 1 with interactive icebergs

Northern hemisphere storm tracks during the last glacial maximum in the PMIP2 ocean-atmosphere coupled models: energetic study, seasonal cycle, precipitation

Methane and nitrous oxide in the ice core record

Contact Info

Product

Resources

About

Changes in the atmospheric CH₄ gradient between Greenland and Antarctica during the Last Glacial and the transition to the Holocene