High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum

Abstract

Reconstructions of past atmospheric methane concentrations are available from ice cores from both, Greenland and Antarctica. The difference observed between the two polar methane concentration levels is a valuable additional parameter which allows to constrain the geographical location of the responsible methane sources. Here we present new high-resolution methane records from the North Greenland Ice Core Project (NGRIP) and the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice cores covering Termination 1, the Last Glacial Maximum, and parts of the last glacial back to 32 000 years before present. Due to the high-resolution records the synchronisation between the ice cores from NGRIP and EDML is considerably improved and the interpolar concentration difference of methane is determined with unprecedented precision and temporal resolution. Relative to the mean methane concentration, we find a rather stable positive interpolar difference throughout the record with its minimum value of 3.7 ± 0.7 % between 21 900–21 200 years before present, which is higher than previously estimated in this interval close to the Last Glacial Maximum. This implies that Northern Hemisphere boreal wetland sources were never completely shut off during the peak glacial. Starting at 21 000 years before present, i.e. severval millenia prior to the transition into the Holocene, the relative interpolar difference becomes even more positive and stays at a fairly stable level of 6.5 ± 0.8 % during Termination 1. We hypothesise that the anti-correlation observed in the monsoon records from the Northern and Southern Hemispheres induces a methane source redistribution within lower latitudes, which could explain parts of the variations in the interpolar difference

Glacial/interglacial wetland, biomass burning, and geologic methane emissions constrained by dual stable isotopic CH4ice core records

“…Fast and significant stadial/interstadial [CH 4 ] increases occurred within a few decades during glacials in parallel to DansgaardOeschger events (8). Furthermore, [CH 4 ] levels in the Northern Hemisphere are mostly higher than those in the Southern Hemisphere (9). These data taken together with our understanding of the present day methane budget (10)(11)(12)(13)(14)(15) show that wetlands and primarily those located in the tropics dominate natural CH 4 emissions.…”

“…The AxCax wetlands are largely located in regions influenced by seasonal swings of the ITCZ (17,(89)(90)(91)(92)(93)(94)(95). Because the sizes of AxCax regions are not evenly distributed in both hemispheres, a good portion of their emissions (located, for example, in Southeast Asia) also contributes to the IPD in methane mixing ratio over a wide range of climate states (9).…”

“…There is an ongoing debate on the relative contributions from tropical vs. boreal wetlands (ref. 9 and references therein). The latter is possibly overestimated, because other high-latitude sources, like thawing permafrost, thermokarst lakes (20), or (cryospherically capped) geologic seeps (21), also contribute to this source from a hemispheric (ice core) point of view.…”

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

“…Second, consequent widespread perturbations in SH hydrometeorology, including increased austral summer subtropical precipitation between ∼15°S and ∼35°S (Figs. 1F and 5), led to enhanced CH 4 wetland emissions (43). Third, the combination of increased subtropical and decreased midlatitude precipitation, lower wind speeds between ∼35°S and ∼50°S (Fig.…”

Independent variations of CH4 emissions and isotopic composition over the past 160,000 years

“…The nature of the CH 4 -climate coupling on glacial-interglacial and millennial timescales is still a matter of debate 7,8 . Studies of the interpolar CH 4 concentration difference using ice cores from both polar regions are interpreted as a constraint of the latitudinal distribution of CH 4 emission sources 9,10 . Furthermore, most CH 4 sources/sinks have characteristic isotope signatures.…”