Two-million-year-old snapshots of atmospheric gases from Antarctic ice

Abstract

Over the past eight hundred thousand years, glacial-interglacial cycles oscillated with a period of one hundred thousand years ('100k world' 1 ). Ice core and ocean sediment data have shown that atmospheric carbon dioxide, Antarctic temperature, deep ocean temperature, and global ice volume correlated strongly with each other in the 100k world [2][3][4][5][6] . Between about 2.8 and 1.2 million years ago, glacial cycles were smaller in magnitude and shorter in duration ('40k world' 7 ). Proxy data from deep-sea sediments suggest that the variability of atmospheric carbon dioxide in the 40k world was also lower than in the 100k world 8-10 , but we do not have direct observations of atmospheric greenhouse gases from this period. Here we report the recovery of stratigraphically discontinuous ice more than two million years old from the Allan Hills Blue Ice Area, East Antarctica. Concentrations of carbon dioxide and methane in ice core samples older than two million years have been altered by respiration, but some younger samples are pristine. The recovered ice cores extend direct observations of atmospheric carbon dioxide, methane, and Antarctic temperature (based on the deuterium/hydrogen isotope ratio δD ice , a proxy for regional temperature) into the 40k world. All climate properties before eight hundred thousand years ago fall within the envelope of observations from continuous deep Antarctic ice cores that characterize the 100k world. However, the lowest measured carbon dioxide and methane concentrations and Antarctic temperature in the 40k world are well above glacial values from the past eight hundred thousand years. Our results confirm that the amplitudes of glacial-interglacial variations in atmospheric greenhouse gases and Antarctic climate were reduced in the 40k world, and that the transition from the 40k to the 100k world was accompanied by a decline in minimum carbon dioxide concentrations during glacial maxima.Earth has been cooling, and ice sheets expanding, over approximately the past 52 million years (Myr) 11 . Superimposed on this cooling are periodic changes in the Earth's climate system driven by variations in the eccentricity (with periods of 400 and 100 kyr) and precession (23 and 19 kyr) of the Earth's orbit around the Sun, and the tilt of the spin axis (about 41 kyr). From around 2.8 to 1.2 Myr ago (Ma), the Earth's climate system oscillated between glacial and interglacial states with a period of about 40 kyr (the 40k world 7 ). Between 1.2 and 0.8 Ma, an interval known as the 'mid-Pleistocene transition' (MPT), the period of glacial cycles lengthened to about 100 kyr and glacial periods became colder 12 , for reasons that are poorly understood. The post-MPT glacial cycles are characterized by a quasi-100-kyr period (the 100k world 1 ).Studies of stratigraphically continuous ice cores have shown that atmospheric CO 2 is directly linked to Antarctic and global temperature over the last 800 kyr 5,6 . The coupling of the Earth's climate and carbon cycle in earlier times, however, has not be...

Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation

“…4). We expect the range of CO 2 variability from the various Antarctic ice cores to be narrower than our marine-based records because of the greater precision associated with the ice core records (± 6 ppm vs. ±20-30 ppm) and the CO 2 data from blue ice from the mid-Pleistocene may not capture a full climate cycle 24,25 . Despite these caveats, and as discussed elsewhere 18,25 , there is good agreement between the ice-core and δ 11 B-derived CO 2 , providing confidence in the accuracy of the distribution (and absolute values) we determine here for the mPWP.…”

“…Also shown are CO 2 projections in line with RCP8.5 at current emission rates to the year 2040 (black broken line). Middle column; MPT CO 2 estimates 18,23 including disturbed ice estimates 24,25 (Note: age adjusted for scale). Right; mPWP estimates of CO 2 (this study combined with Martinez-Boti et al 13 ), new data from T. sacculifer is shown in red squares and shows no offset from G. ruber estimates.…”

Evolution of vegetation and climate variability on the Tibetan Plateau over the past 1.74 million years

“…Boronbased CO 2 reconstructions (Fig. 4) do not support a long-term decrease in pCO 2 , but a more abrupt change around 0.9 Ma BP, from consistently greater than 200 to ~180 parts per million (27,(29)(30)(31), although existing data are generally of low resolution. The 0.9 Ma BP decline in atmospheric CO 2 may be related to a weakening of AMOC during MIS 24-22 and increased deep-ocean carbon storage (32).…”

Interglacials of the Quaternary defined by northern hemispheric land ice distribution outside of Greenland

“…c Sea level and d δ 18 O sw of different studies 29,48,49 . e Atmospheric CO 2 and its radiative forcing of ΔR ½CO 2 based on ice cores 37 , Allan Hills Blue Ice 34 , various marine proxies (δ 11 B from either T sacculifer 10,12,57 or G ruber 11,[58][59][60][61] , alkenones 58,62,63 ) paleosol 33 , model simulation 9 and data-based reconstruction 38,39 . Error bars show 1σ uncertainty.…”