Mode change of millennial CO ₂ variability during the last glacial cycle associated with a bipolar marine carbon seesaw

Abstract

Important elements of natural climate variations during the last ice age are abrupt temperature increases over Greenland and related warming and cooling periods over Antarctica. Records from Antarctic ice cores have shown that the global carbon cycle also plays a role in these changes. The available data shows that atmospheric CO 2 follows closely temperatures reconstructed from Antarctic ice cores during these variations. Here, we present new high-resolution CO 2 data from Antarctic ice cores, which cover the period between 115,000 and 38,000 y before present. Our measurements show that also smaller Antarctic warming events have an imprint in CO 2 concentrations. Moreover, they indicate that during Marine Isotope Stage (MIS) 5, the peak of millennial CO 2 variations lags the onset of Dansgaard/Oeschger warmings by 250 AE 190 y. During MIS 3, this lag increases significantly to 870 AE 90 y. Considerations of the ocean circulation suggest that the millennial variability associated with the Atlantic Meridional Overturning Circulation (AMOC) undergoes a mode change from MIS 5 to MIS 4 and 3. Ocean carbon inventory estimates imply that during MIS 3 additional carbon is derived from an extended mass of carbon-enriched Antarctic Bottom Water. The absence of such a carbon-enriched water mass in the North Atlantic during MIS 5 can explain the smaller amount of carbon released to the atmosphere after the Antarctic temperature maximum and, hence, the shorter lag. Our new data provides further constraints for transient coupled carbon cycleclimate simulations during the entire last glacial cycle.abrupt climate change | CO2-temperature phasing | ice age variability | paleoclimate | greenhouse gas T he climate of the last glacial period is characterized by low global mean temperatures and a number of interhemispheric variations on time scales of several millennia. In the northern hemisphere, in particular on the Greenland ice sheet, large and very rapid temperature jumps of up to 15°C within a few decades, followed by more steady decreases of temperature, have been identified from ice core analyses (1, 2). 25 of these so-called Dansgaard-Oeschger (DO) events have been found during the last glacial period. For each of these events, an associated Antarctic temperature variation has been also documented in Antarctic ice cores (Antarctic Isotope Maximum [AIM] events) (3). Antarctic temperatures increase siteadily when Greenland is in the cold phase and slowly decrease following the abrupt temperature increase in Greenland during a DO event. This behavior is explained by the concept of an oceanic thermal bipolar seesaw, where variations in the Atlantic Meridional Overturning Circulation (AMOC) and associated changes in heat transport across the equator to the North Atlantic modulate the southern and northern hemisphere temperatures during each of these events (4).Previous reconstructions of atmospheric CO 2 concentrations during these millennial-scale variations show that CO 2 varies largely in parallel with the major AIM events (...

A reconstruction of atmospheric carbon dioxide and its stable carbon isotopic composition from the penultimate glacial maximum to the last glacial inception

“…EDC temperature rises by 4 K, according to an increase of δD from −434 to −409 ‰ . At the same time, our CO 2 data show a clear peak of 20 ppm, which is reproduced in the EDML record (Bereiter et al, 2012).…”

“…Gas extraction based on mechanical destruction of the ice matrix as used by Petit et al (1999) and Lourantou et al (2010b) suffers from incomplete and incongruent extraction as release of CO 2 from decomposing air clathrates is slower than for other gases such as O 2 and N 2 . Moreover, larger clathrates may be depleted in CO 2 compared to smaller clathrates but are preferentially released during dry extraction (Bereiter et al, 2012). In contrast, sublimation of the ice sample, as used in our study, ensures a 100 % effective extraction of the air and, therefore, an unbiased CO 2 reconstruction.…”

A 156 kyr smoothed history of the atmospheric greenhouse gases CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub>O and their radiative forcing

“…Ahn et al, 2012;Bereiter et al, 2012;Marcott et al, 2014;Bauska et al, 2015). These offsets may be related to inter-laboratory differences in the calibration or po- Temporal resolution ( t) of the CO 2 data points underlying the spline on a log scale.…”

“…While there are recent developments towards continuous CH 4 records using gas extraction and measurement systems coupled to continuous-flow analysis systems (Schüp-bach et al, 2009;Chappellaz et al, 2013;Rhodes et al, 2013, 364 P. Köhler et al: 156 kyr smoothed history of CO 2 , CH 4 , and N 2 O -For some of the CO 2 records obtained from different ice cores, there exist significant and as yet unexplained offsets (Ahn et al, 2012;Bereiter et al, 2012;Marcott et al, 2014;Bauska et al, 2015). These offsets need to be addressed in our data compilation.…”

Time Lag Between Changes in Global Temperature and Atmospheric Content of Carbon Dioxide Under Non-Greenhouse External Forcing of the Climate System

“…Одним из популярных аргументов в поддержку этих гипотез является вза-имное запаздывание между изменениями температуры и содержания углекис-лого газа в атмосфере, восстанавливаемое по антарктическим ледовым кернам: согласно этим данным, изменения содержания СО 2 отстают от соот-ветствующих изменений температуры на несколько столетий (Monnin et al, 2001;Caillon et al, 2003;Мохов и др., 2005a;Bereiter et al, 2012). Поскольку естественно ожидать, что следствие не может опережать свою причину, суще-ствование подобного запаздывания используется в качестве аргумента для опровержения роли антропогенного парникового эффекта в изменениях кли-мата (напр., Quinn, 2010).…”