scholarly journals Leads and lags between Antarctic temperature and carbon dioxide during the last deglaciation

2017 ◽  
Author(s):  
Léa Gest ◽  
Frédéric Parrenin ◽  
Jai Chowdhry Beeman ◽  
Dominique Raynaud ◽  
Tyler J. Fudge ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Cores ◽  
Atmospheric Co2 ◽  
Last Deglaciation ◽  
High Accumulation ◽  
Volcanic Event ◽  
Sequence Of Events ◽  
The Last Deglaciation ◽  
Paleoclimate Records ◽  
The Antarctic

Abstract. To understand causal relationships in past climate variations, it is essential to have accurate chronologies of paleoclimate records. The last deglaciation, which occurred from 18 000 to 11 000 years ago, is especially interesting, since it is the most recent large climatic variation of global extent. Ice cores in Antarctica provide important paleoclimate proxies, such as regional temperature and global atmospheric CO2. However, temperature is recorded in the ice while CO2 is recorded in the enclosed air bubbles. The ages of the former and of the latter are different since air is trapped at 50–120 m below the surface. It is therefore necessary to correct for this air-ice shift to accurately infer the sequence of events. Here we accurately determine the phasing between East Antarctic temperature and atmospheric CO2 variations during the last deglacial warming based on Antarctic ice core records. We build a stack of East Antarctic temperature variations by averaging the records from 4 ice cores (EPICA Dome C, Dome Fuji, EPICA Dronning Maud Land and Talos Dome), all accurately synchronized by volcanic event matching. We place this stack onto the WAIS Divide WD2014 age scale by synchronizing EPICA Dome C and WAIS Divide using volcanic event matching, which allows comparison with the high resolution CO2 record from WAIS Divide. Since WAIS Divide is a high accumulation site, its air age scale, which has previously been determined by firn modeling, is more robust. Finally, we assess the CO2/Antarctic temperature phasing by determining four periods when their trends change abruptly. We find that at the onset of the last deglaciation and at the onset of the Antarctic Cold Reversal (ACR) period CO2 and Antarctic temperature are synchronous within a range of 210 years. Then CO2 slightly leads by 165 ± 116 years at the end of the Antarctic Cold Reversal (ACR) period. Finally, Antarctic temperature significantly leads by 406 ± 200 years at the onset of the Holocene period. Our results further support the hypothesis of no convective zone at EPICA Dome C during the last deglaciation and the use of nitrogen-15 to infer the height of the diffusive zone. Future climate and carbon cycle modeling works should take into account this robust phasing constraint.

scholarly journals Ice core evidence for decoupling between mid-latitude atmospheric water cycle and Greenland temperature during the last deglaciation

2018 ◽  
Author(s):  
Amaëlle Landais ◽  
Emilie Capron ◽  
Valérie Masson-Delmotte ◽  
Samuel Toucanne ◽  
Rachael Rhodes ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Environmental Changes ◽  
Ice Core ◽  
Ice Cores ◽  
Last Deglaciation ◽  
Sequence Of Events ◽  
Decadal Scale ◽  
Abrupt Changes ◽  
The Last Deglaciation

Abstract. The last deglaciation represents the most recent example of natural global warming associated with large-scale climate changes. In addition to the long-term global temperature increase, the last deglaciation onset is punctuated by a sequence of abrupt changes in the Northern Hemisphere. Such interplay between orbital- and millennial-scale variability is widely documented in paleoclimatic records but the underlying mechanisms are not fully understood. Limitations arise from the difficulty in constraining the sequence of events between external forcing, high- and low- latitude climate and environmental changes. Greenland ice cores provide sub-decadal-scale records across the last deglaciation and contain fingerprints of climate variations occurring in different regions of the Northern Hemisphere. Here, we combine new ice d-excess and 17O-excess records, tracing changes in the mid-latitudes, with ice δ18O records of polar climate. Within Heinrich Stadial 1, we demonstrate a decoupling between climatic conditions in Greenland and those of the lower latitudes. While Greenland temperature remains mostly stable from 17.5 to 14.7 ka, significant change in the mid latitudes of northern Atlantic takes place at ~ 16.2 ka, associated with warmer and wetter conditions of Greenland moisture sources. We show that this climate modification is coincident with abrupt changes in atmospheric CO2 and CH4 concentrations recorded in an Antarctic ice core. Our coherent ice core chronological framework and comparison with other paleoclimate records suggests a mechanism involving two-step freshwater fluxes in the North Atlantic associated with a southward shift of the intertropical convergence zone.

scholarly journals Ice core evidence for decoupling between midlatitude atmospheric water cycle and Greenland temperature during the last deglaciation

2018 ◽  
Vol 14 (10) ◽  
pp. 1405-1415 ◽  
Author(s):  
Amaëlle Landais ◽  
Emilie Capron ◽  
Valérie Masson-Delmotte ◽  
Samuel Toucanne ◽  
Rachael Rhodes ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Large Scale ◽  
Environmental Changes ◽  
Ice Core ◽  
Ice Cores ◽  
Last Deglaciation ◽  
Sequence Of Events ◽  
Decadal Scale ◽  
Abrupt Changes ◽  
The Last Deglaciation

Abstract. The last deglaciation represents the most recent example of natural global warming associated with large-scale climate changes. In addition to the long-term global temperature increase, the last deglaciation onset is punctuated by a sequence of abrupt changes in the Northern Hemisphere. Such interplay between orbital- and millennial-scale variability is widely documented in paleoclimatic records but the underlying mechanisms are not fully understood. Limitations arise from the difficulty in constraining the sequence of events between external forcing, high- and low- latitude climate, and environmental changes. Greenland ice cores provide sub-decadal-scale records across the last deglaciation and contain fingerprints of climate variations occurring in different regions of the Northern Hemisphere. Here, we combine new ice d-excess and 17O-excess records, tracing changes in the midlatitudes, with ice δ18O records of polar climate. Within Heinrich Stadial 1, we demonstrate a decoupling between climatic conditions in Greenland and those of the lower latitudes. While Greenland temperature remains mostly stable from 17.5 to 14.7 ka, significant change in the midlatitudes of the northern Atlantic takes place at ∼16.2 ka, associated with warmer and wetter conditions of Greenland moisture sources. We show that this climate modification is coincident with abrupt changes in atmospheric CO2 and CH4 concentrations recorded in an Antarctic ice core. Our coherent ice core chronological framework and comparison with other paleoclimate records suggests a mechanism involving two-step freshwater fluxes in the North Atlantic associated with a southward shift of the Intertropical Convergence Zone.

scholarly journals Glacial–interglacial dynamics of Antarctic firn columns: comparison between simulations and ice core air-δ<sup>15</sup>N measurements

2013 ◽  
Vol 9 (3) ◽  
pp. 983-999 ◽  
Author(s):  
E. Capron ◽  
A. Landais ◽  
D. Buiron ◽  
A. Cauquoin ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Accumulation Rate ◽  
Ice Core ◽  
Ice Cores ◽  
Detailed Comparison ◽  
Last Deglaciation ◽  
Depth Study ◽  
Dronning Maud Land ◽  
The Last Deglaciation ◽  
Correct Estimation ◽  
Lock In

Abstract. Correct estimation of the firn lock-in depth is essential for correctly linking gas and ice chronologies in ice core studies. Here, two approaches to constrain the firn depth evolution in Antarctica are presented over the last deglaciation: outputs of a firn densification model, and measurements of δ15N of N2 in air trapped in ice core, assuming that δ15N is only affected by gravitational fractionation in the firn column. Since the firn densification process is largely governed by surface temperature and accumulation rate, we have investigated four ice cores drilled in coastal (Berkner Island, BI, and James Ross Island, JRI) and semi-coastal (TALDICE and EPICA Dronning Maud Land, EDML) Antarctic regions. Combined with available ice core air-δ15N measurements from the EPICA Dome C (EDC) site, the studied regions encompass a large range of surface accumulation rates and temperature conditions. Our δ15N profiles reveal a heterogeneous response of the firn structure to glacial–interglacial climatic changes. While firn densification simulations correctly predict TALDICE δ15N variations, they systematically fail to capture the large millennial-scale δ15N variations measured at BI and the δ15N glacial levels measured at JRI and EDML – a mismatch previously reported for central East Antarctic ice cores. New constraints of the EDML gas–ice depth offset during the Laschamp event (~41 ka) and the last deglaciation do not favour the hypothesis of a large convective zone within the firn as the explanation of the glacial firn model–δ15N data mismatch for this site. While we could not conduct an in-depth study of the influence of impurities in snow for firnification from the existing datasets, our detailed comparison between the δ15N profiles and firn model simulations under different temperature and accumulation rate scenarios suggests that the role of accumulation rate may have been underestimated in the current description of firnification models.

scholarly journals The last deglaciation: timing the bipolar seesaw

2011 ◽  
Vol 7 (2) ◽  
pp. 671-683 ◽  
Author(s):  
J. B. Pedro ◽  
T. D. van Ommen ◽  
S. O. Rasmussen ◽  
V. I. Morgan ◽  
J. Chappellaz ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Core ◽  
Time Lag ◽  
Last Deglaciation ◽  
Atmospheric Teleconnections ◽  
The Last Deglaciation ◽  
The Antarctic ◽  
First Time ◽  
Coupling Mechanisms ◽  
Ice Core Records

Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

Centennial-scale evolution of methane during the penultimate deglaciation

2020 ◽  
Author(s):  
Loïc Schmidely ◽  
Lucas Silva ◽  
Christoph Nehrbass-Ahles ◽  
Juhyeong Han ◽  
Jinhwa Shin ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Ice Core ◽  
Ice Cores ◽  
Before Present ◽  
Last Deglaciation ◽  
Rates Of Change ◽  
Maximum Resolution ◽  
The Last Deglaciation ◽  
First Time ◽  
Temporal Coverage

&lt;p&gt; Small air inclusions in ice cores represent a direct archive of past atmospheric compositions, allowing us to measure the concentration of the three most potent non-condensable Greenhouse Gases (GHG) CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O as far back as 800,000 years before present (kyr BP). These records demonstrate that transitions from glacial to interglacial conditions are accompanied by a substantial net increase of CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O in the atmosphere (L&amp;#252;thi et al. 2008, Loulergue et al. 2008, Schilt et al. 2010). A sound understanding of the interplay between the reorganization of the climate system and the perturbation of GHG inventories during glacial terminations is partly limited by the temporal resolution of the records derived from ice cores. In fact, with the exception of the last deglaciation (23-9 kyr BP) centennial-scale GHG variability remained uncaptured for precedings glacial terminations.&lt;/p&gt;&lt;p&gt;In this work, we exploit the exceptionally long temporal coverage of the EPICA Dome C (EDC) ice core to reconstruct, for the first time, centennial-scale fluctuations of CH&lt;sub&gt;4&lt;/sub&gt; mole fractions from 145 to 125 kyr BP, encompassing the entire penultimate deglaciation (138-128 kyr BP). With a temporal resolution of ~100 years, our new record is now unveiling all climate-driven signals enclosed into the EDC ice core, exploiting the maximum resolution possible at Dome C (). This offers us the opportunity to study the timing and rates of change of CH&lt;sub&gt;4&lt;/sub&gt; in unprecedented details.&lt;/p&gt;&lt;p&gt;Preliminary analysis reveals that the deglacial CH&lt;sub&gt;4 &lt;/sub&gt;rise is a superimposition of gradual millennial-scale increases (~0.01-0.02 ppb/year) and abrupt and partly intermittent centennial-scale events (~80-200 ppb in less than a millennium). We will investigate processes modulating the observed changes in the CH&lt;sub&gt;4&lt;/sub&gt; cycle, compare the structure of our record with the CH&lt;sub&gt;4&lt;/sub&gt; profile of the last deglaciation (Marcott, 2014) and contrast it with the EDC CO&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O records over the penultimate glacial termination now available in similar resolution.&lt;/p&gt;

scholarly journals The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years

2013 ◽  
Vol 9 (4) ◽  
pp. 1733-1748 ◽  
Author(s):  
D. Veres ◽  
L. Bazin ◽  
A. Landais ◽  
H. Toyé Mahamadou Kele ◽  
B. Lemieux-Dudon ◽  
...  
Keyword(s):  
Ice Core ◽  
Ice Cores ◽  
Strong Basis ◽  
Last Glacial ◽  
Sequence Of Events ◽  
Global Correlation ◽  
Wide Range ◽  
The Antarctic ◽  
The Last Glacial ◽  
Ice Core Records

Abstract. The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to several thousand years (ka) exist between ice cores over the last climatic cycle. In this context, we are hereby introducing the Antarctic Ice Core Chronology 2012 (AICC2012), a new and coherent timescale developed for four Antarctic ice cores, namely Vostok, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML) and Talos Dome (TALDICE), alongside the Greenlandic NGRIP record. The AICC2012 timescale has been constructed using the Bayesian tool Datice (Lemieux-Dudon et al., 2010) that combines glaciological inputs and data constraints, including a wide range of relative and absolute gas and ice stratigraphic markers. We focus here on the last 120 ka, whereas the companion paper by Bazin et al. (2013) focuses on the interval 120–800 ka. Compared to previous timescales, AICC2012 presents an improved timing for the last glacial inception, respecting the glaciological constraints of all analyzed records. Moreover, with the addition of numerous new stratigraphic markers and improved calculation of the lock-in depth (LID) based on δ15N data employed as the Datice background scenario, the AICC2012 presents a slightly improved timing for the bipolar sequence of events over Marine Isotope Stage 3 associated with the seesaw mechanism, with maximum differences of about 600 yr with respect to the previous Datice-derived chronology of Lemieux-Dudon et al. (2010), hereafter denoted LD2010. Our improved scenario confirms the regional differences for the millennial scale variability over the last glacial period: while the EDC isotopic record (events of triangular shape) displays peaks roughly at the same time as the NGRIP abrupt isotopic increases, the EDML isotopic record (events characterized by broader peaks or even extended periods of high isotope values) reached the isotopic maximum several centuries before. It is expected that the future contribution of both other long ice core records and other types of chronological constraints to the Datice tool will lead to further refinements in the ice core chronologies beyond the AICC2012 chronology. For the time being however, we recommend that AICC2012 be used as the preferred chronology for the Vostok, EDC, EDML and TALDICE ice core records, both over the last glacial cycle (this study), and beyond (following Bazin et al., 2013). The ages for NGRIP in AICC2012 are virtually identical to those of GICC05 for the last 60.2 ka, whereas the ages beyond are independent of those in GICC05modelext (as in the construction of AICC2012, the GICC05modelext was included only via the background scenarios and not as age markers). As such, where issues of phasing between Antarctic records included in AICC2012 and NGRIP are involved, the NGRIP ages in AICC2012 should therefore be taken to avoid introducing false offsets. However for issues involving only Greenland ice cores, there is not yet a strong basis to recommend superseding GICC05modelext as the recommended age scale for Greenland ice cores.

scholarly journals Rapid changes in ice core gas records – Part 2: Understanding the rapid rise in atmospheric CO<sub>2</sub> at the onset of the Bølling/Allerød

2010 ◽  
Vol 6 (4) ◽  
pp. 1473-1501 ◽  
Author(s):  
P. Köhler ◽  
G. Knorr ◽  
D. Buiron ◽  
A. Lourantou ◽  
J. Chappellaz
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Ice Core ◽  
Age Distribution ◽  
Ice Cores ◽  
Atmospheric Co2 ◽  
Current Debate ◽  
Last Deglaciation ◽  
Rapid Changes

Abstract. During the last glacial/interglacial transition the Earth's climate underwent rapid changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A is accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is matter of current debate. In situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10±1 ppmv in 230 yr at the same time. Allowing for the age distribution of CO2 in firn we here show, that atmospheric CO2 rose by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 larger than the CO2 signal recorded in situ in EDC. Based on the estimated airborne fraction of 0.17 of CO2 we infer that 125 Pg of carbon need to be released to the atmosphere to produce such a peak. Most of the carbon might have been activated as consequence of continental shelf flooding during MWP-1A. This impact of rapid sea level rise on atmospheric CO2 distinguishes the B/A from other Dansgaard/Oeschger events of the last 60 kyr, potentially defining the point of no return during the last deglaciation.

scholarly journals On the gas-ice depth difference (Δdepth) along the EPICA Dome C ice core

2012 ◽  
Vol 8 (2) ◽  
pp. 1089-1131 ◽  
Author(s):  
F. Parrenin ◽  
S. Barker ◽  
T. Blunier ◽  
J. Chappellaz ◽  
J. Jouzel ◽  
...  
Keyword(s):  
Flow Model ◽  
Ice Core ◽  
Ice Cores ◽  
Convective Zone ◽  
Column Height ◽  
Last Deglaciation ◽  
Ice Flow ◽  
Depth Difference ◽  
The Last Deglaciation ◽  
Good Agreement

Abstract. We compare a variety of methods for estimating the gas/ice depth offset (Δdepth) at EPICA Dome C (EDC, East Antarctica). (1) Purely based on modelling efforts, Δdepth can be estimated combining a firn densification with an ice flow model. Observations allow direct and indirect estimate of Δdepth. (2) The diffusive column height can be estimated from δ15N and converted to Δdepth using an ice flow model and assumptions about past average firn density and thickness of the convective zone. (3) Ice and gas synchronisation of the EDC ice core to the GRIP, EDML and TALDICE ice cores shifts the ice/gas offset problem into higher accumulation ice cores where it can be more accurately evaluated. (4) Finally, the bipolar seesaw hypothesis allows us to synchronise the ice isotopic record with the gas CH4 record, the later being taken as a proxy of Greenland temperature. The bipolar seesaw antiphase relationship is generally supported by the ice-gas cross synchronisation between EDC and the GRIP, EDML and TALDICE ice cores, which provide support for method 4. Applying the bipolar seesaw hypothesis to the deeper section of the EDC core confirms that the ice flow is complex and can help improving our reconstruction of the thinning function and thus of the EDC age scale. We confirm that method 1 overestimates the glacial Δdepth at EDC and we suggested that it is due to an overestimation of the glacial Close Off Depth by the firn densification model. In contrast we find that the glaciological models probably underestimate the Δdepth during termination II. Finally, we show that method 2 based on 15N data produces for the last deglaciation a Δdepth estimate which is in good agreement with methods 3 and 4.

scholarly journals Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores

2002 ◽  
Vol 17 (4) ◽  
pp. 8-1-8-7 ◽  
Author(s):  
A. Shemesh ◽  
D. Hodell ◽  
X. Crosta ◽  
S. Kanfoush ◽  
C. Charles ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ice Cores ◽  
Last Deglaciation ◽  
Sequence Of Events ◽  
The Last Deglaciation

scholarly journals Modelling firn thickness evolution during the last deglaciation: constraints on sensitivity to temperature and impurities

2017 ◽  
Vol 13 (7) ◽  
pp. 833-853 ◽  
Author(s):  
Camille Bréant ◽  
Patricia Martinerie ◽  
Anaïs Orsi ◽  
Laurent Arnaud ◽  
Amaëlle Landais
Keyword(s):  
Accumulation Rate ◽  
Ice Cores ◽  
East Antarctica ◽  
Ice Age ◽  
Age Difference ◽  
Last Deglaciation ◽  
Densification Rate ◽  
Impurity Effects ◽  
High Accumulation ◽  
The Last Deglaciation

Abstract. The transformation of snow into ice is a complex phenomenon that is difficult to model. Depending on surface temperature and accumulation rate, it may take several decades to millennia for air to be entrapped in ice. The air is thus always younger than the surrounding ice. The resulting gas–ice age difference is essential to documenting the phasing between CO2 and temperature changes, especially during deglaciations. The air trapping depth can be inferred in the past using a firn densification model, or using δ15N of air measured in ice cores. All firn densification models applied to deglaciations show a large disagreement with δ15N measurements at several sites in East Antarctica, predicting larger firn thickness during the Last Glacial Maximum, whereas δ15N suggests a reduced firn thickness compared to the Holocene. Here we present modifications of the LGGE firn densification model, which significantly reduce the model–data mismatch for the gas trapping depth evolution over the last deglaciation at the coldest sites in East Antarctica (Vostok, Dome C), while preserving the good agreement between measured and modelled modern firn density profiles. In particular, we introduce a dependency of the creep factor on temperature and impurities in the firn densification rate calculation. The temperature influence intends to reflect the dominance of different mechanisms for firn compaction at different temperatures. We show that both the new temperature parameterization and the influence of impurities contribute to the increased agreement between modelled and measured δ15N evolution during the last deglaciation at sites with low temperature and low accumulation rate, such as Dome C or Vostok. We find that a very low sensitivity of the densification rate to temperature has to be used in the coldest conditions. The inclusion of impurity effects improves the agreement between modelled and measured δ15N at cold East Antarctic sites during the last deglaciation, but deteriorates the agreement between modelled and measured δ15N evolution at Greenland and Antarctic sites with high accumulation unless threshold effects are taken into account. We thus do not provide a definite solution to the firnification at very cold Antarctic sites but propose potential pathways for future studies.

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