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.

scholarly journals The last deglaciation: timing the bipolar seesaw

2011 ◽  
Vol 7 (1) ◽  
pp. 397-430 ◽  
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 during the Intra-Allerød Cold Period i.e. prior to 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

<p> 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<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>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<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O in the atmosphere (Lüthi 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.</p><p>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<sub>4</sub> 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<sub>4</sub> in unprecedented details.</p><p>Preliminary analysis reveals that the deglacial CH<sub>4 </sub>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<sub>4</sub> cycle, compare the structure of our record with the CH<sub>4</sub> profile of the last deglaciation (Marcott, 2014) and contrast it with the EDC CO<sub>2</sub> and N<sub>2</sub>O records over the penultimate glacial termination now available in similar resolution.</p>

scholarly journals Abrupt Heinrich Stadial 1 cooling missing in Greenland oxygen isotopes

2021 ◽  
Vol 7 (25) ◽  
pp. eabh1007
Author(s):  
Chengfei He ◽  
Zhengyu Liu ◽  
Bette L. Otto-Bliesner ◽  
Esther C. Brady ◽  
Chenyu Zhu ◽  
...  
Keyword(s):  
Climate Changes ◽  
Ice Core ◽  
Winter Precipitation ◽  
Oxygen Isotopic Composition ◽  
The Arctic ◽  
Last Deglaciation ◽  
Cold Event ◽  
Proxy Records ◽  
Oxygen Isotopic ◽  
The Last Deglaciation

Abrupt climate changes during the last deglaciation have been well preserved in proxy records across the globe. However, one long-standing puzzle is the apparent absence of the onset of the Heinrich Stadial 1 (HS1) cold event around 18 ka in Greenland ice core oxygen isotope δ18O records, inconsistent with other proxies. Here, combining proxy records with an isotope-enabled transient deglacial simulation, we propose that a substantial HS1 cooling onset did indeed occur over the Arctic in winter. However, this cooling signal in the depleted oxygen isotopic composition is completely compensated by the enrichment because of the loss of winter precipitation in response to sea ice expansion associated with AMOC slowdown during extreme glacial climate. In contrast, the Arctic summer warmed during HS1 and YD because of increased insolation and greenhouse gases, consistent with snowline reconstructions. Our work suggests that Greenland δ18O may substantially underestimate temperature variability during cold glacial conditions.

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 Palaeoproductivity in the Ross Sea, Antarctica, during the last 15 kyr BP and its link with ice-core temperature proxies

2004 ◽  
Vol 39 ◽  
pp. 445-451 ◽  
Author(s):  
Cristinamaria Salvi ◽  
Gianguido Salvi ◽  
Barbara Stenni ◽  
Antonio Brambati
Keyword(s):  
Organic Carbon ◽  
Carbon Content ◽  
Ross Sea ◽  
Ice Core ◽  
Sediment Cores ◽  
Organic Carbon Content ◽  
Last Deglaciation ◽  
The Holocene ◽  
The Last Deglaciation ◽  
The Antarctic

AbstractA detailed study of organic carbon content obtained from two sediment cores collected in the Joides basin, western Ross Sea, Antarctica, was carried out. The variations observed during the last deglaciation and the Holocene were compared to the high-resolution climatic records (EPICA DC and Taylor Dome) preserved in the ice. The importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated. A dramatic decrease in the Ross Sea palaeoproductivity was observed during the Antarctic Cold Reversal (12.5–14 kyr BP). Another decrease in total organic carbon in the second half of the Holocene (after 5–6 kyr BP) confirms the climate worsening observed in previous studies.

Release of old carbon from the deep South Pacific during the last deglaciation

2020 ◽  
Author(s):  
Yuhao Dai ◽  
Jimin Yu ◽  
Patrick Rafter
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
South Pacific ◽  
Deep South ◽  
Last Deglaciation ◽  
Age Model ◽  
The Last Deglaciation ◽  
The Antarctic ◽  
First Time ◽  
Underlying Processes

<p>The release of old carbon via the Southern Ocean has been thought to contribute to the last deglacial atmospheric CO<sub>2</sub> rise, but underlying processes are not fully understood, in part, due to insufficient high-fidelity radiocarbon (Δ<sup>14</sup>C) reconstructions minimally complicated by age models and release of “dead carbon”. Here, we present a new deep-water Δ<sup>14</sup>C record for a core located at 3.3 km water depth from the Southwest Pacific, based on a robust age model using planktonic Mg/Ca along with co-existing benthic <sup>14</sup>C measurements. Our results confirm previous records that suggest enhanced ventilation in the Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. For the first time, our data show a large Δ<sup>14</sup>C decline during the Antarctic Cold Reversal, indicating strengthened stratification in the deep South Pacific. Our results strongly support that the deep ocean supplied old carbon to the atmosphere during the last deglaciation.</p>

scholarly journals Tightened constraints on the time-lag between Antarctic temperature and CO<sub>2</sub> during the last deglaciation

2012 ◽  
Vol 8 (4) ◽  
pp. 1213-1221 ◽  
Author(s):  
J. B. Pedro ◽  
S. O. Rasmussen ◽  
T. D. van Ommen
Keyword(s):  
Ice Core ◽  
Time Lag ◽  
Ice Cores ◽  
Relative Timing ◽  
Last Deglaciation ◽  
Physical Processes ◽  
Atmospheric Concentration ◽  
Close Coupling ◽  
The Past ◽  
The Last Deglaciation

Abstract. Antarctic ice cores provide clear evidence of a close coupling between variations in Antarctic temperature and the atmospheric concentration of CO2 during the glacial/interglacial cycles of at least the past 800-thousand years. Precise information on the relative timing of the temperature and CO2 changes can assist in refining our understanding of the physical processes involved in this coupling. Here, we focus on the last deglaciation, 19 000 to 11 000 yr before present, during which CO2 concentrations increased by ~80 parts per million by volume and Antarctic temperature increased by ~10 °C. Utilising a recently developed proxy for regional Antarctic temperature, derived from five near-coastal ice cores and two ice core CO2 records with high dating precision, we show that the increase in CO2 likely lagged the increase in regional Antarctic temperature by less than 400 yr and that even a short lead of CO2 over temperature cannot be excluded. This result, consistent for both CO2 records, implies a faster coupling between temperature and CO2 than previous estimates, which had permitted up to millennial-scale lags.

scholarly journals A New 14C Calibration Data Set for the Last Deglaciation Based on Marine Varves

Radiocarbon ◽  
1997 ◽  
Vol 40 (1) ◽  
pp. 483-494 ◽  
Author(s):  
Konrad A. Hughen ◽  
Jonathan T. Overpeck ◽  
Scott J. Lehman ◽  
Michaele Kashgarian ◽  
John R. Southon ◽  
...  
Keyword(s):  
Global Climate ◽  
Ice Core ◽  
Younger Dryas ◽  
Core Layer ◽  
Cariaco Basin ◽  
Calibration Data ◽  
Last Deglaciation ◽  
Data Set ◽  
The Last Deglaciation ◽  
Calibration Data Set

Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10–14.5 cal ka bp). Independent evaluations of the Cariaco Basin calendar and 14C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to 14C age agreement with terrestrial 14C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin 14C reservoir age remained stable throughout the Younger Dryas and late Allerød climatic events and that the varve and 14C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of 14C change not seen in the coral records. 14C plateaus can be identified at 9.6, 11.4, and 11.7 14C ka bp, in addition to a large, sloping “plateau” during the Younger Dryas (∼10 to 11 14C ka bp). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.

scholarly journals CH<sub>4</sub> and N<sub>2</sub>O fluctuations during the penultimate deglaciation

2020 ◽  
Author(s):  
Loïc Schmidely ◽  
Christoph Nehrbass-Ahles ◽  
Jochen Schmitt ◽  
Juhyeong Han ◽  
Lucas Silva ◽  
...  
Keyword(s):  
Ice Core ◽  
Meridional Overturning Circulation ◽  
Trace Gas ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
Modes Of Variability ◽  
Present Composite ◽  
Meridional Overturning ◽  
The Last Deglaciation ◽  
Ch4 And N2o

Abstract. Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 thousand years. Reconstructions of millennial to centennial-scale variability within these periods are mostly restricted to the last deglaciation. In this study, we present composite records of CH4 and N2O concentrations from the EPICA Dome C ice core covering the penultimate deglaciation at temporal resolutions of about ~ 100 years. Our data permit the identification of centennial-scale fluctuations standing out of the overall transition to interglacial levels. These features occurred in concert with reinvigorations of the Atlantic Meridional Overturning Circulation (AMOC) and northward shifts of the Intertropical Convergence Zone. The abrupt CH4 and N2O rises at about ~ 134 and ~ 128 thousand of years before present (hereafter ka BP) are assimilated to the fluctuations accompanying the Dansgaard–Oeschger events of the last glacial period, while rising N2O levels at ~ 130.5 ka BP are assimilated to a pattern of increasing N2O concentrations that characterized the end of Heinrich stadials. We suggest the 130.5-ka event to be driven by a partial reinvigoration of the AMOC. Overall, the CH4 and N2O fluctuations during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation. However, trace gas responses may differ for similar type of climatic events, as exemplified by the reduced amplitude and duration of the 134-ka event compared to the fluctuations of the Bølling–Allerød during the last deglaciation.

scholarly journals The last deglaciation of Peru and Bolivia

2017 ◽  
Vol 43 (2) ◽  
pp. 591 ◽  
Author(s):  
B. Mark ◽  
N. Stansell ◽  
G. Zeballos
Keyword(s):  
General Pattern ◽  
Late Glacial ◽  
Relative Timing ◽  
Last Deglaciation ◽  
Tropical Andes ◽  
Mountain Ranges ◽  
Tropical Glaciers ◽  
Sedimentary Records ◽  
The Last Deglaciation ◽  
The Antarctic

The tropical Andes of Peru and Bolivia are important for preserving geomorphic evidence of multiple glaciations, allowing for refinements of chronology to aid in understanding climate dynamics at a key location between hemispheres. This review focuses on the deglaciation from Late-Pleistocene maximum positions near the global Last Glacial Maximum (LGM). We synthesize the results of the most recent published glacial geologic studies from 12 mountain ranges or regions within Peru and Bolivia where glacial moraines and drift are dated with terrestrial cosmogenic nuclides (TCN), as well as maximum and minimum limiting ages based on radiocarbon in proximal sediments. Special consideration is given to document paleoglacier valley localities with topographic information given the strong vertical mass balance sensitivity of tropical glaciers. Specific valley localities show variable and heterogeneous sequences ages and extensions of paleoglaciers, but conform to a generally cogent regional sequence revealed by more continuous lake sedimentary records. There are clear distributions of stratigraphically older and younger moraine ages that we group and discuss chronologically. The timing of the local LGM based on average TCN ages of moraine groups is 25.1 ka, but there are large uncertainties (up to 7 ka) making the relative timing with the global LGM elusive. There are a significant number of post-LGM moraines that date to 18.9 (± 0.5) ka. During the Oldest Dryas (18.0 to 14.6 ka), moraine boulders date to 16.1 (± 1.1) ka, suggesting that glaciers either experienced stillstands or readvances during this interval. The Antarctic Cold Reversal (ACR; 14.6 to 12.6 ka) is another phase of stillstanding or readvancing glaciers with moraine groups dating to 13.7 (± 0.8) ka, followed by retreating ice margins through most of the Younger Dryas (YD; 12.9 to 11.8 ka). During the early Holocene, groups of moraines in multiple valleys date to 11.0 (± 0.4) ka, marking a period when glaciers either readvanced or paused from the overall trend of deglaciation. The pattern of glacial variability during the Late Glacial after ~14.6 ka appears to be more synchronous with periods of cooling in the southern high latitudes, and out-of-phase with the overall deglacial trend in the Northern Hemisphere. While insolation and CO2 forcing likely drove the general pattern of deglaciation in the southern tropical Andes, regional ocean-atmospheric and hypsometric controls must have contributed to the full pattern of glacial variability.

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