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

2021 ◽  
Vol 17 (4) ◽  
pp. 1627-1643
Author(s):  
Loïc Schmidely ◽  
Christoph Nehrbass-Ahles ◽  
Jochen Schmitt ◽  
Juhyeong Han ◽  
Lucas Silva ◽  
...  
Keyword(s):  
Ice Core ◽  
Last Deglaciation ◽  
Glacial Cycle ◽  
Last Glacial Period ◽  
Modes Of Variability ◽  
The Past ◽  
Present Composite ◽  
The Last Deglaciation ◽  
Ch4 And N2o ◽  
The Last Glacial

Abstract. Deglaciations are characterized by the largest natural changes in methane (CH4) and nitrous oxide (N2O) concentrations of the past 800 000 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 ∼100 years. Our data permit the identification of centennial-scale fluctuations during the transition from glacial to interglacial levels. At ∼134 000 and ∼129 000 years before present (hereafter ka), both CH4 and N2O increased on centennial timescales. These abrupt rises are similar to the fluctuations associated with the Dansgaard–Oeschger events identified in the last glacial period. In addition, gradually rising N2O levels at ∼130 ka resemble a pattern of increasing N2O concentrations on millennial timescales characterizing the later part of Heinrich stadials. Overall, the events in CH4 and N2O during the penultimate deglaciation exhibit modes of variability that are also found during the last deglaciation and glacial cycle, suggesting that the processes leading to changes in emission during the transitions were similar but their timing differed.

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 Near-constant retreat rate of a terrestrial margin of the Laurentide Ice Sheet during the last deglaciation

Geology ◽  
2021 ◽  
Author(s):  
Thomas V. Lowell ◽  
Meredith A. Kelly ◽  
Jennifer A. Howley ◽  
Timothy G. Fisher ◽  
Peter J. Barnett ◽  
...  
Keyword(s):  
Bayesian Modeling ◽  
Gradual Increase ◽  
Ice Core ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
The Last Deglaciation ◽  
Temperature Records ◽  
The Last Glacial

The Laurentide Ice Sheet (LIS) was the largest ice sheet during the last glacial period. An accurate representation of its behavior during the last deglaciation is critical to understanding its influence on and response to a changing climate. We use 10Be dating and Bayesian modeling to track the recession of the southwest sector of the Labrador Dome of the LIS along an ~500-km-long transect west of Lake Superior during the last deglaciation. This transect reflects terrestrial ice-margin retreat and crosses multiple moraine sets, with the southwestern part of the transect deglaciated by ca. 19 ka and the northeastern part deglaciated by ca. 10 ka. The predominant behavior of the ice margin during this interval is near-constant retreat with retreat rates varying between ~59 m/a and 38 m/a. The moraine sets mark standstills and/or readvances that in total constitute only ~17% of the retreat interval. The spatial and temporal pattern of ice-margin retreat tracked here differs from existing reconstructions that are based on using isochrons to define ice-margin positions. Acknowledging the uncertainties associated with the modeled ages of ice-margin retreat, we suggest that the overall retreat pattern is consistent with forcing by a gradual increase in Northern Hemisphere, high-latitude summer insolation. The pattern of ice-margin retreat is inconsistent with Greenland ice-core temperature records, and thus these records may not be suitable to drive models of the LIS.

A 110,000-Yr Record of Explosive Volcanism from the GISP2 (Greenland) Ice Core

1996 ◽  
Vol 45 (2) ◽  
pp. 109-118 ◽  
Author(s):  
Gregory A. Zielinski ◽  
Paul A. Mayewski ◽  
L. David Meeker ◽  
S. Whitlow ◽  
Mark S. Twickler
Keyword(s):  
Ice Core ◽  
Explosive Volcanism ◽  
Climate Forcing ◽  
Last Deglaciation ◽  
The Past ◽  
Or Groups ◽  
Circulation Patterns ◽  
Second Period ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractThe time series of volcanically produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ∼850 volcanic signals (700 of these from 110,000 to 9000 yr ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known to have perturbed global or Northern Hemisphere climate, respectively. This number is a minimum because decreasing sampling resolution with depth, source volcano location, variable circulation patterns at the time of the eruption, and post-depositional modification of the signal can result in an incomplete record. The largest and most abundant volcanic signals over the past 110,000 yr, even after accounting for lower sampling resolution in the earlier part of the record, occur between 17,000 and 6000 yr ago, during and following the last deglaciation. A second period of enhanced volcanism occurs 35,000–22,000 yr ago, leading up to and during the last glacial maximum. These findings further support a possible climate-forcing component in volcanism. Increased volcanism often occurs during stadial/interstadial transitions within the last glaciation, but this is not consistent over the entire cycle. Ages for some of the largest known eruptions 100,000–9000 yr ago closely correspond to individual sulfate peaks or groups of peaks in our record.

scholarly journals Thickness of the divide and flank of the West Antarctic Ice Sheet through the last deglaciation

2019 ◽  
Author(s):  
Perry Spector ◽  
John Stone ◽  
Brent Goehring
Keyword(s):  
Ice Sheet ◽  
Weddell Sea ◽  
Last Deglaciation ◽  
West Antarctica ◽  
Last Glacial Period ◽  
West Antarctic Ice Sheet ◽  
The Past ◽  
West Antarctic ◽  
Grounding Line ◽  
The Last Glacial

Abstract. We report cosmogenic-nuclide measurements from two isolated groups of nunataks in West Antarctica: the Pirrit Hills, located midway between the grounding line and the divide in the Weddell Sea sector, and the Whitmore Mountains, located along the Ross-Weddell divide. At the Pirrit Hills, ice reached a highstand ~ 320 m above present during the last glacial period. Subsequent thinning mostly occurred after ~ 14 kyr B.P., and modern ice levels were established some time after ~ 4 kyr B.P. We infer that, like at other flank sites, these changes were primarily controlled by the position of the grounding-line downstream. At the Whitmore Mountains, cosmogenic 14C concentrations in bedrock surfaces demonstrate that ice there was no more than ~ 190 m thicker than present during the past ~ 30 kyr. Combined with other constraints from West Antarctica, the 14C data imply that the divide was thicker than present for a period of less than ~ 8 kyr within the past ~ 15 kyr. These results are consistent with the hypothesis that the divide initially thickened due to the deglacial rise in snowfall, and subsequently thinned in response to retreat of the ice-sheet margin. We use these data to evaluate several recently-published ice-sheet models at the Pirrit Hills and Whitmore Mountains.

scholarly journals Atmospheric gas records from Taylor Glacier, Antarctica, reveal ancient ice with ages spanning the entire last glacial cycle

2017 ◽  
Vol 13 (7) ◽  
pp. 943-958 ◽  
Author(s):  
Daniel Baggenstos ◽  
Thomas K. Bauska ◽  
Jeffrey P. Severinghaus ◽  
James E. Lee ◽  
Hinrich Schaefer ◽  
...  
Keyword(s):  
Large Scale ◽  
Ice Core ◽  
Ice Sheet ◽  
Last Deglaciation ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Climate Reconstructions ◽  
Age Model ◽  
Taylor Glacier ◽  
The Last Glacial

Abstract. Old ice for paleo-environmental studies, traditionally accessed through deep core drilling on domes and ridges on the large ice sheets, can also be retrieved at the surface from ice sheet margins and blue ice areas. The practically unlimited amount of ice available at these sites satisfies a need in the community for studies of trace components requiring large sample volumes. For margin sites to be useful as ancient ice archives, the ice stratigraphy needs to be understood and age models need to be established. We present measurements of trapped gases in ice from Taylor Glacier, Antarctica, to date the ice and assess the completeness of the stratigraphic section. Using δ18O of O2 and methane concentrations, we unambiguously identify ice from the last glacial cycle, covering every climate interval from the early Holocene to the penultimate interglacial. A high-resolution transect reveals the last deglaciation and the Last Glacial Maximum (LGM) in detail. We observe large-scale deformation in the form of folding, but individual stratigraphic layers do not appear to have undergone irregular thinning. Rather, it appears that the entire LGM–deglaciation sequence has been transported from the interior of the ice sheet to the surface of Taylor Glacier relatively undisturbed. We present an age model that builds the foundation for gas studies on Taylor Glacier. A comparison with the Taylor Dome ice core confirms that the section we studied on Taylor Glacier is better suited for paleo-climate reconstructions of the LGM due to higher accumulation rates.

scholarly journals Climatic and glaciological information inferred from air-content measurements of a Law Dome (East Antarctica) ice core

1999 ◽  
Vol 45 (150) ◽  
pp. 255-263 ◽  
Author(s):  
Marc Delmotte ◽  
Dominique Raynaud ◽  
Vin Morgan ◽  
Jean Jouzel
Keyword(s):  
Ice Core ◽  
East Antarctica ◽  
Seasonal Temperature ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
Annual Variations ◽  
Air Content ◽  
Temperature And Precipitation ◽  
Elevation Changes ◽  
The Last Glacial

AbstractThe total air content(V)of ice has been measured along the Dome Summit South (DSS) core from Law Dome, East Antarctica. The main features of this record are the very well-preserved sub-annual fluctuations ofV(down to at least 900 m depth) and the significant increase of theVvalues during the last deglaciation. The sub-annual variations reflect changes in close-off porosity, and we interpret theVseasonal peaks as tracers of depth-hoar layers. For the longer time-scale, the largeVfluctuations observed are interpreted in terms of elevation and/or close-off porosity changes under different assumptions. We analyze the possible influence of a different global pressure field and/or a change in seasonal temperature and precipitation cycles during the last glacial period. Our estimates of surface elevation changes derived from theVdata are then compared with independent reconstructions of past elevations.

scholarly journals Evolution of mean ocean temperature in Marine Isotope Stages 5-4

2021 ◽  
Author(s):  
Sarah Shackleton ◽  
James A. Menking ◽  
Edward Brook ◽  
Christo Buizert ◽  
Michael N. Dyonisius ◽  
...  
Keyword(s):  
Noble Gas ◽  
Ice Sheet ◽  
Ocean Temperature ◽  
Atmospheric Conditions ◽  
Last Deglaciation ◽  
Glacial Cycle ◽  
The Last Deglaciation ◽  
Gas Measurements ◽  
Mis 5 ◽  
The Last Glacial

Abstract. Deglaciations are characterized by relatively fast and near-synchronous changes in ice sheet volume, ocean temperature, and atmospheric greenhouse gas concentrations, but glacial inceptions occur more gradually. Understanding the evolution of ice sheet, ocean, and atmospheric conditions from interglacial to glacial maximum provides important insight into the interplay of these components of our climate system. Using noble gas measurements in ancient ice samples, we reconstruct mean ocean temperature (MOT) from 74 to 59.5 ka BP, covering the Marine Isotope Stage (MIS) 5-4 boundary, MIS 4, and part of the MIS 4-3 transition. Comparing this MOT reconstruction to previously published MOT reconstructions from the last glacial cycle, we find that the majority of interglacial-glacial ocean cooling occurred across MIS 5, and MOT reached full glacial levels by MIS 4 (−2.7 ± 0.3 °C relative to the Holocene). Comparing MOT to contemporaneous records of CO2 and benthic 𝛿18O, we find that ocean cooling and the solubility pump can explain most of the CO2 drawdown and increase in 𝛿18O across MIS 5. The timing of ocean warming and cooling in our record indicates that millennial scale climate variability plays a crucial role in setting mean ocean temperature during this interval, as seen during other periods, such as the last deglaciation.

scholarly journals Operation of the boreal peatland methane cycle across the past 16 k.y.

Geology ◽  
2019 ◽  
Vol 48 (1) ◽  
pp. 82-86 ◽  
Author(s):  
Yanhong Zheng ◽  
Zhengkun Fang ◽  
Tongyu Fan ◽  
Zhao Liu ◽  
Zhangzhang Wang ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Ice Core ◽  
Ice Cores ◽  
Atmospheric Methane ◽  
Last Deglaciation ◽  
Methane Cycle ◽  
The Past ◽  
Stable Isotopic ◽  
The Last Deglaciation

Abstract The role of boreal wetlands in driving variations in atmospheric methane (CH4) concentrations across the last deglaciation (20–10 ka) and the Holocene is debated. Most studies infer the sources of atmospheric methane via ice-core records of methane concentration and its light stable isotopic composition. However, direct evidence for variations in the methane cycle from the wetlands themselves is relatively limited. Here, we used a suite of biomarker proxies to reconstruct the methane cycle in the Chinese Hani peat across the past 16 k.y. We found two periods of enhanced methanogenesis, at ca. 15–11 ka and ca. 10–6 ka, whereas weak methanogenesis characterized the late Holocene. These periods of enhanced methanogenesis relate to periods of high/increasing temperatures, supporting a temperature control on the wetland methane cycle. We found no biomarker evidence for intense methanotrophy throughout the past 16 k.y., and, contrary to previous studies, we found no clear control of hydrology on the peatland methane cycle. Although the onset of methanogenesis at Hani at ca. 15 ka coincided with a negative shift in methane δ13C in the ice cores, there is no consistent correlation between changes in the reconstructed methane cycle of the boreal Hani peat and atmospheric CH4 concentrations.

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.

The last deglaciation of Cape Adare, northern Victoria Land, Antarctica

2008 ◽  
Vol 20 (6) ◽  
pp. 581-587 ◽  
Author(s):  
Joanne S. Johnson ◽  
Claus-Dieter Hillenbrand ◽  
John L. Smellie ◽  
Sergio Rocchi
Keyword(s):  
Before Present ◽  
Last Deglaciation ◽  
Last Glacial Period ◽  
Radiocarbon Dates ◽  
Exposure Age ◽  
Victoria Land ◽  
Younger Age ◽  
The Last Deglaciation ◽  
Exposure Ages ◽  
The Last Glacial

AbstractWe present two 10Be exposure ages from erratic boulders at Cape Adare, northern Victoria Land. The exposure ages obtained suggest that Cape Adare was covered by ice during the last glacial period, and the younger age points to deglaciation around 16.2 ka. Comparison of our younger 10Be exposure age with published radiocarbon dates for Adélie penguin occupation at Cape Adare suggests that the onset of penguin colonization (at 2–3 kyr before present) lagged behind the deglaciation by at least 11.5 kyr. These observations indicate that penguin colonization did not occur until several thousand years after ice free ground became available.

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