Soluble salts in deserts as a source of sulfate aerosols in an Antarctic ice core during the last glacial period

Abstract. Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates that the climate can change state, the mechanisms that drive that change, and the leads, lags and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using speleothems from the northern rim of the Alps (NALPS), enabling direct chronological comparisons with highly similar shifts in Greenland ice cores. In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18O chronology over the interval 118.3 to 63.7 ka using eleven,newly-available, clean, precisely-dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 15 stalagmites from seven caves. Where speleothems grew synchronously, major transitional events between stadials and interstadials (and vice versa) are all in agreement within uncertainty. Ramp-fitting analysis further reveals good agreement between the NALPS19 speleothem δ18O record, the GICC05modelext NGRIP ice-core δ18O record, and the Asian Monsoon composite speleothem δ18O record. In contrast, NGRIP ice-core δ18O on AICC2012 appears to be considerably too young. We also propose a longer duration for the interval covering Greenland Stadial (GS) 22 to GS-21.2 in line with the Asian monsoon and NGRIP-EDML. Given the near-complete record of δ18O variability during the last glacial period in the northern Alps, we offer preliminary considerations regarding the controls on mean δ18O. We find that as expected, δ18O values became increasingly more depleted with distance from the oceanic source regions, and increasingly depleted with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18O values that are too high in comparison to lower-elevation sites, thus indicating a summer bias in the recorded signal. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as "pre-cursor" events GS-16.2, GS-17.2, GS-21.2, and GS-23.2, as well as the "within-interstadial" GS-24.2 event. Our new high-precision chronology shows that each of these δ18O depletions occurred shortly following rapid rises in sea level associated with increased ice-rafted debris and southward shifts in the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately-sized ice sheets may have been responsible for the cold reversals causing the AMOC to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.

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The ice core record of atmospheric CO2 variability during the Last Glacial Period: new insights from timing and isotopes

10.5194/egusphere-egu2020-7292 ◽

2020 ◽

Author(s):

Thomas Bauska ◽

Shaun Marcott ◽

Ed Brook

Keyword(s):

Climate Variability ◽

Time Scale ◽

Ice Core ◽

Ocean Temperature ◽

Glacial Period ◽

Sea Ice Extent ◽

Last Glacial Period ◽

Last Glacial ◽

Ice Core Record ◽

The Last Glacial

Atmospheric carbon dioxide (CO2) concentrations during the last glacial period (70,000 &#8211; 23,000 years ago) fluctuated on millennial timescales closely following variations in Antarctic temperature. This close coupling has suggested that the sources and sinks driving millennial scale CO2 changes are dominated by processes in the Southern Ocean. However, recent work revealed centennial-scale increases in CO2 during abrupt climate events of the last deglaciation which may represent a second mechanism of carbon cycle variability.&#160;Here we analyze a high resolution CO2 record from the last glacial period from the West Antarctic Ice Sheet (WAIS Divide) that precisely defines the timing of CO2 changes with respect to Antarctic ice core proxies for temperature, dust delivery, and sea-ice extent down to the centennial-timescale. Although CO2 closely tracks all these proxies over millennia, peak CO2 levels most often lag behind all proxies by a few hundred years. This decoupling from Antarctic climate variability is most prominent during the onset of DO interstadial events when CO2, CH4 and Greenland temperature all increase simultaneously. Regression analysis suggests that the CO2 variations can be explained by a combination of two mechanisms: one operating on the time scale of Antarctic climate variability, and a second responding on the Dansgaard-Oeschger time scale.&#160;&#160;Recent &#948;13C-CO2 data from the last glacial period support our finding that CO2 variability is the sum of multiple mechanisms.&#160; The Antarctic climate variability is likely associated with the release of respired organic carbon from the deep ocean.&#160; Superimposed on these oscillations are two types of centennial-scale changes: CO2 increases and &#948;13C-CO2 minima in the middle of Heinrich stadials and ii) CO2 increases and small changes in &#948;13C-CO2 that at the onset of DO interstadial event.To provide a comprehensive and quantitative constraint on the mechanisms of CO2 variability during the last glacial period, we run a large suite of transient box model experiments (n = 500) forced with varying combinations of forcings based on proxy time-series (e.g. AABW formation, NADW formation, ocean temperature, dust delivery, and sea-ice extent).&#160; Using data constraints from the ice core records of CO2, &#948;13C-CO2 and mean ocean temperature, we arrive at an ensemble of scenarios that can explain a large amount of the centennial and millennial-scale variability observed in the ice core record. Parsing this into a series of factorial experiments we find that Southern Hemisphere processes can explain 80% of the observed variability and Northern Hemisphere processes account for the remaining 20%.&#160; A further breakdown on the level of individual mechanisms is marred by the high degree of correlation between carbon cycle forcings likely operating in the Southern Hemisphere.&#160; None-the-less, our results highlight how multiple mechanisms operating over multiple timescales may have interacted during the last glacial period to drive changes in atmospheric CO2.&#160;

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NALPS19: sub-orbital-scale climate variability recorded in northern Alpine speleothems during the last glacial period

Climate of the Past ◽

10.5194/cp-16-29-2020 ◽

2020 ◽

Vol 16 (1) ◽

pp. 29-50 ◽

Cited By ~ 7

Author(s):

Gina E. Moseley ◽

Christoph Spötl ◽

Susanne Brandstätter ◽

Tobias Erhardt ◽

Marc Luetscher ◽

...

Keyword(s):

Climate Variability ◽

Asian Monsoon ◽

Ice Core ◽

High Elevation ◽

Meridional Overturning Circulation ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Northern Alps ◽

The Last Glacial

Abstract. Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates at which the climate can change state, the mechanisms that drive such changes, and the leads, lags, and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using δ18O from speleothems (δ18Ocalc) that grew along the northern rim of the Alps (NALPS), enabling direct chronological comparisons with δ18O records from Greenland ice cores (δ18Oice). In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18Ocalc chronology over the interval 118.3 to 63.7 ka using 11, newly available, clean, precisely dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 16 stalagmites from seven caves. Where speleothems grew synchronously, the timing of major transitional events in δ18Ocalc between stadials and interstadials (and vice versa) are all in agreement on multi-decadal timescales. Ramp-fitting analysis further reveals that, except for one abrupt change, the timing of δ18O transitions occurred synchronously within centennial-scale dating uncertainties between the NALPS19 δ18Ocalc record and the Asian monsoon composite speleothem δ18Ocalc record. Due to the millennial-scale uncertainties in the ice core chronologies, a comprehensive comparison with the NALPS19 chronology is difficult. Generally, however, we find that the absolute timing of transitions in the Greenland Ice Core Chronology (GICC) 05modelext and Antarctic Ice Core Chronology (AICC) 2012 are in agreement on centennial scales. The exception to this is during the interval of 100 to 115 ka, where transitions in the AICC2012 chronology occurred up to 3000 years later than in NALPS19. In such instances, the transitions in the revised AICC2012 chronology of Extier et al. (2018) are in agreement with NALPS19 on centennial scales, supporting the hypothesis that AICC2012 appears to be considerably too young between 100 and 115 ka. Using a ramp-fitting function to objectively identify the onset and the end of abrupt transitions, we show that δ18O shifts took place on multi-decadal to multi-centennial timescales in the North Atlantic-sourced regions (northern Alps and Greenland) as well as the Asian monsoon. Given the near-complete record of δ18Ocalc variability during the last glacial period in the northern Alps, we also offer preliminary considerations regarding the controls on mean δ18Ocalc for given stadials and interstadials. We find that, as expected, δ18Ocalc values became increasingly lighter with distance from the oceanic source regions, and increasingly lighter with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18Ocalc values that are heavier than expected in comparison to lower-elevation sites, possibly caused by a summer bias in the recorded signal of the high-elevation site, or a winter bias in the low-elevation site. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as the Greenland Stadial (GS)-16.2, GS-17.2, GS-21.2, and GS-23.2 “precursor” events, as well as the “within-interstadial” GS-24.2 cooling event. Our new high-precision chronology shows that each of these δ18O depletions occurred in the decades and centuries following rapid rises in sea level associated with increased ice-rafted debris and southward shifts of the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately sized ice sheets may have been responsible for the cold reversals causing the Atlantic Meridional Overturning Circulation to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.

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Millennial and sub-millennial scale climatic variations recorded in polar ice cores over the last glacial period

Climate of the Past ◽

10.5194/cp-6-345-2010 ◽

2010 ◽

Vol 6 (3) ◽

pp. 345-365 ◽

Cited By ~ 113

Author(s):

E. Capron ◽

A. Landais ◽

J. Chappellaz ◽

A. Schilt ◽

D. Buiron ◽

...

Keyword(s):

Climatic Variability ◽

Ice Core ◽

Ice Sheets ◽

Ice Cores ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Mis 5 ◽

The Last Glacial ◽

Millennial Scale

Abstract. Since its discovery in Greenland ice cores, the millennial scale climatic variability of the last glacial period has been increasingly documented at all latitudes with studies focusing mainly on Marine Isotopic Stage 3 (MIS 3; 28–60 thousand of years before present, hereafter ka) and characterized by short Dansgaard-Oeschger (DO) events. Recent and new results obtained on the EPICA and NorthGRIP ice cores now precisely describe the rapid variations of Antarctic and Greenland temperature during MIS 5 (73.5–123 ka), a time period corresponding to relatively high sea level. The results display a succession of abrupt events associated with long Greenland InterStadial phases (GIS) enabling us to highlight a sub-millennial scale climatic variability depicted by (i) short-lived and abrupt warming events preceding some GIS (precursor-type events) and (ii) abrupt warming events at the end of some GIS (rebound-type events). The occurrence of these sub-millennial scale events is suggested to be driven by the insolation at high northern latitudes together with the internal forcing of ice sheets. Thanks to a recent NorthGRIP-EPICA Dronning Maud Land (EDML) common timescale over MIS 5, the bipolar sequence of climatic events can be established at millennial to sub-millennial timescale. This shows that for extraordinary long stadial durations the accompanying Antarctic warming amplitude cannot be described by a simple linear relationship between the two as expected from the bipolar seesaw concept. We also show that when ice sheets are extensive, Antarctica does not necessarily warm during the whole GS as the thermal bipolar seesaw model would predict, questioning the Greenland ice core temperature records as a proxy for AMOC changes throughout the glacial period.

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Natural periodicities and Northern Hemisphere–Southern Hemisphere connection of fast temperature changes during the last glacial period: EPICA and NGRIP revisited

Climate of the Past ◽

10.5194/cp-10-1751-2014 ◽

2014 ◽

Vol 10 (5) ◽

pp. 1751-1762 ◽

Cited By ~ 11

Author(s):

T. Alberti ◽

F. Lepreti ◽

A. Vecchio ◽

E. Bevacqua ◽

V. Capparelli ◽

...

Keyword(s):

Ice Core ◽

Data Sets ◽

Time Behavior ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Mode Decomposition ◽

Cross Correlation Analysis ◽

The One ◽

The Last Glacial

Abstract. We investigate both the European Project for Ice Coring in Antarctica Dronning Maud Land (EDML) and North Greenland Ice-Core Project (NGRIP) data sets to study both the time evolution of the so-called Dansgaard–Oeschger events and the dynamics at longer timescales during the last glacial period. Empirical mode decomposition (EMD) is used to extract the proper modes of both the data sets. It is shown that the time behavior at the typical timescales of Dansgaard–Oeschger events is captured through signal reconstructions obtained by summing five EMD modes for NGRIP and four EMD modes for EDML. The reconstructions obtained by summing the successive modes can be used to describe the climate evolution at longer timescales, characterized by intervals in which Dansgaard–Oeschger events happen and intervals when these are not observed. Using EMD signal reconstructions and a simple model based on the one-dimensional Langevin equation, it is argued that the occurrence of a Dansgaard–Oeschger event can be described as an excitation of the climate system within the same state, while the longer timescale behavior appears to be due to transitions between different climate states. Finally, on the basis of a cross-correlation analysis performed on EMD reconstructions, evidence that the Antarctic climate changes lead those of Greenland by a lag of &approx; 3.05 kyr is presented.

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Comparison of northern and central Greenland ice core records of methanesulfonate covering the last glacial period

Journal of Geophysical Research Atmospheres ◽

10.1029/2006jd007451 ◽

2007 ◽

Vol 112 (D14) ◽

Cited By ~ 6

Author(s):

Ulf Jonsell ◽

Margareta E. Hansson ◽

Marie-Louise Siggaard-Andersen ◽

Jørgen-Peder Steffensen

Keyword(s):

Ice Core ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

The Last Glacial ◽

Ice Core Records

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Model evolution of the middle atmospheric palaeoenvironments

MAUSAM ◽

10.54302/mausam.v52i1.1696 ◽

2021 ◽

Vol 52 (1) ◽

pp. 297-306

Author(s):

GUFRAN BEIG

Keyword(s):

Vertical Distribution ◽

Thermal Structure ◽

Ice Core ◽

Ice Age ◽

Ozone Content ◽

Glacial Period ◽

Last Glacial Period ◽

Last Glacial ◽

Last Ice Age ◽

The Last Glacial

Ice core air analysis has indicated a significant variation in the atmospheric contents of the greenhouse gases CO2, CH4 and N2O from the last ice age to the present period. This may have contributed in altering the vertical distribution of temperature and composition of the atmosphere about which not much information is available. The two dimensional interactive model of radiation, dynamics and chemistry has been used to reconstruct the annual vertical distribution of thermal structure and trace gas concentrations of the middle atmosphere for the periods extending from last ice age to the present. For this purpose, ice core air data of the above mentioned forcing parameters are used as input to the model for different time frames including Mounder Maximum, Roman maximum, pre-industrial period and the last glacial period. Model results show that the considerable reduction in the greenhouse gas content for the last ice age has resulted in colling of troposphere and a warming by about 10 to 15° K in the upper stratosphere as compared to present. The variation in temperature is closely related with the water vapour content. The percentage change in ozone concentration for the last glacial period is to a miximum of 50% near the poles in the upper stratosphere and about 10% in the tropics. A significant decrease in the hydroxyl content in the last ice age must have contributed in increasing the ozone content above 30 km. however, the total integrated ozone content appears to show marginal variations from last ice age to the present due to several counter-balancing effects.

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Bipolar volcanic synchronization of abrupt climate change in Greenland and Antarctic ice cores during the last glacial period

Climate of the Past ◽

10.5194/cp-16-1565-2020 ◽

2020 ◽

Vol 16 (4) ◽

pp. 1565-1580

Author(s):

Anders Svensson ◽

Dorthe Dahl-Jensen ◽

Jørgen Peder Steffensen ◽

Thomas Blunier ◽

Sune O. Rasmussen ◽

...

Keyword(s):

Ice Core ◽

Ice Cores ◽

Volcanic Eruptions ◽

Abrupt Climate Change ◽

Glacial Period ◽

Deuterium Excess ◽

Last Glacial Period ◽

Last Glacial ◽

The Antarctic ◽

The Last Glacial

Abstract. The last glacial period is characterized by a number of millennial climate events that have been identified in both Greenland and Antarctic ice cores and that are abrupt in Greenland climate records. The mechanisms governing this climate variability remain a puzzle that requires a precise synchronization of ice cores from the two hemispheres to be resolved. Previously, Greenland and Antarctic ice cores have been synchronized primarily via their common records of gas concentrations or isotopes from the trapped air and via cosmogenic isotopes measured on the ice. In this work, we apply ice core volcanic proxies and annual layer counting to identify large volcanic eruptions that have left a signature in both Greenland and Antarctica. Generally, no tephra is associated with those eruptions in the ice cores, so the source of the eruptions cannot be identified. Instead, we identify and match sequences of volcanic eruptions with bipolar distribution of sulfate, i.e. unique patterns of volcanic events separated by the same number of years at the two poles. Using this approach, we pinpoint 82 large bipolar volcanic eruptions throughout the second half of the last glacial period (12–60 ka). This improved ice core synchronization is applied to determine the bipolar phasing of abrupt climate change events at decadal-scale precision. In response to Greenland abrupt climatic transitions, we find a response in the Antarctic water isotope signals (δ18O and deuterium excess) that is both more immediate and more abrupt than that found with previous gas-based interpolar synchronizations, providing additional support for our volcanic framework. On average, the Antarctic bipolar seesaw climate response lags the midpoint of Greenland abrupt δ18O transitions by 122±24 years. The time difference between Antarctic signals in deuterium excess and δ18O, which likewise informs the time needed to propagate the signal as described by the theory of the bipolar seesaw but is less sensitive to synchronization errors, suggests an Antarctic δ18O lag behind Greenland of 152±37 years. These estimates are shorter than the 200 years suggested by earlier gas-based synchronizations. As before, we find variations in the timing and duration between the response at different sites and for different events suggesting an interaction of oceanic and atmospheric teleconnection patterns as well as internal climate variability.

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