A spatio-temporal view of variability in pollen records during the last Glacial

2020 ◽  
Author(s):  
Nils Weitzel ◽  
Moritz Adam ◽  
Anna Sommani ◽  
Kira Rehfeld
Keyword(s):  
Climate Variability ◽  
Ice Cores ◽  
Global Network ◽  
Glacial Cycle ◽  
Climate Signal ◽  
Last Glacial ◽  
Additional Information ◽  
Climate Simulations ◽  
Pollen Records ◽  
The Last Glacial

<p>Climate variability influences the probability of extreme events and is therefore of great importance for risk management. Nevertheless, changes in climate variability over time are far less studied than changes in the mean state of the climate system. Proxy records can be used to estimate the dependency of climate variability on the state and timescale, but their climate signal is perturbed by non-climatic processes and dating uncertainties. Analyzing ice cores and marine sediments, it was shown that temperature variability during the Last Glacial Maximum was larger than in the Holocene and that the magnitude of variability change depends on latitude.</p><p>We estimate millennial and orbital scale variability in pollen records during the last Glacial. We draw on a global network of published pollen records, which are influenced by local temperature and moisture availability, and compare these estimates with temperature, precipitation, and vegetation variability in climate simulations of the last Glacial cycle. We discuss the regional consistency of timescale dependent estimates. Differences between Marine Isotope Stages 2, 3, and 4 are examined by comparing spatial patterns during those three periods. Then, we use spectral methods to study the scaling behavior of the pollen records. This provides additional information on the continuum of variability from centennial to orbital scales. Finally, we quantify the co-occurrence of millennial and orbital scale fluctuations across different pollen records with paleoclimate network techniques.</p><p>Our work extends previous estimates to the terrestrial realm and to longer timescales. The results provide new insight on the climate variability differences between glacial and interglacial states, and on the mismatch between climate simulations and proxy data.</p>

scholarly journals NALPS19: Sub-orbital scale climate variability recorded in Northern Alpine speleothems during the last glacial period

2019 ◽  
Author(s):  
Gina E. Moseley ◽  
Christoph Spötl ◽  
Susanne Brandstätter ◽  
Tobias Erhardt ◽  
Marc Luetscher ◽  
...  
Keyword(s):  
Climate Variability ◽  
Asian Monsoon ◽  
Ice Core ◽  
Ice Cores ◽  
High Elevation ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Last Glacial ◽  
Change State ◽  
The Last Glacial

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.

On the timing and mechanism of millennial-scale climate variability during the last glacial cycle

2003 ◽  
Vol 20 (2) ◽  
pp. 257-267 ◽  
Author(s):  
E. Rohling ◽  
P. Mayewski ◽  
P. Challenor
Keyword(s):  
Climate Variability ◽  
Glacial Cycle ◽  
Last Glacial ◽  
The Last Glacial ◽  
Millennial Scale

scholarly journals Andean drought and glacial retreat tied to Greenland warming during the last glacial period

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Arielle Woods ◽  
Donald T. Rodbell ◽  
Mark B. Abbott ◽  
Robert G. Hatfield ◽  
Christine Y. Chen ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Ice Cores ◽  
The Arctic ◽  
Glacier Mass Balance ◽  
Complete Disappearance ◽  
Tropical Andes ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Isotopic Records ◽  
The Last Glacial

Abstract Abrupt warming events recorded in Greenland ice cores known as Dansgaard-Oeschger (DO) interstadials are linked to changes in tropical circulation during the last glacial cycle. Corresponding variations in South American summer monsoon (SASM) strength are documented, most commonly, in isotopic records from speleothems, but less is known about how these changes affected precipitation and Andean glacier mass balance. Here we present a sediment record spanning the last ~50 ka from Lake Junín (Peru) in the tropical Andes that has sufficient chronologic precision to document abrupt climatic events on a centennial-millennial time scale. DO events involved the near-complete disappearance of glaciers below 4700 masl in the eastern Andean cordillera and major reductions in the level of Peru’s second largest lake. Our results reveal the magnitude of the hydroclimatic disruptions in the highest reaches of the Amazon Basin that were caused by a weakening of the SASM during abrupt arctic warming. Accentuated warming in the Arctic could lead to significant reductions in the precipitation-evaporation balance of the southern tropical Andes with deleterious effects on this densely populated region of South America.

scholarly journals Numerical simulations of the Cordilleran ice sheet through the last glacial cycle

2016 ◽  
Vol 10 (2) ◽  
pp. 639-664 ◽  
Author(s):  
Julien Seguinot ◽  
Irina Rogozhina ◽  
Arjen P. Stroeven ◽  
Martin Margold ◽  
Johan Kleman
Keyword(s):  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
High Mountain ◽  
Glacial Cycle ◽  
Mountain Areas ◽  
Last Glacial ◽  
Proxy Records ◽  
Cordilleran Ice Sheet ◽  
The Last Glacial

Abstract. After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2–56.9 ka) and 2 (23.2–16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

scholarly journals Ice-sheet modelling characteristics in sea-level-based temperature reconstructions over the last glacial cycle

2006 ◽  
Vol 52 (176) ◽  
pp. 149-158 ◽  
Author(s):  
Frank Wilschut ◽  
Richard Bintanja ◽  
Roderik S.W. Van De Wal
Keyword(s):  
Sea Level ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
Glacial Cycle ◽  
Deep Sea Sediment ◽  
Last Glacial ◽  
Proxy Records ◽  
Temperature Reconstructions ◽  
The Last Glacial

AbstractA widely used method for investigating palaeotemperatures is to analyze local proxy records (e.g. ice cores or deep-sea sediment cores). The interpretation of these records is often not straightforward, and global or hemispheric means cannot be deduced from local estimates because of large spatial variability. Using a different approach, temperature changes over the last glacial cycle can be estimated from sea-level observations by applying an inverse method to an ice-sheet model. In order to understand the underlying physical mechanisms, we used a 1-D ice-sheet model and a 3-D coupled thermodynamic ice-sheet–ice-shelf–bedrock model to investigate the importance of several physical processes for the inverse temperature reconstructions. Results show that (i) temperature reconstructions are sensitive to the employed formulation of mass balance, (ii) excluding thermodynamics in the ice sheet leads to a smaller temperature amplitude in the reconstruction and (iii) hysteresis in the non-linear relation between sea level and temperature occurs as a consequence of ice redistribution in the process of merging and separation of ice sheets. The ice redistribution does not occur if the geometry does not support the formation of a relatively flat dome, which tends to be preserved in warming conditions.

Northern Hemisphere temperature to precipitation relationships during the last Glacial from pollen records and climate simulations

2020 ◽  
Author(s):  
Anna Sommani ◽  
Nils Weitzel ◽  
Kira Rehfeld
Keyword(s):  
Northern Hemisphere ◽  
Negative Correlation ◽  
Climate Models ◽  
Seasonal Rainfall ◽  
The Holocene ◽  
Last Glacial ◽  
Temperature And Precipitation ◽  
Climate Simulations ◽  
Pollen Records ◽  
The Last Glacial

<p>The hydrological response to radiative forcing is less understood than the thermal one: many climate models have difficulties in simulating seasonal rainfall and its variability. Indeed, future precipitation projections are much more uncertain than those of temperature. However, confident projections of precipitation are of crucial importance, particularly for highly populated regions where agriculture strongly relies on seasonal rainfall, such as South and Central Asia.</p><p>Instrumental data from Eurasia show a negative correlation between temperature and precipitation on short timescales (10<sup>-3</sup> to 10<sup>0</sup> years). However, on longer timescales (10<sup>1</sup> to 10<sup>3</sup> years), proxy data covering the Holocene show a positive correlation between temperature and precipitation. Climate models in contrast simulate a negative correlation on all timescales. To extend previous estimates to longer time scales, we focus on the last Glacial period, characterized by colder temperature than the Holocene as well as pronounced millennial-scale climate fluctuations in the Northern Hemisphere.</p><p>We reconstruct temperature and precipitation from four high resolution pollen records at mid-latitudes in the Northern Hemisphere. The estimates are compared with climate simulations. The chosen proxy sites cover the East and West coasts of both the Eurasian and North American continent. We employ four different statistical reconstruction methods to assess validity and biases of each method. The differences between reconstructed and simulated temperature-precipitation relationships as well as the zonal structure of orbital- and millennial-scale variations are examined. In particular, we explore the thermodynamic and dynamic contributions to the inferred relationships between temperature and precipitation.</p>

From the last interglacial to the future – new insights from modeling the last glacial-interglacial cycle in PalMod

2021 ◽  
Author(s):  
Kerstin Fieg ◽  
Mojib Latif ◽  
Michael Schulz ◽  
Tatjana Ilyina
Keyword(s):  
Climate Variability ◽  
Ice Sheet ◽  
Earth System ◽  
Glacial Cycle ◽  
System Models ◽  
Last Glacial ◽  
The Future ◽  
Fully Coupled ◽  
Earth System Models ◽  
The Last Glacial

<p>We present new insights from the project PalMod, which started in 2016 and is envisioned to run for a decade. The modelling initiative PalMod aims at filling the long-standing scientific gaps in our understanding of the dynamics and variability of the climate system during the last glacial-interglacial cycle. One of the grand challenges in this context is to quantify the processes that determine the spectrum of climate variability on timescales that range from seasons to millennia. Climatic processes are intimately coupled across these timescales. Understanding variability at any one timescale requires understanding of the whole spectrum. If we could successfully simulate the spectrum of climate variability during the last glacial cycle in Earth system models, would this enable us to more reliably assess the future climate change? Such simulations are necessary to deduce, for example, if a regime shift in climate variability could occur during the next centuries and millennia in response to global warming. PalMod is specifically designed to enhance our understanding of the Earth system dynamics and its variability on timescales up to the multimillennial with complex Earth System Models.</p><p>The following major goals were achieved up to now:</p><ul><li>Full coupling of atmosphere, ocean and ice-sheet models, enabling investigation of Heinrich Events and bi-stability of the AMOC, and millennial-scale transient climate-ice sheet simulations.</li> <li>Implementation of a coupled ocean and land biogeochemistry enabling simulations with prognostic atmospheric CO<sub>2</sub> concentrations and including improved representation of methane (CH<sub>4</sub>) in transient deglaciation runs.</li> <li>Systematic comparison of newly compiled proxy data with model simulations.</li> </ul><p>The major goal for the next two years is to set up the fully coupled physical-biogeochemical model which will be tested for three time periods: deglaciation, glacial inception and Marine Isotope Stage 3 (MIS3). This fully coupled model will be eventually used to simulate the complete glacial cycle and project the climate over the next few millennia.</p>

scholarly journals Pollen Records of the Last Glacial Cycle in the Southern Hemisphere Tropics of the PEPII Transect

PAGES news ◽  
2001 ◽  
Vol 9 (2) ◽  
pp. 11-12 ◽  
Author(s):  
Sander Van der Kaars ◽  
P Kershaw ◽  
N Tapper ◽  
P Moss ◽  
C Turney
Keyword(s):  
Southern Hemisphere ◽  
Glacial Cycle ◽  
Last Glacial ◽  
Pollen Records ◽  
The Last Glacial

scholarly journals Widespread global peatland establishment and persistence over the last 130,000 y

2019 ◽  
Vol 116 (11) ◽  
pp. 4822-4827 ◽  
Author(s):  
Claire C. Treat ◽  
Thomas Kleinen ◽  
Nils Broothaerts ◽  
April S. Dalton ◽  
René Dommain ◽  
...  
Keyword(s):  
Ice Cores ◽  
C Sequestration ◽  
Quantitative Agreement ◽  
Glacial Cycle ◽  
Last Interglacial ◽  
Last Glacial ◽  
C Storage ◽  
C Stocks ◽  
Northern Peatlands ◽  
The Last Glacial

Glacial−interglacial variations in CO2 and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum (LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (>40°N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.

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