Erratum: Dynamics of meltwater discharge from Northern Hemisphere ice sheets during the last deglaciation

Abstract. In tropical eastern Africa, vegetation distribution is largely controlled by regional hydrology, which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial for a better understanding of climate variability in the tropical southeastern African region. We present high-resolution pollen records from a marine sediment core recovered offshore of the Rufiji River delta. Our data document significant shifts in pollen assemblages during the last deglaciation, identifying, through changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics and sea-level changes) alterations. Specifically, arid conditions reflected by a maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1), suggesting that the expansion of drier upland vegetation was synchronous with cold Northern Hemisphere conditions. This arid period is followed by an interval in which forest and humid woodlands expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the shift to humid conditions around 14.8 kyr BP in the uplands are consistent with latitudinal shifts of the intertropical convergence zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of well-developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as to the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ~ 14.8 kyr BP, suggesting an increased moisture availability and river runoff in the coastal area. The results of this study highlight the decoupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

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Marine Ice Sheet Instability and Ice Shelf Buttressing Influenced Deglaciation of the Minch Ice Stream, Northwest Scotland

10.5194/tc-2018-116 ◽

2018 ◽

Cited By ~ 1

Author(s):

Niall Gandy ◽

Lauren J. Gregoire ◽

Jeremy C. Ely ◽

Christopher D. Clark ◽

David M. Hodgson ◽

...

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Last Deglaciation ◽

Ice Shelf ◽

Dynamical Processes ◽

Ice Dynamics ◽

Surface Mass ◽

Ice Shelves ◽

Ice Stream ◽

The Last Deglaciation

Abstract. Uncertainties in future sea level projections are dominated by our limited understanding of the dynamical processes that control instabilities of marine ice sheets. A valuable case to examine these processes is the last deglaciation of the British-Irish Ice Sheet. The Minch Ice Stream, which drained a large proportion of ice from the northwest sector of the British-Irish Ice Sheet during the last deglaciation, is well constrained, with abundant empirical data which could be used to inform, validate and analyse numerical ice sheet simulations. We use BISICLES, a higher-order ice sheet model, to examine the dynamical processes that controlled the retreat of the Minch Ice Stream. We simulate retreat from the shelf edge under constant "warm" surface mass balance and subshelf melt, to isolate the role of internal ice dynamics from external forcings. The model simulates a slowdown of retreat as the ice stream becomes laterally confined at a "pinning-point" between mainland Scotland and the Isle of Lewis. At this stage, the presence of ice shelves became a major control on deglaciation, providing buttressing to upstream ice. Subsequently, the presence of a reverse slope inside the Minch Strait produces an acceleration in retreat, leading to a "collapsed" state, even when the climate returns to the initial "cold" conditions. Our simulations demonstrate the importance of the Marine Ice Sheet Instability and ice shelf buttressing during the deglaciation of parts of the British-Irish Ice Sheet. Thus, geological data could be used to constrain these processes in ice sheet models used for projecting the future of our contemporary ice sheets.

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Northern Hemisphere control of deglacial vegetation changes in the Rufiji uplands (Tanzania)

Climate of the Past Discussions ◽

10.5194/cpd-10-3931-2014 ◽

2014 ◽

Vol 10 (5) ◽

pp. 3931-3964

Author(s):

I. Bouimetarhan ◽

L. Dupont ◽

H. Kuhlmann ◽

J. Pätzold ◽

M. Prange ◽

...

Keyword(s):

Northern Hemisphere ◽

Salt Marshes ◽

Atmospheric Precipitation ◽

Eastern Africa ◽

Last Deglaciation ◽

Climatic Fluctuations ◽

Coastal Dynamics ◽

Moisture Availability ◽

Dry Spell ◽

The Last Deglaciation

Abstract. In tropical Eastern Africa, vegetation distribution is largely controlled by regional hydrology which has varied over the past 20 000 years. Therefore, accurate reconstructions of past vegetation and hydrological changes are crucial to better understand climate variability in the tropical Eastern African region. Through high-resolution pollen records from a marine sediment core recovered offshore the Rufiji River, our data show significant shifts in pollen assemblages during the last deglaciation identifying, through respective changes in both upland and lowland vegetation, specific responses of plant communities to atmospheric (precipitation) and coastal (coastal dynamics/sea level changes) alterations. Specifically, an interval of maximum pollen representation of dry and open vegetation occurred during the Northern Hemisphere cold Heinrich event 1 (H1) suggesting the expansion of drier upland vegetation under arid conditions. This dry spell is followed by an interval in which forest and humid woodland expanded, indicating a hydrologic shift towards more humid conditions. Droughts during H1 and the return to humid conditions around ~14.8 kyr BP in the uplands are primarily attributed to latitudinal shifts of the Intertropical Convergence Zone (ITCZ) driven by high-latitude Northern Hemisphere climatic fluctuations. Additionally, our results show that the lowland vegetation, consisting of a well developed salt marshes and mangroves in a successional pattern typical for vegetation occurring in intertidal habitats, has responded mainly to local coastal dynamics related to marine inundation frequencies and soil salinity in the Rufiji Delta as well as the local moisture availability. Lowland vegetation shows a substantial expansion of mangrove trees after ~14.8 kyr BP suggesting also an increased moisture availability and river runoff in the coastal area. The results of this study highlight the de-coupled climatic and environmental processes to which the vegetation in the uplands and the Rufiji Delta has responded during the last deglaciation.

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

10.5194/cp-2018-65 ◽

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.

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The penultimate deglaciation: protocol for Paleoclimate Modelling Intercomparison Project (PMIP) phase 4 transient numerical simulations between 140 and 127 ka, version 1.0

Geoscientific Model Development ◽

10.5194/gmd-12-3649-2019 ◽

2019 ◽

Vol 12 (8) ◽

pp. 3649-3685 ◽

Cited By ~ 4

Author(s):

Laurie Menviel ◽

Emilie Capron ◽

Aline Govin ◽

Andrea Dutton ◽

Lev Tarasov ◽

...

Keyword(s):

Greenhouse Gas ◽

Working Group ◽

Ice Sheets ◽

Last Deglaciation ◽

Transient Simulations ◽

Intercomparison Project ◽

The Last Deglaciation ◽

Continental Ice Sheets ◽

Paleoclimate Modelling Intercomparison Project ◽

Paleoclimate Modelling

Abstract. The penultimate deglaciation (PDG, ∼138–128 thousand years before present, hereafter ka) is the transition from the penultimate glacial maximum (PGM) to the Last Interglacial (LIG, ∼129–116 ka). The LIG stands out as one of the warmest interglacials of the last 800 000 years (hereafter kyr), with high-latitude temperature warmer than today and global sea level likely higher by at least 6 m. Considering the transient nature of the Earth system, the LIG climate and ice-sheet evolution were certainly influenced by the changes occurring during the penultimate deglaciation. It is thus important to investigate, with coupled atmosphere–ocean general circulation models (AOGCMs), the climate and environmental response to the large changes in boundary conditions (i.e. orbital configuration, atmospheric greenhouse gas concentrations, ice-sheet geometry and associated meltwater fluxes) occurring during the penultimate deglaciation. A deglaciation working group has recently been set up as part of the Paleoclimate Modelling Intercomparison Project (PMIP) phase 4, with a protocol to perform transient simulations of the last deglaciation (19–11 ka; although the protocol covers 26–0 ka). Similar to the last deglaciation, the disintegration of continental ice sheets during the penultimate deglaciation led to significant changes in the oceanic circulation during Heinrich Stadial 11 (∼136–129 ka). However, the two deglaciations bear significant differences in magnitude and temporal evolution of climate and environmental changes. Here, as part of the Past Global Changes (PAGES)-PMIP working group on Quaternary interglacials (QUIGS), we propose a protocol to perform transient simulations of the penultimate deglaciation under the auspices of PMIP4. This design includes time-varying changes in orbital forcing, greenhouse gas concentrations, continental ice sheets as well as freshwater input from the disintegration of continental ice sheets. This experiment is designed for AOGCMs to assess the coupled response of the climate system to all forcings. Additional sensitivity experiments are proposed to evaluate the response to each forcing. Finally, a selection of paleo-records representing different parts of the climate system is presented, providing an appropriate benchmark for upcoming model–data comparisons across the penultimate deglaciation.

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Simulation of LGM ice sheets with the Community Earth System Model version 2

10.5194/egusphere-egu21-15463 ◽

2021 ◽

Author(s):

Sarah L Bradley ◽

Michele Petrini ◽

Raymond Sellevold ◽

Miren Vizcaino ◽

William H. Lipscomb ◽

...

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Earth System Model ◽

System Model ◽

Earth System ◽

Last Deglaciation ◽

Model Version ◽

Starting Point ◽

Community Earth System Model ◽

The Last Deglaciation

The last deglaciation provides as unique a framework to investigate the processes of ice sheet and climate interaction during periods of mass loss as in the current climate. Here we simulate the Last Glacial Maximum (LGM) northern hemisphere ice sheets climate, surface mass balance (SMB), and dynamics with the Community Earth System Model version 2 (CESM2, Danabasoglu et al., 2020)) and the Community Ice Sheet Model version 2 (CISM2, Lipscomb et al., 2019). This LGM simulation will be later used as starting point for coupled CESM2-CISM2 simulations of the last deglaciation.&#160;CESM2 is run at the nominal resolution used for IPCC-type projections (approx. 1 degree for all components). The model includes an advanced snow/firn and SMB calculation (van Kampenhout et al, 2019; Sellevold et al, 2019) the land component (CLM, cite) that has been evaluated and applied to the simulation of the future Greenland melt (van Kampenhout et al, 2020, Muntjewerf et al., 2020a,b, Sellevold & Vizcaino, 2020).&#160;Our analysis examines how the global, Arctic, and North Atlantic climate result in the simulated radiative and turbulent heat fluxes over the ice sheets, and the mass fluxes from precipitation, refreezing, runoff, and sublimation. We also examine the simulated ice streams in CISM2, which is run at 8 km under a higher-order approximation for ice flow.

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Reassessing global ice volume: uncertainty and structure in sea level records

10.5194/egusphere-egu21-16334 ◽

2021 ◽

Author(s):

Fiona D. Hibbert ◽

Felicity Williams ◽

Eelco Rohling

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Full Range ◽

Ice Sheets ◽

Change Point Analysis ◽

Last Deglaciation ◽

Ice Volume ◽

Global Ice Volume ◽

Modern Analogue ◽

The Last Deglaciation

Geologically recorded sea-level variations represent the sum total of all contributing processes, be it known or unknown, and may thus help in finding the full range of future sea-level rise. Significant sea-level-rise contributions from both northern and southern ice sheets are not unprecedented in the geological record and offer a well-constrained range of natural scenarios from intervals during which ice volumes were similar to or smaller than present (i.e., interglacial periods), to intervals during which total ice volume was greater (i.e., glacial periods).The last deglaciation is the most recent period of widespread destabilisation and collapse of major continental ice sheets. Records spanning the last deglaciation (as well as the ice volume maxima) are few, fragmentary and seemingly inconsistent (e.g., the timing and magnitude of melt-water pulses), in part due to locational (tectonic and glacio-isostatic) as well as modern analogue considerations (e.g., palaeo-water depth or facies formation depth). We present a new synthesis of sea-level indicators, with particular emphasis on the geological and biological context, as well as the uncertainties of each record. Using this new compilation and the novel application of statistical methods (trans-dimensional change-point analysis, which avoids &#8220;overfitting&#8221; of noise in the data), we will assess global ice-volume changes, sea-level fluctuations and changes in climate during the last deglaciation. Finally, we discuss the implications of these uncertainties on our ability to constrain past cryosphere changes.

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Impact of ice sheet reconstructions on the deglacial climate in iLOVECLIM

10.5194/egusphere-egu21-8776 ◽

2021 ◽

Author(s):

Nathaelle Bouttes ◽

Didier Roche ◽

Fanny Lhardy ◽

Aurelien Quiquet ◽

Didier Paillard ◽

...

Keyword(s):

Boundary Conditions ◽

Ice Sheets ◽

Ice Sheet ◽

Last Deglaciation ◽

Antarctic Ice Sheet ◽

Intermediate Complexity ◽

Climate Evolution ◽

The Last Deglaciation ◽

The Antarctic ◽

The Impact

The last deglaciation is a time of large climate transition from a cold Last Glacial Maximum at 21,000 years BP with extensive ice sheets, to the warmer Holocene 9,000 years BP onwards with reduced ice sheets. Despite more and more proxy data documenting this transition, the evolution of climate is not fully understood and difficult to simulate. The PMIP4 protocol (Ivanovic et al., 2016) has indicated which boundary conditions to use in model simulations during this transition. The common boundary conditions should enable consistent multi model and model-data comparisons. While the greenhouse gas concentration evolution and orbital forcing are well known and easy to prescribe, the evolution of ice sheets is less well constrained and several choices can be made by modelling groups. First, two ice sheet reconstructions are available: ICE-6G (Peltier et al., 2015) and GLAC-1D (Tarasov et al., 2014). On top of topographic changes, it is left to modelling groups to decide whether to account for the associated bathymetry and land-sea mask changes, which is technically more demanding. These choices could potentially lead to differences in the climate evolution, making model comparisons more complicated.We use the iLOVECLIM model of intermediate complexity (Goosse et al., 2010) to evaluate the impact of different ice sheet reconstructions and the effect of bathymetry changes on the global climate evolution during the Last deglaciation. We test the two ice sheet reconstructions (ICE-6G and GLAC-1D), and have implemented changes of bathymetry and land-sea mask. In addition, we also evaluate the impact of accounting for the Antarctic ice sheet evolution compared to the Northern ice sheets only.We show that despite showing the same long-term changes, the two reconstructions lead to different evolutions. The bathymetry plays a role, although only few changes take place before ~14ka. Finally, the impact of the Antarctic ice sheet is important during the deglaciation and should not be neglected.ReferencesGoosse, H., et al., Description of the Earth system model of intermediate complexity LOVECLIM version 1.2, Geosci. Model Dev., 3, 603&#8211;633, https://doi.org/10.5194/gmd-3-603-2010, 2010Ivanovic, R. F., et al., Transient climate simulations of the deglaciation 21&#8211;9&#160;thousand years before present (version&#160;1) &#8211; PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563&#8211;2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016Peltier, W. R., Argus, D. F., and Drummond, R., Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model, J. Geophys. Res.-Sol. Ea., 120, 450&#8211;487, doi:10.1002/2014JB011176, 2015Tarasov,L., &#160;et al., The global GLAC-1c deglaciation chronology, melwater pulse 1-a, and a question of missing ice, IGS Symposium on Contribution of Glaciers and Ice Sheets to Sea-Level Change, 2014

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