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(a) Final grounded ice volume (10 6 km 3 ) and (b) final grounded ice area (10 6 km 2 ) for the control simulations with Bedmap1. Control HadCM3 in red, Control Obs in green. The horizontal dashed lines indicate the PD and Pliocene grounded ice volume and area of the initial ice-sheet topographies.
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In the context of future climate change, understanding the nature and
behaviour of ice sheets during warm intervals in Earth history is of
fundamental importance. The late Pliocene warm period (also known as the
PRISM interval: 3.264 to 3.025 million years before present) can serve as a
potential analogue for projected future climates. Although Pli...
Similar publications
In the context of future climate change, understanding the nature
and behaviour of ice sheets during warm intervals in Earth history
is of fundamental importance. The Late-Pliocene warm period (also
known as the PRISM interval: 3.264 to 3.025 million years before
present) can serve as a potential analogue for projected future
climates. Although Pli...
Citations
... Our sea-level estimates then shift towards the high-355 range estimates , between 15-25 meters. Such an experiment was performed in the study of Dolan et al. (2018) andde Boer et al. (2014). Their results also show that starting from PRISM4 conditions leads to higher sea-level contributions and a less extended AIS during the mPWP. ...
... evolve transiently towards the mPWP(de Boer et al., 2014;Yan et al., 2016;Golledge et al., 2017;Dolan et al., 2018;Berends et al., 2019). The greatest difference is with the studies from DeConto and Pollard(2016)and DeConto et al. (2021) due to their inclusion of the MICI mechanism. ...
Tipping elements, including the Antarctic Ice Sheet (AIS), are Earth system components that can reach critical thresholds due to anthropogenic emissions. Increasing our understanding of past warm climates can help to elucidate the future contribution of the AIS to emissions. The mid-Pliocene warm period (mPWP, 3.3–3.0 million years ago) serves as an ideal benchmark experiment. During this period, CO2 levels were similar to present-day (350–450 ppmv), but global mean temperatures were 2.5–4.0 degrees higher. Sea-level reconstructions from that time indicate a rise of 10–20 meters compared to the present, highlighting the potential crossing of tipping points in Antarctica. In order to achieve a sea-level contribution far beyond 10 m not only the West Antarctic Ice Sheet (WAIS) needs to largely decrease, but a significant response in the East Antarctic Ice Sheet (EAIS) is also required. A key question in reconstructions and simulations is therefore which of the AIS basins retreated during the mPWP. In this study, we investigate how the AIS responds to climatic and bedrock conditions during the mPWP. To this end we use the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) general circulation model ensemble to force a higher-order ice-sheet model. Our simulations reveal that the West Antarctic Ice Sheet experiences collapse with a 0.5 K oceanic warming, the Wilkes basin shows retreat at 3 K oceanic warming, although higher precipitation rates could mitigate such a retreat. Totten glacier shows slight signs of retreats only under high oceanic warming conditions (greater than 4 K oceanic anomaly). We also examine other sources of uncertainty related to initial topography and ice dynamics. we find that the climatologies yield a higher uncertainty than the dynamical configuration, if parameters are constrained with PD observations and that starting from Pliocene reconstructions lead to smaller ice-sheet configurations due to hysteresis behaviour of marine bedrocks. Ultimately, our study concludes that cliff instability is not a prerequisite for the retreat of Wilkes basin. Instead, a significant rise in oceanic temperatures can initiate such a retreat. Our research contributes to a better understanding of Antarctic tipping points and the likelihood of crossing them under future emission scenarios.
... During the Pliocene, the EAIS interior is generally thought to have been thicker than at present 4,25 . A warmer atmosphere carries more moisture 11 , which leads to increased snowfall over the ice sheet 26 and could have resulted in increased accumulation over the EAIS interior. ...
... At the EAIS margins, available numerical models and empirical evidence indicate that the EAIS response to Pliocene warmth was less uniform. Areas where the ice sheet was largely grounded below sea level at the time are thought to have collapsed or retreated significantly, producing a steeper elevation profile 5,25,29,30 . The response of marginal sectors that lie mostly above sea level, however, is less constrained due to a lack of empirical evidence 24 . ...
... 46 . These models have been used in other studies of the Pliocene AIS 25,47 , and here we make use of an updated mid-Pliocene subglacial topography reconstruction 48 . We model equilibrium-state Pliocene ice sheet geometries and show that most ice streams in DML were thinner than today, while Jutulstraumen was thicker under a warmer climate than at present. ...
Ice streams regulate most ice mass loss in Antarctica. Determining ice stream response to warmer conditions during the Pliocene could provide insights into their future behaviour, but this is hindered by a poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution model for Dronning Maud Land (East Antarctica). We show that contrary to dynamic thinning of the region’s ice streams following ice-shelf collapse, the largest ice stream, Jutulstraumen, thickens by 700 m despite lying on a retrograde bed slope. We attribute this counterintuitive thickening to a shallower Pliocene subglacial topography and inherent high lateral stresses at its flux gate. These conditions constrict ice drainage and, combined with increased snowfall, allow ice accumulation upstream. Similar stress balances and increased precipitation projections occur across 27% of present-day East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s future sea-level rise contribution.
... During the Pliocene, the EAIS interior is generally thought to have been thicker than at present [4,21]. A warmer atmosphere carries more moisture [10], which leads to increased snowfall over the ice sheet [22], and could have resulted in accumulation over the EAIS interior. ...
... At the EAIS margins, available numerical models and empirical evidence indicate that the EAIS response to Pliocene warmth was less uniform. Areas where the ice sheet was largely grounded below sea level are thought to have collapsed or retreated significantly, producing a steeper elevation profile [5,21,25,26]. The response of sectors that lie mostly above sea level, however, is largely unknown due to a lack of empirical evidence [27]. ...
... To assess how DML ice streams respond to a warmer climate such as the late Pliocene, we use a high-resolution numerical model [38] to simulate the region's ice streams, with a particular focus on Jutulstraumen, its largest ice stream (Fig. 1). We simulate the response of the entire Jutulstraumen catchment to late Pliocene climate using five of the coupled atmosphere-ocean global climate models from the Pliocene Model Intercomparison Project Phase 1: HadCM3 [21,39], COSMOS [40], IPSLCM5A [41], MIROC4m [42], and MRI-CGCM2.3 [43]. ...
Ice streams regulate most ice mass loss in Antarctica. Determining their response to Pliocene warmth could provide insights into their future behaviour, but is hindered by poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution regional model for Dronning Maud Land (East Antarctica). We show that the region’s largest ice stream, Jutulstraumen, thickens by 700 m under warm late-Pliocene conditions despite ice-shelf collapse and a retrograde bed slope, while nearby ice streams thin. While it is known that unstable retreat on a retrograde slope can be slowed under certain conditions, this finding illustrates that an ice stream can thicken and gain mass. We attribute thickening to high lateral stresses at its flux gate, which constrict ice drainage. Similar stress balances occur today in 27% of East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s sea-level rise contribution.
... By contrast, mid-Pliocene retreat of terrestrial sectors of the EAIS and/or the RSB is largely unknown, owing to a lack of empirical evidence. Some ice-sheet modelling is able to simulate retreat and thinning of the RSB 44,46,81 , alongside the WSB and the ASB (Fig. 1b), but it has generally proved challenging to simulate mid-Pliocene retreat of marine-based sectors 54,82 . The amount of modelled retreat is sensitive to assumed pre-Pliocene ice-sheet configurations 81 , climate-model forcing 83 and ice-sheet-model parameters 84 , with those simulating the most retreat (for example, Fig. 1b) often requiring further processes to enhance mass loss 44,54,81,85 , some of which are debated (such as marine-ice-cliff instability, discussed below) 86 . ...
The East Antarctic Ice Sheet contains the vast majority of Earth’s glacier ice (about 52 metres sea-level equivalent), but is often viewed as less vulnerable to global warming than the West Antarctic or Greenland ice sheets. However, some regions of the East Antarctic Ice Sheet have lost mass over recent decades, prompting the need to re-evaluate its sensitivity to climate change. Here we review the response of the East Antarctic Ice Sheet to past warm periods, synthesize current observations of change and evaluate future projections. Some marine-based catchments that underwent notable mass loss during past warm periods are losing mass at present but most projections indicate increased accumulation across the East Antarctic Ice Sheet over the twenty-first century, keeping the ice sheet broadly in balance. Beyond 2100, high-emissions scenarios generate increased ice discharge and potentially several metres of sea-level rise within just a few centuries, but substantial mass loss could be averted if the Paris Agreement to limit warming below 2 degrees Celsius is satisfied. Analysis of the East Antarctic Ice Sheet response to past warm periods and current observations of change highlight the importance of satisfying the Paris Climate Agreement to avoid a multi-metre contribution to sea level over the next few centuries.
... Our age model suggests that diatom-rich intervals (possibly indicative of a warm regional climate) likely correspond to all mid-to late-Pleistocene interglacials of the past 500 ka (i.e., MIS 13,11,9,7 and 5e;compare Figures 7b and 7f). Modeling of AIS extent suggests that early Pleistocene MIS 49, 47, 37, 31 and 25 may have been "super interglacials" and thus may have been characterized by substantial WAIS retreat relative to modern (Figure 7d;de Boer et al., 2015). Based on our age model, only one of these early Pleistocene interglacials (MIS 37) stands out, however, in our proxy-opal records of NGR and b* as extra diatom-rich intervals at U1538 (Figures 7b and 7c). ...
... Just two hornblendes are older; one of these is Archean (3730 Ma) and the other is Proterozoic (∼810 Ma). . IODP Hole U1538A physical property records and other paleoclimate timeseries: (a) U1538A Natural Gamma Radiation (NGR) on coring depths (meters below seafloor = mbsf); (b) Same U1538A data as shown in a, but on ages following tuning (also see Data Set S5 in Bailey et al., 2022) of this site's NGR record to the Dove Basin (red data) NGR stack (Reilly et al., 2021); (c) U1538A sediment color-b* data on the same age model as used for data in panel b; (d) Modeled Antarctic Ice volume (de Boer et al., 2015). Horizontal dashed blue line marks present day ice-volume; (e) ANDRILL Ross Sea WAIS proximity index (Naish et al., 2009; yellow, open ocean; blue, floating ice shelf; green, grounded ice); (f) Global benthic δ 18 O stack (the LR04; Lisiecki & Raymo, 2005); (g) Raw shipboard-derived archive-half inclination data after 15 mT peak AF for IODP Site U1537 and interpretation of this magnetochron stratigraphy (Reilly et al., 2021). ...
... These layers are, though, found at the stratigraphic top of a ∼366-m thick Pliocene and earliest Pleistocene sequence that appears to be much more dropstone-and gravel-iceberg-rafted debris-rich than the upper ∼307 m of the U1538 record (Figure 2; also see Section 2); an observation we contend may be consistent with the notion that the WAIS mass-balance was highly dynamic throughout the 41-kyr (inter)glacial world and regularly retreated and re-advanced inland/from its interior. This suggestion is broadly consistent with model-(e.g., Figure 7d; de Boer et al., 2014de Boer et al., , 2015Pollard & DeConto et al., 2009) and sedimentological- (Figure 7e; Naish et al., 2009) based evidence that the WAIS was prone to collapse during the Pliocene and earliest Pleistocene, but also with marine core-based evidence for a highly dynamic WAIS in the Amundsen Sea Embayment region during the Pliocene (e.g., Gohl et al., 2021). ...
Ice loss in the Southern Hemisphere has been greatest over the past 30 years in West Antarctica. The high sensitivity of this region to climate change has motivated geologists to examine marine sedimentary records for evidence of past episodes of West Antarctic Ice Sheet (WAIS) instability. Sediments accumulating in the Scotia Sea are useful to examine for this purpose because they receive iceberg‐rafted debris (IBRD) sourced from the Pacific‐ and Atlantic‐facing sectors of West Antarctica. Here we report on the sedimentology and provenance of the oldest of three cm‐scale coarse‐grained layers recovered from this sea at International Ocean Discovery Program Site U1538. These layers are preserved in opal‐rich sediments deposited ∼1.2 Ma during a relatively warm regional climate. Our microCT‐based analysis of the layer's in‐situ fabric confirms its ice‐rafted origin. We further infer that it is the product of an intense but short‐lived episode of IBRD deposition. Based on the petrography of its sand fraction and the Phanerozoic ⁴⁰Ar/³⁹Ar ages of hornblende and mica it contains, we conclude that the IBRD it contains was likely sourced from the Weddell Sea and/or Amundsen Sea embayment(s) of West Antarctica. We attribute the high concentrations of IBRD in these layers to “dirty” icebergs calved from the WAIS following its retreat inland from its modern grounding line. These layers also sit at the top of a ∼366‐m thick Pliocene and early Pleistocene sequence that is much more dropstone‐rich than its overlying sediments. We speculate this fact may reflect that WAIS mass‐balance was highly dynamic during the ∼41‐kyr (inter)glacial world.
... In the following E = 1 will be referred as the "classical case". The upper and lower values of E are extreme but not too far away from currently used values (Ma et al., 2010;de Boer et al., 2015). To test the sensitivity on the assumed friction law we run simulations with m = 1 and m = 3 (Eq. ...
Full-Stokes (FS) ice sheet models provide the most sophisticated formulation of ice sheet flow. However, their applicability is often limited due to the high computational demand and numerical challenges. To balance computational demand and accuracy, the so-called Blatter–Pattyn (BP) stress regime is frequently used. Here, we explore the dynamic consequences of using simplified approaches by solving FS and the BP stress regime applied to the Northeast Greenland Ice Stream. To ensure a consistent comparison, we use one single ice sheet model to run the simulations under identical numerical conditions. A sensitivity study to the horizontal grid resolution (from 12.8 to a resolution of 0.1 km) reveals that velocity differences between the FS and BP solution emerge below ∼ 1 km horizontal resolution and continuously increase with resolution. Over the majority of the modelling domain both models reveal similar surface velocity patterns. At the grounding line of the 79∘ North Glacier the simulations show considerable differences whereby the BP model overestimates ice discharge of up to 50 % compared to FS. A sensitivity study to the friction type reveals that differences are stronger for a power-law friction than a linear friction law. Model differences are attributed to topographic variability and the basal drag, in which neglected stress terms in BP become important.
... As a minimal check for model performance and parameter settings, we first perform steady-state control simulations as in de Boer et al. (2015). These are executed using ERA40 present-day (PD;1957 precipitation and temperature forcing (Uppala et al., 2005). ...
... obtained from remapping the BedMachine data to our grid. Like other SIA-and SSA-based ice-sheet models (see de Boer et al., 2015), IMAU-ICE generally simulates slightly thinner ice in the interior and thicker ice along the margins (Fig. S3). The grounding line is simulated quite well, although it is slightly more advanced in the Filchner-Ronne and the Amery embayments. ...
Benthic δ18O levels vary strongly during the warmer-than-modern early and mid-Miocene (23 to 14 Myr ago), suggesting a dynamic Antarctic ice sheet (AIS).
So far, however, realistic simulations of the Miocene AIS have been limited to equilibrium states under different CO2 levels and orbital settings.
Earlier transient simulations lacked ice-sheet–atmosphere interactions and used a present-day rather than Miocene Antarctic bedrock topography.
Here, we quantify the effect of ice-sheet–atmosphere interactions, running the ice-sheet model IMAU-ICE using climate forcing from Miocene simulations by the general circulation model GENESIS.
Utilising a recently developed matrix interpolation method enables us to interpolate the climate forcing based on CO2 levels (between 280 and 840 ppm), as well as varying ice-sheet configurations (between no ice and a large East Antarctic Ice Sheet).
We furthermore implement recent reconstructions of Miocene Antarctic bedrock topography.
We find that the positive albedo–temperature feedback, partly compensated for by a negative feedback between ice volume and precipitation, increases hysteresis in the relation between CO2 and ice volume.
Together, these ice-sheet–atmosphere interactions decrease the amplitude of Miocene AIS variability in idealised transient simulations.
Forced by quasi-orbital 40 kyr forcing CO2 cycles, the ice volume variability reduces by 21 % when ice-sheet–atmosphere interactions are included compared to when forcing variability is only based on CO2 changes.
Thereby, these interactions also diminish the contribution of AIS variability to benthic δ18O fluctuations.
Evolving bedrock topography during the early and mid-Miocene also reduces ice volume variability by 10 % under equal 40 kyr cycles of atmosphere and ocean forcing.
... By fitting an ELRA model to an SGVEM with a 100-km thick Antarctic lithosphere and an upper-mantle viscosity of 5 × 10 20 Pa s (i.e., close to what is commonly assumed for a 1-D viscoelastic solid Earth; Argus et al., 2014;de Boer et al., 2017;Gomez et al., 2013;Pollard et al., 2017), Le Meur and Huybrechts (1996) determined corresponding uniform values of 10 25 N m for D and 3,000 years for τ. Since then, these reference values (e.g., de Boer et al., 2015;DeConto & Pollard, 2016;Pattyn, 2017;Pollard & DeConto, 2012b;Pollard et al., 2017;Quiquet et al., 2018) or values close to them (Bueler et al., 2007;Maris et al., 2014) have been widely used in the literature. ...
... In this study, we determine ranges of values of D for West and East Antarctica based on values of the elastic lithosphere thickness (Equation 6), with low values of only a few kilometers to a few tens of kilometers estimated in West Antarctica, and predominantly high values in East Antarctica, up to about 150 km (Chen et al., 2018;Pappa et al., 2019). Note that the uniform reference value of D = 10 25 N m defined by Le Meur and Huybrechts (1996) and widely used since then (e.g., Bulthuis et al., 2019;de Boer et al., 2015;Pattyn, 2017;Pollard & DeConto, 2012a;Pollard et al., 2017;Quiquet et al., 2018) lies close to the maximum flexural rigidity estimated for East Antarctica. ...
The Antarctic ice sheet (AIS) lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low‐viscosity upper mantle (weak Earth structure) beneath West Antarctica and an opposing structure beneath East Antarctica. This contrast is known to have a significant impact on the ice‐sheet grounding‐line stability. Here, we embed within an ice‐sheet model a modified glacial‐isostatic Elastic Lithosphere‐Relaxing Asthenosphere model that considers a dual pattern for the Earth structure beneath West and East Antarctica supplemented with an approximation of gravitationally consistent geoid changes, allowing to approximate near‐field relative sea‐level changes. We show that this elementary GIA model captures the essence of global Self‐Gravitating Viscoelastic solid‐Earth Models (SGVEMs) and compares well with both SGVEM outputs and geodetic observations, allowing to capture the essential features and processes influencing Antarctic grounding‐line stability in a computationally efficient way. In this framework, we perform a probabilistic assessment of the impact of uncertainties in solid‐Earth rheological properties on the response of the AIS to future warming. Results show that on multicentennial‐to‐millennial timescales, spatial variability in solid‐Earth deformation plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high‐emissions climate scenarios. On longer timescales and for unmitigated climate scenarios, continent‐wide mass loss projections may be underestimated because spatially uniform Earth models, as typically considered in numerical ice sheet models, will overestimate the stabilizing effect of GIA across East Antarctica, which is characterized by thick lithosphere and high upper‐mantle viscosity.
... Hearty et al., 2007;Naish et al., 2009;Pollard and DeConto, 2009). However, Pliocene model results were shown to be highly dependent on the choice of climate and ice sheet models (de Boer et al., 2015;Dolan et al., 2018). ...
Studying the response of the Antarctic ice sheets during periods when climate conditions were similar to the present can provide important insights into current observed changes and help identify natural drivers of ice sheet retreat. In this context, the marine isotope substage 11c (MIS11c) interglacial offers a suitable scenario, given that during its later portion orbital parameters were close to our current interglacial. Ice core data indicate that warmer-than-present temperatures lasted for longer than during other interglacials. However, the response of the Antarctic ice sheets and their contribution to sea level rise remain unclear. We explore the dynamics of the Antarctic ice sheets during this period using a numerical ice sheet model forced by MIS11c climate conditions derived from climate model outputs scaled by three glaciological and one sedimentary proxy records of ice volume. Our results indicate that the East and West Antarctic ice sheets contributed 4.0–8.2 m to the MIS11c sea level rise. In the case of a West Antarctic Ice Sheet collapse, which is the most probable scenario according to far-field sea level reconstructions, the range is reduced to 6.7–8.2 m independently of the choices of external sea level forcing and millennial-scale climate variability. Within this latter range, the main source of uncertainty arises from the sensitivity of the East Antarctic Ice Sheet to a choice of initial ice sheet configuration. We found that the warmer regional climate signal captured by Antarctic ice cores during peak MIS11c is crucial to reproduce the contribution expected from Antarctica during the recorded global sea level highstand. This climate signal translates to a modest threshold of 0.4 ∘C oceanic warming at intermediate depths, which leads to a collapse of the West Antarctic Ice Sheet if sustained for at least 4000 years.
... Accurate models of past ice sheet states demand a good understanding of these processes despite the fact that they evolve more slowly than other boundary conditions. Several recent studies focused on the reconstruction of past periods of change, such as the last interglacial or the Pliocene as indicators for potential future ice sheet states (Cook et al., 2013;de Boer et al., 2015;Patterson et al., 2014). Knowledge of the nature of the ice sheet bed at these times has been inadequate to constrain such studies within acceptable bounds for them to be used in a predictive capacity. ...
... There are currently insufficient geological constraints on the size and extent of the Pliocene AIS, resulting in many synthesis studies on geological data and climate modeling (de Boer et al., 2015;. Susceptibility of the marine-based WAIS to retreat, for example, during warm intervals of the Pliocene, was suggested by modeling (Pollard & DeConto, 2009) and supported by the deposition of diatomaceous oozes under surface water temperatures a few degrees warmer than today at the ANDRILL AND-1B site in the Ross Sea during Pliocene interglacial periods (McKay, Naish, Carter, et al., 2012;Naish et al., 2009). ...
The Antarctic Ice Sheet (AIS) is out of equilibrium with the current anthropogenic‐enhanced climate forcing. Paleoenvironmental records and ice sheet models reveal that the AIS has been tightly coupled to the climate system during the past and indicate the potential for accelerated and sustained Antarctic ice mass loss into the future. Modern observations by contrast suggest that the AIS has only just started to respond to climate change in recent decades. The maximum projected sea level contribution from Antarctica to 2100 has increased significantly since the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report, although estimates continue to evolve with new observational and theoretical advances. This review brings together recent literature highlighting the progress made on the known processes and feedbacks that influence the stability of the AIS. Reducing the uncertainty in the magnitude and timing of the future sea level response to AIS change requires a multidisciplinary approach that integrates knowledge of the interactions between the ice sheet, solid Earth, atmosphere, and ocean systems and across time scales of days to millennia. We start by reviewing the processes affecting AIS mass change, from atmospheric and oceanic processes acting on short time scales (days to decades), through to ice processes acting on intermediate time scales (decades to centuries) and the response to solid Earth interactions over longer time scales (decades to millennia). We then review the evidence of AIS changes from the Pliocene to the present and consider the projections of global sea level rise and their consequences. We highlight priority research areas required to improve our understanding of the processes and feedbacks governing AIS change.
