Abstract. The long-term evolution of the Greenland Ice Sheet (GrIS) remains a major source of uncertainty in projections of future sea-level rise. Recent advances in coupled climate–ice sheet models provide new opportunities to investigate the role of feedbacks between the ice sheet and the climate system, yet substantial divergence persists across climate-ice sheet model projections. Here, we present results from the Greenland Ice sheet Coupled Model Intercomparison Project (GrICMIP), using three coupled climate–ice sheet models to simulate GrIS evolution under multiple emission scenarios to the year 4000 CE. While projected sea-level contributions remain modest by 2100 (0.03–0.11 m), they diverge strongly on longer timescales, reaching up to 3.5 m by 2500. Under the high-emission scenario, full GrIS disintegration is projected as early as 3000 CE. By means of targeted sensitivity experiments, we identify the dominant sources of diverging GrIS trajectories. Across all models, changes in surface mass balance (SMB), and in particular net surface melt, control the long-term ice-sheet retreat. Differences in SMB formulation, especially in the underlying energy balance models, together with differences in the simulated climate, outweigh the influence of initial ice-sheet geometry. This establishes a hierarchy of uncertainties in which atmospheric processes and their representation within the model systems propagate non-linearly into ice-sheet evolution. Our results demonstrate that reliable long-term projections of the GrIS critically depend on improving the representation of climate and SMB, rather than on refining initial conditions alone.

During the Eocene-Oligocene Transition ([Formula: see text]34.4 to 33.7 Ma), major climatic and tectonic changes initiated Earth's current icehouse climate. Plate motion intensified mountain building, reduced atmospheric CO2, and triggered global cooling. Crucially, the opening of the Tasman Gateway and Drake Passage initiated the formation of the Antarctic Circumpolar Current (ACC), today Earth's strongest ocean current. However, the ACC's initial structure during its onset remains poorly understood, limiting our understanding in controlling global circulation patterns and heat distribution at the time. Here, we present data-validated, high-resolution coupled climate-ice sheet simulations of the Early Oligocene Glacial Maximum ([Formula: see text]33.7 to 33.2 Ma), showing that early ocean-atmosphere circulation around Antarctica was closely tied to Southern Ocean gateway geometry and the presence of the early Antarctic Ice Sheet. Unlike today, however, these gateways were not aligned with the westerly wind belt, hence limiting ACC development and promoting strong Antarctic amplification. We conclude that orogenesis, CO2 drawdown, and Southern Hemisphere gateway opening alone were insufficient to establish a strong ACC [Formula: see text]34 Ma. Only the later alignment of westerly winds with open oceanic gateways enabled the enhancement of interhemispheric overturning circulation, promoted carbon uptake, and the long-term stabilization of Earth's icehouse climate.

The Arctic is undergoing rapid warming, resulting in retreating sea ice and glaciers1, yet how cryospheric changes propagate into the deep ocean remains poorly understood2. Here we identify a climate-driven mechanism linking accelerating glacier disintegration to an increase in deep-sea hard-bottom habitats far beyond calving fronts. Seafloor observations in Fram Strait show a localized increase in the density and patchiness of dropstones delivered by debris-laden icebergs. At the same time, four decades of shipboard records show that the occurrence of icebergs increased abruptly in the early 2000s. Backtracking links these icebergs to the main outlet glaciers in northeast Greenland and the Russian High Arctic. In northeast Greenland, the timing of glacier destabilization coincides with this rise, whereas sparse satellite coverage in the Russian sector limits temporal attribution despite indications of enhanced glacier activity. A model sensitivity study shows that, apart from intensified calving, a more dynamic sea ice cover enhances downstream transport of glacial ice. Along these pathways, increased iceberg activity could reshape deep-sea habitats through enhanced melt and associated lithogenic input, and elevate navigational hazards as maritime traffic expands in the Arctic. Although modest compared with the iceberg discharges of Pleistocene Heinrich events, this mechanism provides a modern analogue of long-range cryospheric influence on the seafloor in a warming climate.

The Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in shaping the global climate system by redistributing heat and influencing large-scale climate patterns. Utilizing the AWI-CM3 model, we investigate the AMOC sensitivity to an abrupt climate change scenario (abrupt-4xCO2) with respect to pre-industrial climate (PI), comparing the AMOC diagnosed in depth (z-AMOC) and density (ρ-AMOC) space. Water mass transformations are assessed to analyze the impact of background climate on surface-forced and interior-mixing-induced transformations. We find that both the location and magnitude of AMOC maximum are directly affected by the framework choice. In PI, the ρ-AMOC maximum is substantially stronger than that of the z-AMOC, while at 26° N the two diagnostics are nearly equivalent. Consequently, the variability of the z-AMOC maximum correlates only with that at 26° N, reflecting isopycnal flattening into constant depth levels in the subpolar North Atlantic inherent to these diagnostics. Strong AMOC weakening is observed under 4xCO2 forcing in both frameworks until simulation year 75. Subsequently, both diagnostics reveal a weaker AMOC with an approximate strength of 7.1 Sv, although with z-AMOC displaying a slight recover towards the end of the simulation and ρ-AMOC oscillating steadily around 5 Sv. At 26° N, variability patterns remain comparable to PI, albeit with an additional ρ-AMOC weakening of approximately 2 Sv, indicating divergence between the representation of AMOC dynamics in the subtropical Atlantic within both frameworks in comparison to PI. The diagnostics in density space allow for the attribution of this further ρ-AMOC weakening to increased entrainment of fresher overflows from amplified GIN seas overturning and reduced deep convection in the Labrador and Irminger Seas. In contrast, the diagnostics in depth space only reveals reduced downwelling around the southwestern Greenland coast and along the path of the Gulf Stream, features that are more challenging to evaluate against available observations. Thus, the comparison between z-AMOC and ρ-AMOC indicates that diagnosing the AMOC in density space provides more physically meaningful information regarding the state of the water mass transformations and their contribution to ocean circulation regimes across the entire Atlantic basin, not only the subpolar North Atlantic, and especially as the climate continues to warm. These findings emphasize the importance of diagnosing AMOC in density space to better understand water mass transformations, which are concealed in depth space and to capture AMOC variability in warmer climates, across all latitudes.

The Greenland ice sheet has lost ice at an increasing pace over recent decades, driven by a combination of human-caused climate change and internal variability in the climate system. In projections of future ice sheet evolution, internal variability in climate results in uncertainty that cannot be reduced through model improvements due to the intrinsically chaotic nature of the climate system. This study describes the Greenland Ice Sheet Large Ensemble (GrISLENS), the first large-ensemble study of ice sheet evolution under climate variability, which resolves individual outlet glaciers and climate variability calibrated to observations. GrISLENS combines multiple advanced modeling methods, including a stochastic ice sheet model, a coupled atmosphere-ocean model, dynamical surface mass balance downscaling, and statistical techniques for constraining stochastic parameterizations of climate forcing. We quantify the role of internal climate variability in 185-year projections of the Greenland ice sheet under both a high-emission scenario and pre-2000 climate conditions. We find that spread between ensemble members due to internal climate variability represents a substantial fraction of the mean ice sheet change in the first 20-30 years of simulations, which may be important for coastal planning efforts on decadal timescales. This spread between ensemble members decreases to a small fraction of the total ice sheet change past 2050. At the ice sheet scale, uncertainty in ice loss is dominated by the response to surface mass balance variability, while the response to ocean variability is relatively small, though its influence is more important within individual catchments. The GrISLENS ensemble spread is relatively small compared to that of previous studies estimating uncertainty from climate variability in coarse models, which indicates that resolving small-scale features in climate forcing and ice sheet dynamics substantially affects the quantification of internal variability in ice sheet mass change. On longer timescales, human emissions of greenhouse gases and structural and parametric uncertainties in climate and ice sheet models are larger contributors to projection uncertainties. Through our analysis, we identify the need for more robust initialization methods and extension of these large-ensemble methods to the Antarctic ice sheet.

Numerical model simulations are an essential tool for assessing effects of global warming on the climate system in future greenhouse gas concentration scenarios. Commonly, these simulations cover only the next few centuries or use low-complexity models for longer periods. However, to assess the dynamics of Earth system components with long response times like the ocean or ice sheets, multi-millennial simulations with comprehensive Earth system models are essential.Here, we present multi-millennial simulations with the complex Earth System Model AWIESM, covering an integration time beyond the typical CMIP time scale. The model runs on a multi-resolution grid with a horizontal resolution of up to 20 km in high latitudes. The model includes an interactive ice sheet for the Greenland domain. The simulations are forced with transient greenhouse gas concentrations obtained from model simulations with the Earth System Model of intermediate complexity CLIMBER-X with an interactive carbon cycle, covering overshoot scenarios that enable assessment of long-term ice sheet and ocean dynamics.Our results reveal a scenario-dependent weakening of the Atlantic Meridional Overturning Circulation (AMOC), followed by partial recovery over the next millennium. All scenarios show sea ice-free or nearly sea ice-free summer conditions in the northern and southern hemispheres. Winter sea ice shows an asymmetric response under future warming. While Arctic winter sea ice changes are small in low- to medium-emission scenarios, Southern Ocean winter sea ice shows a large reduction even in low-emission scenarios. The Greenland ice sheet shows a continuing ice mass loss during the next millennium, even with decreasing greenhouse gas concentrations in medium-emission scenarios. The main area of ice loss is West Greenland.These findings underscore the importance of long-term simulations with comprehensive Earth system models to understand the complex, delayed responses of key climate system components and their broader implications for the Earth system.

It is highly challenging to include both the Antarctic and Greenland ice sheets in a state-of-the-art earth system model. Our presentation demonstrates our system's design, the essential steps before coupling the entire system, the challenges faced in the coupling process, and the initial findings from our series of simulations for warming scenarios spanning the next few centuries until 2500.We will highlight the existing limitations in the computed climate conditions that affect the behavior of ice sheets. These motivate our system's design. For instance, ocean temperature biases in the marginal seas around Antarctica inhibit its direct use to determine basal melting of floating ice shelves fringing Antarctica despite extensive tuning efforts. As a result, we have developed a flexible framework deemed necessary to adequately represent the currently observed ice sheet state. The still delicate integration of ice sheets into climate models directs the spin-up procedure of ice sheet models. The procedure's results and its consequences are presented and discussed. In particular, the available iceberg calving mechanism has been demanding in our simulations because we allow for freely waxing or waning ice shelf edges around Antarctica, unprecedented in coupled climate-ice sheet model systems.Finally, the first results of our fully coupled simulations complete the presentation. These focus on the interaction between the climate system and Antarctica or Greenland and its influence on primary climatic conditions. In our model system, interacting ice sheets shape the climate state, creating feedback loops that affect the ice sheet state itself. This interaction may ultimately counteract the disintegration of ice sheets. Supposed it is a robust result, it implies that standalone ice sheet simulations may overestimate future sea level contributions.

The Eocene-Oligocene Transition (EOT) (~34.4–33.7 Ma) is not only known for its drastic shift from greenhouse to icehouse climate, but also for a dynamic ocean gateway configuration. The Southern Ocean gateways are expected to open during this period, while the Arctic Ocean likely remains largely isolated, resulting in distinct ocean circulation patterns.Using the AWI-Earth System Model (AWI-ESM) coupled to the Parallel Ice Sheet Model (PISM), we explore the ocean dynamics under an ocean straight configuration markedly different from today’s, providing a detailed depiction of global climate during the EOT. Low-latitudinal seaways, which are absent in the present continental configuration, and opening Southern gateways change the global ocean circulation fundamentally. This also has profound impacts on the continental climate, such as the formation of deserts.With a targeted study of the Southern Ocean, we show that deep Southern gateways alone are insufficient to allow an Antarctic Circumpolar Current (ACC). Whether the Antarctic glacial inception came before or after the onset of the ACC is broadly debated. Here we observe, the onset of the ACC is not a necessary condition for East Antarctic glaciation. Instead of the ACC, a large Weddel-Australian gyre dominates the Southern Ocean. This gyre creates mixing and deep water formation and thus influences an Atlantic Ocean that faces very different boundary conditions than today.This study enhances our understanding of Southern Ocean dynamics prior to the establishment of a strong ACC and underscores the critical role of oceanic gateway configurations in assessing their impact on regional and global climate.

The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of our climate system, influencing water mass formation and transformation. It is driven by buoyancy fluctuations and mixing within the water column. The AMOC is often studied using climate models by calculating strength indexes based on constant depth intervals (z-AMOC). However, at high latitudes, where deep water forms in the Atlantic, isopycnals are much steeper than in subtropical regions. This means that the z-AMOC framework may not fully capture the processes involved in interior ocean ventilation due to its failure to consider density gradients. To address the potential biases of the z-AMOC approach, we calculate the AMOC using density surfaces (ρ-AMOC). We compare the z-AMOC and ρ-AMOC frameworks under three scenarios: Pre-Industrial (PI), historical, and quadrupled PI CO2 concentrations (4xCO2). The PI and historical simulations serve as a testbed for evaluating the frameworks, while the 4xCO2 scenario is crucial for assessing climate sensitivity and natural variability in response to extreme CO2 levels. We also analyze water mass transformations driven by surface-induced and interior-mixing processes.Our findings reveal that both the location and strength of AMOC maxima are significantly influenced by the choice of framework. Under constant depth coordinates, the AMOC reaches a maximum transport of 21 Sv at approximately 35oN, while it achieves around 25 Sv at 55oN when calculated from density surfaces for both PI and historical climates. In the 4xCO2 scenario, both frameworks show an abrupt weakening of the AMOC, linked to sea-ice melting and reduced deep convection, followed by a gradual recovery to maximum values of 10-15 Sv due to increased evaporation and salt export to the North Atlantic. Furthermore, we find that the z-AMOC maxima time series correlates more closely with those at 26oN (r ~ 0.7) than with ρ-AMOC maxima (r ~-0.3). This discrepancy arises from the flatter isopycnals in the z framework, even in the subpolar North Atlantic where isopycnals are actually steeper. Based on these results, we argue that the density framework better represents the physics of AMOC by directly incorporating water mass transformations and their density structure.We indicate that including the density framework in climate model output configurations enhances our understanding of uncertainties regarding future climate change impacts. The AMOC is a critical climate tipping point, and there is currently no consensus on its future behavior. Calculating ρ-AMOC also becomes especially relevant when considering the 4xCO2 scenario as the AMOC shutdown and recovery in both frameworks driven by different processes indicates that the z-AMOC depicts the right patterns based on incorrect underlying mechanisms. This inconsistency introduces additional uncertainties to conclusions draw in studies addressing future AMOC strength and variability derived from the z-AMOC framework. Finally, we suggest that analysis across timescales and under different conditions must be performed with density surface outputs as much as possible, to enable a more comprehensive evaluation of these two frameworks and their applications.

The Eurasian ice sheet complex (EIS) was the third largest ice sheet complex at the Last Glacial Maximum (LGM). Although temporal and spatial evolution of the EIS during the last glacial cycle has not been well-established, strong evidence indicates the existence of nearly ice-free conditions during Marine Isotope Stage 3 (MIS 3). Between MIS 3 and the LGM, the EIS likely experienced substantial expansions. These expansions were accompanied by decreasing boreal summer insolation, a slight reduction in greenhouse gases, and millennial-scale abrupt shifts between stadial and interstadial conditions. Using the state-of-the-art Earth system model AWI-ESM with asynchronously coupled dynamic ice sheets, we performed transient simulations focusing on this period. Our study shows that the formation of the EIS resembles a bifurcation transition. Only in case of a relatively weak background Atlantic Meridional Overturning Circulation (AMOC), a sufficiently large thin ice/snow cover develops to accommodate a subsequent ice volume growth as Northern Hemisphere summer insolation further decreases. Furthermore, sensitivity experiments show a large non-linearity in surface mass balance changes in response to varying temperature and precipitation, indicating a high sensitivity of the EIS buildup. Our study highlights the large complexity and strong non-linearity of the Earth system induced by internal climate feedbacks, particularly the interactions between ice sheets and other climate components.

The explicit representation of cryospheric components in Earth system models has become more and more important over the last years. However, there are few advanced coupled Earth system models that employ interactive icebergs, and most iceberg model studies focus on iceberg trajectories or ocean surface conditions.Here, we present multi-centennial simulations with a fully coupled Earth system model including interactive icebergs to assess the effects of heat and freshwater fluxes by iceberg melting on deep-ocean characteristics. The icebergs are modeled as Lagrangian point particles and exchange heat and freshwater fluxes with the ocean. They are seeded in the Southern Ocean, following a realistic present-day size distribution. Total calving fluxes and the locations of discharge are derived from an ice sheet model output which allows for implementation in coupled climate-ice sheet models.The simulations show a cooling of up to 0.2 K of deep-ocean water masses in all ocean basins that propagates from the southern high latitudes northward. We also find enhanced deep-water formation in the continental shelf area of the Ross Sea, a process commonly underestimated by current climate models. The vertical stratification is weakened by enhanced sea ice formation and duration due to the cooling effect of iceberg melting, leading to a 10 % reduction of the buoyancy frequency in the Ross Sea. The deep-water formation in this region is increased by up to 10 %. By assessing the effects of heat and freshwater fluxes individually, we find latent heat flux to be the main driver of these water mass changes. The altered freshwater distribution by freshwater fluxes and synergetic effects play only a minor role. Our results emphasize the importance of realistically representing both heat and freshwater fluxes in the high southern latitudes.

During deglaciation disintegration of large-scale continental ice sheets represents a continuous threat to reduce the strength of the Atlantic meridional overturning circulation (AMOC) via meltwater perturbations to the northern high latitudes. Nevertheless, an abrupt AMOC recovery is detected half-way through the last deglaciation and a growing number of studies using Earth System Models (ESMs) of varying complexity have shown that atmospheric CO2 concentrations and ice sheet volume can influence the operational mode of the AMOC, eventually including the coexistence of multiple states and associated threshold behavior for intermediate climate states between full glacial (e.g. Last Glacial Maximum, LGM) and full interglacial (e.g. pre-industrial, PD) conditions. In this study we present results from coordinated sensitivity experiments conducted as part of the German climate modeling initiative (PalMod), using three complex ESMs (AWI-ESM, CESM and MPI-ESM). Besides differences in the impact of CO2 and ice volume changes, we also investigate how variations in these boundary conditions control the AMOC sensitivity to deglacial meltwater injections in the North Atlantic. We find that the AMOC strength responds to ice sheet and/or CO2 changes in all models, with partly opposing effects. A similar AMOC strength for PD and LGM conditions is detected in AWI-ESM and MPI-ESM, while CESM shows a weaker LGM AMOC. This weaker LGM state is also characterized by a relatively pronounced AMOC sensitivity to freshwater perturbations. Our inter-comparison experiments suggest that this specific behavior in CESM can be detected for atmospheric concentrations between LGM and intermediate levels of ~220 ppm. This further corroborates in particular the impact of CO2 changes to modulate the trajectory of deglacial climate changes by an alteration of the AMOC susceptibility to meltwater injections as recently suggested (Sun et al., Glob. Planet. Change, 2021; Barker & Knorr, Nat. Commun., 2021). References:Sun, Y., Knorr, G., Zhang, X., Tarasov, L., Barker, S., Werner, M. and G. Lohmann (2022): Ice sheet decline and rising atmospheric CO2 control AMOC sensitivity to deglacial meltwater discharge. Global and Planetary Change 210. https://doi.org/10.1016/j.gloplacha.2022.10375Barker, S. and G. Knorr (2021): Millennial scale feedbacks determine the shape and rapidity of glacial termination. Nature Communications 12, 2273. https://doi.org/10.1038/s41467-021-22388-

Icebergs play a crucial role in Earth's climate system. They transport large amounts of fresh water and alter ocean salinity, affect sea-ice formation, and can lead to abrupt climate changes in the past. Hence, a proper representation of icebergs in Earth system models (ESMs) is essential to improve the understanding of processes involved in abrupt climate changes. Despite their importance, icebergs are rarely represented in ESMs. Freshwater fluxes are often parameterized, neglecting the transport via ocean currents and the heat loss due to iceberg melting. Other models that use an interactive iceberg component are typically ocean-only models, do not represent ice sheets and the atmospheric component explicitly, or are models of intermediate complexity. One reason for this deficiency is the considerable computational costs related to iceberg modeling. Here, we present the latest version of the Alfred Wegener Institute-Earth System Model (AWI-ESM) with interactive ice sheets and a Lagrangian iceberg model. The iceberg component runs as a submodel of the ocean–sea-ice model FESOM2 with an asynchronous coupling to enable computationally effective simulations with the iceberg-enhanced coupled model. Total execution times can be strongly reduced compared to a non-overlapping execution of the iceberg model with other components. Iceberg meltwater and the associated heat fluxes are coupled to the ocean. The ice sheet is dynamically coupled to the climate components. A new feature of this model setup is the ice sheet-iceberg coupling: Icebergs are drawn from a specific size distribution to match the calving output of the ice sheet model in regions of iceberg discharge. Therefore, discharge-related freshwater fluxes are represented more realistically than in other ESMs.

Variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC) during the Pleistocene are linked to changes in Southern Ocean surface conditions (Knorr & Lohmann, 2003). The so-called Agulhas Leakage is thought to play a crucial role in this teleconnection, transferring buoyancy anomalies from the Indian Ocean to the South Atlantic (Caley et al., 2011; Marino et al., 2013). Proxy data of ice-rafted debris (IRD) suggest that icebergs originating in the Southern Ocean have affected the freshwater balance at the Agulhas Plateau during Pleistocene glacial conditions. In particular, peaks in IRD were found to precede AMOC slowdowns on a millennial time scale (Starr et al., 2021). However, climate models that were used to study these processes did not include an iceberg component or were not fully coupled. To study the relative role of Agulhas leakage and iceberg freshwater forcing and their likely interactions, we recently developed the atmosphere-ocean-iceberg model AWI-ESM-2.1-IB, which includes a fully coupled Lagrangian iceberg model (Rackow et al., 2017). We present preliminary results for the Last Glacial Maximum with iceberg seeding in the so-called iceberg alley, applying a modern-day size distribution. Caley, T., Giraudeau, J., Malaizé, B., Rossignol, L., & Pierre, C. (2012). Agulhas leakage as a key process in the modes of Quaternary climate changes. Proceedings of the National Academy of Sciences, 109(18), 6835-6839, . Knorr, G., Lohmann, G. (2003). Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation. Nature 424, 532–536, https://doi.org/10.1038/nature01855. Marino, G., Zahn, R., Ziegler, M., Purcell, C., Knorr, G., Hall, I. R., Ziveri, P., and Elderfield, H. (2013). Agulhas salt‐leakage oscillations during abrupt climate changes of the Late Pleistocene, Paleoceanography, 28, 599– 606, doi:. Rackow, T., Wesche, C., Timmermann, R., Hellmer, H. H., Juricke, S., & Jung, T. (2017). A simulation of small to giant Antarctic iceberg evolution: Differential impact on climatology estimates. Journal of Geophysical Research: Oceans, 122(4), 3170-3190, . Starr, A., Hall, I.R., Barker, S. et al. (2021). Antarctic icebergs reorganize ocean circulation during Pleistocene glacials. Nature 589, 236–241, .

Future global warming will affect ocean conditions by different mechanisms. One mechanism is the melting of the Greenland Ice Sheet (GIS), which may lead to a freshening of regions of deep water formation and eventually contribute to a possible slowdown of the Atlantic Meridional Overturning Circulation (AMOC). We simulate the two Coupled Model Intercomparison Project (CMIP) scenarios RCP4.5 and RCP8.5, to assess the effects of melt-induced fresh water on the AMOC. We use a newly developed coupled multi-resolution atmosphere-ocean-ice sheet model with high resolution at the coasts resolving the complex ocean dynamics. Our results show an AMOC recovery for both scenarios in simulations run with and without an included ice sheet model. We find that the ice sheet is not only acting as a source of freshwater to the ocean but also as a sink. This leads to local storage and redistribution of freshwater and largely compensates for the meltwater release. This physical consistency is missing in climate models without dynamic ice sheets. Therefore, we argue that freshwater hosing experiments should be assessed critically, as they might overestimate the North Atlantic freshening, induced by ice sheet melting. Because of the compensating effect, we find little effect of the included ice sheet model on the AMOC. Our results show a main freshwater release in West Greenland. There, the freshwater might be trapped in the Labrador Current and transported away from regions of deep water formation. Our results show an AMOC recovery, starting within the first half of the 22nd century. We assume the increase in net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of this recovery.

Interglacials during the Quaternary represent the youngest climate states in the paleoclimate record that are similar to potential warmer-than-present states during the Anthropocene. In particular, those periods with warmer reconstructed temperatures and/or higher sea levels provide insights into the mechanisms that may be at work now and in the future. To date, climate model simulations of Quaternary Interglacials have been restricted to Atmosphere-BiosphereOcean simulations, with static ice sheet geometries from glaciological, geological, and geophysical reconstructions. Simulations including fully interactive ice sheets have not been widely available. Here, we present the first simulations of the PMIP4 timeslices for the Holocene and the Last Interglacial (LIG) with a fully coupled multi-resolution climate/cryosphere model, the AWI-ESM. We compare the simulated snapshots for the Holocene and LIG to simulations to proxy reconstructions, and to runs without dynamic ice sheets to highlight the processes now represented by the improved model. Furthermore, we show various schemes implemented in our model system to represent the ice sheet mass balance, both from surface ablation as well as ocean interaction. We find that both the Holocene and Last Interglacial ice sheets contain a smaller volume of ice compared to present day, with relative sea level equivalent changes of -3% and -7%, respectively.

North Pacific Intermediate water (NPIW) is a dominant water mass controlling ~400-1200m depth North Pacific Ocean, characterized by its low salinities and relatively lower temperatures. In the modern climate, the interplay between NPIW-related physical and biogeochemical processes among seasons determines annual-mean budget and efficiency of carbon sink into the North Pacific Ocean. Thus, to understand the NPIW physics is key to project roles of the North Pacific Ocean in changing Earth climate and carbon systems in the future. In this study, we provide a modelling view of the NPIW history since Yr 1850 (historical experiment) and its projection to near future (IPCC-defined RCP 4.2 and 8.5 experiments until Yr 2100), using new-generation Alfred Wegener Institute Earth System Model (AWI-ESM). Our results suggest an important role of regional hydroclimate feedback over the NW Pacific and Sea of Okhotsk in determining the NPIW from recent past to near future.

We simulate the two Coupled Model Intercomparison Project scenarios RCP4.5 and RCP8.5, to assess the effects of melt‐induced fresh water on the Atlantic meridional overturning circulation (AMOC). We use a newly developed climate model with high resolution at the coasts, resolving the complex ocean dynamics. Our results show an AMOC recovery in simulations run with and without an included ice sheet model. We find that the ice sheet adds a strong decadal variability on the freshwater release, resulting in intervals in which it reduces the surface runoff by high accumulation rates. This compensating effect is missing in climate models without dynamic ice sheets. Therefore, we argue to assess those freshwater hosing experiments critically, which aim to parameterize Greenland's freshwater release. We assume the increasing net evaporation over the Atlantic and the resulting increase in ocean salinity, to be the main driver of the AMOC recovery.