A Realistic Greenland Ice Sheet and Surrounding Glaciers and Ice Caps Melting in a Coupled Climate Model

Abstract Greenland ice sheet experienced an intensive melting in the last century, especially in the 1920s and over the last decades. The supplementary input into the ocean could disrupt the freshwater budget of the North Atlantic. Simultaneously, some signs of a recent weakening of the Atlantic Meridional Overturning Circulation (AMOC) have been reported. In order to better understand the possible impact of the increasing melting on the North Atlantic circulation, salinity and temperature trends, we construct an observation-based estimate of the freshwater fluxes spanning from 1840 to 2014. The estimate is based on runoff fluxes coming from Greenland ice sheet and surrounding glaciers and ice caps. Input from iceberg melting is also included and spatially distributed over the North Atlantic following an observed climatology. We force a set of historical simulations of the IPSL-CM6A-LR coupled climate model with this reconstruction from 1920 to 2014. The ten-member ensemble mean displays freshened and cooled waters around Greenland, which spread in the subpolar gyre, and then towards the subtropical gyre and the Nordic Seas. Over the whole period, the convection is reduced in the Labrador and Nordic Seas, while it is slightly enhanced in the Irminger Sea, and the AMOC is weakened by 0.32±0.35 Sv at 26°N. The multi-decadal trend of the North Atlantic surface temperature obtained with the additional freshwater forcing is slightly closer to observations than in standard historical simulations, although the two trends are only different at the 90% confidence level. Slight improvement of the Root Mean Square Error with respect to observations in the subpolar gyre region suggests that part of the surface temperature variability over the recent decades may have been forced by the release of freshwater from Greenland and surrounding regions since the 1920s. Finally, we highlight that the AMOC decrease due to Greenland melting remains modest in these simulations and can only explain a very small amount of the 3±1 Sv weakening suggested in a recent study.

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Impact of a realistic Greenland ice sheet melting on the North Atlantic over the period 1920-2014

10.5194/egusphere-egu2020-19096 ◽

2020 ◽

Author(s):

Didier Swingedouw ◽

Marion Devilliers ◽

Juliette Mignot ◽

Julie Deshayes ◽

Gilles Garric ◽

...

Keyword(s):

North Atlantic ◽

Climate Model ◽

Decadal Variability ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Meridional Overturning Circulation ◽

Subpolar Gyre ◽

Nordic Seas ◽

The North ◽

The North Atlantic

Greenland experienced intensive melting over the last century, especially in the 1920s and over the last decades. The supplementary input into the ocean is influencing the freshwater budget of the North Atlantic. Simultaneously, some signs of a recent weakening of the Atlantic meridional overturning circulation (AMOC) have been reported. In order to better understand the possible impact of the melting on the North Atlantic circulation, salinity and temperature trends, we construct an observation-based estimate of the freshwater fluxes from 1840 to 2014 associated to the runoff fluxes from Greenland ice sheet and surrounding glaciers and ice caps. Input from iceberg melting is also included and spatially distributed over the North Atlantic following an observed climatology. We force historical simulations of the IPSL-CM6A-LR coupled climate model with this reconstruction from 1920 to 2014. The 10-member ensemble mean displays freshened and cooled waters around Greenland, which spread in the subpolar gyre, and then towards the subtropical gyre and the Nordic Seas. Over the whole period, the convection is reduced in the Labrador and Nordic Seas, while it is slightly enhanced in the Irminger Sea, and the AMOC is reduced by 0.32&#177;0.35 Sv at 26&#176;N. This highlights that the AMOC decrease due to Greenland melting remains modest in these simulations and can only explain a very moderate amount of the 3&#177;1 Sv weakening suggested in a recent study. The multi-decadal trend of the North Atlantic surface temperature obtained with the additional freshwater forcing is more in line with observations than in standard historical simulations. We also show a clear improvement of the representation of the 1995 abrupt warming in the subpolar gyre in the melting ensemble, which may thus be partly forced by Greenland ice sheet melting. Mechanisms at play imply changes in the variability of the AMOC in the melting ensemble as compared to the historical one. Such an impact on forced decadal variability has crucial consequences for decadal prediction systems that may gain skill by including observed Greenland ice sheet melting.

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Subpolar Gyre Index and the North Atlantic Meridional Overturning Circulation in a Coupled Climate Model

Atmospheric and Oceanic Science Letters ◽

10.1080/16742834.2008.11446764 ◽

2008 ◽

Vol 1 (1) ◽

pp. 29-32 ◽

Cited By ~ 10

Author(s):

Gao Yong-Qi ◽

Yu Lei

Keyword(s):

North Atlantic ◽

Climate Model ◽

Atlantic Meridional Overturning Circulation ◽

Meridional Overturning Circulation ◽

Subpolar Gyre ◽

Coupled Climate Model ◽

Overturning Circulation ◽

The North ◽

Meridional Overturning ◽

The North Atlantic

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Sensitivity of Greenland Ice Sheet surface mass balance to perturbations in sea surface temperature and sea ice cover: a study with the regional climate model MAR

The Cryosphere ◽

10.5194/tc-8-1871-2014 ◽

2014 ◽

Vol 8 (5) ◽

pp. 1871-1883 ◽

Cited By ~ 38

Author(s):

B. Noël ◽

X. Fettweis ◽

W. J. van de Berg ◽

M. R. van den Broeke ◽

M. Erpicum

Keyword(s):

North Atlantic ◽

Climate Model ◽

Regional Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Sea Surface ◽

Surface Mass ◽

The North ◽

The North Atlantic ◽

Sst Anomalies

Abstract. During recent summers (2007–2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North Atlantic Oscillation (NAO), favoring warmer atmospheric conditions than normal over the GrIS. Simultaneously, large anomalies in sea ice cover (SIC) and sea surface temperature (SST) were observed in the North Atlantic, suggesting a possible connection. To assess the direct impact of 2007–2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR forced by ERA-Interim. These simulations suggest that perturbations in SST and SIC in the seas surrounding Greenland do not considerably impact GrIS SMB, as a result of the katabatic wind blocking effect. These offshore-directed winds prevent oceanic near-surface air, influenced by SIC and SST anomalies, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds cease. A topic for further investigation is how anomalies in SIC and SST might have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, hence favoring more frequent warm air advection towards the GrIS.

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Two AMOC States in Response to Decreasing Greenhouse Gas Concentrations in the Coupled Climate Model MPI-ESM

Journal of Climate ◽

10.1175/jcli-d-17-0859.1 ◽

2018 ◽

Vol 31 (19) ◽

pp. 7969-7984 ◽

Cited By ~ 14

Author(s):

Marlene Klockmann ◽

Uwe Mikolajewicz ◽

Jochem Marotzke

Keyword(s):

North Atlantic ◽

Climate Model ◽

Ice Sheets ◽

Ice Sheet ◽

Meridional Overturning Circulation ◽

Salt Transport ◽

Coupled Climate Model ◽

Weak State ◽

The North ◽

The North Atlantic

This study analyzes the response of the Atlantic meridional overturning circulation (AMOC) to different CO2 concentrations and two ice sheet configurations in simulations with the coupled climate model MPI-ESM. With preindustrial (PI) ice sheets, there are two different AMOC states within the studied CO2 range: one state with a strong and deep upper overturning cell at high CO2 concentrations and one state with a weak and shallow upper cell at low CO2 concentrations. Changes in AMOC variability with decreasing CO2 indicate two stability thresholds. The strong state is stable above the first threshold near 217 ppm, and the weak state is stable below the second threshold near 190 ppm. Between the two thresholds, both states are marginally unstable, and the AMOC oscillates between them on millennial time scales. The weak AMOC state is stable when Antarctic Bottom Water becomes dense and salty enough to replace North Atlantic Deep Water (NADW) in the deep North Atlantic and when the density gain over the North Atlantic becomes too weak to sustain continuous NADW formation. With Last Glacial Maximum (LGM) ice sheets, the density gain over the North Atlantic and the northward salt transport are enhanced with respect to the PI ice sheet case. This enables active NADW formation and a strong AMOC for the entire range of studied CO2 concentrations. The AMOC variability indicates that the simulated AMOC is far away from a stability threshold with LGM ice sheets. The nonlinear relationship among AMOC, CO2, and prescribed ice sheets provides an explanation for the large intermodel spread of AMOC states found in previous coupled LGM simulations.

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A realistic Greenland ice sheet and surrounding glaciers and ice caps melting in a coupled climate model

Climate Dynamics ◽

10.1007/s00382-021-05816-7 ◽

2021 ◽

Author(s):

Marion Devilliers ◽

Didier Swingedouw ◽

Juliette Mignot ◽

Julie Deshayes ◽

Gilles Garric ◽

...

Keyword(s):

Climate Model ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Coupled Climate Model ◽

Ice Caps

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Subpolar Gyre – AMOC – Atmosphere Interactions on Multidecadal Timescales in a Version of the Kiel Climate Model

10.5194/egusphere-egu21-4608 ◽

2021 ◽

Author(s):

Jing Sun ◽

Mojib Latif ◽

Wonsun Park

Keyword(s):

North Atlantic ◽

Climate Model ◽

Deep Convection ◽

Meridional Overturning Circulation ◽

Subpolar Gyre ◽

Surface Salinity ◽

The North ◽

Ocean Coupling ◽

Meridional Overturning ◽

The North Atlantic

There is a controversy about the nature of multidecadal climate variability in the North Atlantic (NA) region, concerning the roles of ocean circulation and atmosphere-ocean coupling. Here we describe NA multidecadal variability from a version of the Kiel Climate Model, in which both subpolar gyre (SPG)-Atlantic Meridional Overturning Circulation (AMOC) and atmosphere-ocean coupling are essential. The oceanic barotropic streamfuntions, meridional overturning streamfunctions, and sea level pressure are jointly analyzed to derive the leading mode of Atlantic variability. This mode accounting for about 23.7 % of the total combined variance is oscillatory with an irregular periodicity of 25-50 years and an e-folding time of about a decade. SPG and AMOC mutually influence each other and together provide the delayed negative feedback necessary for maintaining the oscillation. An anomalously strong SPG, for example, drives higher surface salinity and density in the NA&#8217;s sinking region. In response, oceanic deep convection and AMOC intensify, which, with a time delay of about a decade, reduces SPG strength by enhancing upper-ocean heat content. The weaker gyre circulation leads to lower surface salinity and density in the sinking region, which eventually reduces deep convection and AMOC strength. There is a positive ocean-atmosphere feedback between the sea surface temperature and low-level atmospheric circulation over the Southern Greenland area, with related wind stress changes reinforcing SPG changes, thereby maintaining the (damped) multidecadal oscillation against dissipation. Stochastic surface heat-flux forcing associated with the North Atlantic Oscillation drives the eigenmode.

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Greenland melting signatures in model simulations and oceanic observations

10.5194/egusphere-egu21-8225 ◽

2021 ◽

Author(s):

Sophie Stolzenberger ◽

Roelof Rietbroek ◽

Claudia Wekerle ◽

Bernd Uebbing ◽

Jürgen Kusche

Keyword(s):

North Atlantic ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Ocean Model ◽

Freshwater Flux ◽

Model Simulations ◽

The North ◽

Sea Level Anomalies ◽

The North Atlantic ◽

The Impact

The impact of Greenland freshwater on oceanic variables in the North Atlantic has been controversially discussed in the past. Within the framework of the German research project GROCE (Greenland Ice Sheet Ocean Interaction), we present a comprehensive study using ocean modelling results including and excluding the Greenland freshwater flux. The aim of this study is whether signatures of Greenland ice sheet melting found in ocean model simulations are visible in the observations. Therefore, we estimate changes in temperature, salinity, steric heights and sea level anomalies since the 1990s. The observational database includes altimetric and gravimetric satellite data as well as Argo floats. We will discuss similarities/differences between model simulations and observations for smaller regions around Greenland in the North Atlantic. As these experiments are available for two different horizontal resolutions, we will furthermore be able to assess the effects of an increased model resolution.

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On the role of atmospheric feedbacks in sustaining the anomalous warmth of the MIS-11 interglacial

10.5194/egusphere-egu21-7316 ◽

2021 ◽

Author(s):

Brian Crow ◽

Matthias Prange ◽

Michael Schulz

Keyword(s):

North Atlantic ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Meridional Overturning Circulation ◽

Interglacial Period ◽

Climate Modelling ◽

Ice Dynamics ◽

The North ◽

Atmospheric Feedbacks ◽

The North Atlantic

Historical estimates of the melt rate and extent of the Greenland ice sheet (GrIS) are poorly constrained, due both to incomplete understanding of relevant ice dynamics and the magnitude of forcing acting upon the ice sheet (e.g., Alley et al. 2010). Previous assessments of the Marine Isotope Stage 11 (MIS-11) interglacial period have determined it was likely one of the warmest and longest interglacial periods of the past 800 kyr, leading to melt of at least half the present-day volume of the Greenland ice sheet (Robinson et al. 2017). An enhanced Atlantic meridional overturning circulation (AMOC) is commonly cited as sustaining the anomalous warmth across the North Atlantic and Greenland (e.g., Rachmayani et al. 2017), but little is known about potential atmospheric contributions. Paleorecords from this period are sparse, and detailed climate modelling studies of this period have been heretofore very limited. The climatic conditions over Greenland and the North Atlantic region, and how they may have contributed to the melt of the GrIS during MIS-11, are therefore not well understood. By utilizing climate simulations with the Community Earth System Model (CESM), our study indicates that changes in atmospheric eddy behavior, including eddy fluxes of heat and precipitation, made significant contributions to the negative mass balance conditions over the GrIS during the MIS-11 interglacial. Thus, accounting for the effects of atmospheric feedbacks in a warmer-than-present climate is a necessary component for future analyses attempting to better constrain the extent and rate of melt of the GrIS.

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