scholarly journals Heinrich events show two-stage climate response in transient glacial simulations

2019 ◽  
Vol 15 (1) ◽  
pp. 153-168 ◽  
Author(s):  
Florian Andreas Ziemen ◽  
Marie-Luise Kapsch ◽  
Marlene Klockmann ◽  
Uwe Mikolajewicz
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Global Climate ◽  
Discharge Rate ◽  
Ice Sheet ◽  
Climate Response ◽  
Two Stage ◽  
Heinrich Events ◽  
The North ◽  
The North Atlantic

Abstract. Heinrich events are among the dominant modes of glacial climate variability. During these events, massive iceberg armadas were released by the Laurentide Ice Sheet and sailed across the Atlantic where they melted and released freshwater, as well as detritus, that formed characteristic layers on the seafloor. Heinrich events are known for cold climates in the North Atlantic region and global climate changes. We study these events in a fully coupled complex ice sheet–climate model with synchronous coupling between ice sheets and oceans. The ice discharges occur as an internal variability of the model with a recurrence period of 5 kyr, an event duration of 1–1.5 kyr, and a peak discharge rate of about 50 mSv, roughly consistent with reconstructions. The climate response shows a two-stage behavior, with freshwater release effects dominating the surge phase and ice sheet elevation effects dominating the post-surge phase. As a direct response to the freshwater discharge during the surge phase, deepwater formation in the North Atlantic decreases and the North Atlantic deepwater cell weakens by 3.5 Sv. With the reduced oceanic heat transport, the surface temperatures across the North Atlantic decrease, and the associated reduction in evaporation causes a drying in Europe. The ice discharge lowers the surface elevation in the Hudson Bay area and thus leads to increased precipitation and accelerated ice sheet regrowth in the post-surge phase. Furthermore, the jet stream widens to the north, which contributes to a weakening of the subpolar gyre and a continued cooling over Europe even after the ice discharge. This two-stage behavior can explain previously contradicting model results and understandings of Heinrich events.

scholarly journals Heinrich events show two-stage climate response in transient glacial simulations

2018 ◽  
Author(s):  
Florian Andreas Ziemen ◽  
Marie-Luise Kapsch ◽  
Marlene Klockmann ◽  
Uwe Mikolajewicz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Climate Model ◽  
Discharge Rate ◽  
Ice Sheet ◽  
Climate Response ◽  
Two Stage ◽  
Heinrich Events ◽  
The North ◽  
The North Atlantic

Abstract. Heinrich events are among the dominant modes of glacial climate variability. During these events, massive iceberg armadas were released by the Laurentide Ice Sheet, sailed across the Atlantic, and caused large-scale climate changes. We study these events in a fully coupled complex ice sheet–climate model with synchronous coupling between ice sheets and oceans. The ice discharges occur as internal variability of the model with a recurrence period of 5 kyr, an event duration of 1–1.5 kyr, and a peak discharge rate of about 50 mSv, roughly consistent with reconstructions. The climate response shows a two-stage behavior, with freshwater release effects dominating the surge phase and ice-sheet elevation effects dominating in the post-surge phase. As a direct response to the freshwater discharge during the surge phase, the deepwater formation in the North Atlantic decreases and the North Atlantic deepwater cell weakens by 3.5 Sv. With the reduced oceanic heat transport, the surface temperatures across the North Atlantic decrease, and the associated reduction in evaporation causes a drying in Europe. The ice discharge lowers the surface elevation in the Hudson Bay area and thus leads to increased precipitation and accelerated ice sheet regrowth in the post-surge phase. Furthermore, the jet stream widens to the north and becomes more zonal. This contributes to a weakening of the subpolar gyre, and a continued cooling over Europe even after the ice discharge. This two-stage behavior can explain previously contradicting model results and understandings of Heinrich Events.

Statistical Projection of the North Atlantic Storm Tracks

2019 ◽  
Vol 58 (7) ◽  
pp. 1509-1522 ◽  
Author(s):  
Kajsa M. Parding ◽  
Rasmus Benestad ◽  
Abdelkader Mezghani ◽  
Helene B. Erlandsen
Keyword(s):  
North Atlantic ◽  
Geopotential Height ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Storm Tracks ◽  
Cmip5 Models ◽  
The North ◽  
The Future ◽  
The North Atlantic

AbstractA method for empirical–statistical downscaling was adapted to project seasonal cyclone density over the North Atlantic Ocean. To this aim, the seasonal mean cyclone density was derived from instantaneous values of the 6-h mean sea level pressure (SLP) reanalysis fields. The cyclone density was then combined with seasonal mean reanalysis and global climate model projections of SLP or 500-hPa geopotential height to obtain future projections of the North Atlantic storm tracks. The empirical–statistical approach is computationally efficient because it makes use of seasonally aggregated cyclone statistics and allows the future cyclone density to be estimated from the full ensemble of available CMIP5 models rather than from a smaller subset. However, the projected cyclone density in the future differs considerably depending on the choice of predictor, SLP, or 500-hPa geopotential height. This discrepancy suggests that the relationship between the cyclone density and SLP, 500-hPa geopotential height, or both is nonstationary; that is, that the statistical model depends on the calibration period. A stationarity test based on 6-hourly HadGEM2-ES data indicated that the 500-hPa geopotential height was not a robust predictor of cyclone density.

scholarly journals 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

2014 ◽  
Vol 8 (5) ◽  
pp. 1871-1883 ◽  
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.

scholarly journals Climate response of the Florida Peninsula to Heinrich events in the North Atlantic

2018 ◽  
Vol 194 ◽  
pp. 1-11 ◽  
Author(s):  
T. Elliott Arnold ◽  
Aaron F. Diefendorf ◽  
Mark Brenner ◽  
Katherine H. Freeman ◽  
Allison A. Baczynski
Keyword(s):  
North Atlantic ◽  
Climate Response ◽  
Heinrich Events ◽  
The North ◽  
The North Atlantic

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

2021 ◽  
Author(s):  
Marion Devilliers ◽  
Didier Swingedouw ◽  
Juliette Mignot ◽  
Julie Deshayes ◽  
Gilles Garric ◽  
...  
Keyword(s):  
North Atlantic ◽  
Climate Model ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Subpolar Gyre ◽  
Coupled Climate Model ◽  
Nordic Seas ◽  
Ice Caps ◽  
The North ◽  
The North Atlantic

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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