Ice Sheet Action Versus Reaction: Distinguishing between Heinrich Events and Dansgaard-Oeschger Cycles in 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.

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

10.5194/cp-2018-16 ◽

2018 ◽

Cited By ~ 1

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.

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Heinrich events: Massive late Pleistocene detritus layers of the North Atlantic and their global climate imprint

Reviews of Geophysics ◽

10.1029/2003rg000128 ◽

2004 ◽

Vol 42 (1) ◽

Cited By ~ 869

Author(s):

Sidney R. Hemming

Keyword(s):

Late Pleistocene ◽

North Atlantic ◽

Global Climate ◽

Heinrich Events ◽

The North ◽

The North Atlantic

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Marine productivity response to Heinrich events: a model-data comparison

Climate of the Past ◽

10.5194/cp-8-1581-2012 ◽

2012 ◽

Vol 8 (5) ◽

pp. 1581-1598 ◽

Cited By ~ 23

Author(s):

V. Mariotti ◽

L. Bopp ◽

A. Tagliabue ◽

M. Kageyama ◽

D. Swingedouw

Keyword(s):

North Atlantic ◽

General Circulation ◽

Circulation Model ◽

Global Ocean ◽

Biogeochemical Model ◽

Heinrich Events ◽

The North ◽

Heinrich Event ◽

The North Atlantic ◽

Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.

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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

<p>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.</p>

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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

<p>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.</p>

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A Eurasian Ice-Sheet Study Using A Combined Ice-Sheet/ Ice-Shelf Numerical Model

Annals of Glaciology ◽

10.3189/s0260305500009125 ◽

1990 ◽

Vol 14 ◽

pp. 345-345

Author(s):

Dean R. Lindstrom

Keyword(s):

Numerical Model ◽

Mass Loss ◽

North Atlantic ◽

Ice Sheet ◽

The Arctic ◽

North Atlantic Current ◽

Ice Shelf ◽

The North ◽

The North Atlantic ◽

Atlantic Current

A numerical model which simultaneously computes grounded and ice-shelf flow was used to develop an equilibrium ice-sheet–ice-shelf system over Eurasia and the Arctic region. Present-day net accumulation rates and mean annual and July temperature values were used as base values for climatic variable specifications. The values were adjusted during the model run to account for changes in the ice-surface elevation and atmospheric CO2 concentration. The model-determined equilibrium ice-sheet configuration was used as input for additional runs to observe what effect removing the Arctic ice shelf and increasing the CO2 concentration from glacial to present-day values has on the ice sheet.At equilibrium, an ice shelf formed over the Arctic Ocean and Greenland and Norwegian seas. Ice easily grounded over the Barents, Kara, East Siberian, and Laptev seas. The grounded ice-sheet profile differs in Europe from most glacial geological reconstructions because the North Atlantic Current effect was not removed from the climatic adjustments. As a result, ice did not extend over the North Sea and onto the British Isles because of the North Atlantic Current's warming effect. Also, the precipitation rate over Europe was too high because of the moisture source the North Atlantic Current carries, and the ice sheet expanded beyond the field-determined ice-sheet margins in the region south-east of Finland.Removing most of the Arctic region's ice-shelf cover had little effect on the grounded ice sheet unless it rested upon a deformable sediment layer. The ice sheet was able to collapse within 10 000 years, however, when the CO2 concentration was gradually increased toward present-day values using the Vostok ice core's CO2 record from the last 18 000 years. Initially, most mass loss resulted from surface melting. Once the thickness decreased enough over some regions for the grounded ice to become ungrounded, however, most mass loss resulted from the ice shelf rapidly transporting the ice to the ice-shelf front and discharging it to the sea.

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