Unstable Behavior of the Laurentide Ice Sheet over Deforming Sediment and Its Implications for Climate Change

1994 ◽  
Vol 41 (1) ◽  
pp. 19-25 ◽  
Author(s):  
Peter U. Clark
Keyword(s):  
North Atlantic ◽  
Thermohaline Circulation ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
Climate Oscillations ◽  
Unstable Behavior ◽  
The North ◽  
The North Atlantic

AbstractGeologic records of fluctuations of the Laurentide ice sheet margin following the most recent glacial maximum (ca. 20,000 14C yr B.P.) identify fundamental differences in ice-sheet behavior depending on subglacial bed conditions. Rapid and irregular icemargin fluctuations occurred only over areas of deforming sediment, indicating nonclimatic forcing controlled by the inherent instability of coupled ice sheet-deforming sediment dynamics. In contrast, largely uninterrupted ice-margin retreat with no evidence of significant readvance occurred over rigid-bed areas, indicating stable behavior. Unstable ice-sheet behavior was most pronounced from 15,000 until 10,000 14C yr B.P., by which time most of the ice margin had retreated onto a rigid bed. Unstable ice-sheet behavior would have been an integral component in controlling variable fluxes of icebergs and meltwater, as well as meltwater routing, to the North Atlantic, thus affecting thermohaline circulation. The abrupt climate oscillations in the North Atlantic region that ended at 10,000 14C yr B.P. may thus have their origin in the inherently unstable behavior of the Laurentide ice sheet overriding deforming sediment.

scholarly journals The impact of different glacial boundary conditions on atmospheric dynamics and precipitation in the North Atlantic region

2012 ◽  
Vol 8 (3) ◽  
pp. 935-949 ◽  
Author(s):  
D. Hofer ◽  
C. C. Raible ◽  
A. Dehnert ◽  
J. Kuhlemann
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Ice Sheet ◽  
Atmospheric Dynamics ◽  
Laurentide Ice Sheet ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract. Using a highly resolved atmospheric general circulation model, the impact of different glacial boundary conditions on precipitation and atmospheric dynamics in the North Atlantic region is investigated. Six 30-yr time slice experiments of the Last Glacial Maximum at 21 thousand years before the present (ka BP) and of a less pronounced glacial state – the Middle Weichselian (65 ka BP) – are compared to analyse the sensitivity to changes in the ice sheet distribution, in the radiative forcing and in the prescribed time-varying sea surface temperature and sea ice, which are taken from a lower-resolved, but fully coupled atmosphere-ocean general circulation model. The strongest differences are found for simulations with different heights of the Laurentide ice sheet. A high surface elevation of the Laurentide ice sheet leads to a southward displacement of the jet stream and the storm track in the North Atlantic region. These changes in the atmospheric dynamics generate a band of increased precipitation in the mid-latitudes across the Atlantic to southern Europe in winter, while the precipitation pattern in summer is only marginally affected. The impact of the radiative forcing differences between the two glacial periods and of the prescribed time-varying sea surface temperatures and sea ice are of second order importance compared to the one of the Laurentide ice sheet. They affect the atmospheric dynamics and precipitation in a similar but less pronounced manner compared with the topographic changes.

scholarly journals Synoptic Forcing of Precipitation over Greenland: Climatology for 1961–99

2009 ◽  
Vol 10 (1) ◽  
pp. 60-78 ◽  
Author(s):  
Keah C. Schuenemann ◽  
John J. Cassano ◽  
Joel Finnis
Keyword(s):  
North Atlantic ◽  
Winter Season ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Synoptic Climatology ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
Synoptic Patterns ◽  
The North ◽  
The North Atlantic

Abstract Analysis of the synoptic climatology and precipitation patterns over the North Atlantic region allows for a better understanding of the atmospheric input to the mass balance of the Greenland ice sheet. The self-organizing map (SOM) technique was applied to the 40-yr European Centre for Medium-Range Weather Forecasts Re-Analysis (ERA-40) daily sea level pressure (SLP) data from 1961 to 1999 to objectively identify synoptic SLP patterns over the North Atlantic region. A total of 35 different SLP patterns were identified. Patterns common to the winter season are characterized by deep low pressure systems that approach Greenland through an active North Atlantic storm track, whereas patterns most common to the summer months are generally weaker and approach the ice sheet from the west through Baffin Bay. The blocking, splitting, and intensification of cyclones by the high elevations of the Greenland ice sheet were identified in this analysis. Analysis of ERA-40 precipitation associated with each SLP pattern revealed that the largest precipitation events were associated with passing cyclones that created onshore flow, allowing the air to be lifted orographically by the steep margins of the ice sheet. The ERA-40 annual mean precipitation over Greenland from 1961 to 1999 was 35.8 cm yr−1. Greenland was divided into five subregions, and the preferred synoptic patterns for receiving precipitation in each region include cyclones positioned to allow dynamic and orographic lift in each region. Annual precipitation contributions from each SLP pattern were isolated to reveal that half of the annual mean precipitation over Greenland comes from only 11 of the 35 identified synoptic patterns (31.4%), highlighting the importance of studying Greenland precipitation on an event-by-event basis on a daily time scale.

scholarly journals The impact of different glacial boundary conditions on atmospheric dynamics and precipitation in the North Atlantic region

2012 ◽  
Vol 8 (1) ◽  
pp. 63-101
Author(s):  
D. Hofer ◽  
C. C. Raible ◽  
A. Dehnert ◽  
J. Kuhlemann
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
General Circulation ◽  
Ice Sheet ◽  
Atmospheric Dynamics ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract. Using a highly resolved atmospheric general circulation model the impact of different glacial boundary conditions on precipitation and atmospheric dynamics in the North Atlantic region is investigated. Seven 30-yr time slice experiments of the Last Glacial Maximum (21 ka ago) and of a less pronounced glacial state – the Middle Weichselian (65 ka ago) – are compared to analyse the sensitivity to changes in the ice sheet distribution, in the radiative forcing, and in the prescribed time-varying lower boundary conditions, which are taken from a lower-resolved but fully-coupled atmosphere-ocean general circulation model. The strongest differences are found for simulations with different heights of the Laurentide ice sheet. A large altitude of this ice sheet leads to a southward displacement of the jet stream and the storm track in the North Atlantic region. These changes in the atmospheric dynamics generate a band of increased precipitation in the mid-latitudes across the Atlantic to southern Europe in winter, while the precipitation pattern in summer is only marginally affected. The impact of the radiative forcing differences between the two glacial periods and of the prescribed time-varying lower boundary conditions – evaluated using two simulations of the Last Glacial Maximum with a global mean temperature difference of 1.1 °C – are of second order compared to the one of the Laurentide ice sheet. They affect the atmospheric dynamics and precipitation in a similar but less pronounced manner as the topographic changes.

Major ice sheet response in eastern New England to a cold North Atlantic region, ca. 16–15 cal ka BP

2007 ◽  
Vol 68 (2) ◽  
pp. 280-283 ◽  
Author(s):  
Michael R. Kaplan
Keyword(s):  
New England ◽  
North Atlantic ◽  
Ice Sheet ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
Time Period ◽  
Meridional Overturning ◽  
The North Atlantic ◽  
Almost All

AbstractA large ice sheet still covered almost all of Maine and eastern New England until ca. 15 cal ka BP, reaching south of 45 °S, despite rising summer insolation intensity and major ice recession elsewhere outside the North Atlantic region. Furthermore, the well-studied moraine belt along eastern coastal Maine, including the prominent Pineo Ridge delta/moraine complex and Pond Ridge moraine, indicates repeated readvances and stillstands between ca. 16 and 15 cal ka BP. This moraine belt reflects a considerable ice sheet response over eastern North America during this time period, coeval with the latter half of the European Oldest Dryas period. Moraine deposition was concurrent with reduction or elimination of North Atlantic meridional overturning, starting with the earlier onset of peak IRD and Heinrich Event 1 (HE-1). The existing 14C chronology suggests that the coastal moraine belt and the persistence of the ice sheet until ∼ 15 cal ka BP was a response to the severe cooling of the North Atlantic region after ∼ 17 cal ka BP.

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