Coupled Modes of North Atlantic Ocean‐Atmosphere Variability and the Onset of the Little Ice Age

Abstract The inception of the Little Ice Age (~1400–1700 AD) is believed to have been driven by an interplay of external forcing and climate system internal variability. While the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions, the understanding of mechanisms shaping the climate on a continental scale is less robust. In an ensemble of transient model simulations and a new type of sensitivity experiments with artificial sea ice growth, the authors identify a sea ice–ocean–atmosphere feedback mechanism that amplifies the Little Ice Age cooling in the North Atlantic–European region and produces the temperature pattern suggested by paleoclimatic reconstructions. Initiated by increasing negative forcing, the Arctic sea ice substantially expands at the beginning of the Little Ice Age. The excess of sea ice is exported to the subpolar North Atlantic, where it melts, thereby weakening convection of the ocean. Consequently, northward ocean heat transport is reduced, reinforcing the expansion of the sea ice and the cooling of the Northern Hemisphere. In the Nordic Seas, sea surface height anomalies cause the oceanic recirculation to strengthen at the expense of the warm Barents Sea inflow, thereby further reinforcing sea ice growth. The absent ocean–atmosphere heat flux in the Barents Sea results in an amplified cooling over Northern Europe. The positive nature of this feedback mechanism enables sea ice to remain in an expanded state for decades up to a century, favoring sustained cold periods over Europe such as the Little Ice Age. Support for the feedback mechanism comes from recent proxy reconstructions around the Nordic Seas.

Download Full-text

Linking North Atlantic ocean-atmosphere teleconnection patterns and hydrogeological responses in temperate groundwater systems

Hydrological Processes ◽

10.1002/hyp.7466 ◽

2009 ◽

Vol 23 (21) ◽

pp. 3123-3126 ◽

Cited By ~ 15

Author(s):

I. P. Holman ◽

M. Rivas-Casado ◽

N. J. K. Howden ◽

J. P. Bloomfield ◽

A. T. Williams

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Teleconnection Patterns ◽

Ocean Atmosphere ◽

Groundwater Systems

Download Full-text

The Atmosphere’s Response to the Ice Sheets of the Last Glacial Maximum

Annals of Glaciology ◽

10.1017/s0260305500008211 ◽

1990 ◽

Vol 14 ◽

pp. 32-38 ◽

Cited By ~ 4

Author(s):

Kerry H. Cook

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Age ◽

Laurentide Ice Sheet ◽

Stationary Waves ◽

The North ◽

The Last Glacial

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean. One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

Download Full-text

Deep water formation in the North Atlantic Ocean during the last ice age

Nature ◽

10.1038/286479a0 ◽

1980 ◽

Vol 286 (5772) ◽

pp. 479-482 ◽

Cited By ~ 156

Author(s):

Jean-Claude Duplessy ◽

J. Moyes ◽

C. Pujol

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Deep Water ◽

North Atlantic Ocean ◽

Ice Age ◽

Deep Water Formation ◽

The North ◽

Water Formation ◽

Last Ice Age ◽

The North Atlantic

Download Full-text

Eight Centuries of North Atlantic Ocean Atmosphere Variability

Science ◽

10.1126/science.286.5445.1709 ◽

1999 ◽

Vol 286 (5445) ◽

pp. 1709-1713 ◽

Cited By ~ 159

Author(s):

D. E. Black

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Ocean Atmosphere

Download Full-text

Identifying non-stationary groundwater level response to North Atlantic ocean-atmosphere teleconnection patterns using wavelet coherence

Hydrogeology Journal ◽

10.1007/s10040-011-0755-9 ◽

2011 ◽

Vol 19 (6) ◽

pp. 1269-1278 ◽

Cited By ~ 59

Author(s):

Ian Paul Holman ◽

Monica Rivas-Casado ◽

John P. Bloomfield ◽

Jason J. Gurdak

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

Groundwater Level ◽

North Atlantic Ocean ◽

Wavelet Coherence ◽

Teleconnection Patterns ◽

Ocean Atmosphere

Download Full-text

The Atmosphere’s Response to the Ice Sheets of the Last Glacial Maximum

Annals of Glaciology ◽

10.3189/s0260305500008211 ◽

1990 ◽

Vol 14 ◽

pp. 32-38

Author(s):

Kerry H. Cook

Keyword(s):

Atlantic Ocean ◽

North Atlantic ◽

North Atlantic Ocean ◽

Ice Sheets ◽

Ice Sheet ◽

Ice Age ◽

Laurentide Ice Sheet ◽

Stationary Waves ◽

The North ◽

The Last Glacial

This paper discusses some modeling results that indicate how the atmospheric response to the topography of the continental ice of the Last Glacial Maximum (LGM) may be related to the cold North Atlantic Ocean of that time. Broccoli and Manabe (1987) used a three-dimensional general circulation model (GCM) of the atmosphere coupled with a fixed-depth, static ocean mixed-layer model with ice-age boundary conditions to investigate the individual influences of the CLIMAP ice sheets, snow-free land albedos, and reduced atmospheric CO2 concentrations. They found that the ice sheets are the most influential of the ice-age boundary conditions in modifying the northern hemisphere climate, and that the presence of continental ice sheets alone leads to cooling over the North Atlantic Ocean.One approach for extending these GCM results is to consider the stationary waves generated by the ice sheets. Cook and Held (1988) showed that a linearized, steady-state, primitive equation model can give a reasonable simulation of the GCM’s stationary waves forced by the Laurentide ice sheet. The linear model analysis suggests that the mechanical effect of the changed slope of the surface, and not changes in the diabatic heating (e.g. the high surface albedos) or time-dependent transports that necessarily accompany the ice sheet in the GCM, is largely responsible for the ice sheet’s influence. To obtain the ice-age stationary-wave simulation, the linear model must be linearized about the zonal mean fields from the GCM’s ice-age climate. This is the case because the proximity of the cold polar air to the region of adiabatic heating on the downslope of the Laurentide ice sheet is an important factor in determining the stationary waves. During the ice age, cold air can be transported southward to balance this downslope heating by small perturbations in the meridional wind, consistent with linear theory. Since the meridional temperature gradient is more closely related to the surface albedo (ice extent) than to the ice volume, this suggests a mechanism by which changes in the stationary waves and, therefore, their cooling influence at low levels over the North Atlantic Ocean, can occur on time scales faster than those associated with large changes in continental ice volume.

Download Full-text

Holocene bond cycles: Real or imaginary?

Geografie ◽

10.37040/geografie2008113040338 ◽

2008 ◽

Vol 113 (4) ◽

pp. 338-350

Author(s):

Heinz Wanner ◽

Jonathan Butikofer

Keyword(s):

North Atlantic ◽

Little Ice Age ◽

Late Holocene ◽

North Atlantic Ocean ◽

Decisive Role ◽

Ice Age ◽

The Holocene ◽

The North ◽

Single Process ◽

Trigger Mechanisms

During the Holocene (last 12,000 years) nine cold relapses were observed mainly in the North Atlantic Ocean area and its surroundings. Based on the pioneering studies by Bond et al. (1997, 2001) these events are called Bond Cycles and thought to be the Holocene equivalents of the Pleistocene Dansgaard-Oeschger cycles. The first event was the Younger Dryas (~12,000 BP; Broecker 2006), the last one was the Little Ice Age (AD 1350-1860; Grove 1988). A number of trigger mechanisms is discussed (see Table 1), but a theory for the Bond Cycles does not exist. Based on spectral analyses of both, forcing factors and climatological time series, we argue that one single process did likely not cause the Holocene cooling events. It is conceivable that the early Holocene coolings were triggered by meltwater pulses. However, the late Holocene events (e.g., the Little Ice Age) were rather caused by a combination of different trigger mechanisms. In every case it has to be taken in mind that natural variability was also playing a decisive role.

Download Full-text