scholarly journals Holocene Environmental Variability in Southern Greenland Inferred from Lake Sediments

2002 ◽  
Vol 58 (2) ◽  
pp. 149-159 ◽  
Author(s):  
Michael R. Kaplan ◽  
Alexander P. Wolfe ◽  
Gifford H. Miller
Keyword(s):  
Environmental Changes ◽  
Environmental Variability ◽  
North Atlantic Ocean ◽  
Regional Climate ◽  
High Amplitude ◽  
Ice Age ◽  
Lake Productivity ◽  
The North ◽  
Ocean Region ◽  
Future Warming

AbstractSediments from Qipisarqo Lake provide a continuous Holocene paleoenvironmental record from southern Greenland. Following deglaciation and glacio-isostatic emergence of the basin from the sea ∼9100 cal yr B.P., proxies of lake paleoproductivity, including biogenic silica and organic matter, increased markedly until 6000 cal yr B.P. and thereafter remained stable over the ensuing warm three millennia. Subsequent decreases in these proxies, most dramatically between 3000 and 2000 cal yr B.P., show the lake's responses to initial Neoglacial cooling. Intervals of ameliorated limnological conditions occurred between 1300 and 900 and between 500 and 280 cal yr B.P., briefly interrupting the decreasing trend in productivity that culminated in the Little Ice Age. Increased lake productivity during the latter half of the 20th century, which reflects the limnological response to circum-arctic warming, still has not reached peak Holocene values. The Neoglacial climate of the last 2000 yr includes the most rapid high-amplitude environmental changes of the past nine millennia. The Norse thus migrated around the North Atlantic Ocean region in the most environmentally unstable period since deglaciation. Lacustrine sediment records provide a context with which to consider future environmental changes in the Labrador Sea region. In particular, any future warming will be superposed on a regional climate system that is currently exhibiting highly unstable behavior at submillennial timescales.

Chrysophyte microfossils record marked responses to recent environmental changes in high- and mid-arctic lakes

2001 ◽  
Vol 79 (6) ◽  
pp. 747-752 ◽  
Author(s):  
Alexander P Wolfe ◽  
Bianca B Perren
Keyword(s):  
Environmental Changes ◽  
Arctic Lakes ◽  
Ice Age ◽  
Algal Community ◽  
North Coast ◽  
Baffin Island ◽  
Lake Ecosystems ◽  
The North ◽  
Ecological Changes ◽  
Community Shifts

Rapid stratigraphic changes are recorded in recent assemblages of subfossil Chrysophyceae from the sediments of two highly contrasted arctic lakes, one situated in the polar desert of west-central Ellesmere Island, and the other on eastern Baffin Island in the mid-Arctic climatic zone. In Sawtooth Lake on the Fosheim Peninsula, concentrations of chrysophycean stomatocysts increase dramatically in sediments deposited since AD 1920. Only trace abundances of stomatocysts are encountered in older sediments. In Kekerturnak Lake, on the north coast of Cumberland Peninsula, scales of Mallomonas spp., previously absent from the sediment record, appear suddenly in the upper 5.5 cm of sediment and subsequently become ubiquitous in the top 1.0 cm. These results corroborate diatom stratigraphic data from other sites in the Canadian Arctic Archipelago, together suggesting that unprecedented ecological changes are presently occurring across this vast region. In all likelihood, these abrupt algal community shifts reflect the response of arctic lake ecosystems to well-documented climate warming since the Little Ice Age, with the implications that recent rates of environmental change are unprecedented in the context of the Holocene.Key words: Paleolimnology, arctic lakes, Chrysophyceae, stomatocysts, Mallomonas.

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

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.

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

Nature ◽  
1980 ◽  
Vol 286 (5772) ◽  
pp. 479-482 ◽  
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

scholarly journals Initiation of the last ice age in Canada by extreme precipitation resulting from a cascade of oceanic salinity increases

2015 ◽  
Vol 3 (1) ◽  
pp. 237-250
Author(s):  
Robert G. Johnson
Keyword(s):  
Sea Ice ◽  
North Atlantic ◽  
Regional Climate ◽  
Ice Sheet ◽  
Northern Africa ◽  
Ice Age ◽  
Baffin Bay ◽  
The North ◽  
Last Ice Age ◽  
Polar Ocean

Numerical modeling has failed to confirm the classical Milankovitch hypothesis of initiation of the last ice age by Northern Hemisphere high latitude cooling due to decreasing summer insolation caused by orbital effects. The modeling failed to confirm ice sheet growth even with a widespread layer of glacial ice as an initial condition to embody positive feedback. The failure probably occurred because the initial conditions of the calculation did not include the actual effects of an altered climate in northeastern Canada that brought a sharp cooling to Europe and extreme amounts of precipitation to cloud-covered lands west of Greenland. In the conceptual model proposed here, diminishing orbital summer insolation in northern Africa is causally linked to this regional climate change by a cascade of oceanic salinity changes. The summer cooling in northern Africa weakened the monsoons, reduced the Nile River flow, and increased Mediterranean salinity and outflow at Gibraltar. The salt in the outflow contributes substantially to the salinities of the North Atlantic Drift and the Greenland Sea, to the formation rate of North Atlantic Deep Water (NADW) there, and to the northward flow of the Spitsbergen-Atlantic Current (SAC) that replaces the sinking NADW. When the increasing salt in the Mediterranean outflow made the SAC replacement flow sufficiently strong, the flow penetrated into the polar ocean along the north coast of Greenland. Denser and more saline Atlantic water then replaced the polar water flowing southward into Baffin Bay through the Nares Strait and Lancaster Sound, thus eliminating the stratification in the bay that enables freezing of winter sea ice. Without the southward flow of sea ice out of Baffin Bay, the Labrador Sea became much warmer. The warmer seas west of Greenland then triggered a persistent cyclonic circulation that caused large amounts of precipitation in eastern Canada and a much colder northern Europe. The resulting Canadian erosion yielded a 500yr-long deep-sea sediment record of the ice-free condition. Heavy snowfall started new ice sheet growth on Baffin Island, northern Quebec, Labrador, western Greenland, and the Barents Sea, causing world sea level to fall at a rate of 0.5cmyr-1. The modern increasing salinity of the Mediterranean Sea and extension of SAC flow into the polar ocean are now following the cascade steps toward an ice-free Baffin Bay and possible near term regional climate deterioration.

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

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.

scholarly journals Holocene bond cycles: Real or imaginary?

Geografie ◽  
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.

scholarly journals Volcanic origin for Younger Dryas geochemical anomalies ca. 12,900 cal B.P.

2020 ◽  
Vol 6 (31) ◽  
pp. eaax8587
Author(s):  
N. Sun ◽  
A. D. Brandon ◽  
S. L. Forman ◽  
M. R. Waters ◽  
K. S. Befus
Keyword(s):  
North Atlantic ◽  
Environmental Changes ◽  
North Atlantic Ocean ◽  
Younger Dryas ◽  
Volcanic Emissions ◽  
Volcanic Gas ◽  
Concentration Data ◽  
Volcanic Origin ◽  
The North ◽  
Cave Sediments

The Younger Dryas (YD) abrupt cooling event ca. 12.9 ± 0.1 ka is associated with substantial meltwater input into the North Atlantic Ocean, reversing deglacial warming. One controversial and prevailing hypothesis is that a bolide impact or airburst is responsible for these environmental changes. Here, highly siderophile element (HSE; Os, Ir, Ru, Pt, Pd, and Re) abundances and 187Os/188Os ratios were obtained in a well-dated sediment section at Hall’s Cave, TX, USA to test this hypothesis. In Hall’s Cave, layers below, above, and in the YD have 187Os/188Os ratios consistent with incorporation of extraterrestrial or mantle-derived material. The HSE abundances indicate that these layers contain volcanic gas aerosols and not extraterrestrial materials. The most likely explanation is that episodic, distant volcanic emissions were deposited in Hall’s Cave sediments. Coupled 187Os/188Os ratios and HSE concentration data at close stratigraphic intervals are required to effectively differentiate between bolide and volcanic origins.

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