Response of interior North America to abrupt climate oscillations in the North Atlantic region during the last deglaciation

2001 ◽  
Vol 52 (4) ◽  
pp. 333-369 ◽  
Author(s):  
Zicheng Yu ◽  
H.E. Wright
Keyword(s):  
North America ◽  
North Atlantic ◽  
Last Deglaciation ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
Climate Oscillations ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic

scholarly journals Towards understanding potential atmospheric contributions to abrupt climate changes: Characterizing changes to the North Atlantic eddy-driven jet over the last deglaciation

2018 ◽  
Author(s):  
Heather J. Andres ◽  
Lev Tarasov
Keyword(s):  
North America ◽  
North Atlantic ◽  
Wind Forcing ◽  
Eastern North America ◽  
Last Deglaciation ◽  
Sea Ice Extent ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic ◽  
Background Climate

Abstract. Abrupt climate shifts of large amplitude were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately twenty thousand years ago, but their causes are not yet established. Mid-latitudinal atmospheric dynamics may have played an important role in these oscillations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterises deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations we performed using the PlaSim earth system model, as well as in the TraCE-21ka simulation. We detect multiple instances of NAtl jet transitions that occur within 10 simulation years and a sensitivity of the jet to background climate conditions. Thus, we suggest that changes to the NAtl jet may play a critical role in abrupt glacial climate oscillations. We identify two types of simulated wind changes over the last deglaciation. Firstly, the latitude of the NAtl eddy-driven jet shifts northward over the deglaciation in a sequence of distinct steps. Secondly, the variability of the NAtl jet gradually shifts from a Last Glacial Maximum (LGM) state with a strongly preferred jet latitude and a restricted latitudinal range to one with no single preferred latitude and a range that is at least 11° broader. Changes to the position of the NAtl jet alter the location of the wind forcing driving oceanic surface gyres and the limits of sea ice extent, whereas a shift to a more variable jet reduces the effectiveness of the wind forcing at driving surface ocean transports. The processes controlling these two types of changes differ on the upstream and downstream ends of the NAtl eddy-driven jet. On the upstream side over eastern North America, the elevated ice sheet margin acts as a physical barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability of the jet at LGM, so the jet shifts in sync with ice sheet margin changes. In contrast, the downstream side over the eastern NAtl is more sensitive to the thermal state of the background climate. Our results suggest that knowing the position of the south-eastern margin of the North American ice complex strongly constrains the deglacial position of the jet over eastern North America and the western North Atlantic as well as its variability.

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.

They did not Live by Grass Alone: the Politics and Palaeoecology of Animal Fodder in the North Atlantic Region

1998 ◽  
Vol 1 (1) ◽  
pp. 41-54 ◽  
Author(s):  
Tom Amorosi ◽  
Paul C. Buckland ◽  
Kevin J. Edwards ◽  
Ingrid Mainland ◽  
Tom H. McGovern ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
The North ◽  
The North Atlantic

scholarly journals The Meridional Shift of the Midlatitude Westerlies over Arid Central Asia during the Past 21 000 Years Based on the TraCE-21ka Simulations

2020 ◽  
Vol 33 (17) ◽  
pp. 7455-7478
Author(s):  
Nanxuan Jiang ◽  
Qing Yan ◽  
Zhiqing Xu ◽  
Jian Shi ◽  
Ran Zhang
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Last Deglaciation ◽  
The Past ◽  
The North ◽  
External Forcings ◽  
The Indian Ocean ◽  
The Last Deglaciation ◽  
The North Atlantic

AbstractTo advance our knowledge of the response of midlatitude westerlies to various external forcings, we investigate the meridional shift of midlatitude westerlies over arid central Asia (ACA) during the past 21 000 years, which experienced more varied forcings than the present day based on a set of transient simulations. Our results suggest that the evolution of midlatitude westerlies over ACA and driving factors vary with time and across seasons. In spring, the location of midlatitude westerlies over ACA oscillates largely during the last deglaciation, driven by meltwater fluxes and continental ice sheets, and then shows a long-term equatorward shift during the Holocene controlled by orbital insolation. In summer, orbital insolation dominates the meridional shift of midlatitude westerlies, with poleward and equatorward migration during the last deglaciation and the Holocene, respectively. From a thermodynamic perspective, variations in zonal winds are linked with the meridional temperature gradient based on the thermal wind relationship. From a dynamic perspective, variations in midlatitude westerlies are mainly induced by anomalous sea surface temperatures over the Indian Ocean through the Matsuno–Gill response and over the North Atlantic Ocean by the propagation of Rossby waves, or both, but their relative importance varies across forcings. Additionally, the modeled meridional shift of midlatitude westerlies is broadly consistent with geological evidence, although model–data discrepancies still exist. Overall, our study provides a possible scenario for a meridional shift of midlatitude westerlies over ACA in response to various external forcings during the past 21 000 years and highlights important roles of both the Indian Ocean and the North Atlantic Ocean in regulating Asian westerlies, which may shed light on the behavior of westerlies in the future.

scholarly journals Sea Mayweed Tripleurospermum maritimum and Scentless Mayweed T. inodorum (Asteraceae) intermediates in Orkney

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
John Crossley ◽  
Christopher A. Skilbeck
Keyword(s):  
North Atlantic ◽  
Population Level ◽  
North Atlantic Region ◽  
Atlantic Region ◽  
Orkney Islands ◽  
Far North ◽  
The North ◽  
The North Atlantic

This article describes a study of Tripleurospermum maritimum (L.) W.D.J. Koch and T. inodorum (L.) Sch. Bip. (Asteraceae) in the Orkney Islands (v.c.111), the results of which suggest that intermediates between these taxa may be rather common, and that T. maritimum subsp. nigriceps and subsp. maritimum are both involved, the former more frequently. Obviously this results in a complex taxonomic situation, evidently not confined to Orkney in the far north. Key identifying characters of the taxa are systematically examined and guidance offered on determining hybrids using a population level approach. The taxonomic complexities of these northern populations are discussed, with regard in particular to the identity of T. inodorum occurring there and the place of T. maritimum subsp. nigrescens in the forms and subspecies of T. maritimum found in the north Atlantic region.

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