scholarly journals Supplementary material to "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 Atlantic ◽  
Climate Changes ◽  
Last Deglaciation ◽  
The North ◽  
Supplementary Material ◽  
The Last Deglaciation ◽  
The North Atlantic

Meltwater driven abrupt climate changes in the North Atlantic simulated in a Heinrich Stadial 1 background

2021 ◽  
Author(s):  
Yvan Romé ◽  
Ruza Ivanovic ◽  
Lauren Gregoire
Keyword(s):  
North Atlantic ◽  
Climate Changes ◽  
Climate Models ◽  
Meridional Overturning Circulation ◽  
The Arctic ◽  
Last Deglaciation ◽  
Great Opportunity ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic

<div> <p>Heinrich stadial 1 is one of the most enigmatic episodes in the study of the last deglaciation. Following the Lamospheric forcing increased driving the vast ice sheets over North America and Europe to melt. Yet, the climate in the North Atlantic remained cold for another 6000 years before eventually switching to a warm interstadial state in an event referred to as the Bolling warming. If there is now a consensus on the central role of the Atlantic Meridional Overturning Circulation (AMOC), the mechanisms at stake are still highly debated, which is a real challenge when it comes to reproducing such behaviour in climate models.</p> <p>We studied this period looking spest Glacial Maximum (LGM, ~21 thousand years ago), orbital and atcifically at the feedback between the climate and the freshwater released from melting ice. From a transient record of meltwater discharge across the last deglaciation derived from the GLAC1D ice sheet reconstruction, we produced General Circulation Model (GCM) simulations of the LGM climate with different freshwater forcing. More precisely, we examined three notable melting events that happened during the early deglaciation: a local minimum of discharge at the LGM, a peak in meltwater discharging the North Atlantic signal and a peak in meltwater discharging in the Arctic signal. The three experiments generated very different patterns in AMOC and in North Atlantic climate, including alternatively warm, cold and oscillating regimes depending on the forcing.  </p> </div><div> <p>These results provide a good framework to analyse further the relationship between abrupt climate changes and meltwater discharge and to highlight the key parameters to trigger climate transitions in state-of-art climate models in the context of the last deglaciation. It is also a great opportunity to describe some mechanisms at stake with salt oscillations in the Atlantic, sea-ice cover and deep-water formation sites feedback and shifts in the subpolar gyre during interstadial-stadial transitions.</p> </div>

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

2019 ◽  
Vol 15 (4) ◽  
pp. 1621-1646
Author(s):  
Heather J. Andres ◽  
Lev Tarasov
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Climate Changes ◽  
Ice Sheet ◽  
Wind Forcing ◽  
Last Deglaciation ◽  
Sea Ice Extent ◽  
The North ◽  
The Last Deglaciation ◽  
Background Climate

Abstract. Abrupt climate shifts of large amplitudes were common features of the Earth's climate as it transitioned into and out of the last full glacial state approximately 20 000 years ago, but their causes are not yet established. Midlatitude atmospheric dynamics may have played an important role in these climate variations through their effects on heat and precipitation distributions, sea ice extent, and wind-driven ocean circulation patterns. This study characterizes deglacial winter wind changes over the North Atlantic (NAtl) in a suite of transient deglacial simulations using the PlaSim Earth system model (run at T42 resolution) and the TraCE-21ka (T31) simulation. Though driven with yearly updates in surface elevation, we detect multiple instances of NAtl jet transitions in the PlaSim simulations 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 an important role in abrupt glacial climate changes. 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 in 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. These changes can significantly affect ocean circulation. 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 barrier to the winds in both the PlaSim simulations and the TraCE-21ka experiment. This constrains both the position and the latitudinal variability in 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 the presence of an elevated ice sheet margin in the south-eastern sector 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.

Immediate temperature response in northern Iberia to last deglacial changes in the North Atlantic

Geology ◽  
2021 ◽  
Author(s):  
J.L. Bernal-Wormull ◽  
A. Moreno ◽  
C. Pérez-Mejías ◽  
M. Bartolomé ◽  
A. Aranburu ◽  
...  
Keyword(s):  
North Atlantic ◽  
Deep Convection ◽  
Temperature Response ◽  
Last Deglaciation ◽  
Climate Feedbacks ◽  
The North ◽  
Heinrich Event ◽  
Northern Iberian Peninsula ◽  
The Last Deglaciation ◽  
The North Atlantic

Major disruptions in the North Atlantic circulation during the last deglaciation triggered a series of climate feedbacks that influenced the course of Termination I, suggesting an almost synchronous response in the ocean-atmosphere system. We present a replicated δ18O stalagmite record from Ostolo cave in the northern Iberian Peninsula with a robust chronological framework that continuously covers the last deglaciation (18.5–10.5 kyr B.P.). The Ostolo δ18O record, unlike other speleothem records in the region that were related to humidity changes, closely tracks the well-known high-latitude temperature evolution, offering important insights into the structure of the last deglaciation in the Northern Hemisphere. In addition, this new record is accompanied by a clear signal of the expected cooling events associated with the deglacial disruptions in North Atlantic deep convection during Heinrich event 1.

Dating rapid climate change in the North Atlantic during Heinrich Stadial 1

2020 ◽  
Author(s):  
Andrea Burke ◽  
Rosanna Greenop ◽  
James Rae ◽  
Rhian Rees-Owen ◽  
Paula Reimer ◽  
...  
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Last Deglaciation ◽  
Large Reservoir ◽  
The North ◽  
The Last Deglaciation ◽  
The North Atlantic ◽  
Reservoir Age

<p>Paleoclimate records from the North Atlantic show some of the most iconic signals of abrupt climate change during the ice ages. Here we use radiocarbon as a tracer of ocean circulation and air-sea gas exchange to investigate potential mechanisms for the abrupt climate changes seen in the North Atlantic over the last deglaciation. We have created a stack of North Atlantic surface radiocarbon reservoir ages over the past 20,000 years, using new synchronized age models from thirteen sediment cores refined with thorium normalization between tie-points. This stack shows consistent and large reservoir age increases of more than 1000 years from the LGM into HS1, dropping abruptly back to approximately modern reservoir ages before the onset of the Bolling-Allerod. We use the intermediate complexity earth system model cGENIE to investigate the potential drivers of these reservoir age changes. We find that sea ice, circulation and CO<sub>2</sub> all play important roles in setting the reservoir age. We use these coherently dated records to revisit the sequence and timing of climatic events during HS1 and the last deglaciation, and show that Laurentide Heinrich Events are a response to stadial conditions, rather than their root cause.</p>

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