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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 21 Nov 2018

Research article | 21 Nov 2018

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

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

Heather J. Andres and Lev Tarasov Heather J. Andres and Lev Tarasov
  • Memorial University of Newfoundland, St. John's, NL, CANADA

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.

Heather J. Andres and Lev Tarasov
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Status: final response (author comments only)
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Heather J. Andres and Lev Tarasov
Heather J. Andres and Lev Tarasov
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Publications Copernicus
Short summary
Abrupt climate shifts of large magnitude were common during glacial states, with explanations centered on the oceans. However, winds drive ocean surface currents, so shifts in wind climatologies could also have played a critical role.  In a small ensemble of transient deglacial simulations, we find nonlinear shifts in both jet stream location and variability over the North Atlantic.  We show the eastern North American ice sheet margin strongly constrains regional jet characteristics.
Abrupt climate shifts of large magnitude were common during glacial states, with explanations...