Influence of glacial ice sheets on the Atlantic meridional overturning circulation through surface wind change

Sherriff‐Tadano, Sam; Abe‐Ouchi, Ayako; Yoshimori, Masakazu; Oka, Akira; Chan, Wing‐Le

doi:10.1007/s00382-017-3780-0

Cited by 56 publications

(77 citation statements)

References 103 publications

(138 reference statements)

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“…Note that in the PI simulation, the location of the deep convection in the subpolar North Atlantic is typically mostly located near the British Isles, instead of the Labrador and Greenland‐Iceland‐Norwegian seas. However, the location of deepwater formation south of Greenland in LGM simulations is similar to more sophisticated coupled climate models (Otto‐Bliesner & Brady, ; Sherriff‐Tadano et al, ).…”

Section: Resultssupporting

confidence: 58%

“…In contrast, the most recent climate models that participated in the Paleoclimate Model Intercomparison Project Phase 3 (PMIP3) showed that when forced with LGM boundary conditions they generally have a stronger and deeper AMOC (Muglia & Schmittner, ). The stronger modeled LGM AMOC was attributed to stronger Northern Hemisphere westerly wind likely resulting from the North American ice sheet and interactions with sea ice (Oka et al, ; Sherriff‐Tadano et al, ). This uncertainty in the mean state of the AMOC impacts how the deglacial ocean responded to freshwater input (Weber et al, ).…”

Section: Introductionmentioning

confidence: 99%

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The Stability of the AMOC During Heinrich Events Is Not Dependent on the AMOC Strength in an Intermediate Complexity Earth System Model Ensemble

Góes

Murphy

Clement

2019

Paleoceanog and Paleoclimatol

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Previous studies that used Earth system models of intermediate complexity showed that stronger background winds drove a more vigorous and stable Atlantic Meridional Overturning Circulation (AMOC), while those with weaker winds had a more sluggish and unstable AMOC. In other studies, ensembles under vertical mixing uncertainty showed the opposite effect, where the simulations with a stronger AMOC were more unstable. To tackle this conundrum, we produce a model ensemble featuring uncertainties related to wind forcing and vertical mixing to understand the role of feedbacks on the AMOC stability. We show that the stability of the AMOC is not influenced by vertical mixing and the AMOC strength, and rather, it is determined by the strength of the Northern Hemisphere winds. Paleoproxies indicate an AMOC shutdown during the last Heinrich Stadial. Our comparisons to sea surface temperature proxies show a better fit with the simulations under a stable AMOC, which corresponds to a forced off‐state. The sign of the AMOC‐driven freshwater transport in the South Atlantic, which is regarded as an index for its stability, is shown not to be an absolute measure, although its evolution agrees with the salt advection feedback.

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Section: Resultssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

The Stability of the AMOC During Heinrich Events Is Not Dependent on the AMOC Strength in an Intermediate Complexity Earth System Model Ensemble

Góes

Murphy

Clement

2019

Paleoceanog and Paleoclimatol

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“…The wind shift and cooling appear to drive the AMOC strengthening shown in Fig. 4d, as has previously been observed in other models (Pausata et al 2011;Zhang et al 2014;Zhu et al 2014;Gong et al 2015;Muglia and Schmittner 2015;Klockmann et al 2016;Sherriff-Tadano et al 2017). When compared with the influences of CO 2 and orbital forcing, this suggests that Dansgaard-Oeschger-like AMOC disruptions would be most likely to have occurred in a 'sweet spot' of low CO 2, low obliquity and a relatively small (low-elevation) Laurentide ice sheet.…”

Section: Effects Of Laurentide Ice Sheet Topography and Albedomentioning

confidence: 49%

Response of a comprehensive climate model to a broad range of external forcings: relevance for deep ocean ventilation and the development of late Cenozoic ice ages

Galbraith

Lavergne

2018

Clim Dyn

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Over the past few million years, the Earth descended from the relatively warm and stable climate of the Pliocene into the increasingly dramatic ice age cycles of the Pleistocene. The influences of orbital forcing and atmospheric CO 2 on landbased ice sheets have long been considered as the key drivers of the ice ages, but less attention has been paid to their direct influences on the circulation of the deep ocean. Here we provide a broad view on the influences of CO 2 , orbital forcing and ice sheet size according to a comprehensive Earth system model, by integrating the model to equilibrium under 40 different combinations of the three external forcings. We find that the volume contribution of Antarctic (AABW) vs. North Atlantic (NADW) waters to the deep ocean varies widely among the simulations, and can be predicted from the difference between the surface densities at AABW and NADW deep water formation sites. Minima of both the AABW-NADW density difference and the AABW volume occur near interglacial CO 2 (270-400 ppm). At low CO 2 , abundant formation and northward export of sea ice in the Southern Ocean contributes to very salty and dense Antarctic waters that dominate the global deep ocean. Furthermore, when the Earth is cold, low obliquity (i.e. a reduced tilt of Earth's rotational axis) enhances the Antarctic water volume by expanding sea ice further. At high CO 2 , AABW dominance is favoured due to relatively warm subpolar North Atlantic waters, with more dependence on precession. Meanwhile, a large Laurentide ice sheet steers atmospheric circulation as to strengthen the Atlantic Meridional Overturning Circulation, but cools the Southern Ocean remotely, enhancing Antarctic sea ice export and leading to very salty and expanded AABW. Together, these results suggest that a 'sweet spot' of low CO 2 , low obliquity and relatively small ice sheets would have poised the AMOC for interruption, promoting Dansgaard-Oeschger-type abrupt change. The deep ocean temperature and salinity simulated under the most representative 'glacial' state agree very well with reconstructions from the Last Glacial Maximum (LGM), which lends confidence in the ability of the model to estimate large-scale changes in water-mass geometry. The model also simulates a circulation-driven increase of preformed radiocarbon reservoir age, which could explain most of the reconstructed LGM-preindustrial ocean radiocarbon change. However, the radiocarbon content of the simulated glacial ocean is still higher than reconstructed for the LGM, and the model does not reproduce reconstructed LGM deep ocean oxygen depletions. These ventilation-related disagreements probably reflect unresolved physical aspects of ventilation and ecosystem processes, but also raise the possibility that the LGM ocean circulation was not in equilibrium. Finally, the simulations display an increased sensitivity of both surface air temperature and AABW volume to orbital forcing under low CO 2 . We suggest that this enhanced orbital sensitivity contributed to the developm...

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“…The LGM AMOC strength is modulated by several processes including the buoyancy of surface waters in the NADW formation region, itself being a function of the North Atlantic/Nordic Sea temperature and freshwater budget, the density contrast between NADW and AABW (Weber et al, 2007), North Atlantic windstress (Muglia & Schmittner, 2015;Sherriff-Tadano et al, 2018), and the closure of the Bering Strait (Hu et al, 2012). A stronger halocline in the Nordic Seas at the LGM would lead to sea ice advance, and a weakening of NADW formation (Oka et al, 2012).…”

Section: Discussionmentioning

confidence: 99%

Enhanced Mid‐depth Southward Transport in the Northeast Atlantic at the Last Glacial Maximum Despite a Weaker AMOC

Menviel

Spence

Skinner

et al. 2020

Paleoceanog and Paleoclimatol

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While previous studies consistently suggest that North Atlantic Deep Water (NADW) was shallower at the Last Glacial Maximum (LGM) than at pre‐industrial, its strength is still controversial. Here, using a series of LGM experiments, we show that proxy records are consistent with a shallower and ∼50% weaker NADW, associated with a ∼3° equatorward shift of the sea ice edge and convection sites in the Norwegian Sea. A shoaling and weakening of NADW further allow penetration of Antarctic Bottom Water in the North Atlantic, despite Antarctic Bottom Water transport being reduced by ∼40%. While the Deep Western Boundary Current in the northwest Atlantic weakens with NADW, the mid‐depth southward flow on the east side of the north Mid‐Atlantic Ridge strengthens, consistent with paleorecords. This northeast Atlantic intensification is due to a change in density gradients: a weaker AMOC reduces the transport of equatorial waters to the northeast Atlantic, thus weakening the North Atlantic zonal density gradient. The resultant globally weaker oceanic circulation at the LGM would have contributed to an increase in oceanic carbon content and thus a decrease in atmospheric CO 2 concentration.

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Influence of glacial ice sheets on the Atlantic meridional overturning circulation through surface wind change

Cited by 56 publications

References 103 publications

The Stability of the AMOC During Heinrich Events Is Not Dependent on the AMOC Strength in an Intermediate Complexity Earth System Model Ensemble

The Stability of the AMOC During Heinrich Events Is Not Dependent on the AMOC Strength in an Intermediate Complexity Earth System Model Ensemble

Response of a comprehensive climate model to a broad range of external forcings: relevance for deep ocean ventilation and the development of late Cenozoic ice ages

Enhanced Mid‐depth Southward Transport in the Northeast Atlantic at the Last Glacial Maximum Despite a Weaker AMOC

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