The glacial thermohaline circulation: Stable or unstable?

Prange, Matthias; Romanova, V.; Lohmann, Gerrit

doi:10.1029/2002gl015337

Cited by 41 publications

(52 citation statements)

References 27 publications

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“…In our MIS 3 climates, a relatively strong freshwater perturbation is required to alter the Atlantic THC. Our findings are corroborated by those of Prange et al (2002), who found that in an ocean general circulation model, the glacial THC can only remain slowed down or shut down with a strong additional fresh water flux. In the experiments of Ganopolski and Rahmstorf (2001) based on an LGM reference climate, imposing a strong freshwater flux of 0.1Sv resulted in a shutdown THC, while only a small negative forcing was imposed to obtain their warm and strong simulated interstadial THC mode, respectively small positive forcing for their cold (but strong) simulated stadial THC mode.…”

Section: Freshwater Forcing Required To Mimic Stadialssupporting

confidence: 80%

How did Marine Isotope Stage 3 and Last Glacial Maximum climates differ? – Perspectives from equilibrium simulations

Meerbeeck¹,

Renssen²,

Roche³

2009

Clim. Past

147

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Abstract. Dansgaard-Oeschger events occurred frequently during Marine Isotope Stage 3 (MIS3), as opposed to the following MIS2 period, which included the Last Glacial Maximum (LGM). Transient climate model simulations suggest that these abrupt warming events in Greenland and the North Atlantic region are associated with a resumption of the Thermohaline Circulation (THC) from a weak state during stadials to a relatively strong state during interstadials. However, those models were run with LGM, rather than MIS3 boundary conditions. To quantify the influence of different boundary conditions on the climates of MIS3 and LGM, we perform two equilibrium climate simulations with the threedimensional earth system model LOVECLIM, one for stadial, the other for interstadial conditions. We compare them to the LGM state simulated with the same model. Both climate states are globally 2 • C warmer than LGM. A striking feature of our MIS3 simulations is the enhanced Northern Hemisphere seasonality, July surface air temperatures being 4 • C warmer than in LGM. Also, despite some modification in the location of North Atlantic deep water formation, deep water export to the South Atlantic remains unaffected. To study specifically the effect of orbital forcing, we perform two additional sensitivity experiments spun up from our stadial simulation. The insolation difference between MIS3 and LGM causes half of the 30-60 • N July temperature anomaly (+6 • C). In a third simulation additional freshwater forcing halts the Atlantic THC, yielding a much colder North Atlantic region (−7 • C). Comparing our simulation with proxy data, we find that the MIS3 climate with collapsed THC Correspondence to: C. J. Van Meerbeeck (cedric.van.meerbeeck@falw.vu.nl) mimics stadials over the North Atlantic better than both control experiments, which might crudely estimate interstadial climate. These results suggest that freshwater forcing is necessary to return climate from warm interstadials to cold stadials during MIS3. This changes our perspective, making the stadial climate a perturbed climate state rather than a typical, near-equilibrium MIS3 climate.

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Section: Freshwater Forcing Required To Mimic Stadialssupporting

confidence: 80%

How did Marine Isotope Stage 3 and Last Glacial Maximum climates differ? – Perspectives from equilibrium simulations

Meerbeeck¹,

Renssen²,

Roche³

2009

Clim. Past

147

View full text Add to dashboard Cite

show abstract

“…Monostability of the glacial AMOC was already demonstrated by Ganopolski and Rahmstorf (2001) in the CLIMBER-2 model, where a collapsed LGM state does not exist (but which allows for two closely-related modes with an active AMOC during the LGM). Also, the glacial AMOC was found to be monostable in experiments with an ocean-only model by Prange et al (2002). The present results suggest that most models exhibit similar behavior.…”

Section: S L Weber Et Al: the Modern And Glacial Amoc In Pmip Simusupporting

confidence: 58%

The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations

et al. 2007

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Abstract. This study analyses the response of the Atlantic meridional overturning circulation (AMOC) to LGM forcings and boundary conditions in nine PMIP coupled model simulations, including both GCMs and Earth system Models of Intermediate Complexity. Model results differ widely. The AMOC slows down considerably (by 20-40%) during the LGM as compared to the modern climate in four models, there is a slight reduction in one model and four models show a substantial increase in AMOC strength (by 10-40%). It is found that a major controlling factor for the AMOC response is the density contrast between Antarctic Bottom Water (AABW) and North Atlantic Deep Water (NADW) at their source regions. Changes in the density contrast are determined by the opposing effects of changes in temperature and salinity, with more saline AABW as compared to NADW consistently found in all models and less cooling of AABW in all models but one. In only two models is the AMOC response during the LGM directly related to the response in net evaporation over the Atlantic basin. Most models show large changes in the ocean freshwater transports into the basin, but this does not seem to affect the AMOC response. Finally, there is some dependence on the accuracy of the control state.

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“…However, some previous simple model studies on AMOC hysteresis show diversified results under these climate conditions. Some indicate that AMOC hysteresis exists under both last glacial maximum (LGM) and present-day conditions, but with a narrower AMOC hysteresis width in the former than in the latter (36)(37)(38). Others suggest that under LGM conditions, the AMOC only has one stable mode (28).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability

Meehl

Han

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Abrupt climate transitions, known as Dansgaard-Oeschger and Heinrich events, occurred frequently during the last glacial period, specifically from 80–11 thousand years before present, but were nearly absent during interglacial periods and the early stages of glacial periods, when major ice-sheets were still forming. Here we show, with a fully coupled state-of-the-art climate model, that closing the Bering Strait and preventing its throughflow between the Pacific and Arctic Oceans during the glacial period can lead to the emergence of stronger hysteresis behavior of the ocean conveyor belt circulation to create conditions that are conducive to triggering abrupt climate transitions. Hence, it is argued that even for greenhouse warming, abrupt climate transitions similar to those in the last glacial time are unlikely to occur as the Bering Strait remains open.

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The glacial thermohaline circulation: Stable or unstable?

Cited by 41 publications

References 27 publications

How did Marine Isotope Stage 3 and Last Glacial Maximum climates differ? – Perspectives from equilibrium simulations

How did Marine Isotope Stage 3 and Last Glacial Maximum climates differ? – Perspectives from equilibrium simulations

The modern and glacial overturning circulation in the Atlantic ocean in PMIP coupled model simulations

Role of the Bering Strait on the hysteresis of the ocean conveyor belt circulation and glacial climate stability

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