Thermohaline Oscillations Induced by Strong Steady Salinity Forcing of Ocean General Circulation Models

Winton, Michael; Sarachik, E. S.

doi:10.1175/1520-0485(1993)023<1389:toibss>2.0.co;2

Cited by 167 publications

(143 citation statements)

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“…We furthermore assume millennial-scale variability as registered in the GRIP record reflects variations in NADW formation that have an imprint on subsurface temperatures in antiphase with respect to the surface state. Stadials are thus associated with periods of reduced NADW formation and weakened AMOC and warm subsurface temperatures, whereas during interstadials a stronger AMOC with active NADW formation cools the subsurface, in agreement with previous studies (15,16,19,20,23,24). Considering a fast relaxation time of the subsurface temperature when convection resumes, and slow relaxation when convection is weak (20), we generate a subsurface warming index that slowly peaks during stadial climatic periods and more abruptly collapses when entering interstadial climatic periods (Fig.…”

Section: Significancesupporting

confidence: 89%

Iceberg discharges of the last glacial period driven by oceanic circulation changes

Álvarez-Solas

Robinson

Montoya

et al. 2013

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

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Proxy data reveal the existence of episodes of increased deposition of ice-rafted detritus in the North Atlantic Ocean during the last glacial period interpreted as massive iceberg discharges from the Laurentide Ice Sheet. Although these have long been attributed to self-sustained ice sheet oscillations, growing evidence of the crucial role that the ocean plays both for past and future behavior of the cryosphere suggests a climatic control of these ice surges. Here, we present simulations of the last glacial period carried out with a hybrid ice sheet-ice shelf model forced by an oceanic warming index derived from proxy data that accounts for the impact of past ocean circulation changes on ocean temperatures. The model generates a time series of iceberg discharge that closely agrees with ice-rafted debris records over the past 80 ka, indicating that oceanic circulation variations were responsible for the enigmatic ice purges of the last ice age.glacial climate variability | climate modeling | abrupt changes C ompared with the present interglacial period, the last glacial period (LGP) (∼110-10 ka before the present), and almost certainly previous ones (1), were characterized by substantial climatic variability on millennial timescales. This variability is mainly manifested in two types of events. Dansgaard-Oeschger (D/O) events are most notable in Greenland ice core records and involve decadal-scale warming of more than 10 K (interstadials) followed by slow cooling lasting several centuries and a final more rapid fall to cold background (stadial) conditions (2). Heinrich (H) events consist of massive iceberg discharges from the Laurentide Ice Sheet at intervals of ∼7 ka during peak glacial conditions throughout the LGP (3). Both D/O and H events are associated with widespread centennial-to millennial-scale climatic changes, including a synchronous temperature response over the North Atlantic and an antiphase temperature relationship over Antarctica and most of the Southern Ocean, as revealed by a wealth of deep-sea sediments, ice core, and terrestrial records (4). The Atlantic meridional overturning circulation (AMOC) is thought to play a central role in these abrupt glacial climatic changes. Although the paleoceanographic evidence on this link is scarce and mostly restricted to a few highresolution deep-sea sediment records of the last deglaciation (5, 6), both modeling studies and reconstructions provide strong support for the hypothesis that D/O events were caused by reorganizations of the AMOC (7,8). H events, identified as enhanced ice-rafted detritus (IRD) in North Atlantic deep-sea sediments (3, 9), occur during climatic minima of the Northern Hemisphere. They have classically been attributed to internal oscillations of the Laurentide (10) and assumed to lead to important disruptions of the Atlantic Ocean circulation (11). However, paleoclimate data have revealed that most H events likely occurred about a thousand years after North Atlantic Deep Water (NADW) formation had already slowed down or largely coll...

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Section: Significancesupporting

confidence: 89%

Iceberg discharges of the last glacial period driven by oceanic circulation changes

Álvarez-Solas

Robinson

Montoya

et al. 2013

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

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“…Dividing L y × W × D by Ψ, the time delay is about 16 years. The scale of the time delay is consistent with the overturning time on the order of one decade or more, which represents the timescale of overturning advection (Winton and Sarachik 1993;Ou 2011). Moreover, the time delay estimated by the ratio…”

Section: Possible Mechanisms Involvedsupporting

confidence: 64%

A delayed oscillator model for the quasi-periodic multidecadal variability of the NAO

2015

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that resembles the negative NAO phase, and subsequently the oscillation proceeds, but in the opposite sense. Based on these mechanisms, a simple delayed oscillator model is established to explain the quasi-periodic multidecadal variability of the NAO. The magnitude of the NAO forcing of the AMOC/AMO and the time delay of the AMOC/AMO feedback are two key parameters of the delayed oscillator. For a given set of parameters, the quasi 60-year cycle of the NAO can be well predicted. This delayed oscillator model is useful for understanding of the oscillatory mechanism of the NAO, which has significant potential for decadal predictions as well as the interpretation of proxy data records.

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“…It is possible to construct a box model of the Eastern Mediterranean that includes a simple form of these effects, similar to [33]. Such a model can be based on the Stommel box model [22], as done above, and on Winton [34,35] relaxation oscillations deep convection box model.…”

Section: Discussionmentioning

confidence: 99%

Box modeling of the Eastern Mediterranean sea

Ashkenazy

Stone

Malanotte‐Rizzoli

2012

Physica A: Statistical Mechanics and its Applications

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In ∼1990 a new source of deep water formation in the Eastern Mediterranean was found in the southern part of the Aegean sea. Till then, the only source of deep water formation in the Eastern Mediterranean was in the Adriatic sea; the rate of the deep water formation of the new Aegean source is 1 Sv, three times larger than the Adriatic source. We develop a simple three box-model to study the stability of the thermohaline circulation of the Eastern Mediterranean sea. The three boxes represent the Adriatic sea, Aegean sea, and the Ionian seas. The boxes exchange heat and salinity and may be described by a set of nonlinear differential equations. We analyze these equations and find that the system may have one, two, or four stable flux states. We conjecture that the change in the deep water formation in the Eastern Mediterranean sea is attributed to a switch between the different states on the thermohaline circulation; this switch may result from decreased temperature and/or increased salinity over the Aegean sea.

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Thermohaline Oscillations Induced by Strong Steady Salinity Forcing of Ocean General Circulation Models

Cited by 167 publications

References 0 publications

Iceberg discharges of the last glacial period driven by oceanic circulation changes

Iceberg discharges of the last glacial period driven by oceanic circulation changes

A delayed oscillator model for the quasi-periodic multidecadal variability of the NAO

Box modeling of the Eastern Mediterranean sea

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