The mythical thermohaline oscillator?

Ruddick, Barry; Zhang, Lingqi

doi:10.1357/002224089785076109

Cited by 8 publications

(13 citation statements)

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“…It involves oscillations in the oceans thermohaline circulation. The theoretical basis for such oscillations is given in papers by Stommel, 1961;Welander, 1982, and Ruddick and Zhang, 1989. Schnitker [1982 purports to have found evidence for such changes based on benthic foraminifera records for cores from the northwestern Atlantic.…”

Section: The Atla•c Salt Osce•tormentioning

confidence: 99%

A salt oscillator in the glacial Atlantic? 1. The concept

Broecker¹,

Bond²,

Klas³

et al. 1990

Paleoceanography

509

238

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As shown by the work of Dansgaard and his colleagues, climate oscillations of one or so millennia duration punctuate much of glacial section of the Greenland ice cores. These oscillations are characterized by 5øC air temperature changes, severalfold dust content changes and 50 ppm CO2 changes. Both the temperature and CO2 change are best explained by changes in the mode of operation of the ocean. In this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50øN. Based on this finding, we suggest that the Greenland climate changes are driven by oscillations in the salinity of the Atlantic Ocean which modulate the strength of the Atlantic's conveyor circulation. INTRODUCTIONOne of the most puzzling features of the ice core records from Greenland is the series of large and rather abrupt changes in oxygen isotope composition during the last period of glaciation [Dansgaard et al., 1971[Dansgaard et al., , 1982[Dansgaard et al., , 1989]. Based on the correlation between the b180 in present-day precipitation and mean annual temperature for high-latitude stations, these changes translate into 5øC jumps in air temperature. Correlating with the oxygen isotope changes are severalfold changes in the dust content of the ice (see Figure 1), Copyfight 1990 by the American Geophysical Union. Paper number 90PA01194. 0883-8305/90/90PA-01194 $10.00 50 ppm changes in the CO2 content of the air trapped in the ice [Stauffer et al., 1984], changes in the SO4 concentration in the ice [Finkle and Langway, 1985] and changes in 10Be content of the ice [Beer et al., 1984]. As the 180 signature for these events has now been found in three Greenland ice cores (Camp Century [Dansgaard et al., 1971], Dye 3 [Dansgaard et al., 1982], and Renland (W. Dansgaard personal communication, 1990)), they must be real climatic events. However, the validity of the CO2 signal as a record of atmospheric composition remains in limbo. The reason is that similar events were not found in a study of an Antarctic ice core [Neftel et al., 1988]. As discussed by Dansgaard and Oeschger [1989], this absence could reflect either a smoothing of the record in low deposition Antarctic record or meltwater layers in the Dye 3 ice. Oeschger et al. [1984], fin'st suggested that the Greenland events constitute jumps between two modes of operation of the climate system. Broecker et al. [1985] went a step further and postulated that Oeschger's modes involved a turning on and off of the Atlanfic's conveyor circulation system. Rather than pursuing the cause of the entire series of oscillations, recent attention has been focused on a single event, the Younger Dryas, which followed upon the heels of the last glacial termination. This event has roughly the same shape, amplitude, and duration as those during the glacial period. The lure of the Younger Dryas is that in contrast to the others it is well documented in pollen records from the lands surrounding the northern Atlantic [W...

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Section: The Atla•c Salt Osce•tormentioning

confidence: 99%

A salt oscillator in the glacial Atlantic? 1. The concept

Broecker¹,

Bond²,

Klas³

et al. 1990

Paleoceanography

509

238

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“…Gargett and Holloway (1992) Ruddick and Zhang (1989) found that the "salt oscillator" mechanism (Welander 1986) in a box model could be completely stabilized by incorporating salt fingers into the model. Recently, Gargett and Ferron (1996) found that multibox models with non-equal heat and salt diffusivities exhibited extended ranges of multiple equilibria, a different mode transition near present-day values of freshwater forcing magnitude, and the possibility of quasi-periodic oscillatory states compared to an equal diffusivity run.…”

Section: Double Diffusion and Thermohaline Circulationmentioning

confidence: 99%

Impacts of double-diffusive processes on the thermohaline circulation

Zhang¹

1998

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“…Multiple equilibria and non‐linear oscillations are particularly sensitive to the approximations made. For example, Ruddick and Zhang (1989) included internal transport laws for heat and salinity and found an absence of oscillations whereas earlier, simpler models predicted oscillations.…”

Section: Introductionmentioning

confidence: 97%

Laboratory observations and simple models of slow oscillations in cooled salt-stratified bodies

Whitehead¹,

Raa²,

Tozuka³

et al. 2005

Tellus A

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A laboratory basin of saltwater with a freshwater layer at the top is exposed to cooling from above and inflow of freshwater from a layer that lies alongside. It exhibits oscillations of temperature, salinity, and layer depth when certain parameters are set. A simple analytical model illustrates the basic mechanism. Upon cooling, the layer gradually becomes denser. Ultimately, a density inversion at the interface between the layer and deeper fluid causes a gravitational instability. The layer is mixed with the deeper water and it vanishes. The emplacement of a new thin layer from freshwater inflow at the top repeats the cycle. Layered numerical models duplicate this cycle. Examples incorporate transport of heat out of the top and into the bottom of the layer. In addition, there is salinity transport up through the bottom from turbulent mixing. They reproduce the qualitative structure of the experimental data, but the many simplifications in the model do not permit precise quantitative agreement.

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The mythical thermohaline oscillator?

Cited by 8 publications

References 0 publications

A salt oscillator in the glacial Atlantic? 1. The concept

A salt oscillator in the glacial Atlantic? 1. The concept

Impacts of double-diffusive processes on the thermohaline circulation

Laboratory observations and simple models of slow oscillations in cooled salt-stratified bodies

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