On the Sensitivity of Thermocline Depth and Meridional Heat Transport to Vertical Diffusivity in OGCMS

Hu, Dingming

doi:10.1175/1520-0485(1996)026<1480:otsotd>2.0.co;2

Cited by 15 publications

(16 citation statements)

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“…In addition to K V , the independent parameters are g, the acceleration due to gravity, ρ, the equator-to-pole density difference, ρ 0 , a reference density, f , a characteristic value of the Coriolis parameter and L, a characteristic horizontal length scale. Park and Bryan (2000) established a good agreement between these relations and their model results, and were able to explain the deviations from classical scaling found in earlier studies (Bryan, 1987;Colin de Verdière, 1988;Hu, 1996;Marotzke, 1997).…”

Section: Introductionsupporting

confidence: 77%

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

Toom¹,

Dijkstra²

2011

TELLUSA

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A B S T R A C T An important expression of the non-linear character of the ocean's meridional overturning circulation (MOC) is the scaling of its amplitude with the magnitude of the vertical mixing coefficient (diffusivity) of heat and salt. This paper extends recent work that indicated that the Atlantic and Pacific MOC exhibit different scaling behaviour. An idealized two-basin model configuration is used to study the meridional overturning circulation under restoring boundary conditions. In particular, the effects of wind forcing and the choice of the parametrization of lateral mixing are examined.Without wind, the scaling is similar in the two basins and consistent with theoretical predictions, provided that the diffusivity is small enough. Towards higher diffusivities the scaling of the overturning diverges. With non-zero wind, the sensitivity is strongly determined by the choice of the lateral mixing scheme. In case of traditional horizontal diffusion, the scaling behaviour is asymmetric due to spurious diapycnal mixing. With the Gent-McWilliams parametrization, the scaling is symmetric for the lower range of diffusivities, where results agree partly with theoretical scaling relations. In all cases considered, the pycnocline depth has the same sensitivity to diffusivity in both basins, implying that there is no universally valid relation between overturning strength and pycnocline depth.

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Section: Introductionsupporting

confidence: 77%

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

Toom¹,

Dijkstra²

2011

TELLUSA

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“…The situation is complicated further by differing exchange times of surface waters with waters of the deep sea, which is the largest ocean reservoir for CO2. Simple box models of the ocean circulation (which impose circulation and exchange fluxes between a handful of well-mixed water masses in the ocean and allow for gas exchange with the atmosphere) have been used to develop a theory called the "high-latitude outcrop model" for the interaction of CO2 between the ocean and the atmosphere [ [Ledwell et al, 1993] find low rates of diffusion, similar to the thermocline diffusivity used in the isopycnic model [Hu, 1996]. However, the density stratification of the thermocline and deep sea [Munk and Wunsch, 1998] and various geochemical measurements near the sea surface (such as oxygen [Spitzer and Jenkins, 1989] and helium concentrations [Jenkins, 1988] …”

Section: Most Of the Carbon On Earth Is Incorporated Intomentioning

confidence: 99%

What caused the glacial/interglacial atmospheric pCO₂ cycles?

Archer

Winguth²,

Lea

et al. 2000

Reviews of Geophysics

455

472

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Abstract. Fifteen years after the discovery of major glacial/interglacial cycles in the CO2 concentration of the atmosphere, it seems that all of the simple mechanisms for lowering pCO 2 have been eliminated. We use a model of ocean and sediment geochemistry, which includes new developments of iron limitation of biological production at the sea surface and anoxic diagenesis and its effect on CaCO 3 preservation in the sediments, to evaluate the current proposals for explaining the glacial/ interglacial pCO 2 cycles within the context of the ocean carbon cycle. After equilibration with CaCO 3 the model is unable to generate glacial pCO 2 by increasing ocean NO•-but predicts that a doubling of ocean H4SiO 4 might suffice. However, the model is unable to generate a doubling of ocean H4SiO 4 by any reasonable changes in SiO 2 weathering or production. Our conclusions force us to challenge one or more of the assumptions at the foundations of chemical oceanography. We can abandon the stability of the "Redfield ratio" of nitrogen to phosphorus in living marine phytoplankton and the ultimate limitation of marine photosynthesis by phosphorus. We can challenge the idea that the pH of the deep ocean is held relatively invariant by equilibrium with CaCO 3. A third possibility, which challenges physical oceanographers, is that diapycnal mixing in ocean circulation models exceeds the rate of mixing in the real ocean, diminishing the model pCO 2 sensitivity to biological carbon uptake. The ice age cycles underwent a midlife transition

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“…The exchange coefficients vary somewhat from model to model, but our tests show that abiotic CO, is _ relatively insensitive to gas exchange velocities. The Pandora model has 10 boxes [Broecker and Peng, 1987], the Cyclops model has 13 [Keir, 1988] [Hu, 1996]. The passive tracer (e.g., CO2) advection code was upgraded to the same leapfrog scheme that is used for salinity in MICOM, decreasing execution speed somewhat but drastically improving tracer conservation.…”

Section: Appendix: Abiotic Co• Computation Detailsmentioning

confidence: 99%

Atmospheric pCO₂ sensitivity to the biological pump in the ocean

Archer¹,

Eshel²,

Winguth³

et al. 2000

Global Biogeochemical Cycles

126

155

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Abstract. In models of the global carbon cycle, the pCO 2 of the atmosphere is more sensitive to the chemistry of the high-latitude surface ocean than the tropical ocean. Because sea-surface nutrient concentrations are generally high in the high latitudes, pCO 2 sensitivity to high-latitude forcing also determines pCO 2 sensitivity to the biological pump globally. We diagnose highlatitude sensitivity of a range of ocean models using atmospheric pCO 2 above an abiotic ocean; cold high-latitude waters pull abiotic pCO 2 to low values. Box models are very high-latitude sensitive, while most global circulation models are considerably less so, including a twodimensional overturning model, two primitive equation models, the Hamburg class of large scale geostrophic (LSG) general circulation models (GCMs), and the MICOM isopycnic GCM. Highlatitude forcing becomes more important in a depth-coordinate GCM when lateral diffusion is oriented along isopycnal surfaces, rather than horizontally, following Redi [1982]. In two different GCMs (a primitive equation model and LSG), addition of the Gent and McWillams [ 1990] isopycnal thickness diffusion scheme had only minor impact on high-latitude sensitivity. Using a simplified box model, we show that high-latitude sensitivity depends on a high-latitude monopoly on deep water formation. In an attempt to bridge the gap between box models and GCMs, we constructed a simple slab overturning model with an imposed stream function which can be discretized at arbitrary resolution from box model to GCM scale. High-latitude sensitivity is independent of model resolution but very sensitive to vertical diffusion. Diffusion acts to break the high-latitude monopoly, decreasing high-latitude sensitivity. In the isopycnal GCM MICOM, however, high-latitude sensitivity is relatively insensitive to diapycnal diffusion of tracers such as CO2. This would imply that flow pathways in MICOM take the place of vertical diffusion in the slab model. The two nominally most sophisticated ocean models in the comparison are the isopycnal model MICOM and the depth-coordinate GCM with Redi [ 1982] and Gent and McWilliams [1990] mixing. Unfortunately, these two models disagree in their abiotic CO2 behavior; the depth-coordinate isopycnal mixing GCM is high-latitude sensitive, in accord with box models, while MICOM is less so. The rest of the GCMs, which have historically seen the most use in geochemical studies, are even less high-latitude sensitive than MICOM. This discrepancy needs to be resolved. In the meantime, the implication of the MICOM/traditional GCM result would be that box models overestimate high-latitude sensitivity of the real ocean.

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On the Sensitivity of Thermocline Depth and Meridional Heat Transport to Vertical Diffusivity in OGCMS

Cited by 15 publications

References 0 publications

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

What caused the glacial/interglacial atmospheric pCO₂ cycles?

Atmospheric pCO₂ sensitivity to the biological pump in the ocean

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On the Sensitivity of Thermocline Depth and Meridional Heat Transport to Vertical Diffusivity in OGCMS

Cited by 15 publications

References 0 publications

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

Scaling of the strength of the meridional overturning with vertical diffusivity in an idealized global geometry

What caused the glacial/interglacial atmospheric pCO2 cycles?

Atmospheric pCO2 sensitivity to the biological pump in the ocean

Contact Info

Product

Resources

About

What caused the glacial/interglacial atmospheric pCO₂ cycles?

Atmospheric pCO₂ sensitivity to the biological pump in the ocean