Rates of Water Mass Formation in the North Atlantic Ocean

Speer, Kevin; Tziperman, Eli

doi:10.1175/1520-0485(1992)022<0093:rowmfi>2.0.co;2

Cited by 264 publications

(349 citation statements)

References 21 publications

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“…Moreover, its action is precisely limited to bottom water (an endpoint of the T-S diagram), which means that geothermal heating tends to transform the densest water masses into warmer, lighter ones, much like air-sea fluxes transform surface waters. Indeed, a parcel of Antarctic Bottom Water (AABW) experiences a steady warming while heading North in the vicinity of the seafloor, in the same fashion as air-sea fluxes determine the thermal history of North Atlantic surface water while it ascends to high Northern latitudes (Walin, 1982;Speer and Tziperman, 1992;Large and Nurser, 2001;Marshall et al, 1998;Nurser et al, 1999;Iudicone et al, 2008b). To observe this analogy, one just needs to conceptually flip the ocean upside down, as done in Fig.…”

Section: The Formation/consumption Cycle Of Bottom Watermentioning

confidence: 99%

Geothermal heating, diapycnal mixing and the abyssal circulation

Emile‐Geay

Madec

2009

Ocean Sci.

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Abstract. The dynamical role of geothermal heating in abyssal circulation is reconsidered using three independent arguments. First, we show that a uniform geothermal heat flux close to the observed average (86.4 mW m −2 ) supplies as much heat to near-bottom water as a diapycnal mixing rate of ∼10 −4 m 2 s −1 -the canonical value thought to be responsible for the magnitude of the present-day abyssal circulation. This parity raises the possibility that geothermal heating could have a dynamical impact of the same order. Second, we estimate the magnitude of geothermally-induced circulation with the density-binning method (Walin, 1982), applied to the observed thermohaline structure of Levitus (1998). The method also allows to investigate the effect of realistic spatial variations of the flux obtained from heatflow measurements and classical theories of lithospheric cooling. It is found that a uniform heatflow forces a transformation of ∼6 Sv at σ 4 =45.90, which is of the same order as current best estimates of AABW circulation. This transformation can be thought of as the geothermal circulation in the absence of mixing and is very similar for a realistic heatflow, albeit shifted towards slightly lighter density classes. Third, we use a general ocean circulation model in global configuration to perform three sets of experiments: (1) a thermally homogenous abyssal ocean with and without uniform geothermal heating; (2) a more stratified abyssal ocean subject to (i) no geothermal heating, (ii) a constant heat flux of 86.4 mW m −2 , (iii) a realistic, spatially varying heat flux of identical global average; (3) experiments (i) and (iii) with enhanced vertical mixing at depth. Geothermal heating and diapycnal mixing are found to interact non-linearly through the density field, with geothermal heating eroding the deep stratification supporting a downward diffusive flux, while diapycnal mixing acts to map near-surface temperature gradientsCorrespondence to: J. Emile-Geay (julieneg@usc.edu) onto the bottom, thereby altering the density structure that supports a geothermal circulation. For strong vertical mixing rates, geothermal heating enhances the AABW cell by about 15% (2.5 Sv) and heats up the last 2000 m by ∼0.15 • C, reaching a maximum of by 0.3 • C in the deep North Pacific. Prescribing a realistic spatial distribution of the heat flux acts to enhance this temperature rise at mid-depth and reduce it at great depth, producing a more modest increase in overturning than in the uniform case. In all cases, however, poleward heat transport increases by ∼10% in the Southern Ocean. The three approaches converge to the conclusion that geothermal heating is an important actor of abyssal dynamics, and should no longer be neglected in oceanographic studies.

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Section: The Formation/consumption Cycle Of Bottom Watermentioning

confidence: 99%

Geothermal heating, diapycnal mixing and the abyssal circulation

Emile‐Geay

Madec

2009

Ocean Sci.

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“…Tandon and Garrett [ 1997] and Garrett and Tandon [ 1997] included in this the effects of seasonal and diurnal variation of mixed layer thickness. These ideas have been used to address the mismatch [Speer and Tziperman, 1992] between rates of water mass formation calculated from Ekman pumping and those calculated from buoyancy forcing. Rates of diapycnal diffusion in the interior have also been calculated by using this concept.…”

Section: V_mentioning

confidence: 99%

Estuarine salt flux through an isohaline surface

MacCready¹,

Geyer²

2001

J. Geophys. Res.

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Abstract. The salinity budget in an estuary is analyzed using an isohaline as the seaward bounding surface of the volume of integration. It is found that the rate of change of volume integrated salinity is governed by two processes: (1) the "drift" of the isohaline through the fluid, and (2) turbulent salt flux through the isohaline. This analysis highlights the role of turbulent salt flux in maintaining the salinity intrusion. In contrast, more standard budgets using a stationary, vertical cross section as the seaward end of the volume of integration attribute almost all along-estuary salt flux to advective processes such as the gravitational circulation. The isohaline budget is explored using an analytical model and using results from a threedimensional numerical model. The numerical results highlight the complex spatial and temporal interplay between turbulent mixing and the shape of the isohaline. Averaging over a time period during which the freshwater volume behind the isohaline is constant reduces the isohaline budget to a balance of two terms: the time-mean, area-integrated turbulent salinity flux across the isohaline being equal to the mean fiver flow times the salinity of the isohaline.

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“…Walin's (1982) ideas about direct estimation of water mass formation using air sea exchange data were a major boost to the field, yet application to EDW formation (eg. Speer andTziperman 1992, Maze et al 2009) yielded greatly different estimates of EDW formation. This has prompted a concerted effort to collect field observations and conduct modeling studies to better understand the different physical processes in the ocean associated with water mass formation (advection, subduction, mixing) and better parameterize turbulent exchanges with the atmosphere in the northern Sargasso Sea: this experiment was called CLIMODE (CLIvar MOde water Dynamics Experiment, The Climode Group 2009).…”

Section: Introductionmentioning

confidence: 99%

New perspectives on eighteen-degree water formation in the North Atlantic

Joyce

2011

New Developments in Mode-Water Research

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In this report, Eighteen Degree Water (EDW) formation will be discussed, with emphasis on advances in understanding emerging within the past decade. In particular, a recently completed field study of EDW (CLIMODE) is suggesting that EDW formation within a given winter can have at least two different dominant physics and distinct locations: one type formed in the northern Sargasso Sea, largely away from the strong flows of the Gulf Stream where 1D physics may apply, and a second type formed along the southern flank of the Gulf Stream, in a region where the background vorticity of the flow and cross-frontal mixing plays a key role in the convective formation process.

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Rates of Water Mass Formation in the North Atlantic Ocean

Cited by 264 publications

References 21 publications

Geothermal heating, diapycnal mixing and the abyssal circulation

Geothermal heating, diapycnal mixing and the abyssal circulation

Estuarine salt flux through an isohaline surface

New perspectives on eighteen-degree water formation in the North Atlantic

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