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Geothermal Heating, Diapycnal Mixing and the Abyssal Circulation : Volume 5, Issue 2 (19/06/2009)

By Emile-geay, J.

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Book Id: WPLBN0004020380
Format Type: PDF Article :
File Size: Pages 15
Reproduction Date: 2015

Title: Geothermal Heating, Diapycnal Mixing and the Abyssal Circulation : Volume 5, Issue 2 (19/06/2009)  
Author: Emile-geay, J.
Volume: Vol. 5, Issue 2
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2009
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Madec, G., & Emile-Geay, J. (2009). Geothermal Heating, Diapycnal Mixing and the Abyssal Circulation : Volume 5, Issue 2 (19/06/2009). Retrieved from http://worldlibrary.net/


Description
Description: Department of Earth Sciences, University of Southern California, Los Angeles, USA. 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 m2 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 Σ4=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 gradients 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.

Summary
Geothermal heating, diapycnal mixing and the abyssal circulation

Excerpt
Adcroft, A., Scott, J R., and Marotzke, J.: Impact of geothermal heating on the global ocean circulation, Geophys. Res. Lett., 29, 1735–1738, 2001.; Adkins, J., McIntyre, K., and Schrag, D P.: The Salinity, Temperature, and $\delta^18$O of the Glacial Deep Ocean, Science, 298, 1769–1773, 2002.; Adkins, J., Ingersoll, A., and Pasquero, C.: Rapid climate change and conditional instability of the glacial deep ocean from the thermobaric effect and geothermal heating, Quaternary Sci. Rev., 24, 581–594, 2005.; Arhan, M., Mercier, H., Bourles, B., and Gouriou, Y.: Hydrographic sections across the Atlantic at 7 degrees 30N and 4 degrees 30S, Deep-Sea Res. Pt. I, 45, 829–872, 1998.; Beckmann, A. and Doescher, R.: A method for improved representation of dense water spreading over topography in geopotential-coordinate models, J. Phys. Oceanogr., 27, 581–591, 1997.; Blanke, B. and Delecluse, P.: Variability of the tropical Atlantic Ocean simulated by a general circulation model with two different mixed-layer physics, J. Phys. Oceanogr., 23, 1363–1388, 1993.; Bryan, K.: Parameter sensitivity of primitive equation ocean general circulation, J. Phys. Oceanogr., 17, 970–985, 1987.; Delecluse, P. and Madec, G.: Ocean modelling and the role of the ocean in the climate system, in: Modeling the Earth's Climate and its Variability, Les Houches, Session LXVII 1997, edited by: Holland, W R., Joussaume, S., and David, F., Elsevier Science, 237–313, 1999.; Dutay, J., Emile-Geay, J., Iudicone, D., Jean-Baptiste, P., Madec, G., and Carouge, C.: Helium Isotopic constraints on simulated ocean circulations. Implications for abyssal theories, Environ. Fluid Mech., submitted, 2008.; Ganachaud, A. and Wunsch, C.: Improved estimates of global ocean circulation, heat transport and mixing from hydrographic data, Nature, 408, 453–457, 2000.; Gent, P. and Williams, J M.: Isopycnal mixing in ocean circulation models, J. Phys. Oceanogr., 20, 105–155, 1990.; Gregg, M C.: Scaling turbulent dissipation in the thermocline, J. Geophys. Res.-Oceans, 94, 9686–9698, 1989.; Huang, R.: Mixing and energetics of the thermohaline circulation, J. Phys. Oceanogr., 29, 727–746, 1999.; Harris, R N. and Chapman, D S.: Deep-seated oceanic heat flow, heat deficits and hydrothermal circulation, in: Hydrogeology of the oceanic lithosphere, edited by: Davis, E. and Elderfield, H., Cambridge University Press, Cambridge, UK, 311–-336, 2004.; Hutnak, M. and Fisher, A T.: Influence of sedimentation, local and regional hydrothermal circulation, and thermal rebound on measurements of seafloor heat flux, J. Geophys. Res., 112, B12101, doi:10.1029/2007JB005022, 2007.; Iudicone, D., Madec, G., Blanke, B., and Speich, S.: The role of Southern Ocean surface forcings and mixing in the global conveyor, J. Phys. Oceanogr., 38, 1377–1400, 2008a.; Iudicone, D., Madec, G., and McDougall, T.: Watermass transformations in a neutral density framework and the key role of light penetration, J. Phys. Oceanogr., 38, 1357–1376, 2008b.; Iudicone, D., Speich, S., Madec, G., and Blanke, B.: The global conveyor belt from a Southern Ocean perspective, J. Phys. Oceanogr., 38, 1401–1425, 2008c.; Jackett, D R. and McDougall, T J.: Minimal adjustment of hydrographic data to achieve static stability, J. Atmos. Ocean. Tech., 12, 381–389, 1995.; Jaupart, C., Labrosse, S., and Marechal, J.-C.: Temperatures, heat and energy in the mantle of the Earth, in: Treatise on Geophysics, edited by: Schubert, G. and Bercovici, D., Elsevier, 253–303, 2007.; Kunze, E. and Sanford, T.: Abyssal Mixing: Where It Is Not, J. Phys. Oceanogr., 26, 2286–2296, 1996.; Large, W. and Nurser, A. J G.: Ocean surface water mass transformation, in: Ocean Circulation and Climate: Observing and Modelling the Global Ocean, edited by: Siedler, G., Church, J., and Gould, J., vol 77 of International Geophysics Series, Academic Press, 317–336, 2001.; Lazar, A., Madec, G., and Delecluse, P.: The Deep Interior Downwelling, the Veronis Effect and Mesoscale Tracer

 

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