Transport of Freshwater into the Deep Ocean by the Conveyor

  • Scott J. Lehman
  • Daniel G. Wright
  • Thomas F. Stocker
Conference paper
Part of the NATO ASI Series book series (volume 12)

Abstract

The upper limb of the ocean’s conveyor-belt circulation transports about one petaWatt of heat across the equator in the Atlantic, of which approximately two-thirds is released to the atmosphere in the northern part of the basin as a result of deepwater formation. If all of this heat were taken up in melting ice, it would yield approximately 60,000 km3 of meltwater per year. Thus it is conceivable that peak deglacial melting rates of 5,000–15,000 km3/yr (Fairbanks 1989) were achieved in response to sudden start-up or strengthening of the conveyor at the end of the last glaciation. Of course, a portion of the heat borne and released by the conveyor radiates to space, and much of the glacial ice at high elevation and high latitude must have been warmed prior to melting, consuming additional energy. But the point here is that even without sunlight at high latitudes, the transient heat gain associated with strengthening of the conveyor may have been sufficient or near-sufficient to account for the melting of the former ice sheets of the Northern Hemisphere. The potential role of the conveyor in melting the ice sheets is further underscored by Figure 1 showing that melting rates during the last deglaciation varied in accordance with the relative strength of the conveyor’s upper limb (Lehman and Keigwin 1992). However, in most numerical ocean models the convection which drives the conveyor circulation is extremely sensitive to small changes in the freshwater balance at the surface (Maier-Reimer and Mikolajewicz 1989; Stocker et al. 1992). If such model sensitivities are close to being correct, it is difficult to understand how the conveyor remained “on” long enough to promote the large pulses of ice sheet melting seen in Figure 1.

Keywords

Convection Depression Calcite Fractionation Holocene 

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References cited

  1. Atkinson, T.C., K.R. Briffa, and G.R. Coope (1987). “The seasonal temperatures in Britain during the past 22.000 years, reconstructed using beetle remains.” Nature 325: 587–592.CrossRefGoogle Scholar
  2. Baumgarter, A. and E. Reichel (1975). The World Water Balance. New York, Elsevier. 179 pp.Google Scholar
  3. Boyle, E. A. and L. Keigwin (1987). “North Atlantic thermohaline circulation during the past 20,000 years linked to high-latitude surface temperature.” Nature 330 (6143): 35–40.CrossRefGoogle Scholar
  4. Broecker, W. S. (1986). “Oxygen Isotope Constraints on Surface Ocean Temperatures.” Quaternary Research 26 (1): 121–134.CrossRefGoogle Scholar
  5. Broecker, W. S. (1991). “The Great Ocean Conveyor.” Oceanography 4 (2): 79–89.Google Scholar
  6. Broecker, W. S. (1991). The Strength of the Nordic Heat Pump. The Last Deglaciation: Absolute and Radiocarbon Chronologies. Berlin, Springer-Verlag. 173–181.Google Scholar
  7. Broecker, W. S., M. Andree, et al. (1988). “The chronology of the last deglaciation: implications to the cause of the Younger Dryas event.” Paleoceanography 3 (1): 1–19.CrossRefGoogle Scholar
  8. Broecker, W. S., T.-H. Peng, et al. (1990). “The magnitude of global fresh-water transports of importance to ocean circulation.” Climate Dynamics 4: 73–79.CrossRefGoogle Scholar
  9. Bryan, F. (1986). “High-latitude salinity effects and interhemisphere thermohaline circulations.” Nature 323: 301–304.CrossRefGoogle Scholar
  10. Charles, C. D. and R. G. Fairbanks (1992). “Evidence from Southern Ocean sediments for the effect of North Atlantic deep-water flux on climate.” Nature 355: 416–419.CrossRefGoogle Scholar
  11. Craig, H. and L. I. Gordon (1965). Deuteriumngsj oxygen-11 variations in Pie ocean Dading atmosphere: Stable isotopes in oceanographic studies and paleotemperatures. Third Spoleto Conference, Spoleto, Italy, Sischi and Figili.Google Scholar
  12. Dansgaard, W., H.B. Clausen, et al. (1982). “A new Greenland deep ice core.” Science 218: 1273–1277.CrossRefGoogle Scholar
  13. Dansgaard, W., J. W. C. White, et al. (1989). “The abrupt termination of the Younger Dryas climate event.” Nature 339: 532–533.CrossRefGoogle Scholar
  14. Duplessy, J. C., G. Delibrias, et al. (1981). “Deglacial warming of the Northeastern Atlantic Ocean: correlation with the Paleoclimatic evolution of the European continent.” Palaeogeograpy, Palaeoclimatology, Palaeoecology 35: 121–144.CrossRefGoogle Scholar
  15. Duplessy, J. C., L. Labeyrie, et al. (1992). “Changes in surface salinity of the North Atlantic Ocean during the last deglaciation.” Nature 358: 485–488.CrossRefGoogle Scholar
  16. Duplessy, J. C., L. Labeyrie, et al. (1991). “Surface salinity reconstruction of the North Atlantic Ocean during the last glacial maximum.” Oceanologica Acta 14: 311–324.Google Scholar
  17. Erez, J. and B. Luz (1983). “Experimental paleotemperature equation for planktonic foraminifera.” Geochimica gl Cosmochimica Acta 47: 1025–1031.CrossRefGoogle Scholar
  18. Fairbanks, R. G. (1989). “Glacio-eustatic sea level record 0–17,000 years before present: influence of glacial melting rates on Younger Dryas event and deep ocean circulation.” Nature 342: 637–642.CrossRefGoogle Scholar
  19. Gordon, A. L. (1986). “Interocean Exchange of Thermohaline Water.” Journal of Geophysical Research 91 (C4): 5037–5046.CrossRefGoogle Scholar
  20. Jansen, E. and T. Veum (1990). “Evidence for two-step deglaciation and its impact on North Atlantic deep-water circulation.” Nature 343: 612–616.CrossRefGoogle Scholar
  21. Keigwin, L. D., G. A. Jones, et al. (1991). “Deglacial Meltwater Discharge, North Altantic Deep Circulation, and Abrupt Climate Change.” Journal of Geophysical Research 96 (C9): 16811–16826.CrossRefGoogle Scholar
  22. Labeyrie, L. D., J. C. Duplessy, et al. (1987). “Variations in mode of formation and temperature of oceanic deep water over the past 125000 years.” Nature 327: 477–482.CrossRefGoogle Scholar
  23. Lehman, S. J. and L. D. Keigwin (1992). “Sudden changes in North Atlantic circulation during the last deglaciation.” Nature 356: 757–762.CrossRefGoogle Scholar
  24. Maier-Reimer, E. and U. Mikolajewicz (1989). Experiments with an OGCM on the cause of the Younger Dryas. Max-Planck-Institut fur Meteorologie.Google Scholar
  25. Manabe, S. and R. J. Stouffer (1988). “Two Stable Equilibria of a Coupled Ocean-Atmosphere Model.” Journal of Climate 1: 841–866.CrossRefGoogle Scholar
  26. O’Neil, J. R., R. N. Clayton, et al. (1969). “Oxygen isotope fractionation in divalent metal carbonates.” Journal Qf. Chemical Physics. 51: 5547–5558.CrossRefGoogle Scholar
  27. Semtner, A. J. (1976). “A model for the thermodynamic growth of sea ice in numerical investigations of climate.” Journal of Physical Oceanography 6: 379–389.CrossRefGoogle Scholar
  28. Shackleton, N. J. (1987). “Oxygen Isotopes, Ice Volume and Sea Level.” Quaternary Science Reviews 6: 183–190.CrossRefGoogle Scholar
  29. Stocker, T. F., D. G. Wright, et al. (1992). “A zonally averaged, coupled ocean-atmosphere model for paleoclimate studies.” Journal of Climate 5: 773–797.CrossRefGoogle Scholar
  30. Teller, J. T. (1990). “Volume and Routing of Late-Glacial Runoff from the Southern Laurentide Ice Sheet.” Quaternary Research 34: 12–23.CrossRefGoogle Scholar
  31. Winton, M. and E. S. Sarachik (1993 in press). “Thermohaline Oscillations Induced by Strong Steady State Forcing of Ocean General Circulation Models.” Journal of Physical Oceanography:Google Scholar
  32. Wright, D. G. and T. F. Stocker (1991). “A Zonally Averaged Ocean Model for the Thermohaline Circulation. Part I: Model Development and Flow Dynamics.” Journal of Physical Oceanography 21: 1713–1724.CrossRefGoogle Scholar
  33. Wright, D. S. and T. F. Stocker (1993 in press). “Younger Dryas Experiments.”, this volume.Google Scholar
  34. Zahn, R. (1992). “Deep ocean circulation puzzle.” Nature 356: 744–746.CrossRefGoogle Scholar
  35. Zahn, R. and A. C. Mix (1991). “Benthic Foraminiferal d18O in the Ocean’s Temperaturesalinity-density Field: Constraints on Ice Age Thermohaline Circulation.” Paleoceanography 6 (1): 1–20.CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1993

Authors and Affiliations

  • Scott J. Lehman
    • 1
  • Daniel G. Wright
    • 2
  • Thomas F. Stocker
    • 3
  1. 1.Woods Hole Oceanographic Inst.Woods HoleUSA
  2. 2.Bedford Inst. of OceanographyDartmouthCanada
  3. 3.Lamont-Doherty Earth ObservatoryPalisadesUSA

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