Transport of Freshwater into the Deep Ocean by the Conveyor

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


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.


Southern Ocean Deep Ocean Benthic Foraminifera Surface Salinity Planktonic Foraminifera 
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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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