394 



60 OCEANOGRAPHY IN THE NEXT DECADE 



and atmosphere are difficult to obtain with adequate accuracy, 

 and at the present time there are serious conflicts among values 

 estimated from atmospheric models and data, from oceanic mod- 

 els and data, and from the boundary layers in the two media. 



The ocean and atmosphere contribute roughly equally to the 

 transport of heat from lower latitudes toward the polar regions — a 

 transport that is required to maintain the global radiation balance 

 at the top of the atmosphere — although the relative importance of 

 the two transport mechanisms varies with latitude. The massive 

 amounts of water moving in the ocean render it a crucial trans- 

 porter of moisture, but we have little idea of the sizes of freshwa- 

 ter sources and sinks over the ocean (Baumgartner and Reichel, 

 1975). Their distribution must have profound effects on the dis- 

 tribution of rainfall over land, an important component of the 

 climate in habitable regions of the world. Low surface salinity 

 caps the ocean, attenuating convection and deep-reaching water 

 mass formation. High surface salinity, combined with surface 

 cooling, allows deep convection and ventilation of the interior of 

 the ocean. 



We need to monitor changes in ocean surface salinity globally. 

 Satellite sensors monitor sea surface temperature and its anoma- 

 lies, but monitoring sea surface salinity and its anomalies on a 

 global scale is beyond present capabilities, as is determination of 

 the temperature below the very surface. 



Over the last decade, oceanographers have begun making di- 

 rect estimates of the north-south ocean heat and freshwater trans- 

 ports using transoceanic hydrographic sections and modern mea- 

 surements of strong boundary currents and then comparing them 

 with the more uncertain indirect estimates based on atmospheric 

 data. To understand heat and freshwater transport fully, oceanog- 

 raphers must describe the general ocean circulation and its vari- 

 ability. It is discouraging, however, that since 1985, only six 

 transoceanic hyi.irographic sections, the backbone of the observa- 

 tions needed to determine the north-south fluxes, have been car- 

 ried uut: at 4"^, 24=, and 10° north latitude in the Pacific; 32" 

 south latitude m the Indian Ocean; and 11^ north latitude in the 

 Atlantic. OverLoming organizational and funding obstacles for 

 these long hydrographic sections takes major effort by individual 

 scientists. However, WOCE has plans to make the necessary mea- 

 surements for determining the ocean heat transport in each ocean 

 basjn at several latitudes (WOCE Scientific Steering Group, 1986). 

 This work is a central focus of WOCE and is clearly needed if 

 understanding of how the present climate system works is to progress. 



