PART IV — DYNAMICS OF THE ATMOSPHERE-OCEAN SYSTEM 



base of the extensive ice shelves of 

 Antarctica; (c) rapid cooling and evap- 

 oration resulting from the outbreaks 

 of cold, dry antarctic air masses. 

 Recently, a fourth method was pro- 

 posed which is based purely on 

 molecular exchange of heat and salt 

 between a warm salty lower layer 

 and a cold fresh upper layer. Which 

 of these methods is the dominant one 

 is not known. Method (a) has gen- 

 erally been considered the key 

 method; however, recent studies 

 show that method (b) may be most 

 important. It is probable that all 

 the methods are active to a varying 

 degree, depending on the location, 

 and a variety of AABW types are 

 formed. 



The AASW flows slowly north- 

 ward (see Figure IV-3); on meeting 

 the less dense sub-antarctic water 

 (near 55" S.), it sinks, contributing 

 to the "antarctic intermediate water" 

 (AAIVV). The cold, relatively fresh 

 AAIW flows northward at depths of 

 nearly one kilometer. It reaches the 

 equator in the Indian and Pacific 

 oceans and up to 20 N. in the 

 Atlantic Ocean. 



The zone where the AAIW forms 

 is called the "polar front zone," or 

 Antarctic Convergence. The proc- 

 esses occurring within the zone are 

 not understood; even the concept of 

 a "convergence" process is question- 

 able. The structure and position of 

 the polar front zone varies with time. 

 How, and in what frequency, and 

 how it influences the AAIW forma- 

 tion are not known at all. The polar 

 front zone should be subjected to 

 much study in the coming years. 

 It is of major importance to the 

 overturning process of ocean waters 

 and to climatic characteristics of the 



southern hemisphere and perhaps the 

 world. The only way to study this 

 feature effectively is by multi-ship 

 expeditions and/or time-series meas- 

 urements from numerous anchored 

 arrays of instruments. 



Exclmngc of Water Masses — From 

 salt studies, the general rate of me- 

 ridional exchange has been deter- 

 mined. The CDW southward trans- 

 port is 77 million cubic meters per 

 second, of which only 15 million cubic 

 meters per second have been derived 

 from the sub-arctic regions (mainly 

 from the North Atlantic). The rest is 

 the return flow from the two north- 

 ward antarctic components (AAIW 

 and AABW). The CDW also brings 

 heat into the antarctic region. It is 

 calculated that 14 to 19 kilogram 

 calories per cm 2 per year are released 

 into the atmosphere by the ocean. 

 This has a great effect in warming 

 the antarctic air masses and, hence, 

 in modifying the influence of Antarc- 

 tica on world climate. 



The exchange of CDW for AAIW 

 and AABW has the important result 

 of taking out the warm, low-oxygen- 

 ated water and replacing it with cold, 

 high-oxygen-content water. Were it 

 not for this, the abyssal waters would 

 warm considerably by geothermal 

 heating and downward flux of heat 

 across the thermocline. They would 

 also become devoid of oxygen by 

 organic decomposition. 



Need for More Information 



Though the gross features of the 

 circulation pattern can be found, we 

 do not know enough detail about 

 the process of conversion of CDW 

 into the antarctic water masses. In 

 what regions does this conversion 



take place? Is it seasonal or does it 

 vary with another frequency? By 

 what methods is the CDW converted 

 into antarctic water masses? 



To accomplish these tasks, long 

 time-series measurements of currents, 

 temperature, and salinity are needed 

 along the continental margins of Ant- 

 arctica and within the polar front 

 zone. Multi-ship expeditions and 

 satellite observations would also be 

 useful in studying time-variations of 

 the water structure. Geochemical 

 studies of the isotopic makeup of the 

 ice and sea water are necessary to 

 yield information as to "residence" 

 times within water masses and in- 

 sight into methods of bottom-water 

 production. 



The antarctic waters are also of 

 importance in that they connect each 

 of the major oceans via a circum- 

 polar conduit. The rate of the cir- 

 cumpolar flow is not known, though 

 recent studies indicate a volume 

 transport of well over 200 million 

 cubic meters per second, making it 

 the largest current system in the 

 world ocean. A program of direct 

 current observations is needed to 

 study the circumpolar current. Satel- 

 lite surveillance of drogues will be 

 a useful method to study the current 

 systems. 



In short, scientists need to know 

 in more detail the methods, rates, 

 and location of the formation of the 

 antarctic water masses. They can 

 accomplish this task by hydrographic 

 and geochemical observations in cir- 

 cumpolar waters using modern tech- 

 niques. In addition, detailed time- 

 series observations would be needed 

 at particular points such as the Wed- 

 dell Sea, Ross Sea, the Amery Ice 

 Shelf, and other appropriate regions. 



Tropical Air-Sea Rhythms 



Tropical air-sea rhythms are best 

 seen in the time-series of air and 

 sea temperature at Canton Island, 

 an equatorial island in the Pacific 



(2°48'S. 171°43'W.); this is the only 

 locality where temperature observa- 

 tions have been maintained uninter- 

 ruptedly over a long period, 1950 



through 1967. However, there is now 

 no way of continuing this important 

 time-series because the Canton Island 

 observatory, with its modern equip- 



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