RIDGE CLUSTER ARRAY 



500m 



1000m if?- 



2000m 



Poleward 



SHIP TRACK 



I60°E 170° 



I60°W 



60°S 



60°S 



I60°E 



I60°E 



Cruise tracks for the two KNORR cruises. The southern end 

 of the sections will be determined by ice conditions. 

 Thermistor chains will be moored at A, and the current 

 meter cluster array will be moored at B. 



Figure 26. — ISOS experiment ridge cluster array and ships tracks. 



The thermistor chain mooring monitors the development of 

 winter deep-mixed layers in the upper waters of the subantarctic 

 zone. Temperature will be recorded over the upper 600 m from 

 early fall through midspring 1978. The analysis of the therm- 

 istor chain data (and associated hydrographic work done from 

 the Tangeroa and Knorr) will focus on the seasonal convec- 

 tive renewal of subantarctic-mode water. The 8°C subantarctic- 

 mode water is found upstream, south of the Tasman Sea, and 

 apears to be converted to 7°C subantarctic-mode water by 

 air-sea heat exchange over the Campbell Plateau. Analysis and 

 interpretation of the data will be supplemented by the meteoro- 

 logical data routinely collected at Campbell Island, 100 nmi 

 northwest of the mooring. 



The hydrographic program from the Knorr will be used for 

 study of several features. The formation of the deep western 

 boundary current in the southwest Pacific Basin will be studied: 

 how does the transition from the observed zonal flow along the 

 midocean ridge at 170°E, 62°S to the observed meridional flow 

 at 43 °S, 168°W occur? The intensity and variability of winter- 

 overturned water in the polar frontal zone and in the antarctic 

 zone will be studied. Data will be gathered to study the smaller 

 scale structure of the polar frontal zone. Interpretation of 



40 



the various water mass structures (subantarctic-mode water, 

 antarctic-intermediate water, and deep water) will be aided by 

 a tritium and helium isotope sampling program. 



An intensive study of the polar frontal zone will be made at 

 58 °S, 165°E on the last leg of the Knorr cruise in December 

 1978. The Antarctic Circumpolar Current seems to have a per- 

 manent meander over the Macquarie Ridge near this location, 

 and barotropic models show that the region could be an active 

 generator for eddies. Because of large lateral gradients at this 

 location, interleaving could also be greatly enhanced. A closely 

 spaced CTD section will be made across the polar front, and 

 XBTs will be used to map the local mesoscale structure of the 

 polar frontal zone and to study the spatial persistence of inter- 

 leaving. Two vertical current meters will be placed in the polar 

 frontal zone and tracked for a 2- to 3-day period with repeated 

 CTDs over the floats. This data set will be suitable for analysis 

 of fine-structure statistics. By using data from the earlier Knorr 

 cruises, a comparison between broad and narrow polar frontal 

 zones will be possible. By comparing results to those obtained 

 in the Drake Passage in 1976, the universality of the interleav- 

 ing properties of the circumpolar front can also be studied. 



