OCEANOGRAPHIC CONDITIONS, 1974 



R. W. Scobie 

 (U.S. COAST GUARD OCEANOGRAPHIC UNIT) 



During the 1974 Ice Patrol Season, two oceano- 

 graphic cruises (April 2 — May 9 and June 4 — 

 July 9) were conducted in the vicinity of the 

 Grand Banks aboard CGC EVERGREEN 

 (WAGO-295). The primary purpose of these 

 cruises was to provide Commander, International 

 Ice Patrol (CUP) with current data which could 

 be utilized in forecasting the drift of icebergs 

 threatening North Atlantic shipping. The sec- 

 ondary purpose was to conduct research projects 

 relating to Ice Patrol. One of these projects was 

 designed to determine how icebergs are affected 

 by wind and ocean currents, while another proj- 

 ect consisted of measuring deep ocean currents. 



Surface currents were calculated from salinity 

 and temperature data collected with a Salinity, 

 Temperature, Depth Environmental Profiling 

 System (STD). STD casts were taken along 

 standard Ice Patrol sections to a depth of 1000 

 meters in deep water and to as close to the bottom 

 as practicable in the shallower water along the 

 continental slope. All STD data were processed 

 real-time aboard ship using a Digital Data 

 Logger/Computer arrangement and were sub- 

 sequently transmitted to CUP. 



Dynamic topography charts were produced 

 from STD data and are presented here. To 

 maintain synopticity, each chart represents half 

 of one cruise. The Labrador Current, as usual, 

 was flowing along the eastern edge of the Grand 

 Banks during the first part of the first cruise 

 (figure 21). The dynamic trough east of the 

 Labrador Current is wider than normal and very 

 flat. The steep gradient across the North Atlantic 

 Current can be seen in the southeast portion of 

 the survey area. 



The survey conducted during the second part 

 of the first cruise (figure 22), was an abbrevia- 

 tion of the survey conducted earlier in April. It 

 appears that no significant changes occurred to 

 the dynamic topography between these two sur- 

 veys. The counterclockwise flow, which normally 

 appears around Flemish Cap, was located below 

 Flemish Cap during the second survey. 



By the first half of the second cruise (figure 

 23), the dynamic topography had returned to 

 nearly normal conditions and the gradients in the 

 North Atlantic Current meander were not as 

 steep as expected. Similar conditions were also 

 observed during the second half of the second 

 cruise (figure 24). 



Iceberg tagging and tracking experiments were 

 conducted twice (Aril 20—24 and June 20—29) 

 during the Ice Patrol Season. The first experi- 

 ment proved to be of only limited value primar- 

 ily due to severe weather conditions. The second 

 study was more successful with six icebergs being 

 tracked; one of these icebergs was tracked for 

 four days and nearly 100 miles. 



A deep subsurface current meter array, which 

 had been set at 44° 42.6'U, 48° 58.0'W from CGC 

 EDISTO (WAGB-284) on February 11, 1974, 

 was recovered on April 8. That array was re- 

 placed the same day by a similar array which was 

 recovered on June 12. On June 13, a third array 

 was set at 44° 40'N, 48° 59'W. Plans have been 

 made to recover this array during the 1975 Ice 

 Patrol Season. All these current meters were set 

 to test the validity of using the 1000 decibar sur- 

 face as a reference level for dynamic calculations. 



More complete analysis of the STD data and 

 results of the research projects will be reported 

 in the U.S.C.G. Oceanographic Report Series 

 (CG 373). 



