OCEANOGRAPHIC CONDITIONS— 1977 



The International Ice Patrol oceanographic 

 mission in 1977 consisted of two USCGC EVER- 

 GEEEN (WAGO 295) cruises to the Grand 

 Banks of Newfoundland from 1 April to 1 May 

 and 23 May to 28 June 1977. These provided 

 sea current data from hydrographic surveys for 

 the computer prediction of iceberg drift. Satel- 

 lite-tracked drogued buoys (BTT's) were used 

 for the second consecutive year to verify and 

 improve operational iceberg drift by making 

 Lagrangian measurements of sea current to com- 

 pare with estimates obtained by the hydrographic 

 method. As an additional mission of the IIP- 

 2-77 cruise, iceberg and drogued buoy drift data 

 were collected aboard the EVERGREEN for an 

 on-going research project with the objective of 

 improving the iceberg drift model presently used 

 by the International Ice Patrol. Furthermore, a 

 researcher from the University of "Washington, 

 Seattle, Washington conducted an investigation 

 examining the physical aspects of iceberg de- 

 terioration. 



The dynamic topography surveys were accom- 

 plished using a Plessey Environmental Systems. 

 Inc., Conductivity/Temperature/Depth (C/T/ 

 D), Model 9040, Environmental Profiling Sys- 

 tem. The data were recorded and processed on 

 the Wang Laboratories, Inc. Model 600-14-TP 

 Programmable Calculator, the Wang Model 629 

 Dual Tape Drive, and the Wang Counting Inter- 

 face (Electronics Lab, USCG Station Alexandria, 

 Virginia). 



Corrections were applied to the C/T/D tem- 

 perature and salinity data from measurements 

 made by Nansen bottles with deep-sea reversing 

 thermometers. Salinity was determined from 

 Samples analyzed on the Guildline Instruments, 

 Inc. (Larchmont, N.Y.) Autosal. The tempera- 

 ture quality control values were applied as a 

 constant correction with depth from an average 

 difference between C/T/D System and Nansen 

 bottle for each oceanographic section. The salin- 

 ity quality control differences were computed for 

 the surface and the bottom, averaged for each 



oceanographic section. Temperature quality con- 

 trol corrections ranged from +.02°C to + .03°C 

 and salinity corrections ranged from — .07°/ oo to 

 + .05%o. 



Operations during the 1977 season included 

 deployment and recovery of two current meter 

 moorings in the Ice Patrol area. One mooring 

 was located in the Labrador Current at 43°47'N, 

 49°00'W in 493m of water. The second was at 

 43°20'N, 47°46'W in 3560m of water near the 

 western edge of the North Atlantic Current. 

 The moorings were of 3 / 16 " coated wire and each 

 included two vector averaging current meters at 

 approximately 100m and 400m depth. The deep 

 mooring also included a film recording depth 

 gauge above the upper current meter. 



The current meter mooring design and the 

 method of deployment were similar to that de- 

 scribed in the Report of the International Ice 

 Patrol Service in the North Atlantic Ocean, 

 Season of 1976 (CG-188-31, Bulletin 62). The 

 major differences in the mooring were the use of 

 % 6 " plastic-coated wire for the entire mooring 

 line except the bottom 60 meters leading to the 

 singer, which consisted of %" plaited nylon. A 

 single 500 lb buoyant float replaced the two 300 

 lb buoyant spheres used for the 1976 moorings. 



Deployment of the moorings occurred on 7-8 

 April during the first cruise and was accomplished 

 by an anchor last techniques from the fantail of 

 the EVERGREEN using a winch system de- 

 signed for mooring operations. Recovery of the 

 moorings took place on 24 June during the second 

 cruise. The acoustic release mechanisms were 

 interrogated and commanded to release. The 

 transmitters on the recovery floats were located 

 by an ADF onboard the ship. A problem was 

 encountered in the recovery of the deep mooring 

 where the acoustic release failed to respond to 

 repeated interrogation, although it ultimately 

 did release successfully. 



The current meters on the shallow mooring 

 provided good records for the entire deployment 

 period, yielding 77 days of data from each meter. 



22 



