THE WATER COLUMN 



The cluster of icebergs was in a 

 tongue of tfie Labrador Current as 

 evidenced from botfi sea surface 

 temperatures and the XBT profiles 

 (see Figure E-4). The tongue of 

 Labrador water had a cold (-1°C) 

 core at 60m, below a shallow 

 thermocline at 40m. Surface 

 temperatures ranged between 3.4 

 and 7.6°C. Temperatures of -1°C 

 or colder, that would preclude melt 

 (White et al, 1980), existed from 

 40m to 90m in the eastern portion 

 of the study area, and from 40m to 

 1 60m in the western portion. XBT 

 casts taken in the vicinity (within 

 28km) and within 6 hours of the 

 OOOOZ interpolated iceberg's 

 positions were used to estimate 

 the average heat available in the 

 water column to melt the iceberg. 

 When there was no XBT cast near 

 a particular iceberg within six hours 

 of OOOOZ, the temperature informa- 

 tion was calculated by linearly 

 interpolating in time. The water 

 temperature, relative to -1°C, was 

 averaged over 10m intervals over 

 the estimated draft of the iceberg. 

 Iceberg draft was estimated as 

 3.95 times the average sail height 

 observed during the study (Robe, 

 1975). 



118 



From analyzing temperature 

 profiles taken about four days 

 apart, this tongue of the Labrador 

 Current had advected south 74km. 

 The advection of the cold core at 

 60m agrees well with the deep- 

 drogued drifter. Its drift indicated 

 a predominantly southerly flow 

 (186°T at 21cm/sec) for 4 days 

 (from 15 June/OOOOZ through 

 19 June/OOOOZ), then an easterly 

 flow (1 12°T at 12cm/sec) for the 

 last 1 .5 days of drift. The west- 

 ward displacement of the thermal 

 field above the thermocline agreed 

 well with the shallow-drogued 

 drifter. From 15 June/OOOOZ to 17 

 June/1 600Z the drift was 193°T at 

 27cm/sec. From 17 June/1 600Z 

 until recovered on 20 June/1 243Z, 

 the drifter showed a steady 

 deceleration, averaging 206°T at 

 9cm/sec. Figure E-5 summarizes 

 the drifts of all icebergs and 

 drifters and shows the XBT 

 transects used to describe the 

 thermal characteristics of the 

 water column. All of the drifters 

 recorded sea temperature at 1m 

 depth between 3 and 5°C, which 

 agreed well with the bucket 

 thermometer measurements. 



DETERIORATION MODEL 

 EVALUATION CRITERIA 



The deterioration processes were 

 evaluated based on observations 

 compiled for the four medium, non- 

 tabular icebergs #747, #734, #785, 

 and #787 which had estimated 

 drafts from 98 to 1 46m. This 

 cluster was studied for 5 days. 



Based on in situ temperature, 

 icebergs #747 and #787 had 

 insignificant melt from convective 

 processes below 40m depth. 

 Therefore the buoyant and forced 

 heat convection contributions 

 below 40m depth were calculated 

 and evaluated for only icebergs 

 #784 and #785. 



