PHYSICAL OCEANOGRAPHIC, BIOLOGICAL, AND CHEMICAL DATA 

 SOUTH ATLANTIC COAST OF THE UNITED STATES 

 THEODORE N. GILL CRUISE 3 



This is the third in a series of reports 

 presenting basic data from cruises of the 

 Theodore N. Gill in waters off the South Atlan- 

 tic Coast of the U . S . 



Background of the investigations, objec- 

 tives, procedures on station, and chemical, 

 biological, and oceanographic methods and 

 procedures were presented in the report for 

 Cruise l^Ander sop, Gehringer; and Cohen, 1956). 

 The basic station plan is shown in figure 1. 



BIOLOGICAL METHODS AND PROCEDURES 

 Plankton Tows 



On Cruises 1 and 2 the plankton tows on 

 station were- made with a standard half -meter 

 No . 1 silk net (Anderson, Gehringer, and Cohen, 

 1956). 



Beginning with Cruise 3, plankton tows 

 on station were taken with an all-metal half- 

 meter sampler (fig. 2) designated as Gulf III 

 (Arnold and Gehringer 1952), except during ad- 

 verse sea conditions --when the standard half- 

 meter silk net was used. The Gulf III sampler 

 was towed obliquely to depths of 70 meters or 

 less in the same manner as the silk net was 

 towed on Cruises 1 and 2 except that towing 

 speed was increased to 5 to 6 knots cind main- 

 tained regardless of the angle of towing cable . 

 When it was necessary to use the silk net - - 

 during periods of adverse sea conditions which 

 made towing the Gulf III unsafe --it was towed at 

 a constant speed of 1 to 2 knots with no atcempt 

 to maintain a constant wire angle . In towing 

 either the Gulf 111 or the silk net, additional 

 cable was used to compensate for greater wire 

 angles (wire angles recorded each minute as 

 was done on Cruises 1 and 2). 



Several improvements in the design of 

 the Gulf HI sampler were accomplished; the 

 towing cable was attached by a chain bridle (fig. 

 2); a shock absorber, modified from a commer* 

 cial design, was placed between the sampler and 



towing cable to reduce cable vibration and absorb 

 surges when towing or handling; and the filtering 

 unit (monel wire cloth, 50 mesh x .008", appro* - 

 imately equal to No. 1 silk) was fitted at the 

 after end with a ring stand to permit standing the 

 unit while washing plankton into the terminal 

 bucket or cup. Water volumes strained were 

 determined by the flow meter in the after meter 

 housing. 



Initiated on Cruise 3 also was use of a 

 high-speed plankton sampler designated as Gulf lA 

 (Arnold and Gehringer 1952) which was towed at 

 the surface between stations at normal cruising 

 speed of about 8 to 10 knots. The original de- 

 sign was modified by the addition of a heavy brass 

 ring supported by struts over the exposed pwrtion 

 of the flow meter in the after end of the sampler 

 to protect the meter during handling. Wet vol- 

 umes of plankton were determined in the same 

 manner as they were for half-meter net samples. 

 In quantitative determination of major organisms 

 the sample was adjusted to 100 ml., two 10-ml. 

 portions examined, and total numbers and num- 

 bers-per-M^ determined accordingly. 



The Gulf II continuous plankton sampler 

 was operated over most of the cruise route and 

 the samples processed as on previous cruises. 



NARRATIVE ACCOUNT OF CRUISE 3 



The Theodore N. Gill departed from 

 Brunswick, Georgia, on July 15, 1953, proceed- 

 ing to special station 5 which was reached and 

 occupied on July 16. Special stations 6, 7, and 

 8 were worked on July 17 and 18, and the vessel 

 arrived at standard station on the 18th. Approx- 

 imately 50 hours were spent on the standard 

 station during which time 15 oceanographic casts 

 were made- -all to 1,000 meters. Bathythermo- 

 graph observations, routine meteorological 

 observations, and special plankton tows for deep 

 scattering layer smd other studies were also 

 accomplished. 



