OPERATIONS he water, sediments, marine life, and air in the EPG. The positions of observations are shown in Figure 2.1. The Horizon was equipped with devices for sampling, storage, and assay of marine specimens. Water samples were collected from the surface, near bottom, and inter- mediate depths with 1-liter Nansen bottles at thirty stations. Duplicate vertical water sample profiles were taken for radioassay and for salinity determinations. Surface water samples of 5 liters were obtained in the open ocean and lagoons. Zooplankton were collected at seventeen stations with a standard 1-meter diameter a eee During the months of Apri] and early May 1956 the research vessel Horizon undertook a cruise throughout the EPG in order to measure the amounts of radioactivity associated with the oceanic environment. A study was made of the radioactivity of the Oe ee 1.4 27.3 « 3.1 (8/gm K)/sec K® specific gammaactivity 3.24 ¢ 1.5 (y/gm K)/sec 194 + 9 (y/min)/gm K Potassium concentration in sea water 380 mg/kg 74 (y/min)/lter 640 (8/min)liter K® specific gamma activity K® concentration in sea water K* concentration in sea water K*®concentration in sea water 325 puc/liter Average uranium concentration in Pacific water Average radium concentration in Pacific water 2.82 x 107 © gm/liter 3.2 2074 gm/liter Radium concentration in clay sediments 10 to 20 x 107 gm/gm dry clay Rb" concentration in sea water 6 puc/liter (no gamma) Activity ratio radium/uranium Activity ratio radium/uranium 0.16 in sea water 6.4 in pelagic sediments 1.5 to 2.5 x 107® gm/gm dry clay Uranium in deep sea sediments 5x 107" gm/gm dry clay Thorium in deep sea sediments Thorium in manganese nodules 24 to 124 ppm (Reference 8) Ten vertical phytoplankton net hauls were taken in the open ocean and in Bikini and Ailinginae Lagoons. The net used was a 17-cm diameter, No. 20, phytoplankton net filter, having a mesh size of 70 yw andfiltering approximately 1,500 liters of water per haul. No identification of the contents was attempted and no means were available to separate inorganic debris from living organisms. Three samples of the deep-sea fauna were obtained in the area, using a 10-foot Isaacs-Kidd midwater trawl as the sampling device. The depths sampled ranged from 730 to 2,560 meters. The trawl fished continuously during the time required for lower- ing and retrieving, therefore it is not possible to state with certainty at what depth any individual was captured. However, as the trawl remained at the towing depth for 10 16 PY K“ specific negatron activity rn 0.1174 pet 1.28 x 10° years kK“ isotopic abundance kK“ half life “A CONCENTRATIONS OF SOME NATURAL RADIOISOTOPES IN THE OCEAN oe en TABLE 1.2 OM ee Rokre in 15 minutes time while the vessel proceeded at about 2 knots. The main portion of the net was made of Nitex cloth, 60 mesh per inch, and the cod end, of the same material, 90 mesh per inch. The net was designed to sample organisms larger than 0.5 mm. A er eee ed a ee te nylon plankton net towing obliquely from approximately 280 meters depth to the surface