FISHERY BULLETIN: VOL. 71. NO. 1 



Turner Fluorometer/ Water samples from the 

 same casts were preserved with neutral Forma- 

 lin for subsequent phytoplankton enumeration. 

 Additional measurements have routinely in- 

 cluded temperature and salinity, determined 

 with an STD; oxygen, determined by the Win- 

 kler procedure; and phosphate, silicate, nitrate, 

 and nitrite, measured with the spectrophotom- 

 eter or the autoanalyzer (Strickland and Par- 

 sons, 1968). On CLIMAX II and ARIES III 

 ammonia was assayed (Solorzano, 1968). On 

 stations occupied at noon, the transparency of 

 the water was measured with a secchi disk and 

 the compensation depth was estimated by mul- 

 tiplying the terminal depth by three. A wide 

 variety of zooplankton samples were collected 

 on all expeditions. 



On the expeditions CLIMAX I, CLIMAX II, 

 and ARIES III, observations were concentrated 

 in two areas of the North and South Pacific, 

 near the axes of the Central Pacific Gyres. In 

 these regions, in addition to the above measure- 

 ments, productivity was routinely measured by 

 the uptake of C-14 by samples incubated on deck 

 in simulated in situ incubators (Owen and Zeit- 

 zschel, 1970) and less frequently by samples in- 

 cubated in situ (Steeman Nielsen, 1952). Pen- 

 etration of light into the ocean was measured 

 with a submarine photometer (Austin and Lou- 

 dermilk, 1968). Coincident secchi disk determi- 

 nations tended to overestimate the depth of 1% 

 light, though the agreement was usually within 

 6 m. A submersible pump with a deck mounted 

 filtering system was used to obtain stratified 

 samples for determination of biomass (dry 

 weight) of three size categories of zooplankton 

 (333 fx and greater, 332-103 /jl, and 102-35 /i). 

 The same pump supplied water to the fluorom- 

 eter, equipped with a flow-through door, and to 

 the autoanalyzer for continuous vertical profiles 

 of chlorophyll and nutrients (Beers, Stewart, 

 and Strickland, 1967). 



In September 1968 (CLIMAX I Expedition), 

 a pair of parachute drogues, set at 10 m depth, 

 were released at lat 27°N, long 155°W, and fol- 

 lowed for 10 days, during which time they moved 



' Reference to trade names does not imply endorse- 

 ment by the National Marine Fisheries Service, NOAA. 



northwest approximately 150 miles. Physical, 

 chemical, and biological properties were sampled 

 continuously on a 24-hr schedule. In September- 

 October 1969 (CLIMAX II Expedition), a grid 

 of ten 24-hr stations was occupied along long 

 155°W between lat 27°10' and 28°30'N, and a 

 grid of six 24-hr stations was occupied along 

 the same meridian between lat 24°40' and 

 25°20'S. This latter pattern was repeated in 

 March 1971 (ARIES III Expedition) . The sam- 

 pling routine was similar on each of these ex- 

 peditions. Each 24-hr station included four 

 casts for nutrients and chlorophyll, day and night 

 samples for biomass of micro- and macrozoo- 

 plankton, and a simulated in situ productivity 

 experiment. In 1969 and 1971 a single in situ 

 productivity experiment followed the routine sta- 

 tion plan. 



In addition to data collected on S.I.O. (Scripps 

 Institution of Oceanography) expeditions, we 

 have available data from the California Current 

 collected by institutions participating in the 

 CalCOFI (California Cooperative Oceanic Fish- 

 eries Investigations) program. We have made 

 use of data from station 100.80 which is located 

 near the western edge of the California Current. 



GEOGRAPHICAL DISTRIBUTION 



Chlorophyll data collected on several expedi- 

 tions have been combined and contoured in Fig- 

 ure 2. It is clear from these that a subsurface 

 layer of high chlorophyll concentration is present 

 across vast areas of the Pacific Ocean during 

 many months of the year. South of lat 46°N, 

 the maximum concentrations of chlorophyll are 

 frequently observed at greater depths than the 

 estimated 1% light level. The depth of the 

 maximum along the meridianal transects shows 

 no relationship with either temperature, salinity, 

 or density. 



The chlorophyll maximum layer shoals near 

 land, and in regions of general upwelling such 

 as the North Subarctic Gyre and the Equatorial 

 belt. It deepens near the axes of the Central 

 Pacific Gyres. The meridianal continuity of the 

 layer is especially remarkable considering that 

 it passes through three major epipelagic envi- 

 ronments: the Subarctic, where it is likely to 



44 



