PROGRAM OF OBSERVATIONS
program of observations followed during principal EASTROPAC cruises was
based on three types of stations, designated A, B, and C, which were
arranged by the time of day. At A stations there was a Nansen bottle
cast to 500 m, a lowering of the salinity-temperature-depth recorder
(STD) to 500 m, a lexan bottle cast for primary production and plant
pigment samples, an oblique plankton haul from 200 m to the surface
using paired 1-m and 50-cm nets along with a simultaneous surface haul
with a 1-m net and a micronekton haul from 200 m to the surface using a
5-ft-square net. A stations were made twice daily at approximately 0000
and 1200 local time. B stations were taken at approximately 0400 and
1600 local time and consisted of a 1000-m Nansen cast, 1000-m STD
lowering, and oblique plankton haul and surface haul as on A stations.
The original program of observations called for a 1000-m Nansen and STD
cast at A stations and 500-m casts of both types at B stations. This
system was changed in the course of the project in order to make the
time on station at A and B stations more equal. On one monitor cruise,
cruise 30, a 500-m Nansen cast was paired with a 1000-m STD cast on A
stations and vice versa on B stations. There were four C stations each
day, scheduled approximately at mid-time between departure from an A
station and arrival at a following B station or vice versa. C stations
usually consisted of expendable bathythermograph (XBT) drops underway
although sometimes STD lowerings to 300 m or 500 m were substituted.
This made the sequence of stations for a 12-hour period starting at
midnight as follows: A (0000) -C-B-C-A (1200). On principal cruises all
stations were numbered consecutively regardless of type. The two-digit
cruise number described previously was combined with a three-digit
consecutive number to form a five-digit number that uniquely identifies
each station; thus station 12.025 indicates the 25th consecutive
station of Jordan cruise 12.
There were modifications to this routine of observations, and other types of observations were made which also contributed information to this atlas. Within 5° of latitude on each side of the equator most ships ran the so-called "equatorial detail" pattern where additional C stations, either XBT or shallow STD lowerings, were run in between the stations mentioned above. These made a 12-hour sequence : A-C-C-C-B-C-C-C-A. Bird observations by observers from the Smithsonian Institution were made on cruises 11, 12, 13, 30, 45, 46, 50, 75, and 76. The observers were usually stationed on the ship's bow or flying bridge during daylight hours. Equipped with binoculars and cameras, they attempted to identify and count all birds seen. A few birds were collected for study specimens. In addition, they made valuable observations of fish schools and marine mammals. Weather observers from the Weather Bureau, ESSA, were aboard during cruises 13, 20, 30, 47, and 77, and on Oceanographer, where they made twice daily radio-sonde observations to measure upper air conditions. Table 2 is a summary of observations made on EASTROPAC cruises.
TABLE 2. - Summary of types of observations made on EASTROPAC cruises.
The information presented in this atlas is based primarily on the observations described above. There were a number of other measurements and observations made during EASTROPAC. Some were made on several cruises and others only on one. Some of the former are described below. Continuous recordings of bottom depths were made on most of the major cruises. In fact, the north-south portions of the monitor cruise tracks were shifted each time a few miles either to the east or west of the base meridians of 98° W, 105° W, 112° W, 119° W, so as to provide different bathymetric coverage. Table 3 shows the longitudes covered during monitor cruises. Sounding information from San Diego-based EASTROPAC ships has been turned over to the Department of Earth Sciences, SIO, for analysis. Although the data shown in this atlas extended only to 1000-m depth, there were 163 stations occupied during the project where Nansen casts deeper than 1000 m were made. In some cases these casts extended to within 100 m of the bottom. There are tentative plans for these deep-station data to be published in a separate data report, but in any case, they will be sent to the National Oceanographic Data Center. The Scripps Institution of Oceanography provided two instrument platforms (buoys) to be moored in the study area during the period of EASTROPAC. These buoys were set out during the first survey cruise at two locations on longitude 119° W in the Equatorial Counter Current, at approximately 6° N and 9.5° N. They were equipped to measure and record subsurface temperatures at seven depths as well as surface water temperature and meteorological properties. The buoys were visited during each subsequent voyage to service the equipment. The buoy at 6° N was not found in August 1967, during cruise 45, apparently having been swept away by bad weather. The one at 9.5° N was located in October on cruise 50, but all sensors except one were inoperative so the instrument package was removed from the buoy. The buoy itself had disappeared when the area was searched in December during cruise 60. A preliminary data report issued by SIO (Evans, Schwartzlose, and Isaacs, 1968) showed that a maximum of 3307 hours of observations was obtained from the 6° N buoy and 2369 hours from the one at 9.5° N.
Details of the observations made during the EASTROPAC cruises will be found in the various EASTROPAC Information Papers (Wooster, 1966a, 1966b, 1966c; Wooster and Love, 1967; Longhurst and Love, 1967; Longhurst, 1967a, 1967b, 1968, 1969a, 1969b; Love, 1969). In particular, Numbers 6, 8, and 9 of this series contain lists of stations occupied on all cruises showing date, time, position, and observations made. It is intended that most of the information collected, whether or not it appears in the atlas, will be made the subject of detailed research reports by the various investigators concerned.
Some of the Latin American cooperating ships and ships of opportunity followed the EASTROPAC routine of observations as well as their equipment, personnel, and time schedules would permit, while others followed their own routines. During the EASTROPAC portion of the Oceanographer voyage the prescribed routine was followed. Plans for the Unanue and Yelcho cruises called for the three types of stations previously mentioned and also for station spacing based on time of day. These ships were not equipped with an STD, however, nor were they able to make all the specified plankton or micronekton collections. Charles H. Davis ran the extra detail requested in equatorial regions during her transit on 85° W.
TABLE 3. Longitudes covered on north-south lines during EASTROPAC monitor cruises.