ORGANIZATION OF THE ATLAS
Arrangement of Volumes
          The EASTROPAC Atlas consists of 11 volumes. There are 10 volumes containing data from the principal participating ships plus Oceanographer and 1 volume containing data from the Latin American cooperating ships and other ships of opportunity. The first 10 volumes are arranged chronologically and by two general subject headings; 5 volumes contain physical oceanography and meteorology, and 5 volumes contain biological properties and nutrient chemistry. The following table indicates the arrangement. It should be noted that charts of horizontal distribution of properties which appear in the first 10 volumes do contain data from the Latin American ships and ships of opportunity as well as principal ship data. It is the vertical sections based on Latin American and ships of opportunity data which are found in volume 11.

Volume number Contents Ships and
cruise period(s)		 Dates
1
 Physical properties
and meteorology		 Principal ships –
First survey cruise
(10-series)		 February-
March 1967
2
 Biological properties
and nutrient chemistry
3
 Physical properties
and meteorology		 Principal ships –
First and second
monitor cruises
(20, 30-series)		 April-May,
June-July
1967
4
 Biological properties
and nutrient chemistry
5
 Physical properties
and meteorology		 Principal ships –
Second survey cruise
(40-series)		 August-
September
1967
6
 Biological properties
and nutrient chemistry
7
 Physical properties
and meteorology		 Principal ships
and Oceanographer –
Third and fourth
monitor cruises
(50, 60-series)		 October-
November 1967,
December 1967 –
January 1968
8
 Biological properties
and nutrient chemistry
9
 Physical properties
and meteorology		 Principal ships –
Third survey cruise
(70-series)		 February-
March 1968
10
 Biological properties
and nutrient chemistry
11
 All properties Latin American
cooperating ships and
ships of opportunity-
All cruises		 February 1967 –
March 1968

  
Color of Pages
           In order to assist users to find the pages they want, pages showing different groups of properties have been printed on differently colored paper [in the original atlases. These colors have not been reproduced for the on-line figures].

Figure Designation System
           Although the atlas will initially be published in volumes arranged chronologically, as explained above, looseleaf binding permits users to rearrange the pages to suit their own needs. It was necessary to devise a figure designation system compatible with this flexibility. The system used consists of a series of numbers and letters or symbols which indicate the cruise or cruise period, the property represented, and whether it is a vertical section or horizontal distribution. In the latter case the designator further indicates whether the property is shown at a constant depth (phosphate-phosphorus at 10 m), integrated over a layer (chlorophyll-a integrated over the euphotic layer), on a surface of constant thermosteric anomaly (salinity on the 300 cl/t surface), or whether the contours represent numbers collected or observed per station, per day, etc. (total Auxis larvae taken in 1-m oblique hauls). Sample figure designators and a complete list of abbreviations used are shown below. It should be noted that each figure bears a caption and each vertical section is also accompanied by a small index map to indicate its location so that the reader does not have to rely on the figure designator alone for a description of what the figure represents.

The following sample designators will illustrate the system:
  12-T-v1 – First vertical section from cruise 12 showing distribution of tem-perature.
  45-P-v2 – Second vertical section from cruise 45 showing distribution of phosphate-phosphorous.
The vertical sections are assigned consecutive numbers, v1, v2, etc., within each cruise which follow the chronological order in which the ship ran the sections.
  40-N03-10 – Distribution of nitrate-nitrogen at 10-m during second survey cruise (40-series).
  20-δ300-z – Depth of 300 cl./t. thermosteric anomaly surface during the first monitor period.
  30-O2-δ160 – Distribution of oxygen on the 160 cl/t thermosteric anomaly surface during second monitor period.
  50-Ch-ei – Distribution of chlorophyll-a integrated over the euphotic layer during third monitor period.
  70-ZhN – Standing stock of zooplankton taken in 50-cm net hauls at night during third survey cruise period.

Table 4 shows all the abbreviations used in figure designators.
 
Remarks Concerning the Charts
          The editorial policy of the atlas allowed each contributor to decide whether or not he wanted to use shading to enhance his presentation. A uniform shading scheme was adopted and was followed on all charts where shading was used. Shading scales are not shown on most charts in the belief that the combination of shading and contours is self-explanatory. In cases where it was not considered so, a shading scale is used or an explanatory remark placed in the caption.
          Since the atlas is in effect serving as a data report for the EASTROPAC field work, the editors decided that the charts should be as objective as possible. To this end, an effort was made not to extend contours or shading across areas where there were no data even though the trend of the truncated contours and their relation to other contours in the vicinity might indicate a logical extension across such an area. The principal lines of observations on most cruises ran north-south; in the case of the lines run on all monitor cruises and most survey cruises, these lines were 7° of longitude, or less, apart. For horizontal distributions it was decided not to extend contours or shading between north-south lines which were more than 7° of longitude apart. It was difficult to make definite rules for other lines of observations, and decisions where to end contours and shading in such areas were made by the contributors and the editor. An effort was also made not to extend the shading up to the coastline. EASTROPAC was a deepwater project, and the EASTROPAC Manual of Observations (Staff, EASTROPAC, 1967) specified that when leaving the coast, observations should not be begun until a water depth of at least 500 m. was reached. There were some exceptions made to this rule, but in general, shallow nearshore waters were not sampled.
          Vertical sections extending to a depth greater than 300 m. have been divided into two panels, with the depth scale in the upper panel twice that of the lower panel. The sections showing geostrophic velocity components are an exception. They consist of one panel extending to 500 m, with no change of depth scale. Since the original versions of the vertical sections were drawn with a horizontal scale of 3 cm. equal to 1° of latitude or 60 nautical miles (111.2 km) and a vertical scale of 1 cm equals 10-m depth on the upper panel or 1 cm equals 20-m depth on the lower panel, the vertical exaggeration of the upper panel is 3707 times and that of the lower panel 1853 times. Tick marks showing the location of all stations used in preparing the section are shown in the space between the top and bottom panels. In addition, location marks and numbers of all stations which were sampled to 1000 m or deeper appear along the bottom of the section. On sections based on Nansen or Texan cast observations (oxygen, nutrient chemicals, phyto-plankton) the station numbers of all stations used in the section also appear in the space between panels. Because STD observations were made more often than Nansen casts in some areas, it was found to be impossible to show all the STD station numbers in the space between panels. Therefore, sections of temperature, salinity, etc., do not have this latter feature. If a user wants to identify a particular station in one of the STD sections, it is believed that the information on the figure plus the listings of station positions and observations given in the previously cited Information Papers will enable him to do so. On sections which extend only to 500 m, all station numbers appear in the space between panels.
          Vertical sections of temperature, salinity, thermosteric anomaly, and geostrophic velocity components from all principal cruises as well as Oceanographer are based on STD observations. Since the STD is a continuous sampling instrument, no sampling depths at each station need be shown. Sections of temperature, salinity, etc. from ships not equipped with an STD as well as sections of oxygen, nutrient chemicals, and phytoplankton properties are based on data collected with Nansen or lexan bottles. On these sections dots indicate the sampling depths in the conventional manner. On some sections the deepest sampling depth at each station is indicated by an inverted T symbol superimposed on the dot.
          On STD sections some small, enclosed contours are not labeled. This should cause no confusion as generally such contours have the same value as the nearest continuous contour. Also, some of these contours are accented or dashed indicating they have the same value as the nearest continuous contour similarly marked.
          On north-south sections the station location marks are positioned by latitude, and on the few east-west sections they are positioned by longitude. On sections which run in a direction which is neither north-south nor east-west, or close to those directions, both latitude and longitude scales are shown. Since lines of oceanographic stations rarely lie in a straight line, a combination graphical-computational method was used to project the position of each station onto a base line drawn between the first and last station of the section. Thus, the station location marks indicate the distance along the base line between the projected station positions, and the latitude and longitude marks appear where the parallels and meridians cross the base line.
          As was explained above, the vertical sections have been numbered consecutively (v1, v2, etc.) within each cruise in the chronological order in which the ship ran the sections. Section v1 of cruise 11, for instance, represents the same geographical location regardless of the property represented. On some sections of some cruises, there were STD observations but no Nansen or Lexan bottle casts. In these cases there are sections showing temperature, salinity, thermosteric anomaly etc., but no corresponding sections of oxygen, nutrient chemicals, or phytoplankton properties.