The first GEOSECS field work in the Atlantic Ocean, and the second test and intercalibration exercise during the GEOSECS program, took place from 25 August to 2 September 1970. It was designated as KNORR 9, the ninth expedition of R/V KNORR, operated by Woods Hole Oceanographic Institution. (The first GEOSECS effort at sea occurred in September 1969 aboard R/V MELVILLE. The shipboard results of that and other test and/or intercalibration cruises to the location off Baja California known as "GEOSECS I" are presented in Volume 3 of the GEOSECS Atlas Series, hdl:10013/epic.42895.d001). During a seven day period, 41 casts were made at or near the position 35°47' N, 68°00' W, named "GEOSECS II" to a depth of 4980 to 5080 meters.