Line P Program

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An Update of the Statistics of Hydrographic/CTD Data taken at Ocean Station P (May 1956-September 1990)

by
S. Tabata and W.E. Weichselbaumer
Institute of Ocean Sciences, Department of Fisheries and Oceans, Sidney, B.C. V8L 4B2

Introduction
In recent years the importance of the oceans to global climatic changes has been given much attention and consequently the study of the ocean climatology has received major consideration in global climate studies. Interest in large-scale oceanographic events and general ocean circulation is more widespread than ever before. This shift in interest has necessitated the requirement for examining the ocean within a greater time frame. However, long ocean time series data needed for such a study are not readily available. The sets of data from Station P and Line P along with those from Station M for the Norwegian Sea, are a few of the time series data of sufficient quality and of suitable length to be useful in examining the variability of the oceans, if only for over a period of a few decades. Ocean Station P (50 00°N, 145 00°W, depth 4220 metres) was operated as an ocean weather station from 19 December, 1949 through 20 June, 1981. The first oceanographic observation there, in the form of a bathythermograph cast, was made on 19 December, 1949 (Leipper et al., 1954). The oceanographic program at Station P and Line P has undergone many changes since then as can be seen from a summary as shown in Table 1. In view of the importance of long ocean time series the observations at Station P and Line P were continued, although at much less frequent intervals than in the past, after the withdrawal of the weatherships in June 1981. The observations are carried out mainly by the staff of the Institute of Ocean Sciences using, to a large measure, their own ships. The present ship schedule permits only 3 to 4 cruises there per year. The statistics of representative oceanographic data for Station P and Line P, based on oceanographic observations made during August 1956 through June 1981 by the Canadian weatherships, have been published previously (Tabata and Peart,1985a, 1985b, 1986). Since then observations have continued there to this day (October 1991). The present report comprises the statistics based on data collected during May 1956 through September 1990. It is to be noted that the staff of the University of Washington made observations at Station P during May, June and July 1956 (Scripps Institution of Oceanography of the University of California, 1963). These data have also been utilised in the preparation of the statistics.

Table 1 A summary of Oceanographic observations at Station P and Line P
December 1949 Occupation of Station P began. Station operated by U.S. Weather Bureau with vessels manned by U.S. Coast Guard. Bathythermograph casts started immediately and continued until November 1950.
December 1950 Occupation of Station P by Canadian weathership commenced.
July 1952 Twice-daily bathythermograph casts initiated and continued to June 1981.
July 1956 Oceanographic observations including hydrographic casts to maximum depth of 1200 metres (m), plankton hauls, etc. commenced. They were scheduled for one of the two weatherships and provide data through alternate six-week periods. The maximum was increased to 2000 m later but only in a few instances did the cast reach 2000 m during 1957 through 1959. However, one cast to 3000 m was recorded in 1957. Note that University of Washington obtained hydrographic casts to maximum depth of approximately 3500 m, 2500 m and 1000 m in May, June and July, respectively.
April 1959 Hydrographic casts at 5 stations along Line P initiated. However, a line of stations here was occupied by CNAV Oshawa in January 1959.
March 1960 Maximum depth of hydrographic casts at Station P increased to 4200 m.
May 1960 Positions of Line P stations altered
February 1962 Number of stations along Line P increased to maximum of 10.
August 1964 Two more stations added to Line P.
April 1967 New weathership, CCGS Vancouver, replaced CCGS St. Catharines.
October 1967 Second, new weathership, CCGS Quadra, replaced CCGS Stonetown.
January 1969 Both weatherships commenced regular oceanographic observations.
April 1969 Bissett-Berman STD used for the first time. From this time onward both STD (or CTD), as well as hydrographic casts, were made.
April-October 1974 CSS Parizeau replaced CCGS Quadra while the latter was occupied with GATE program.
August 1974 Guildline CTD introduced to make observations.
August 1978 Plessey STD (previously called Bissett-Berman STD) used for the last time.
June 1981 Final series of observations made by the weathership (CCGS Quadra).
August 1981 From this month onward observations continued at Station P and Line P at intervals of 3-6 times per year. Number of stations along the line doubled.
(the following entries were added after publication of the original report)
October 1991 Line P /Station P sampling become part of WOCE (PR6) beginning with IOS cruise ID 91-15
September 1992 Line P /Station P sampling become part of the Canadian JGOFS program (Phase I) beginning with IOS cruise ID 92-15.
May 1994 Final Line P /Station P sampling as part of the Canadian JGOFS program (Phase I), ending with IOS cruise ID 94-02.
February 1995 Line P /Station P sampling become part of the Canadian JGOFS program (Phase II) beginning with IOS cruise ID 95-01.
February 1997 Final Line P /Station P sampling as part of WOCE (PR6) program, ending with IOS cruise ID 97-02.
June 1997 Final Line P /Station P sampling as part of the Canadian JGOFS program (Phase II), ending with IOS cruise ID 97-11.

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