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OCADSAccess DataNDP-082NDP-082 - Brief Cruise Summary

Brief Cruise Summary

For the section AR24 (cruise 147-2), the TCO2 and TALK systems were placed on board and set up on the R/V Knorr in Woods Hole, Massachusetts, during the period October 21-24, 1996, by the University of Miami TALK and the UH/BNL TCO2 measurement groups. The systems were successfully tested, and the Knorr departed Woods Hole on October 24, for the Azores with Mike McCartney as chief scientist. C. Winn was the CO2 group leader during the transit to the Azores and was present when one of the benches supporting one of the SOMMA-coulometer systems broke loose, threatening to destroy the analytical system. Fortunately, the analytical equipment suffered only minor damage, and the minor repairs required were completed by the time the ship was ready to begin the AR24 section. C. Winn left the ship in the Azores and was replaced by R.Rotter, A. Adams, and J. Tegeder, with R. Rotter serving as the group leader. The ship departed on the AR24 cruise from Ponta Delgada on November 1, 1996. The cruise track was, with minor deviations, basically a winter version of the two transoceanic A24 sections completed during the summer of 1997 (see Fig. 1).

During the AR24 section, the principal problem with the TCO2 SOMMA systems Nos. 004 and 030 was the malfunctioning of the solenoid pinch valves used to dispense the sample. Some were damaged and ceased to work, while others were sensitive to power fluctuations and worked intermittently. Replacement valves were quickly consumed, so that SOMMA system No.30 became the primary system. As a consequence, the bulk of the sample TCO2 analyses completed during the AR24 section (see Table 4) were made on system 030. These problems also resulted in the sampling of 10 fewer stations sampled for TCO2 than for TALK during the cruise, with most of the discrepancies occurring between November 14 and 20, 1996. After the concluding station 176 on December 2, 1996, the Knorr docked in South Hampton, United Kingdom, on December 3, 1996.

Following the AR24 section, the analytical systems were repaired and re-calibrated. They were then set up on the R/V Knorr in Woods Hole, during the week of May 13-19, 1997, by the University of Miami TALK and the BNL TCO2 measurement groups. Three SOMMA-coulometer systems and three TALK titrators were set up for the three WOCE sections (A24, A20, and A22). In addition to the discrete TCO2 systems (S/Ns 004 and 030), a third system (S/N 006) was set up for underway surface TCO2 measurements. The equilibrator-infrared (IR) gas analyzer system for the determination of partial pressure of CO2 (pCO2) in discrete sea water samples was set up by the scientists from LDEO. The discrete TCO2 systems were successfully calibrated using both CO2 calibration gas and the certified reference material (CRM) on May 17, 1997, while the calibration of the underway system (006) was completed on May 30. The Knorr departed Woods Hole on May 20 (Leg 151_1) with Dr. Tom Rossby as chief scientist. The TALK group remained onboard to test the instruments on the shake-down transit from Woods Hole to the embarkation point for Leg 151-2, Ponta Delgada on the island of St. Michael, Azores.

Some 300 underway surface samples were drawn and analyzed for TALK during the shake-down cruise, but these data are not reported to the Carbon Dioxide Information Analysis Center (CDIAC). Greg Eischeid of WHOI completed the plumbing connections between the ships underway intake and the underway SOMMA (006). After correcting some minor problems, he obtained the required flow of 1 L/min through the underway system. Problems with operating the underway pipette were also encountered, but they were eliminated by software changes coordinated through BNL, so that by the time the ship arrived in Ponta Delgada, the underway system was operational. The most serious problem with the discrete TCO2 systems was that an erratic transmission reading with the system 030 coulometer madeking titrations impossible. This program was temporarily corrected by jiggling the voltage -to -frequency converter (VFC) and ensuring that all associated chips were properly seated. System 004 was tested successfully during the shake-down cruise, which ended on May 29, 1997, in Ponta Delgada.

K. M. Johnson departed JFK Airport in New York on May 27, 1997, for Ponta Delgada via Lisbon and arriveding on May 28 in the Azores on May 28, where he joined L. Arlen, who was already in Ponta Delgada. The TALK and TCO2 measurement groups moved onboard ship on May 29, and readied the systems for the following day, when the ship departed Ponta Delgada on section A24 with Dr. Lynne Talley as chief scientist. Sample analysis began on system 004 immediately, but the system 030 coulometer once again exhibited unstable erratic transmission readings and was immediately replaced with the back-up unit. Sample analysis with this unit began on May 31, 1997.

The cruise track for section A24 was basically rectangular, encompassing four separate sections (see Fig. 1) starting and ending in the Azores. The first section began at Terceira, Azores, proceeding northeastward towards the Goban Spur and crossing the Mediterranean Water/Labrador Sea Water mixing zone obliquely. Upon completion of the first section, the ship was diverted to Cork, Ireland, for an emergency exchange of crew members. The second section crossed the southern Rockall Trough, from Porcupine Bank to the southern end of the Rockall Bank. The third section crossed the northern part of the subpolar gyre, from the Hebrides to Rockall Bank, to Hatton Bank, to the Reykjanes Ridge and to Greenland near Angmassalik, crossing the Rockall Trough just north of the Anton Dohrn Seamount. Ice conditions at Greenland were favorable, and sampling was completed at stations well onto the shelf (average depth 500 meters). After a transit southward to Cape Farewell, Greenland, the fourth section began at Cape Farewell and proceeded southeastward to the Charlie Gibbs Fracture Zone, and then back to Terceira with the last Station on June 28, 1997. After a 6-day transit, the ship docked in Halifax, Nova Scotia, on July 5.

The weather remained uniformly good throughout Leg A24, and all carbonate measurement systems were operated essentially without major problems. Perhaps the biggest disappointment was the failure to rendezvous with the nearby R/V Meteor in early June for a social gathering. Some 153 hydrographic stations were occupied during A24. TCO2 was measured on 92 of these stations and TALK was measured on 90. Therefore, roughly 60% of the stations occupied on this cruise were sampled for TALK and TCO2. This proportion was somewhat higher than the 50% of stations sampled on typical WOCE cruises due toas a result of an accelerated frequency of sampling. The increased frequency was brought about by making the A24 station interval dependent on bathymetry, which often varied radically over distances much less than the proscribed WOCE station interval of 30 nm. The carbon group sampled as many stations as possible given the limits imposed by the length of time required for the TCO2 and TALK determinations. In addition, discrete surface samples were taken at most stations, and the underway system was operated continuously on Section A24. Originally the A24 section was scheduled to terminate in St. Johns, but because repairs were required, the Knorr put into Halifax on July 4, 1997. An attempt was made to arrange for a back-up coulometer or to repair the damaged coulometer before the next cruise. Unfortunately, this did not work out, and scientists were still left without a back-up coulometer for the coming cruises.

Because of the delay for repairs in Halifax, no direct handoff between CO2 measurement crews was made. The TCO2 relief team consisting of Rick Wilke and Ken Erickson arrived well after the first crew had left and just prior to the Knorr's departure on July 17, 1997, on section A20. However, Wilke had been briefed at BNL concerning the performance of the TCO2 systems and possible problems due to de-powering of the ship during the repairs. The relief crew for TALK consisted of Chris Sabine and Carrie Thomas, who were also responsible for the 14C samples.

The Knorr left Halifax bound for Port of Spain, Trinidad, on July 17, 1997, with Dr. Robert Pickart as chief scientist and 31 other scientists. From July 17 until August 10, 1997, except for a couple of dog legs across the shelf regions, the Knorr occupied a series of stations in a straight line from the Newfoundland Shelf to the Suriname Shelf along approximately 52° W (WOCE Section A20). This Section is also a part of the ACCE and one of two North Atlantic WOCE meridional long-lines (the second long-line, A22, was visited during the subsequent cruise). In the early days of the cruise, heavy fog off of the Grand Banks made for slow going. Otherwise, the excellent weather experienced during the cruise allowed for the sampling of 95 hydrographic stations, which was more than planned. After the initial test station in 3000 m at 57° W, the ship steamed to the 1000-m isobath and the work commenced. During A20, the water masses sampled included the slopewaters, the Laborador Current, the Labrador Sea Water, the Deep Western Boundary Current, the Gulf Stream with a warm core ring, the Sargasso Sea, and finally, as the ship turned toward Trinidad, the North Brazil Current system. On the depths less than 1000 m, a 24-position conductivity, temperature, and depth (CTD) sensor was used, while for greater depths, a 36-position CTD was used. Hydographic station intervals ranged from 3 nm on the shelf, to 10-15 nm across the slopes, to 15-25 nm across the Gulf Steam, and 40 nm in the Sargasso Sea. Other physical oceanographic tasks completed included the deployment of 11 floats and drifters and the deployment or recovery of 4 moorings. The TCO2 systems 004 and 006 continued to operate well, but system 030 required the replacement of one pinch valve and a faulty isolation valve on July 19. Thereafter, this instrument functioned satisfactorily. The Knorr arrived in Port of Spain, Trinidad, on August 10, 1997.

K. Johnson left New York on August 12 to relieve R. Wilke of the TCO2 measurement group, while K. Erickson and C. Thomas remained on board to continue the TCO2 and TALK measurements for the next section A22.

The Knorr departed Port of Spain at 9 A.M. on August 15, and the first station was sampled only 12 hours out of port. Station 1 was a joint station with the R/V Hermano Gines from the EDIMAR Laboratory, Margarita, Venezuela, just outside the sill of the Cariaco Basin. Some joint nutrient samples were taken and analyzed aboard each ship. Then the Knorr began the Caribbean portion of the A22 transect, which ended with Station 23 on 300-m depth south of Puerto Rico on August 20, 1997. The Knorr jogged around the eastern end of the Island, and the transect was resumed north of Puerto Rico along approximately 66° W and continued until Station 77 in 200 m of water on the shelf south of Cape Cod, Massachusetts, on September 2, 1997. Some 77 WOCE hydrostations were occupied during the this leg. In addition, 10 floats and 9 drifters were deployed and one mooring was recovered. All of the carbon parameter instruments, including the underway SOMMA, functioned satisfactorily until the end of the cruise; and fortunately a back-up coulometer was never needed. The R/V Knorr docked in Woods Hole on September 3, where it was met by R. Wilke and E. Lewis from the BNL TCO2 group who helped pack the equipment, and the entire TCO2 measurement group with its equipment departed Woods Hole on the afternoon of September 4, 1997.

Last modified: 2021-03-17T18:30:28Z