Brief Cruise Summary
Unlike other CO2 survey cruises where a single institution was responsible for all phases of the work, these cruises were a group effort in which the measurement groups used the same ship and instrumentation for a 14-month period. BNL supplied two single-operator multiparameter metabolic analyzers (SOMMA) systems [S/N 004(I) and 006(II)] that were certified at BNL. A complete back-up system (S/N 023) was supplied by WHOI. The alkalinity titrators were supplied by RSMAS. Preparation began with a 4-day workshop held in September 1994 at RSMAS under the direction of and in the laboratory of F. J. Millero. Cruise participants and group leaders from BNL, LDEO, SIO, RSMAS, PU, WHOI, and UH were instructed in the use of the alkalinity titrators by F. J. Millero and D. Campbell and in the use of the SOMMA-coulometer systems by K. M. Johnson and R. W. Wilke. The day after Thanksgiving the BNL and RSMAS TCO2 groups left for Australia. Setup of the alkalinity and coulometric titration systems began on November 28, 1994. The I8SI9S cruise began on December 1, 1994.
The first of the nine cruises on the R/V Knorr was the longest continuous cruise during the survey. It occupied a series of CTD stations along two north-south tracks essentially proceeding from Australia to the ice edge (I8S) along 90° E and then back again to Australia (I9S) at approximately 110° E. Station spacing ranged from 5 to 40 nautical miles (nm). Testing and selection of the best of the available titration systems and components was completed during I8S. The alkalinity and especially the coulometric titration systems benefitted from this "shake-out" period. Components damaged during transit were identified and repaired or replaced. By the beginning of the I9S, operations were more or less routine. Except for one approximately 12-h period when high winds of ~60 knots (kn) made sampling impossible, work proceeded pretty much on schedule during the 50-day cruise. During the cruise the ability of a team of four marine mammal and bird observers onboard from PMEL, under the direction of C. Tynan, to remain in the cold weather and identify whales that were little more than blips on the horizon amazed all participants of the expedition. Both Christmas and New Year holidays were celebrated aboard the ship. The fine Christmas dinner was highlighted by the appearance of three humpback whales, who put on a spectacular display, jumping and passing under and about the ship. The ship docked in Fremantle, to the relief of the CO2 team members, on January 19, 1995, after 147 stations were occupied. Measurement crews were exchanged, and the new team brought along some badly needed spare parts and components.
The ship departed Fremantle for I9N on January 24 with A. Gordon as Chief Scientist and a CO2 measurement group from PU. This section was basically a northward continuation of I8S. The weather was perfect during all 43 days of the cruise. The participants celebrated the equator crossing on February 14. This cruise ended on March 5 in Colombo, Sri Lanka, with 131 stations logged. During the stopover, the carrier gas supply for the coulometric titrators was shifted from bottled high purity nitrogen to a calibration gas generator (Peak Scientific), which supplied CO2-free carrier gas for the remaining cruises.
I8NI5E began in Colombo on March 10 with L. Talley as chief scientist and a CO2 measurement group from UH on board. No problems were noted for the sampling program, and the weather remained excellent for most of this leg. The ship track proceeded southward from Sri Lanka along 88° E to 24° S, then angled southeastward to the junction of the Ninety-East Ridge and Broken Ridge. Next, the ship followed a 1987 section along approximately 32° S. This zonal section included the Central Indian Basin, and crossed the northward flow of deep water just west of Australia. Due to the good weather, some extra sampling was carried out, and by the time the ship docked in Fremantle on April 15, 166 stations had been occupied. On station 296, the rosette accidentally hit bottom at 3630 m, but the cast was successfully completed. A postcruise inspection showed no apparent damage to the equipment. This cruise included sampling for particulate organic carbon (POC) in the surface waters near the equator. POC samples were also taken at 65 stations for 13C/12C analyses. Between April 15 and 23, measurement crews were exchanged and spare parts inventories were updated.
On April 23, the R/V Knorr departed Fremantle for section I3 with W. Nowlin as chief scientist and a CO2 measurement group from RSMAS. The ship had to detour almost immediately back to Fremantle for a medical emergency. The injured analyst was able to rejoin the ship in Port Louis, Mauritius. In addition to the CTD work, this cruise included the deployment of current meters, drifters, and autonomous Lagrangian circulation explorer (ALACE) floats. The cruise track ran along 20° S from Australia to Mauritius to Madagascar, crossing the West Australian Basin, Ninety-East Ridge, Central Indian Basin, and Central Indian Ridge before veering southward to 22° S around Rodrigues Island. After this, it proceeded to the east coast of Mauritius, where a 2-day port stop was made in Port Louis. Returning to sea, the ship continued sampling westward along 20° S from the continental shelf to Madagascar. Weather was characterized by southeasterly winds of 10-20 kn, mostly sunny skies, occasional rain squalls, and 4-6 ft swells with slightly higher winds and seas in mid-May. The Knorr returned to Port Louis, Mauritius, on June 5 with 120 stations logged.
The next cruise, I4I5W, began on June 11 with J. Toole as chief scientist and a CO2 measurement group from BNL on board. This leg focused on major circulation features of the southwest region of the Indian Ocean, including the region where the Agulhas Current originates and where dense waters filtering through fractures in the Southwest Indian Ridge form a northward deep boundary current east of Madagascar. The cruise track formed a closed box to aid in deducing the absolute circulation. A stop was made in Durban, South Africa, on June 21 to pick up a replacement drum of CTD wires. Attempts were also made to repair the ship's bow thruster, which had failed very early in the leg; although the repair was not successful, the lack of a bow thruster had no effect on the scientific work. The R/V Knorr departed Durban on June 22 and began I5W including reoccupation of stations where data had been taken in 1987. Bad weather was experienced on June 30 when wind gusts of 40-50 kn and high seas slowed winch operations. As the ship moved across the Madagascar Basin toward port, station spacing was decreased to 20 nm. When the ship arrived in port on July 11, 136 stations had been occupied 20 more than planned.
After four days in port, the R/V Knorr departed on I7N with D. Olson as chief scientist and a CO2 measurement group from UH. The director of the U.S. WOCE office, Piers Chapman, was aboard and served as a salt analyst during the section. I7N was designed to define the water mass properties and transports across the Mascarene Basin and to measure water mass properties and baroclinic structure on a short section across the Amirante Passage, located between the Mascarene and Somali Basins. It included a cross-equatorial section and a reoccupation of stations previously sampled to confirm water mass flows. This work included sampling along 65° E in the central Arabian Basin. The concluding phase of the cruise was a deep line of stations up the center of the Gulf of Oman. The last station of this phase was in the Strait of Hormuz, and it identified inflows of Arabian (Persian) Gulf water into the Arabian Basin. The cruise terminated on August 24 in Muscat, Oman, with 156 stations occupied.
After a 5-day layover, the R/V Knorr departed Muscat on I1 with J. Morrison as chief scientist and a CO2 measurement group from WHOI. I1 was the northernmost Indian Ocean section. It enclosed the Arabian Sea and Bay of Bengal, which are important sources of salt and fresh water, respectively. The Knorr proceeded from Muscat to the southern end of the Red Sea and then to the coast of Somali, where the zonal section started at a nominal latitude of 8° N. The section crossed the Arabian Sea, in part to study the carbon transport in and out of the Arabian Sea, and ended on the continental shelf of India. After a brief port stop in Colombo, Sri Lanka, on September 28-30, the leg continued from the Sri Lankan shelf across the Bay of Bengal to the Myanmar continental shelf. CTD problems caused considerable difficulty for the scientific party and resulted in a somewhat noisy hydrographic data set compared to data obtained from the other sections. After the last station on the Myanmar shelf, the Knorr deadheaded to Singapore, arriving on October 16 with 158 stations logged. I1 was not only the northernmost section, it was clearly the most adventurous. ALACE float deployments had to be canceled in the territorial waters of India because the Indian observer on board refused to allow them, and then the threat of pirates caused the cancellation of a planned section across the Gulf of Aden. In the vicinity of Colombo, the ship had to be escorted by four Sri Lankan gunboats, and planned stops at stations over the Trincomalee Canyon could not be taken because of the threat of attack by the Tamil Tigers. Nevertheless, the Knorr was able to coordinate scientific activities and physical oceanographic measurements with the nearby R/V Meteor (F. Schott, chief scientist) in an area of German current meter moorings near Socotra. Sampling during I1 enabled comparison of bottle and TCO2 data with earlier JGOFS results and Meteor, Pegasus, and Knorr lowered acoustic Doppler current profiler (LADCP) horizontal velocities. From Singapore, the Knorr proceeded to Dampier, Australia, where it was placed in dry dock from October 19 until November 5.
With the R/V Knorr back in the water, the I10 CO2 measurement group from PU arrived. This group was required to do some additional work not normally part of the crew exchange routine. During the dry dock period, the CO2 instrumentation had been depowered, and the measurement group had to repower and check the instrumentation. Some minor repairs were required for the coulometric titrators, including the replacement of one or two solenoid valves (the only valves replaced during the cruises). In addition, the sample pipettes and coolant lines were dismounted and cleaned of algal growth.
The R/V Knorr departed Dampier, Australia, on November 11 with N. Bray as chief scientist. WOCE Section I10 was set to run from Shark Bay, Western Australia, to the Indonesian Exclusive Economic Zone (EEZ) 120 nm south of Sunda Strait. However, constraints imposed by the Indonesian government caused the endpoint to be moved from the Sunda Strait to near central Java. The Knorr was not granted permission to enter the EEZ of Indonesia, and concluding stations had to be taken along the boundary of the EEZ. These restrictions prevented full resolution of the South Java current. Throughout the Indian Ocean survey, bottle casts were normally made to within 5-20 m of the bottom; however, on I10 four stations over the Java Trench this could not be done. Instead, the casts were made to the maximum CTD depth of 6000 m. The quality of the bottle data was considered to be excellent throughout with very few mis-trips. ALACE floats were also released during this cruise. A festive Thanksgiving was celebrated aboard the ship, and after the last station (1075), the Knorr steamed to Singapore, arriving on November 28, with 61 stations logged.
The R/V Knorr departed Singapore on December 2 for the last Indian Ocean WOCE section, I2, with G. Johnson as chief scientist and the UH CO2 measurement group aboard. Again, clearance for work in the Indonesian EEZ was not available, and after a 3-day steam, work commenced with a reoccupation of the final station of the I10 Section (station 1075). The Knorr skirted the Indonesian EEZ and moved westward, crossing the Ninety-East Ridge and the Chagos-Laccadive Ridge. The ship continued at approximately 8° S until it made a brief port call in Diego Garcia from December 28-30. At this point, the chief scientist departed the ship and was replaced by Bruce Warren, accompanied by two Kenyan observers. The Knorr returned to the 8° S line, passing the crest of the Central Indian Ridge and then the Mascarene Plateau before it turned southwestward and crossed the Amirante Passage on the way to the northern tip of Madagascar. Rounding the tip, the ship headed northwest toward Africa, making a dogleg to avoid the Tanzanian EEZ. After completing the final Indian Ocean Survey station 1244, it proceeded to Mombasa, arriving on January 22, 1996, with 168 stations logged.
For inorganic carbon, the principal analytical problems for the cruise centered on the breakage of glass components in the alkalinity titrators; resupply; accumulation of bubbles in the acid lines of the alkalinity titrators; damaged coulometric cathode electrodes; algal growth in the sample lines, baths, pipettes, and alkalinity cells; wide swings in laboratory temperature (19-33°C), and the failure of the TCO2 glassware drying oven. Fortunately, glassware drying oven was repaired. Temperature swings (21-29°C ) were also noted for the salinometer and nutrient laboratories. The most vexing problem for the inorganic carbon analysts was the failure of the refrigerated baths used by both the alkalinity and coulometric titration systems. The baths had to be constantly jury-rigged so that one bath did the work of two, repaired by ship's technicians when possible, or replaced when possible. The two groups used almost 12 different baths, and by the time the work ended, not one could be considered in reliable condition. Some were never repaired, while others were repaired and used for the North Atlantic survey in 1997.