Cruise Summary

The objective of this cruise was to occupy a hydrographic section nominally along 149 E from Papua, New Guinea, to the shelf of Japan near Yokohama as part of the one-time WOCE Hydrographic Program (WHP) survey of the Pacific Ocean. A CTD with a 36-place, 10-L rosette was used on a total of 94 small-volume (SV) stations with water sampling for salinity, oxygen, nutrients, CFCs, tritium/helium, TALK, TCO₂, and ¹⁴C. The station spacing ranged from 5 to 40 nautical miles (nm), and most lowerings were made to within 10 m of the bottom. A lowered ADCP was attached to the rosette on 53 of the stations. At seven stations, additional casts were made for large-volume (LV) sampling of ¹⁴C in the deep and mid-depth waters. These LV casts were usually made with nine, 250-L Gerard barrels. Underway measurements along the cruise track included pCO₂, ADCP, digital echo-sounding, thermosalinograph, and meteorology.

The P10 cruise was the third in a series of three WHP one-time cruises aboard the R/V Thomas G. Thompson in 1993, following P17N and P14N. The ship departed Suva, Fiji, on November 5, 1993, and steamed north-west to the northern coastline of Papua, New Guinea, where the section began at the 200-m isobath. During the 7-day deadhead, three test stations were occupied (not included in the station numbering scheme) to shake down equipment and water-sampling methodology. The station track, designed in early planning documents for 145° E, was shifted eastward in an effort to depart the New Guinea coastline perpendicular to the bathymetry, then skirt the Mariana Ridge and Trough to the east, thus making the whole section in the East Mariana Basin, rather than in both that basin and the Philippine Basin farther west. Where bottom depths changed rapidly (near the coast and passing the Caroline Seamounts around 6-8° N), station spacing was dictated by topographic changes; within 3° of the Equator, spacing was every 15 min of latitude along the ship track (nominally 15 nm, but slightly more due to the track angle), stretching to 30 nm up to 10.5° N, then 40 nm from there to station 73 at 28.5° N. At that point the cruise track was going straight toward the Japan coast in order to cross the Kuroshio Current. The ADCP results indicated that this crossing was approximately perpendicular to the current. Over the northern dogleg, station spacing gradually decreased to resolve the strong front of the Kuroshio Current, and ultimately, to accommodate rapid topographic changes near the coast. Stations generally went to within 10 m of the bottom except over the Japan Trench and a few other stations where bottom depths exceed 6000 dbar. No stations were lost due to weather, and the ship arrived in Yokohama on November 10, 1993.

The general sampling strategy for the carbon work was to collect and analyze as many full profiles for TCO₂ and TALK as practical. The TCO₂ analysis was slightly faster than the TALK analysis and generally determined the frequency of sampling. Full profiles were collected at 32 of the 94 hydrographic stations occupied on this leg, with gaps of no more than two consecutive stations between profiles (Fig. 2). Duplicate samples were collected at every sample station from Niskins tripped in shallow, mid-depth, and deep waters for both TCO₂ and TALK to evaluate the quality and precision of sampling and analysis. All TCO₂ samples were analyzed at sea; however ~20% (220 samples) of the TALK samples were returned to Princeton University for shore-based analysis. To preserve the continuity of the profiles, all of the TALK samples at select stations were bottled for return to the laboratory. At least three additional replicate TALK samples were collected at these stations and analyzed at sea to ensure the compatibility of the two data sets [see further explanation in quality assurance / quality control (QA/QC) section]. In addition to the TCO₂ samples collected for on-board analysis, 40 samples were collected at 10 stations for shore-based TCO₂ analysis by vacuum extraction and manometry by Charles D. Keeling of Scripps Institute of Oceanography (SIO).