P04E: Majuro to Panama City

Overview

GO-SHIP P04E ran roughly 56 days along 9.5°N across the full width of the Pacific aboard the R/V Marcus G. Langseth, from Majuro, Marshall Islands, to Panama City, Panama, under Chief Scientist Andrew R. Babbin and Co-Chief Scientist Rolf Sonnerup, carrying 27 science crew, 5 marine technicians, and 21 marine crew, with France and Costa Rica granting full-water-column sampling permission in their EEZs.

Operations

Departure slipped two days to May 11 after port delays and a late-arriving ship, and the opening days were dominated by a cascade of equipment failures: persistent power flare-ups from the science party’s load demands, near-uninhabitable lab air conditioning (the dry lab alone exceeded 80°F until portable units, a mussel-clogged chilled-water system repair, and added insulation brought it under control), and, most seriously, a CTD that lost communications at nearly 4,957 m during Station 3’s first cast when the primary wire’s electrical lead failed; after a blown fuse, a failed re-termination, and careful load-testing, the team switched to the secondary winch and completed the cast to 5,200 m, then restructured the plan for the next 15 deep (>5,800 m) stations to alternate full 5,200 m/36-bottle casts with shallower 3,000 m/24-bottle casts and widened spacing to a full degree of longitude to recover roughly 40 hours.

A second major equipment crisis struck in Week 6 when the ODF 36-bottle carousel sprang a leak that flooded its internal electronics beyond repair; the team responded by building a “Franken-CTD,” splicing the ship’s 24-place pylon into the ODF rosette’s frame (preserving the LADCP, UVP, Japanese collaborators’ instruments, and high-resolution oxygen/pH sensors, with select bottles double-pinned for the biology team) in a roughly 12-hour effort by nine crew members.

Station spacing evolved repeatedly with the trip’s fortunes, shrinking from a planned ~156 stations down toward 89-109 during the worst delays, then partially recovering as Tropical Storm/Depression Amanda cleared favorable weather ahead of the ship and later stretches of good luck allowed extra “bonus” shallow casts to be added back for detailed oxygen-deficient-zone (ODZ) sampling.

Scientific highlights

Scientific highlights included the discovery of the cruise’s first ODZ water column at Station 46 (measured with five independent oxygen sensors including SBE-43, RINKO, and Unisense STOX electrodes), a well-resolved intrusion of relatively oxygenated, fast-moving, less-denitrified water wedging into the ODZ near 500 m at Station 58, and a crossover with the December 2016 P18 line at 110°W (Station 71) allowing direct decadal comparison of silicate, alkalinity, oxygen, and CFC-11 data.

The cruise deployed a full complement of Core, Deep, and Biogeochemical Argo floats plus Lagrangian surface drifters, sampled the crest of the East Pacific Rise near 104.25°W, and crossed a point roughly 1,430 miles from both the Marquesas Islands and Clipperton Atoll, among the most remote stretches of open ocean on Earth.

Fun facts

The science party crafted a menagerie of beaded fish “lures” for the sharks, mahi, and rays that visited nightly; a caught mahi became shipboard ceviche; two separate stashes of hidden ice cream were discovered and gleefully consumed within days; the Chief Scientist was caught sampling in an ITCZ downpour without foul-weather gear (heroically shielding an N2O isotope sample); World Cup matches were followed avidly between casts; and the voyage closed with a pod of dolphins greeting the ship as land came into view ahead of arrival in Panama.