FS Poseidon Cruise 240, 19 Jun-10 Jul 1998. The Fluxes at AMAR Experiment: FLAME 2

The principal objective of the cruise was to recover a series of 11 long-term (12 month) current meter and sediment trap moorings deployed in Summer 1997 to monitor the neutrally-buoyant hydrothermal plume overlying the Rainbow hydrothermal field on the Mid-Atlantic Ridge, near 36°15’N. Secondary objectives were to continue CTD investigations of the physical and geochemical evolution of the plume and to attempt box-coring in sedimented areas identified from TOBI sidescan sonar records beneath the dispersing neutrally buoyant plume. Mooring recovery was completely successful for all three of the sediment trap moorings with the exception that one 2-week sample was lost from one of the 5 multi-collector sediment traps deployed. Seven of the eight current meter moorings deployed were also recovered, with 100% data-recovery from the 21 current meters recovered inboard. A total of 35 CTD-nephelometer profile stations were occupied to the North and South of the Rainbow hydrothermal field, together with one background station , east of the MAR. In situ CTD and nephel data were complemented by water sampling for He-3 and CH4 and shipboard analysis of rosette samples for salinity and TDMn. A total of 4 box-cores were attempted at depths of 2400-2600m beneath the neutrally buoyant plume. All four cores were successful yielding core lengths of 43, 30, 18 and 18cm at distances of 2, 5, 12 and 29km downstream from the known hydrothermal vent-field, respectively.