Compositional variability in the ascending fluxes from a hydrothermal plume

Abstract

Sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast Pacific Ocean between July 1994 and May 1995. One mooring was deployed near the Main Vent field on Endeavour Ridge (On‐Axis site, 47°57.0′N, 129°05.7′W), a second, 3 km west of the Main vent site (West site), and the third, 43 km northeast of the Main vent site (East or background site). Ascending and descending particles were collected near 1600 and 2000 m depth, well above and within the top of laterally spreading hydrothermal plumes. The elemental composition of particles was used to evaluate their origins: biogenic fluxes were indicated by elevated Ca or Si, hydrothermal fluxes by elevated Fe, Mn, and Cu, and lithogenic fluxes by elevated Ti. We link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean. The relatively low hydrothermal Fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material. These results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below.