Lam, Phoebe J., Todd J. Wood, James K.B. Bishop

University of California, Berkeley, CA 94720-4767, Tel: 510-643-4248, E-mail: pjlam@socrates.berkeley.edu

Large volume in-situ filtration during SOFeX: The fate of particles in the upper 1000m

We deployed the Multiple Unit Large Volume in-situ Filtration System (MULVFS) during the Southern Ocean Iron Experiment (SOFeX) in Jan/Feb 2002 from the R/V Revelle. The MULVFS collected size-fractionated particles (>51µm, 1-51µm, and nominally <1µm) over 4 hours of pumping (up to 12,000L of seawater). A total of eight MULVFS profiles were collected in the Si-poor “North Patch” at 55ºS and in the Si-rich “South Patch” at 66ºS, with each profile comprising samples from up to 12 depths between the surface and 1000m. Here, we focus on the major chemical constituents of >51µm and 1-51µm particles: Si, CaCO₃, and organic matter. The >51µm biomass and particulate silica were more than an order of magnitude higher at the surface in the South Patch than in the North Patch. Remineralization efficiency was lower in the North Patch, as indicated by higher biomass concentrations penetrating to mid-depths. A higher %CaCO₃ in particles in the North patch (more ballast) may explain the lower efficiency of remineralization of P in the North. The >51µm MULVFS samples did not record a strong export signal in response to iron fertilization in either patch. Similar data for the 1-51µm fraction will be presented.