as a tracer of particulate organic carbon export in the subarctic northeast Pacific Ocean Academic Article uri icon

abstract

  • Profiles of particulate and dissolved super(234)Th ( t sub( one half ) =24.1 d) were collected during the Canadian JGOFS program (February, May, and August 1996 and February 1997) along a transect from 125 degree W to 145 degree W at 50 degree N (Ocean Station Papa--OSP). Persistent features included a deficit of super(234)Th relative to its parent super(238)U in the upper similar to 75 m and occasionally an excess of total super(234)Th (particulate+dissolved) at similar to 150--200 in attributed to redissolution of the particulate-bound nuclide. To calculate POC export fluxes, a steady-state model of super(234)Th export was combined with measurements of the POC/ super(234)Th ratio determined on particles >1- mu m collected by in situ filtration. Along the transect, e-ratios (POC export/primary production) calculated for the 0.1% light level were similar during February 1997 and May 1996, 0.06--0.08 (avg. POC flux = 2.8--7.1 mmol C/m super(2)/d). During August 1996, e-ratios reached a maximum, averaging 0.13 (avg. POC flux=7.6 mmol C/m super(2)/d). Particulate super(234)Th fluxes measured by drifting cylindrical sediment traps were 3-fold greater than the flux calculated for the water column super(234)Th deficit. Finally, to study changes in super(234)Th and POC export on short time-scales, some stations were sampled twice within 36 hours. During February 1997, super(234)Th increased nearly 50% from 60--100 m in a 36 h period. Hydrographic data suggest that this change was due to advective processes.

publication date

  • November 1999