Although primary production in the Antarctic Circumpolar Current is not above the world average and carbon burial rates are low, 70% of the world's opal burial occurs in this zone and it has been suggested that blooms of large diatoms are responsible for this extraordinary situation. Here we compare export fluxes during bloom and steady-state situations near the Antarctic Polar Front in the SE Atlantic.In a previous expedition during the austral spring, we observed the development of a bloom that led to the sudden export of particles (Rutgers van der Loeff et al., 1997). Here we report the results of a second expedition to the same area in summer (Dec-Jan), 3 years later. 234Th was monitored in the surface water and in Rosette casts down to a water depth of 500m as tracer of export production in an intensive sampling program within a box of 275 x 375 km.The distribution of particulate and dissolved 234Th was remarkably constant over time and location. Total (dissolved + particulate) 234Th activities were depleted relative to its parent 238U at the surface (234Th/238U activity ratio approximately 83%), reaching equilibrium at a depth of around 190m. This constant depletion corresponds to a 234Th export rate of 1115 dpm m-2 d-1, 35% of the value observed during the spring bloom.
AWI Organizations > Geosciences > Marine Geology and Paleontology