THE BENTHIC CYCLE OF BIOGENIC OPAL AT THE BERMUDA ATLANTIC TIME-SERIES SITE

Measurements of the particulate rain of biogenic opal, the flux of dis solved SiO2 across the sea water-sediment interface, pore-water profil es of dissolved SiO2, and opal burial at the Bermuda Atlantic Time Ser ies site are reported for a 5-year period, 1988-1943. Opal rain was de termined on samples collected by a sediment trap deployed at 3200 m, 1 200-m above the sea floor. Samples were collected almost continuously over the 5-year period (94% of the time). Benthic dissolution fluxes w ere measured in situ with benthic chambers several times each year. Si O2 diagenesis was defined with pore-water profiles of SiO2 concentrati on determined on samples collected in situ. The data collected are use d to describe the benthic biogeochemical cycle of biogenic opal for th is oligotrophic ocean environment. Despite strong seasonal variation i n the rain of opal at 3200 m, driven by the cycle of primary productio n in the surface waters, dissolution fluxes from the sediments were co nstant throughout the period of our study. Pore-water profiles indicat e that similar to 90% of SiO2 dissolution within the sediments takes p lace in the upper 5 cm, and that the residence time of opal in this in terval is 100-350 years. The long residence time is consistent with th e lack of response to seasonal variation in opal input. Dissolution fl uxes, determined with benthic chambers and estimated from pore-water p rofiles, provide no evidence of SiO2 dissolution at the water-sediment interface. The average particulate opal rain and the benthic dissolut ion flux, 0.0052 and 0.0047 mu mol cm(-2) day(-1), respectively, are n ot significantly different, indicating little opal burial. The burial efficiency of opal based on mass balance considerations is estimated t o be similar to 6%. Copyright (C) 1996 Elsevier Science Ltd.