The preservation of opal in marine sediments Site - specific studies Summary - opal burial efficiency Si & C fluxes through the water column The marine Si budget

Studies of the Preservation Rate of Opal in deep-sea sediments Components of the studies: Rain rate to sea floor : time-series sediment traps Benthic remineralization rates : flux chambers ; pore waters Burial rates : solid phase measurements We’ll discuss 2 and show summary of several

Opal cycling at the seafloor at BATS Sayles et al., 1996, DSRI 43, Bermuda Atlantic Time Series site (BATS) 31°50’N, 64°10’W ; water depth = 4400m 1. Sediment trap data (3200m, 1200mab)

2. Benthic flux chamber data : opal dissolution flux

3. Pore water data -- 2nd estimate of dissolution flux Using in situ sampling methods… Issue of near-interface resolution

3 - cont. : comparison of dissolution flux estimates ** no convincing temporal trends ** good agreement between bfc and pw fluxes

4. Solid phase data : burial rate CaCO 3 Opal Note: variation in %CaCO 3 ==> variation in % opal Sed. Rate = 0.7 cm/ky Use: % opal = 1.5% Sed. Dens. = 2.6 Deep porosity = 0.7

5. Conclusion Opal rain: ± mol/m2/y Dissolution: ± Burial: Opal Preservation rate = 6%

Opal Diagenesis in the deep sea at Porcupine Abyssal Plain Ragueneau et al., 2001, Prog. Oceanog. 50, Porcupine Abyssal Plain 48°50’N, 16°25’W water depth ~ 4800m 1. Sediment trap data Mean flux: 43 mmol/m 2 /y

2. Benthic flux chamber data

3. Pore water data Organized by time of sampling … lots of profiles!

3. Cont : pore water / bfc comparison From sed. Traps: mean rain = 0.12 FallSpring Summary: Dissolution fluxes

4. Solid phase data -- burial rate Sed. Rate = 7.5 cm/ky Burial flux = mol/m 2 /y

5. Summary Rain rate a) sed trap0.043 mol/m 2 /y b) diss+burial0.065 Dissolution flux0.057 Burial Burial efficiency = 12%

Opal preservation efficiency in sediments : summary Sources: Ragueneau et al., 2001 Nelson et al., 2002, DSRII 49, Summary of fluxesSummary of burial efficiencies

Vertical fluxes of biog. SiO2 and C through the water column Southern Ocean - Pacific (US JGOFS) Nelson et al., 2002

Vertical fluxes vs. water depth

Si : C flux ratio vs water depth

A marine Si budget DeMaster, 2002, DSR II 49,