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FP5

ORFOIS Report Summary

Project ID: EVK2-CT-2001-00100
Funded under: FP5-EESD
Country: France

1-D sediment process study

The processes controlling preservation and recycling of particulate biogenic silica in superficial sediments must be understood in order to calculate oceanic mass balances for this element. Three models representing early digenesis of silica were used to calculate the vertical distributions of pore water and solid phase silica in the sediment. The first model contains one type of biogenic silica and dissolution rate is constant, the second model contains one type of biogenic silica and dissolution rate is variable with sediment depth (term of aging), the third contains two types of biogenic silica which differ by their reactivity (fast dissolving and slow dissolving are constants). The porosity is variable exponentially with sediment depth. An explicit term of re-precipitation was incorporated into these models.

The distributions of pore water and solid silica predicted by the steady state models were compared to experimental data reported from the Southern Ocean, the Equatorial Pacific and the North Atlantic (Porcupine Abyssal Plain). Models cannot reflect the observed data for dissolved and solid silica using the measured biogenic silica flux and dissolution rates.

After parameter estimations, the first model cannot reflect the observed data for dissolved and solid silica. For the second and third models, good agreements were found between predicted and measured dissolved and solid silica, over a wide range of oceanic areas and sediment composition, from opal rich to opal poor sediments. The apparent silica dissolution rate constants, the biogenic silica flux deposited at the sediment-water interface, the dissolved silica re-precipitation rate constant, and the saturation concentration for silica re-precipitation were the critical parameters. The non steady state of the second and third models was tested on the Southern Ocean, the Equatorial Pacific and the North Atlantic.

Reported by

CEA/DSM/LSCE
LSCE; CEN Saclay; L'Orme des Merisiers, Bât. 701
91191 Gif-sur-Yvette
France
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