Biogenic silica and silicic acid benthic fluxes of a North-eastern Atlantic Abyssal Locality


Within the framework of the EU-funded BENGAL programme, the effects of seasonality on biogenic silica early diagenesis have been studied at the Porcupine Abyssal Plain (PAP), an abyssal locality located in the northeast Atlantic Ocean. Nine cruises were carried out between August 1996 and August 1998. Silicic acid (DSi) increased downward from 46.2 to 213 µM (mean of 27 profiles). Biogenic silica (BSi) decreased from ca. 2% near the sediment-water interface to <1% at depth. Benthic silicic acid fluxes as measured from benthic chambers were close to those estimated from non-linear DSi porewater gradients. Some 90% of the dissolution occurred within the top 5.5 cm of the sediment column, rather than at the sediment-water interface and the annual DSi efflux was close to 0.057 mol Si/m2/yr. Biogenic silica accumulation was close to 0.008 mol Si/m2/yr and the annual opal delivery reconstructed from sedimentary fluxes, assuming steady state, was 0.065 mol Si/m2/yr. This is in good agreement with the mean annual opal flux determined from sediment trap samples, averaged over the last decade (0.062 mol Si/m2/yr). Thus ca. 12% of the opal flux delivered to the seafloor get preserved in the sediments. A simple comparison between the sedimentation rate and the dissolution rate in the uppermost 5.5 cm of the sediment column suggests that there should be no accumulation of opal in PAP sediments. However, by combining the BENGAL high sampling frequency with our experimental results on BSi dissolution, we conclude that non-steady state processes associated with the seasonal deposition of fresh biogenic particles may well play a fundamental role in the preservation of BSi in these sediments. This comes about though the way seasonal variability affects the quality of the biogenic matter reaching the seafloor. Hence it influences the intrinsic dissolution properties of the opal at the seafloor and also the part played by non-local mixing events by ensuring the rapid transport of BSi particles deep into the sediment to where saturation is reached.

Supplement to: Ragueneau, Olivier; Gallinari, Morgane; Corrin, Lydie; Grandel, Sibylle; Hall, Per; Hauvespre, Anne; Lampitt, Richard Stephen; Rickert, Dirk; Ståhl, Henrik; Tengberg, Anders; Witbaard, Rob (2001): The benthic silica cycle in the Northeast Atlantic: annual mass balance, seasonality, and importance of non-steady-state processes for the early diagenesis of biogenic opal in deep-sea sediments. Progress in Oceanography, 50(1-4), 171-200

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Creator Ragueneau, Olivier ORCID logo; Gallinari, Morgane ORCID logo; Corrin, Lydie; Grandel, Sibylle; Hall, Per; Hauvespre, Anne; Lampitt, Richard Stephen; Rickert, Dirk; Ståhl, Henrik ORCID logo; Tengberg, Anders; Witbaard, Rob
Publisher PANGAEA
Publication Year 2001
Funding Reference Fourth Framework Programme Crossref Funder ID MAS3950018 Benthic Biology and Geochemistry of a North-eastern Atlantic Abyssal Locality
Rights Creative Commons Attribution 3.0 Unported;
OpenAccess true
Resource Type Supplementary Publication Series of Datasets; Collection
Format application/zip
Size 33 datasets
Discipline Biology; Life Sciences
Spatial Coverage (-19.859W, 47.601S, -16.271E, 48.992N); Bengal
Temporal Coverage Begin 1996-08-14T16:50:00Z
Temporal Coverage End 1998-08-30T22:47:00Z