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| Titel |
Temperate carbonate cycling and water mass properties from intertidal to bathyal depths (Azores) |
| VerfasserIn |
M. Wisshak, A. Form, J. Jakobsen, A. Freiwald  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 8 ; Nr. 7, no. 8 (2010-08-13), S.2379-2396 |
| Datensatznummer |
250004928
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| Publikation (Nr.) |
 copernicus.org/bg-7-2379-2010.pdf |
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| Zusammenfassung |
The rugged submarine topography of the Azores supports a diverse heterozoan
association resulting in intense biotically-controlled carbonate-production
and accumulation. In order to characterise this cold-water (C) factory a
2-year experiment was carried out in the southern Faial Channel to study the biodiversity of hardground
communities and for budgeting carbonate production and degradation along a
bathymetrical transect from the intertidal to bathyal 500 m depth.
Seasonal temperatures peak in September (above a thermocline) and bottom in
March (stratification diminishes) with a decrease in amplitude and absolute
values with depth, and tidal-driven short-term fluctuations. Measured
seawater stable isotope ratios and levels of dissolved nutrients decrease
with depth, as do the calcium carbonate saturation states. The
photosynthetic active radiation shows a base of the euphotic zone in ~70 m and a dysphotic limit in ~150 m depth.
Bioerosion, being primarily a function of light availability for
phototrophic endoliths and grazers feeding upon them, is ~10 times
stronger on the illuminated upside versus the shaded underside of substrates
in the photic zone, with maximum rates in the intertidal (−631 g/m2/yr). Rates rapidly decline towards deeper waters where bioerosion
and carbonate accretion are slow and epibenthic/endolithic communities take
years to mature. Accretion rates are highest in the lower euphotic zone
(955 g/m2/yr), where the substrate is less prone to hydrodynamic force.
Highest rates are found – inversely to bioerosion – on down-facing
substrates, suggesting that bioerosion may be a key factor governing the
preferential settlement and growth of calcareous epilithobionts on
down-facing substrates.
In context of a latitudinal gradient, the Azores carbonate cycling rates
plot between known values from the cold-temperate Swedish Kosterfjord and
the tropical Bahamas, with a total range of two orders in magnitude.
Carbonate budget calculations for the bathymetrical transect yield a mean
266.9 kg of epilithic carbonate production, −54.6 kg of bioerosion, and
212.3 kg of annual net carbonate production per metre of coastline in the
Azores C factory. |
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