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| Titel |
Impact of internal and external Alkalinity fluxes on the carbonate system in the German Bight / SE North Sea - A model study for the years 2001 - 2009 |
| VerfasserIn |
Fabian Schwichtenberg, Johannes Pätsch, Thorben Amann, Markus Schartau, Helmuth Thomas, Vera Winde, Olaf Dellwig, Justus van Beusekom, Michael Böttcher, Sebastian Grashorn, Lesley Salt |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250079677
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| Zusammenfassung |
| Rising atmospheric CO2 concentrations may cause enhanced oceanic CO2 concentrations
and thus ongoing acidification of the marine environment. Effects of acidification
on the coastal ocean exhibit large variabilities due to shallow water column, tight
benthic-pelagic coupling, nutrient cycling, and discharge from land. As a result of enhanced
biogeochemical processes, seasonal pH variations in coastal and shelf regions can be up to an
order of magnitude higher than in the open ocean and may potentially mask the
decadal trend of decreasing pH. Total Alkalinity (TA) is an essential part of the
carbonate system as it regulates the oceanic CO2 buffer capacity. Variations in
TA are vital to understand observed pH variations. In the coastal zone variations
in TA are particularly pronounced because of diverse external sources like river
discharge, anaerobic degradation of organic material or methane fluxes in tidal flats in
association with pore water exchange across the sediment-water interface. Beside
these external fluxes TA also changes due to physical, chemical and biological
processes.
To better understand and quantify the effect of acidification in the southern North Sea as
part of the northwest European Shelf we applied the ecosystem model ECOHAM with a
prognostic treatment of TA. For the first step we included monthly varying TA and DIC
concentrations of the main continental rivers draining to the North Sea. For the
Dutch rivers we calculated these data from other parameters of the carbonate system
(bicarbonate and pH) that have been measured in the respective estuaries. For the
river Elbe we used data of TA and DIC concentrations that have been measured
in the estuary. Simulation results reveal that the river contribution to TA flux is
insufficient to explain the seasonal variations observed in the German Bight. As
high summer concentrations remain unresolved in this model setup, elevated TA
concentrations during summer in that area must originate from sources other than the river
loads.
In a second step, we considered the Wadden Sea as an additional source and
sink for TA and DIC. Exchange rates between North Sea and Wadden Sea were
calculated. For this we included differences in measured concentrations during
flood and ebb tide in the Wadden Sea and simulated tidal exchange volumes. With
this new approach it was possible to reproduce the observed high TA variations
and especially the high concentrations in the German Bight in summer. Modelled
TA concentrations in different scenarios were 20 to 60 μmol kg-1 higher than in
previous simulations. The simulated export rates were approximately 40 Gmol yr-1. |
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