 |
| Titel |
Impact of alkalinity fluxes on the carbon cycle in the southern North Sea between 1970 and 2006 |
| VerfasserIn |
Fabian Schwichtenberg, Johannes Pätsch, Ina Lorkowski, Markus Schartau, Helmuth Thomas, Vera Winde, Olaf Dellwig, Justus van Beusekom, Michael Böttcher |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056319
|
|
|
|
|
|
| Zusammenfassung |
| Rising atmospheric and oceanic CO2 concentrations cause an ongoing acidification
of the marine environment. pH-variations in coastal- and shelf regions can be up
to an order of magnitude higher than in the open ocean. The nearshore effects of
acidification are difficult to determine, because of their shallow water column and
the tight coupling to the benthic environment. Strong variations in fluxes of Total
Alkalinity (TA) exist in association with inflow of nutrients from rivers and from
pore water exchange in sediments. TA is an essential part of the carbonate system
and hence vital to understand and reliably attribute the observed decreasing pH
values. Recent studies in the south-eastern bight of the North Sea, as part of the
north-east North Atlantic shelf, reveal increasing TA values from spring to late
summer, which buffer the seasonally decreasing pH and also increase the CO2 buffer
capacity.
Studying the TA-variations requires reliable estimations of TA–fluxes. The
latter depend on physical, chemical and biological processes. For budgeting TA in
the southern North Sea we applied the ecosystem model ECOHAM (Pätsch and
Kühn, 2008) with a prognostic treatment of TA and the corresponding TA-fluxes
for the years 1970 - 2006. Dissolution of CaCO3, the release of ammonium into
the water column and the uptake of nitrate are processes that increase TA. Vice
versa, CaCO3 formation, uptake of ammonium and the release of nitrate reduce
TA. Additionally, the external sources of nitrate and ammonium are identified as
TA-fluxes.
First one-dimensonal model simulations (without riverine input) were carried out to
study internal processes in the water column. They showed only small seasonal
variations in TA-concentration of about 7 mmol m-3. In a recent study by Thomas et al.
(2009) annual TA-export rates were estimated within the North Sea. Based on field
data collected in 2001/2002, an annual TA-export of about 190 Gmol from the
south-eastern bight into the adjacent North Sea was calculated. About 120 Gmol can be
attributed to riverine input of TA and nitrate and in a smaller part to atmospheric nitrate
inputs. The remaining 70 Gmol were referred to anaerobic processes in the Wadden
Sea.
In our three-dimensional model-study we investigate two different sources of TA, riverine
input and atmospheric nitrogen deposition, initially ignoring the Wadden Sea generated TA.
We quantify their contributions to TA within the southern North Sea and compare
them to internal processes in the water column. We finally address the following
questions:
Are there noticeable trends in the external sources and how do they contribute to
the TA concentration?
Do the different TA fluxes react on periods of high eutrophication?
How does the carbonate system react on these TA variations and increasing
pCO2?
Does our model reproduce reliable TA concentrations within the southern North
Sea?
Is it necessary to include the Wadden Sea as a source of TA in the model?
Is it necessary to include additional TA-contributors like phosphate or sulphate
in the model?
References:
J. Pätsch and W. Kühn (2008). Nitrogen and carbon cycling in the North Sea and
exchange with the North Atlantic - A model study. Part I. Nitrogen budget and
fluxes. Continental Shelf Research, 28: 767-787
H.Thomas, L.-S. Schiettecatte, K. Suykens, Y.J.M. Koné, E.H. Shadwick,
A.E.F. Prowe, Y. Bozec, H.J.W. de Baar and A.V. Borges (2009). Enhanced
ocean carbon storage from anaerobic alkalinity generation in coastal sediments.
Biogeosciences, 6, 267 - 274 |
|
|
|
|
|
|