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| Titel |
Spatial extent and historical context of North Sea oxygen depletion in August 2010 |
| VerfasserIn |
B. Y. Queste, L. Fernand, T. D. Jickells, K. J. Heywood |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058672
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| Zusammenfassung |
| Prompted by recent observations of seasonal low dissolved oxygen from two moorings in the
central North Sea, a hydrographic survey in August 2010 mapped the spatial extent of
summer oxygen depletion. In marine environments, the oxygen either diffuses from the
atmosphere or is produced by photosynthesising organisms in the euphotic layer, and is then
transported by currents to different regions or mixed to depths where it is utilised. Dissolved
oxygen depletion arises in situations where the rate of oxygen supply is less than the rate of
consumption for a significant period.
Typical near bed dissolved oxygen saturations in the stratified regions of the North Sea
were 75-80% while the well-mixed regions of the southern North Sea reached 90%. Two
regions of strong thermal stratification, the area between the Dooley and Central North Sea
Currents and the area known as the Oyster Grounds, had oxygen saturations as low as 65%
and 70% (200 and 180 μmol dm-3) respectively.
Low dissolved oxygen was apparent in regions characterised by low advection, high
stratification, elevated organic matter production from the spring bloom and a deep
chlorophyll maximum. The constant consumption of oxygen for the remineralisation of the
matter exported below the thermocline exceeded the supply from horizontal advection or
vertical diffusion.
Historical data over the last century from the International Council for the Exploration of
the Sea (ICES) oceanographic database highlight an increase in seasonal oxygen depletion
and a warming over the past 20 years. Regions showing sub-saturation oxygen
concentrations were identified in the central and northern North Sea post-1990
where previously no depletion was identified. This correlated with an increased
temperature signal but could not be entirely explained by the temperature-driven
decrease in solubility. The 2010 survey is consistent with, and reinforces, the signal of
recent depleted oxygen at key locations seen in the (albeit sparse) historical data. |
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