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| Titel |
Significance of the Autumn Bloom within the Seasonal Cycle of Primary Production in a Temperate Continental Shelf Sea |
| VerfasserIn |
Juliane U. Wihsgott, Jonathan Sharples, Joanne Hopkins, Malcolm Woodward, Naomi Greenwood, Dave Sivyer, Tom Hull |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250142825
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| Publikation (Nr.) |
 EGU/EGU2017-6490.pdf |
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| Zusammenfassung |
| Autumnal phytoplankton blooms are considered characteristic features of the seasonal cycle
of primary productivity in most temperate and subpolar oceans. While observations of their
occurrence and strength have been documented extensively, their significance within the
seasonal cycle of primary production is not well quantified.
Our aim is to establish the role the autumn bloom plays within the seasonal cycle and
estimate its contribution to the annual primary production of a temperate continental shelf. In
particular, we will illustrate that the autumn bloom has the potential to be as productive as the
well-studied summer sub-surface chlorophyll maximum (SCM) and the capacity to
significantly contribute to the drawdown of atmospheric CO2. We do this by combining
long-term, high resolution observations of water column structure, meteorological forcing,
nitrate and chlorophyll fluorescence over the entire seasonal cycle observed in a temperate
shelf sea.
We present a new series of continuous measurements spanning 17 months (March 2014 -
July 2015), which were collected in a temperate shelf sea on the North West European Shelf.
A long-term mooring array recorded full depth vertical density structure, dynamics and
meteorological data as well as surface chlorophyll fluorescence biomass and inorganic
nutrient data over a full seasonal cycle at a station 120 km north-east from the continental
shelf break. Eight process cruises supplied additional full depth profiles of chlorophyll
fluorescence biomass and macronutrients.
The breakdown of stratification in 2014 commenced in early October due to increased
winds compared to summer months, and a predominantly negative net heat flux (the ocean
lost heat to the overlying atmosphere). Vertical mixing in autumn not only transformed the
vertical density structure but also the vertical structure of chlorophyll biomass and surface
nutrients. The SCM became eroded and instead a vertically homogeneous profile of
chlorophyll biomass established itself above the pycnocline. This increased mixing
also led to replenishment of surface nutrients and drove enhanced growth, which
was almost 4 times stronger than observed during the summer months: We find
an increase in depth integrated chlorophyll biomass of ∼50 mg m−2 in autumn
2014 compared to values of ∼20 mg m−2 during the summers of 2014 and 2015. |
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