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| Titel |
Planktonic foraminifera as indicators of water masses north and south of the Azores Front/Current: Evidence from abundance and stable isotopes data |
| VerfasserIn |
Andreia Rebotim, Antje H. Voelker, Joanna Waniek |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035896
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| Zusammenfassung |
| The wide occurrence of pteropods and planktonic foraminifera in the marine environment of
the modern ocean and ultimately their contribution to the marine sediments, make them
especially important for the study of past and present marine ecosystems and their reaction to
climatic changes.
In the present study, pteropods and planktonic foraminifera were collected from the upper
2000 m of the water column along two transects at 20 and 22ºW between 38ºN and 31ºN in
April 2007 and December 2008, respectively. Both transects cross the Azores Frontal
System that forms the northern boundary of the North Atlantic’s subtropical gyre.
The abundance of both organisms and of specific planktonic foraminifera species
were quantified in each tow sample. Additionally, stable oxygen and carbon isotope
measurements were done in the following planktonic foraminifera species: Globorotalia
scitula, Globigerinoides ruber, Globorotalia hirsuta, Globigerinella siphonifera,
Globorotalia inflata, Hastigerina pelagica, Globorotalia truncatulinoides, and Orbulina
universa.
In April 2007, the distribution of pteropods and planktonic foraminifera abundances and
planktonic foraminifera species on both sides of the Azores Front seems to be related to the
spring bloom. Comparing the two transects in abundance and fauna composition, there are
higher abundance and diversity at the 22ºW transect than at 20Ë W indicating high
variability in the plankton although the hydrographic conditions were not much
different. In the water column, pteropods are present mostly in the upper 100 m, while
foraminifera become dominant below this depth. Seasonally, the abundance and
diversity of pteropods and planktonic foraminifera is often higher in April 2007 than in
December 2008. Being surface dwellers, G. ruber, O. universa and G. siphonifera were
present in the upper 200 m. H. pelagica, G. inflata and G. truncatulinoides (dextral)
were found in the upper 400 m. The deep dwelling species like G. truncatulinoides
(sinistral), G. scitula and G. hirsuta occurred in deeper waters, between surface
and 1200 m. Both north and south of the Azores Front, the species occurring with
highest abundances were G. scitula and G. hirsuta. North of the Front, abundance of
G. scitula varied from 55 to 77% and of G. hirsuta from 9 to 18%. South of the
Front, G. scitula occurred between 18 and 77% and G. hirsuta range was 16 to
35%.
Stable isotopes values of living specimens of planktonic foraminifera generally reflect the
environmental parameters of the waters in which the carbonate shell was calcified.
Deep-dwelling species, like G. scitula, G. hirsuta and G. truncatulinoides seem to be good
indicators for the water masses of Azores Front and therefore for the reconstruction of past
conditions. |
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