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| Titel |
Microfossil evidence for trophic changes during the Eocene–Oligocene transition in the South Atlantic (ODP Site 1263, Walvis Ridge) |
| VerfasserIn |
M. Bordiga, J. Henderiks, F. Tori, S. Monechi, R. Fenero, A. Legarda-Lisarri, E. Thomas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1814-9324
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| Digitales Dokument |
URL |
| Erschienen |
In: Climate of the Past ; 11, no. 9 ; Nr. 11, no. 9 (2015-09-30), S.1249-1270 |
| Datensatznummer |
250117408
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| Publikation (Nr.) |
 copernicus.org/cp-11-1249-2015.pdf |
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| Zusammenfassung |
The biotic response of calcareous
nannoplankton to environmental and climatic changes during the
Eocene–Oligocene transition was investigated at a high resolution at Ocean
Drilling Program (ODP) Site 1263 (Walvis Ridge, southeast Atlantic Ocean) and
compared with a lower-resolution benthic foraminiferal record. During this
time interval, global climate, which had been warm under high levels of
atmospheric CO2 (pCO2) during the Eocene, transitioned into the
cooler climate of the Oligocene, at overall lower pCO2. At Site 1263,
the absolute nannofossil abundance (coccoliths per gram of sediment;
N g−1) and the mean coccolith size decreased distinctly after the E–O
boundary (EOB; 33.89 Ma), mainly due to a sharp decline in abundance of
large-sized Reticulofenestra and Dictyococcites, occurring
within a time span of ~ 47 kyr. Carbonate dissolution did not vary
much across the EOB; thus, the decrease in abundance and size of nannofossils
may reflect an overall decrease in their export production, which could have
led to variations in the food availability for benthic foraminifers.
The benthic foraminiferal assemblage data are consistent with a global
decline in abundance of rectilinear species with complex apertures in the
latest Eocene (~ 34.5 Ma), potentially reflecting changes in the food
source, i.e., phytoplankton. This was followed by a transient increased
abundance of species indicative of seasonal delivery of food to the sea floor
(Epistominella spp.; ~ 33.9–33.4 Ma), with a short peak in
overall food delivery at the EOB (buliminid taxa; ~ 33.8 Ma).
Increased abundance of Nuttallides umbonifera (at ~ 33.3 Ma)
indicates the presence of more corrosive bottom waters and possibly the
combined arrival of less food at the sea floor after the second step of
cooling (Step 2).
The most important changes in the calcareous nannofossil and benthic
communities occurred ~ 120 kyr after the EOB. There was no major
change in nannofossil abundance or assemblage composition at Site 1263 after
Step 2 although benthic foraminifera indicate more corrosive bottom waters
during this time. During the onset of latest-Eocene–earliest-Oligocene
climate change, marine phytoplankton thus showed high sensitivity to
fast-changing conditions as well as to a possibly enhanced, pulsed nutrient
supply and to the crossing of a climatic threshold (e.g., pCO2
decline, high-latitude cooling and changes in ocean circulation). |
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