A) N. pachyderma (sin.) test microstructure of the final (f) and penultimate chambers (f-1 to f-3) of the last whorl. The average total number of chambers prior reproduction is 15. The primary organic membrane (POM) is the site of initial calcification and has two active surfaces, one calcifying on...
| Main Authors: | , , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.553.1240 http://www.geology.wisc.edu/~wiscsims/BGSW5/posters/KozdonPoster BGSW 2008 new version.pdf |
| Summary: | A) N. pachyderma (sin.) test microstructure of the final (f) and penultimate chambers (f-1 to f-3) of the last whorl. The average total number of chambers prior reproduction is 15. The primary organic membrane (POM) is the site of initial calcification and has two active surfaces, one calcifying on the outer and the other on the inner side. Every time these organisms form a new chamber, their whole pre-existing test is covered with a new layer of calcite. The crust, which may contribute more than 70 % of the total test weight in this foraminiferal species (Kohfeld et al., 1996), is secreted at the end of their life cycle. B) Spiral view of N. pachyderma (sin.) embedded in epoxy. The illustrated polished surface corresponds to the analyzed cross sections. Intratest oxygen isotope variations in the planktonic foraminifera Neogloboquadrina pachyderma sinistral (left coiling) from North Atlantic core 18top and multi-net samples were assessed by ion microprobe analysis from 2 to 6 µm spots with precision better than 0.7 ‰ in O (2 SD). Within 18 18a single foraminiferal test, O values vary from 0.5 ‰ to 3.7 ‰ [PDB], exceeding the range of equilibrium O in the specimens ' habitat by a factor of three. The isotopic difference between the ontogenetic calcite and the crust averages 1.8‰. Neither of the two types of foraminiferal calcite precipitates in equilibrium with ambient seawater. The ontogenetic calcite exhibits a negative vital effect 18 18 18O = O – O ranging from –0.5 to –1‰. The highest negative fractionation is associated with the inner walls of juvenile (M E) (measured) (equilibrium) chambers. In contrast, a positive vital effect of about +0.8 ‰ was observed in the outer crust. Hence two vital effects which are different in sign are effective within a single foraminiferal test, indicating that 'whole test ' values of this species are highly sensitive to the degree of encrustation and amplify or attenuate environmental signals. |
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