The commonly used size ranges are 125 um, 250 um or 400 um. However, the most common is 250 um
It depends on what you want to do. The 150 um fraction and stick to the adults. Benthic formanifera live in just in one water mass.
okies. Thanks alot guyz. it seems 300um forams will be satisfactory size range for isotopic analysis for paleoclimatic studies. Please suggest if i need to do something also to use forams for paleoclimatic studies.
If you want consistent downcore results a narrow size fraction (50µm) is preferred, that is also centered on the most abundant size range (e.g. 300-350µm).
yeah. i am actually processing a core from arabian sea for isotopic studies. I find it very difficult to study 50um fossil due its large population in the sample. However, >300 um fossils are less in popultation. could you tell me any other method to make it in easier way??
The dutch have been very active in the Arabian Sea on foram isotopes. You may wish to get papers by Dick Kroon and Gerald Ganssen.
Bingo. got a proper publication for the size of globigerina bulloides as "Our results suggest that for paleoceanographic applications, shells in the 270–320 μm size range are optimal for paleoenvironmental reconstructions" Reference : http://www.sciencedirect.com/science/article/pii/0377839896000035
Full paper is needed ! Please send me if anyone has !!
It's rather dependent upon the species you are using. The isotopic composition of symbiotic species (e.g. G. ruber, G. sacculifer) might change during growth as symbiotic output overprints the ambient signal (see the early papers by Wolfgang Berger or http://www.bioone.org/doi/abs/10.1666/11027.1), but it appears to level off at larger sizes. Whilst changes in isotope values of asymbiotic species is likely the result of depth habitat-migration, for G. bulloides I would use 300-355 μm (though it doesn't seem to matter) and a larger size for globorotalids (e.g. G.truncatulinoides, G. inflata etc.) so that your certain its recording a deeper signal.
The size fraction 250-300um or 300-355um is being preferred for these species because they are adults and also they are abundant (as mentioned by Peter and Brett). In addition to the size fraction it is important to consider sampling statistics and natural seasonal variability. Picking 5/8 individuals for d18O from a large pool of individuals may not be representative compared to if they are picked from smaller split sub-sample. You can look at some of the single specimen work to see the variability that can be found in a sample.
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