Supplemental material
Annex 1: Diatoms quantification
For quantitative analysis, 2 cc. of fresh sediment were taken from each sample, weighed, dried,
weighed again and cleaned according to the method of Fenner [1982]. Slides were prepared using
the evaporation tray method of Battarbee [1973], and mounted with Permount medium. Diatom
quantification was done under a Nikon Labophot 2A microscope equipped with Differential
Interference Contrast, using 10 x eyepieces and 100 x oil objectives.
Diatom quantification was conducted following the counting procedures of Schrader and
Schuette [1968]. Diatom frustules were counted in 100 randomly selected fields of view for one
slide prepared from each sample. Diatom counts were then converted to valves/g of sediment
according to the following expression:
Number of valves/g= [(Vn_ (At/As)) _ (V/v)] / W,
where Vn is the number of valves counted, At is the area of the evaporation tray, As is the area
of the slide counted, V is the volume of solution in the beaker, v is the volume of solution splitted
into the evaporation tray, and W is the weight of raw sample.
Diatom flux, expressed as valves/cm2/ka, was finally calculated by multiplying the sediment
flux (230Th Ðnormalized flux) by the diatom content (valves/g) at each level, according to the
following equation:
Total Diatom Flux = Total Diatoms (valves/g) x 230Th normalized flux at the same level
References
Battarbee, R. W. (1973), A new method for the estimation of absolute microfossil numbers,
with reference especially to diatoms, Limnology and Oceanography, 18, 647-653.
Fenner, J. (1982), Diatoms in the Eocene and Oligocene sediments off NW Africa, their
stratigraphic and paleogeographic occurrences, University of Kiel, Kiel.
Schrader, H.-J. and G. Schuette (1968) Marine Diatoms. In The Sea, edited by Emiliani, C.,
pp. 1179-1231, John Wiley & Sons, New York.