Pollen sum0
Taxa seen0
Exotic marker0
Last—
while you count
One press is one grain. The board keeps your own taxa at the top once you
have used them, so the list gets shorter as the slide goes on rather than longer. Everything is
saved as you go — you can close the phone mid-count and come back to it.
the decision that matters most
A pollen diagram is a set of percentages, and a percentage needs a
denominator. What goes into the sum is the most consequential choice in the whole exercise,
and two workers who choose differently will draw different diagrams from the same slide.
The convention here is the usual one: terrestrial pollen in, everything else out. Change it if
your material calls for it, but change it deliberately.
Pollen sum0
Trees and shrubs (AP)—
Herbs (NAP)—
AP : NAP—
A taxon kept out of the sum is shown against the sum plus its own group —
a spore cannot sensibly be a percentage of a total it was excluded from.
nearest modern analogue
Count something first.
Matched by squared chord distance against reference assemblages —
the same measure used in the modern analogue technique. Below about 0.15 is a close analogue;
above 0.30 there is no good modern equivalent, which is itself a real and interesting
result rather than a failure.
the human signal
The indicator set is Behre's: Plantago lanceolata, Rumex,
Artemisia, Urtica, Centaurea cyanus and cereal-type pollen. Cereal-type is
the strong one — grass pollen above about 40 µm with a thick annulus. It is also the easiest
to over-call, because several wild grasses reach that size.
what the percentages hide
Pollen production and dispersal differ by more than an order of magnitude
between taxa, so an assemblage is not a vegetation census. The correction below uses
relative pollen productivity estimates, which are approximate and regionally variable — treat
the direction as reliable and the magnitude as indicative.
ask about this assemblage
The counts, percentages and diversity of the current sample are sent
with your question. Nothing else leaves the phone — no position, no notes, no photographs.
Stockmarr exotic marker
Percentages are relative, so they can only ever tell you about proportions.
Concentration is the absolute number, and it is the only way to tell a real decline from
a taxon being crowded out of the percentages by something else rising.
Concentration—
95% interval—
Relative error—
Influx—
richness, corrected for effort
Count longer and you will find more taxa. That is arithmetic, not ecology.
Rarefaction asks how many taxa you would have seen had you stopped at a common count,
which is the only fair way to compare one sample with another.
Counted—
Taxa observed—
Rarefied richness—
Shannon H—
Evenness J—
Hill N1 / N2—
A stratigraphic diagram needs at least two samples with depths.
CONISS, stratigraphically constrained
Samples are joined only to their neighbours, because a core has an order and
a zonation that ignores it is not a zonation. Distance is the chord distance on square-root
proportions; clusters join by the smallest increase in within-zone sum of squares.
how many are real
Compared against the broken stick model. A split that explains less than
a random partition would is not a zone boundary, however tidy it looks on the dendrogram.
what changes at each boundary
what am I looking at
Pollen is keyed on apertures first — how many, and of what kind — then
on sculpture, then size. Get the aperture right and the field narrows to a handful.
Two cautions that catch everyone. Grains swell in glycerol and shrink in
silicone oil, so a size quoted without the mountant is nearly meaningless. And a crumpled or
folded grain can hide an aperture entirely — roll it before you call it inaperturate.
hydrofluoric acid
HF dissolves silicate, and it dissolves you without hurting at the time.
A splash on skin can be painless for hours while fluoride strips calcium from the blood; the
cardiac arrest that follows a large exposure is the usual cause of death, not the burn.
Calcium gluconate gel must be in the room before the bottle is opened, and somebody else
must know you are working. Never alone, never in a glass vessel, never without a face shield.
The full reagent hazards →
acetolysis
Acetic anhydride with concentrated sulphuric acid reacts violently with
water. Everything that touches the mixture must be dry — the sample must be washed through
glacial acetic acid first, and the tubes must be dry. A wet tube is how acetolysis mixtures end
up on the ceiling.
the order of operations
the marker goes in FIRST
The Lycopodium tablet must be dissolved into the sample before any
step that could lose material. A marker added late counts only the losses after it arrived,
and the concentration it gives you will be wrong in a direction you cannot estimate.
Dissolve the tablet in dilute HCl, and record the batch number — it is printed on the tube and
it is the number the whole concentration rests on.