Dear Roy and John,
Roy wrote:
> The one point I think you have possibly misunderstood is the one about
> 'miscellaneous'. It's not the word, so much as the possibility of the
> concept having meaning that changes with time that worries me. This
> can be addressed through the definition by a statement that
> 'miscellaneous means phytoplankton that are not diatoms, diazotrophs,
> calcareous phytoplankton or picophytoplankton'. I did briefly
consider
> the phrase 'phytoplankton_not_diatom_diazotroph_calcareous_pico' in
the
> standard name, but then thought better of it.
>
Yes, I see now. I agree that the definitions should contain a statement
such as the one you suggest. Thanks for not suggesting the other
version of the name :)
John wrote:
> > > (1) I don't understand what the definition of picophytoplankton
> > (carbon
> > > concentration from the picophytoplankton (<2 um; < 5um) component
> > > alone) means Does it mean cells between 2 and 5 um in size, in
> > which> case it should be expressed as 2-5um, or does it mean
> > something else?
> > >
> >
> > I agree that this definition doesn't make sense as it stands - I'll
> > check with John Dunne.
>
> The wishy-washiness of this definition was intended to account for the
> fact that some groups make their distinction of smallest phytoplankton
> class at the <2um size, while others do it at the <5um size. I agree
> that it would be better to have a single cut off for clarity. Perhaps
> we should use the '2um' designation to be consistent with the
> traditional definition of 'picoplankton' (where nanoplankton is the
2-5
> umclass), and leave the individual participants to determine whether
> they think their definition is consistent with this designation.
>From the CF point of view, adopting a single cut off of <2um for
picophytoplankton would certainly be clear. However, will this cause
problems for modelling groups with different cut off sizes? I.e. will it
make intercomparison between models difficult? As an alternative, we
could write the definitions to cope with the vagueness, for example:
"Picophytoplankton are the smallest class of phytoplankton. The maximum
size of picophytoplankton is in the range 2-5 um and may vary between
models. A scalar coordinate variable should be used to specify the
maximum size of picophytoplankton included in the data variable."
This would then require the different modelling groups to specify the
threshold they used, but would allow them all to write their data with
the same standard name. (We could even give the coordinate variable a
standard name such as 'plankton_size_threshold'). Would that be a
suitable solution? Or do you still prefer to stick with the single cut
off?
John wrote:
> > > (3) 'mole_concenration_of_dissolved_iron_in_sea_water'. Besides
> the
> > > typo (concentration), does this refer to iron in all oxidation
> > states> (Fe2+/Fe3+) and chemical environments. If so, calling it
> > 'total iron'
> > > might be better.
> >
> > Thanks for pointing out the typo - I'll correct it. I think
whenever
> > the word "total" has come up in standard names proposals in the past
> > that we have tried to avoid using it. Indeed, there are no standard
> > names that use the term. I think "iron" essentially should be
> > understood to mean "total iron" and if we want more specific names
> for
> > Fe2+, etc, we should introduce terms such as "divalent iron" in the
> > waythat we have done for elemental and divalent mercury in the
> > atmosphere.Having said all that, I think it would be helpful if
> > John could clarify
> > the definition.
>
> In the geochemical literature, 'total' iron refers to the sum of iron
> associated with the particulate organic, particulate inorganic,
> dissolved organic and dissolved inorganic components (both Fe2+ and
> Fe3+). As we treat phytoplankton iron and particulate detrital iron
> separately from dissolved, 'total' does not equal 'dissolved'. As
> most,
> if not all, of the models do not distinguish between Fe2+ and Fe3+, I
> think we could simply add a note in the definition to the effect that
> 'dissolved' is intended to represent both Fe2+ and Fe3+.
Agreed. I'll add a sentence to the definitions.
Best wishes,
Alison
------
Alison Pamment Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre Fax: +44 1235 446314
Rutherford Appleton Laboratory Email: alison.pamment at stfc.ac.uk
Chilton, Didcot, OX11 0QX, U.K.
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Received on Thu Apr 01 2010 - 06:27:41 BST
