A nice, new #study out by Jörg Lippold & colleagues on #radiocarbon differences in co-occurring planktic #foraminifera. They document how subsurface-dwellers like G. truncatulinoides have ages offset, on average, by ~300 14-C yrs compared to surface-ocean species (like G. ruber & T. sacculifer).
@bee8bit Ah! So it has to do with the fact that the subsurface-dwelling planktic foraminifera are living in "older", deeper waters (~500 m), as opposed to the others which are living in upper waters at the surface (0-50 m). While making shells, the surface bugs readily equilibrate with atmospheric radiocarbon (and hence gives accurate dates). The scientists are looking at dating sediment cores taken from the bottom of the ocean, which contain shells deposited from above; but plankton that lived in 0-50 m and >300 m (and even those living at the ocean bottom), all "co-occur" in the sediments (or mud/clay) that is brought in by rivers or wind. This is why its important to only date shells of surface-ocean species of plankton from marine sediment cores as opposed to the deeper-dwelling ones (w nice experiment borne out in that article).
If two types of plankton were living in the same waters, their source of carbon is the same, and hence their shells will not give different ages.
Sorry to be long, but hopefully simple!
@kau Ah, yes. The part about old waters makes totally sense to me now. I was wondering how plankton would be able to uptake only specific isotopes - which they don't.
Thank you for clarifying.
@kau So, in simpler terms: Does that mean that scientists who try to estimate the age of something by C-14, they might be wrong by ~1200 years if they measure the C-14 in some plankton, because those species already have a lower (or is it higher?) percentage of C-14 in them while still alive?