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Big, unicellular science


A shallow water foraminifer, Ammonia sp. (it’s about 0.4 mm big)

Metres of sea-level change. Hundreds of thousands of years. The entire globe. The scale of the iGlass research project is rather large. But some of the research is based on the humblest of creatures: benthic foraminifera.
If you have a really big one it might be an entire millimetre. Benthic foraminifera are unicellular protists who live on top of, or in the top layer of, marine sediment. Every species has its own niche; for instance, some like coarse sediments, some like fresh food, some like warm water, etcetera. Some of the more adventurous species even live in salt marshes. These are, if you will, the scuba divers among foraminifera; all foraminifera need salt water to live, but these brave souls have become accustomed to do without for substantial amounts of time.

Three specimens of Aubignyna perlucida; two of these have their shells filled with pyrite nodules

The reason why foraminifera, in spite of being such modest creatures, get so much attention from the palaeoclimate community is that they build some sort of skeleton, and aretherefore often very well preserved in sediments. They can be tens of millions of years old and still look like they died last week. They take the information they contain into their graves, and in this case that’s a good thing. If you know which species prefers what environment, you can “read” sediments they are found in.

Drilling a core in sediments that are several hundreds of thousands of years old

The York and Durham teams drilled cores through interglacial sediments.

We drilled in the middle of Norfolk, but we know that area has been inundated in previous interglacials, and indeed, we found both freshwater and marine sediments in our cores. And using the foraminifera in them, we are reading them. We are looking for changes reflected in the various species encountered; will we get a gradual change from the shallowest foraminifera, which are the ones that actually live above sea level but still within reach of high tide, through the ones that live in shallow water, to those that prefer deeper waters? Or will we see several of such sequences? Or an instantaneous shift from no foraminifera to relatively deep-water species? Watch this space for results…

The foraminifera sorted by species
(each numbered rectangle is about 2.3 mm wide)

We found some 10, 000 foraminifera (and counting). They were picked out of the samples by two different scholars, so we keep them all in order to be able to check we have comparable ideas of which species is which (since you ask; no, identifying the species is not a straightforward task). Keeping them also allows us to always go back to the source material in case of questions arising. And after the questions iGlass asks have been answered, who knows what other questions such a collection can help tackle!

November 2020

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