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If diatoms could talk

07 Jul 2021 | Science Notes

The oceans would be very noisy since these little single-celled algae organisms make up nearly half the living matter in the oceans. Despite their silence they still tell a story, because when the sea surface warms and cools, and ice cover changes, their abundance varies, and by looking at density of diatom layers in the ocean floor scientists can infer what the surface climate was like in the past. A new study (h/t No Tricks Zone) notes that researchers have assumed that three different diatom species can all be grouped together for this purpose, but they turn out to respond differently to ice and temperature variations and should be analyzed separately. And when that is done, the northern North Atlantic Ocean is revealed to have cooled and gained ice cover since the 1960s. Say what?

The study, in case you were put off by the racy title, “Improving the paleoceanographic proxy tool kit – On the biogeography and ecology of the sea ice-associated species Fragilariopsis oceanica, Fragilariopsis reginae-jahniae and Fossula arctica in the northern North Atlantic”, concerns the three Latin-named diatoms in question. The standard practise up to now has been to treat them all as Fossula arctica, like assuming your kids will all want to watch the same movie. Alas, the resulting quarrel proves they don’t, and neither do Fragilariopsis reginae-jahniae enjoy ice cover as much as Fossula arctica. So to each its own, say the scientists, and they figured out the patterns the distribution of each of the diatoms reveals. The result was this graph showing (top) August Sea Surface Temperature and (bottom) April sea ice cover from about 1930 to 2014.

The dashed line is the estimate when all three diatoms are analysed as a group, and the solid line is what happens when they are analysed separately. In the top panel the result is the ocean surface looks cooler, and from 1960 onward the cooling trend is steeper.

Wait, cooling trend? Yes, which matches the increasing trend in spring sea ice cover in the bottom chart. Again, starting at 1960 the dashed line moves up a little, but when the diatoms are analysed separately the sea ice cover estimate trends up more steeply.

So if the diatoms could talk they’d insist we recognize their individuality. And they’d tell us the northern North Atlantic has been getting colder and icier since the 1960s.

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