Frozen poo gathers Antarctic moss

Posted: July 8, 2012 at 3:45 pm

Over on the BBC Nature site is an amazing story explaining how the cold, desolate Antarctic, with poor quality soil, can play host to several species of moss and the reason is enough to get anyone with a slightly childish mind (including me) excited – frozen penguin poo.

— Arctic moss can grow into large beds despite the harsh environment

The elevated site in East Antarctica hasn’t had any penguins for several thousand years but between 3000 and 8000 years ago the site was home to a colony of Adelie penguins, as evidenced by the remains of the penguins’ rock nests and the nutrients from the birds’ poo. In the BBC story they just say that a ‘chemical signature’ shows that the nitrogen in the soil passed through a marine predator, so what does this mean? Well at a wild guess I figured this might be something to do with our good friends isotopic ratios. Long used to date and trace the origin of archaeological finds, in recent years ecologists have started to use the technique to map food webs.

You see, it seems that soil that has been pooed on by seabirds is enriched with more ¹⁵N than normal, but why? Well, when producing urea and uric acid, ¹⁴N is preferentially used and then excreted, leaving behind more ¹⁵N than found in the environment. This, I suspect, is due to the kinetic isotope effect, making the rates of reactions using ¹⁴N faster than those using the heavier element. Any predator will then ingest more ¹⁵N and further concentrate it, until you get up to the apex predator. Therefore a predator high up the food chain, like penguins, will have a higher concentration of ¹⁵N in their flesh, and presumably their poo will have an isotopic ratio reflecting their isotopically enriched diet.

Of course, this has got me wondering whether that means we’re also ¹⁵N enriched due to our protein heavy diets? Could you even distinguish a seafood eater from a meat eater and/or a vegetarian based on the amount of ¹⁵N in our bodies? Well I’m behind the times: there are studies doing just that to work out the diets of our predecessors and suggestions that the same can be used to diagnose eating disorders.

So now you that it’s the remains of ancient penguin poo that fertilised the Antarctic, creating a habitat for small insects and other animals, and how that was worked out.

Laura Howes