Krill and the Carbon Cycle

Krill And The Carbon Cycle 2013-01-14 (07.17.03-407 PM)

What do krill have to do with the carbon cycle?  Well, maybe I should start with, “What the heck is the carbon cycle? (oh, and why do I care?)”.  As many of you readers out there know, the carbon cycle is immensely complex and I couldn’t hope to explain it all in one measly blog post.  But in a nutshell, it’s the cycle that describes the overall budget of carbon, in its many forms, on/in our planet – that means, in the earth, the ocean, plants, animals, the atmosphere, everything.  The carbon is balanced in such a way that our planet can sustain life – excellent!  I don’t know about you, but I think that’s pretty great.

The ocean plays a huge part.  There is a constant exchange of carbon between the atmosphere and the ocean.  And it turns out that if there is an increase in atmospheric carbon, the ocean can suck it down… to a certain extent, at least.  Why? Well, blame it on chemistry (I blame most things I dislike on chemistry, but that’s just me).  The ocean can take up that CO2 because of chemical reactions that happen relatively quickly near the surface.  The uptake relies in large part on the weathering of rocks, which provides an input of ions that drive the chemical reactions.

Once the ocean reaches its limit, it just can’t take up any more CO2.  What then?  That’s when the krill (and, okay, some other helpful zooplankton) come to the rescue.  They eat up phytoplankton that have converted dissolved inorganic carbon (DIC) at the ocean’s surface to organic carbon (part of the whole photosynthesis thing).  Turns out krill are really messy eaters, spitting out spitballs containing clumps of uneaten phytoplankton.  They also have really inefficient digestive systems, and their fecal matter contains a lot of carbon and other nutrients.  These spit balls and fecal strings (yes, they kind of look like strings) sink WAY faster than individual phytoplankton, which means that those carbon packets sink deep into the ocean.

Source: Uwe Kils.  In this image you can see the feeding basket formed by the anterior legs (thorecopods).  The small red dot near the feeding basket is probably a small copepod (lunch!).  There’s a spit ball in the lower right corner, and a fecal string in the lower left.

This is an important way in which carbon is exported away from the surface waters, where it can be stored at depth, drifting with the deep ocean currents or being deposited on the seafloor to be incorporated into sediments.  Krill of the world:  thank you!

Sadly, if atmospheric CO2 continues to rise, the ocean will not be able to handle it, even with the help of the amazing krill.  And another very significant effect of just shoving the excess carbon into the ocean:  the ocean becomes more and more acidic, which is harmful to many of the animals that live there, especially corals and those with shells.

Which brings us to the “why do I care?” question from the beginning.  You might want to consider caring because your livelihood depends on it.  And if not yours, then certainly your children and grandchildren. If CO2 in the atmosphere continues to rise, the climate on our planet will be seriously affected.  In addition to this, the devastating effects of ocean acidification will have cascading implications for the ocean ecosystem – which in turn will have implications for us terrestrial types.

I’ve glossed over a lot here, and kind of ended on a downer.  So here’s something to cheer you up – Ernst Haeckel’s drawings of copepods (my new favorite thing ever since Tuesday, thanks, Owen and Anna).  No, copepods aren’t some kind of krill.  But they are zooplankton, and they’re pretty, aren’t they?

Copepoda – by Ernst Haeckel

If I’ve made any mistakes, whether they’re small, or total doozies, be sure to let me know so I can fix them up and not confuse people!

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