All organisms breathe, in one way or another. Animals breathe in oxygen and breathe out carbon dioxide (a.k.a. respiration), and plants do the opposite.  Oxygen is essential to animal life because it is required to burn fuel (the food we eat) and produce energy to power the body--we all know the best way to put out a fire is to smother it.

Oxygen’s critical role in the body makes it very useful for measuring metabolism.  Several members of our team are using oxygen to look at how fast different organisms in the marine food web burn up the food that is available.

All of us have different rates of metabolism, meaning that we burn and/or store fuel at a different rate—my husband can eat an entire large pizza by himself and not gain an ounce, but me, not so much.

 Photo credit: Brendan Smith

Photo credit: Brendan Smith

Metabolism also varies by species, and is affected by lots of different things including lifestyle.  For example, if you live attached to a rock and never move, you are likely to have a lower metabolic rate than an animal that swims constantly. But temperature also has a big impact on metabolic rate, which is why we are so interested in measuring it in the Arctic.

For most polar marine organisms, metabolism is pretty slow because the water is so cold.  This may seem counter-intuitive to those of us that live in cold climates, because it seems like we need to eat more calories in cold weather to keep warm.  But that’s because mammals are warm-blooded and use up energy to keep a constant body temperature, no matter how cold it is outside.  The vast majority of marine animals are cold-blooded, meaning their body temperature fluctuates in tune with the surrounding environment because they don’t have much capacity to regulate temperature.  You car’s engine runs rougher in the winter when all the fluids are more viscous, and lots of processes occurring in the cells of animals happen more slowly in the cold. The flip side is that when you warm up the water, metabolism speeds up as well.

That may not seem like a bad thing, but in the Arctic, most of the “fuel” that keeps marine organisms going all year is produced during the short spring bloom season. When you consider that there is only so much food in the fridge and it needs to last all winter, burning through it too fast might not be so good.  We need to understand how fast the material produced in spring gets used up by the marine food web, and what parts of the food web use the most, in order to better predict how things might change if the temperature continues to creep up.  Getting some real numbers for these important biological rates is a central goal of our project.

The sediments on the sea floor “breathe” too.  It may not look too exciting down there (certainly the mud I collect doesn’t generate as much buzz around here as the animals that come up in the trawls or get spotted through binoculars from the bridge), but sediments are packed with bacteria that are critically important to breaking down plant and animal remains and releasing nutrients back to the environment to support more plant growth, just like they do in your compost pile.

 Photo credit: Brendan Smith

Photo credit: Brendan Smith

Bacteria are also food for other microscopic organisms that live in the sediments, which are in turn food for larger organisms.  And bacterial decomposition of organic material that settles to the sea floor is, of course, very temperature-dependent.  That’s why my team is conducting experiments on this cruise to measure how much the sediment community “breathes” at different temperatures, which will give us a way to estimate how much food they are consuming.  The multi-corer gives us a way to collect intact sediment communities that we can hold at different temperatures on the ship while we measure how much oxygen they are using up (and how many nutrients they are returning to the environment).  Others on the ship are making similar measurements with individual species (like clams and small crustaceans) and even bacteria living on sinking particles.  But we can’t measure every single species individually, so working with the whole sediment cores let’s us kill a lot of birds with one stone, so to speak.