When I talk to people around McMurdo, or classrooms of fabulous Polar Enthusiasts back in the States, I always describe dissolved organic matter (DOM) very simply as microscopic bits of organic matter that are suspended in liquid or frozen water. Now that I have worked with the DOM team in Antarctica for over a month collecting samples of water and preparing the water in a variety of ways to test for DOM and microbes, my understanding of DOM has deepened. Today, Yo helped me understand even more by creating a great analogy to describe DOM and why we use systems such as those on the Cotton Glacier to study this abundant source of organic matter. If I was to take my very simple description, "microscopic bits of organic stuff suspended in water," and change just a few words to, "dissolved material that is a nanometer to 10's of nanometers in size suspended in water, and my explanation comes closer to the truth. DOM is the largest repository of organic material in the whole world, it actually dwarfs all other living organisms, and yet, it is the least understood. Every plant, animal, protist, fungi, or other life form that dies and decays becomes a component of the DOM pool. Again, this is not when there are hunks of dead leaves hanging around on the ground, nor is it when those leaves rot away to mush. DOM is the mush of the mush of the mush that comes from the break down at a chemical level of the material making up an organism. No, wait, DOM is even more than the breakdown at the chemical level- it is also the recombination of the chemicals from one part of an organism with other chemicals of that organism or even other organisms. Whew, what a lovely, mysterious mess DOM is! It is very exciting to involve myself with a team trying to learn more about this vast unknown. One of the largest pools of DOM is located in the marine environment- all those decomposed plankton, algae, fish, marine mammals eventually chemically add to the DOM pool in the oceans. Additionally, there is DOM entering the marine environment from land too, through water runoff to the ocean, or blown in by the winds. Hence, the DOM in the oceans is a very complicated system and difficult to study. This is where the DOM team here in Antarctica steps in and provides tools to help study large systems with DOM coming from the earth, the sea, and the air. The glacier where we are collecting our most important samples from is amazingly pristine- it is deep enough within the Transantarctic Mountains to not have too many air-borne pollutants from the sea or McMurdo, and the stream system is newly formed every year. The stream never follows the path of the year before. Therefore, the DOM team hypothesizes that the DOM and bacteria they discover in their water, ice core, and air samples are really truly a part of the Cotton Glacier and not blown in from some other place. The dissolved organic matter that the DOM team finds at the Cotton Glacier does not appear too similar to the DOM in marine or terrestrial systems. It is DOM in the most graceful and clean form, as the organisms that contribute to this DOM pool are relatively simple themselves- there are no terrestrial plants or animals in Antarctica to contribute to the pool- just very small algae and bacteria. The team hopes that understanding the components of this unique DOM and how the different components combine, as well as the influences its structure has on this specific environment helps us understand DOM in larger water bodies such as the ocean, lakes, and rivers. Okay, so I mentioned that Yo had a great DOM analogy and here it is. Imagine an environment as a blackboard- you write on the blackboard with chalk and erase it, leaving smears of white over the whole board. This is like a marine environment with its very first infusion of DOM (which on earth took place millions and millions of years ago). You continue to write on the chalkboard and erase whatever it is you write, but never clean the eraser, nor give the board a good scrubbing down. Eventually, you will write on the board, but not be able to distinguish what you wrote because the board is so thick with the remnants of earlier words. This is like a marine environment that has years upon years of DOM in its waters coming from the marine world and spilling over from land, too. What an undistinguishable board you end up with. The glacier the DOM team is looking at is like a brand new, squeaky-clean chalkboard. One day you write just one, one-letter word on the board and erase it using soap and a thorough water rinse, leaving not a single trace of chalk on the surface. This is the environment and the DOM we are studying down here in Antarctica. The more we know about our chalkboard the more we will understand about what happens when the board gets too dirty, or what happens with all the chalk dust, or the bits that get stuck to the eraser. Thanks again, Yo, for helping to explaining dissolved organic matter!