guest post by Sara Rivera
Sara Rivera is a graduate student in the Aluwihare Lab at Scripps Institution of Oceanography. Here, she recounts some of her challenges in sampling at sea.
Being at sea for research requires innovative solutions for problems not typically experienced on land. One of the main issues faced when sampling for microorganisms and organic chemistry is the impact of light on samples. On land, it is easy to grab a piece of foil to cover a rack of vials. At sea, it is not so easy because it is fast, windy, and there are limited supplies. At first, I used foil to cover my tube rack, like I would on land, to block the sunshine. I found that with the fast pace at sea that I needed to get my samples done, I constantly ripped the foil and needed to get a new piece. I would also end up chasing pieces of foil as they were blown across the deck. As my supply of foil dwindled, I contemplated what else would efficiently block the sunshine while allowing easy and efficient access to the sample tubes.
Lo and behold, the answer sat in front of me in an essential piece of cruise equipment: a roll of duct tape. I created a barn-like structure out of duct tape that would slide over the tube rack and completely block out any sunlight. It is waterproof and reusable. It is also removable, allowing me to continue to use the tube rack for other experiments as needed.
Why do I care this much about keeping the samples out of the sunlight? Sunlight impacts both chemical and biological processes. The untraviolet (UV) region of sunlight leads to photo-oxidation of organic molecules, changing the chemistry of the sample before I have time to process it. Recent work by Neal Arakawa (Science Advances, September 2017) demonstrated that a single type of molecule, β-carotene, can photooxidize to generate a slew of carotenoid degradation products that is linked to 4% of the total dissolved organic matter in the ocean. If one molecule can degrade to such a large number of other molecules, from simply sitting in the sunshine, I do not want that happening in my samples! I want the samples to reflect the chemistry of the sea water from the depth from which I collected it.
UV also damages biological cells. The biological damage can impact both the biology and chemistry as distressed cells will take up and release different molecules than in their normal state. Since I measure both the biology and chemistry, this one is doubly bad.
The visible light regions of sunlight are absorbed by the green pigment chlorophyll, found in the organelles called chloroplasts, which is essential to photosynthesis in the majority of marine phytoplankton. These chloroplasts also give the phytoplankton their green color. Light is attenuated as you go deeper in the ocean. We sample at a variety of depths from the surface down to 515 meters (1690 ft). The organisms below the surface are not acclimated or adapted to the light on the deck of the ship- it is much too bright for them. It can also lead to fast growth and production from increased photosynthesis. Because I want to capture the biology at the different depths we sample, I don’t want them to suddenly start growing faster because of the additional light.