Thursday, June 18, 2015

UVP photos of the day

I’m not a biologist, or a zoologist. I work with an underwater camera system designed to capture marine particles. Many of those particles happen to be zooplankton, the ocean’s tiny drifting animals. Every day, I’ve been posting some choice snapshots on the door of the CTD computer lab, in the hopes that the other scientists on board can help me identify some of the more mysterious animals.

How does the camera system capture all of these images? With flashing red lights! The Underwater Vision Profiler (UVP) takes pictures of 1-liter parcels of water as it descends toward the seafloor. (In the attached photo, my face is taking up the space that gets photographed by the camera.) The camera itself sits at the bottom of the metal cylinder, and the horizontal red lights are the inward-facing camera “flash.” The camera identifies all of the objects within each picture that are 100 micrometers to several centimeters in size. For scale, that’s anything larger than the width of one human hair and smaller than my face.  As it goes down with the CTD rosette, it can capture up to five 1-liter chunks of water per second, saving thousands of images every single cast.

Some of the larger objects caught on camera are pretty difficult to sample using other methods. Take jellyfish, for example – gelatinous zooplankton. If you try to catch a gelatinous organism in a net, it might be smashed into pieces by the force of the plastic net hurtling through the water.

Or, think about the challenge of capturing a piece of “marine snow.” Marine snowflakes, dubbed the “dust bunnies of the sea,” are aggregates of many bits of things all stuck together with transparent exoploymeric substances, the ocean’s snotty glue. These fluffy light snowflakes sink so slowly that if you try to catch one in a sediment trap, it may never happen.

  What’s the point? As marine particles sink - including phytoplankton, zooplankton, and detritus (plants, animals and dead stuff) - organic carbon gets transferred from the surface of the ocean down to deep, cold waters where it can be stored long-term. This is called the Biological Carbon Pump, and it has the ability to sequester carbon dioxide from the earth’s atmosphere on a global scale. To better understand it, we need to understand how much stuff is sinking and how quickly it is sinking. That depends on how large and how dense the particles are. The UVP shows us all of this, and gives images of the largest objects so we can see what they actually are…including the elusive gelatinous organisms and marine snowflakes.  

By Jessie Turner