The interactions of plankton with oil droplets is a
fascinating but relatively unexplored area. Scientists in the DROPPS Consortium
previously looked at oil droplets rising though thin layer of plankton to see
how they interact with oil. This time DROPPS wanted to look further into what
may have happened in the dispersed oil layers between the well head, at
approximately 5000 feet below sea level, and the ocean surface. DROPPS
Scientists used holography technology, small scale experiments in the lab, and
a recently constructed tower tank, measuring approximately 4 meters tall, for
their latest experiments.
During the week of June 22nd 2015, DROPPS scientists
Ed Buskey, Brad Gemmell, Jian Sheng, Joe Katz, David Murphy, Cheng Li, Larry
David, Vincent d'Albignac and Jeffrey Cordero convened at the University of
Texas Marine Science Institute (UTMSI) in Port Aransas, Texas to participate in
the experiments.
DROPPS’ recent experiments involved holography technology
which allows you to construct volume in 3D. This shows a 3D distribution of
water and how it interacts with particles. DROPPS scientists were able to take a
closer look at what could have happened to plumes of oil released from the Deepwater
Horizon well head that had been mixed with dispersant. Studies showed dispersants
created subsurface plumes of tiny oil droplets. DROPPS recreated this in the laboratory by
creating a layer of microscopic droplets (by adding dispersant to oil and mixing
it up with seawater using stir plates), mimicking the subsurface layers associated
with the Deepwater Horizon. They also created varying density layers in the
water (by slightly changing the salinity), with the most dense water at the
bottom, intermediate water in the middle, and lighter water at the top. They
wanted to see how quickly oil would diffuse through these layers. Seawater density
can change throughout the water column, with the most rapid changes often
occurring near the bottom of the thermocline.
With the tower tank experiments, they set up layers to see how the micro
oil droplets would disperse naturally, with and without small organisms
swimming through it or with larger organisms stirring up the water. This would help measure the importance of
biogenic mixing (mixing of the ocean by animals), an idea that has recently
been of great interest to biologists and oceanographers.
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| Small scale experiment in lab. Photo by Jeffery Cordero |
First, DROPPS scientists conducted small scale experiments in the lab. In these experiments, they added small zooplankton, copepods mostly, and used PIV to examine how or if they mixed a layer of oil. The copepods did not seem to have much effect on the dispersion of the oil layer, probably because they were too small. Tiny oil droplets have natural fluorescence so they glow when exposed to certain wavelengths of light. This allows DROPPS scientists to measure how well the animals mix the oil-water emulsion layer in comparison to natural diffusion.
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| A ctenophore suspended in water. Photo by Jeffery Cordero |
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| Tower Tank. Photo by Jeffery Cordero |
In the future they
hope to use intermediate sized organisms such as shrimp and small fish to
examine their effects of biogenic mixing of dispersed oil. In the future,
DROPPS scientists also wanted to study how these organisms interact with the
dispersed oil layers; do copepods and other small zooplankton feed on the oil?
Does this make them more susceptible to their predators (jellyfish and small
fish)?
Video by Jeffery Cordero
Research sponsored by the Gulf of Mexico Research Initiative
