“It’s a really exciting place to do oceanography, because you can throw almost any kind of instrument over the side, and it will come up with observations that lead to new science,” said Skidaway Institute scientist Catherine Edwards. A former postdoctoral fellow at Florida State University, Edwards describes her recent research cruise to the little-studied “Big Bend” section of the northeastern Gulf of Mexico.
In an effort to extend FSU’s coastal ocean observatory in the Florida Big Bend, Edwards deployed two self-contained bottom-mounted sensors that measure temperature, salinity, currents, and how they vary from the seafloor to the surface. The sensor packages are moored on the outer shelf to help Edwards and FSU scientists learn more about how the Gulf wind and tidal currents transport material from the shelf edge to the shore. Edwards was assisted by Austin Todd, a graduate student in physical oceanography at Florida State University.
Many fish are spawned at the shelf break, but spend their juvenile stages in the salt marshes and estuaries. Distances of 50 to 75 miles are too far for fish larvae to swim on their own and physical models, by themselves, do not fully explain how larvae are able make the journey.
“Whether you’re tracking fish larvae or oil, the science question is the same,” Edwards said. “We are trying to develop a clearer picture of how the physics and biology interact.”
Edwards does have an idea. Coastal sea breezes shift on- and off-shore between day and night during spawning season in the Gulf of Mexico. The winds push the surface water in one direction, while deeper waters compensate with currents in the opposite direction.
“Fish larvae don’t swim far horizontally, but they do migrate up and down the water column on day-night cycles fundamentally tied to the timing of the solar cycle and thus sea breeze,” Edwards said. “Depending on the larval migration, they may simply shift their position in the water column to ride the diurnal shifts in the current to shore.”
The cruise wasn’t easy to arrange. Edwards had access to the needed instruments, but no money for ship-time, which often runs thousands to tens of thousands of dollars a day for capable oceanographic vessels. She was able to hitch a ride on a NOAA National Marine Fisheries Service (NMFS) vessel that was conducting a twice-annual cruise to studying fish biology throughout the Gulf of Mexico.
“I’m a physicist by training, so I really enjoyed the chance to ‘play biologist’ for the two week leg of the cruise,” she said. “That interaction was really valuable for planning future work with NMFS scientists.”
Edwards set up two sets of instruments very near a NOAA weather buoy. While the weather buoy collects data on the conditions above the surface, Edwards’ instruments will do the same for the conditions in the water column. Since weather conditions often drive water movement, the ability to combine the two data sets will provide valuable information.
Edwards will return in six months to collect her instrument packages and the data they have recorded.