NOAA Teacher at Sea
Aboard NOAA Ship Oregon II
June 27-July 5, 2018
Mission: SEAMAP Summer Groundfish Survey
Geographic Area of Cruise: Gulf of Mexico
Date: July 3, 2018
Weather Data from the Bridge
Conditions at 1610
Latitude: 29° 30’ N
Longitude: 92° 51’ W
Relative Humidity: 83%
Temperature: 26° C
Wind Speed: 13 knots
Cloudy with rain
Science and Technology Log
“The solution to pollution is dilution” was a common refrain during the midcentury as large scale factories became more common. This mindset applied to both air and water as both seemed limitless. Looking out over the Gulf of Mexico, a relatively small body of water, it’s easy to see how this logic prevailed. Even the Great Lakes, the largest body of fresh surface water in the world, accepted incalculable amounts of pollution and sewage from coastal factories, steel and wood mills, and of course major cities.
The rise of the modern technological age that took humans to the moon gave us the first glimpse of the fallacy of the “solution”. “Earthrise” is the first photo of the entire Earth taken from space, showing us how thin our protective atmosphere really is and how delicately the Blue Planet floats in the vastness of space. This is the beginning of the modern environmental movement.
To truly guide the development of national policies including those that protect air and water quality, federal agencies such as NOAA are responsible for collecting data about our atmosphere and oceans, now knowing that these ecological compartments cannot endlessly dilute the pollution we generate. What seemed to be an obvious solution has today ballooned into a number of serious problems, from acid rain and blinding smog in cities to burning rivers, mass fish die offs that wash up on Lake Michigan beaches and dying coral reefs in the oceans.
A major pollutant in the Gulf is sourced from industrial agriculture practices from as far away as Illinois and the rest of the Midwest farm belt. Fertilizer and pesticides enter local rivers that find their way to the Mississippi River which carries contaminants into the Gulf of Mexico.
We have reached the Gulf’s “Dead Zone”, yielding a few tiny catches. Station W1601 may have given the smallest catch ever—a clump of seaweed and a whole shrimp.
Hypoxia literally means “low oxygen”. When fertilizers used to grow corn and soy enter bodies of water, they likewise feed the growth of algae, which are not technically plants but they are the aquatic equivalent. But plants make oxygen, how can this lead to low oxygen? Algae and land plants only produce oxygen during the day. At night, they consume oxygen gas through respiration. They do this during the day as well, but overall produce more oxygen in the light through photosynthesis. For hundreds of millions of years, that’s been fine, but the recent addition of fertilizers and the warm Gulf waters cause an explosion of the kind of microscopic algae that are suspended in the water column and turn water bright green, or red in the case of “red tides”. These explosions are called algal blooms.
Algal blooms can cloud up water, making life hard for other photosynthetic organisms such as coral symbionts and larger seaweeds. At night, animals can suffocate without oxygen. During red tides, some algae release toxins that harm other life. When these organisms die and sink, bacteria go to work and decompose their bodies. The population of bacteria explodes, consuming the remaining oxygen at the sea floor. Animals that wander into the hypoxic zone also suffocate and die, feeding more decomposer bacteria that can survive with little to no oxygen. Thus, hypoxic areas are also called “dead zones”. The hypoxic zone is just above the sea floor, as little as a half a meter above, and oxygen levels can drop precipitously within a meter of the bottom.
NOAA scientists including those conducting the SEAMAP Summer Groundfish survey on Oregon II track the location, size and movement of the Gulf hypoxic zone using the conductivity-temperature-dissolved oxygen probe, or CTD. The CTD is sent into the water before every trawl to take a variety of measurements. Besides conductivity (a measure of ions), temperature and oxygen, the CTD also checks the salinity, clarity and amount of photosynthetic pigments in the water, which gives an idea of plankton populations. Ours uses two different sensors for conductivity, salinity, temperature and oxygen, double-checking each other. A pump pulls water through the various sensors and the measurements are sent directly to a computer in the dry lab to record these data.
The CTD is lowered to just under the surface of the water to make sure the pump is working and to flush the system. Then it is lowered to within a meter of the bottom. The CTD also has an altimeter to measure the distance from the bottom, while the ship also uses sonar to determine the water depth at each station. Water is measured continuously as the CTD is lowered and raised, creating a graph that profiles the water column. Crewmen are on deck controlling the winches according to the directions from a scientist over the radio who is monitoring the water depth and measurements in the dry lab.
The CTD also has bottles that can store water samples so oxygen can be tested a third time in the lab onboard. When we only get a few fish where the CTD recorded normal oxygen, the CTD is launched again to verify oxygen levels using all three methods. In the CTD output, oxygen is coded in green as a line on the graph and in the data tables. Most stations read in the 5-6 range, the cutoff for hypoxia is 2. We are reading less than 1 in the Dead Zone.
With storms in the path and not-so-plenty of fish in the sea, today is a slow day.
Looking out over the water, I can’t help but think how intrepid, even audacious, early mariners must have been. I know we are within a couple miles of the coast but there’s no sign of land anywhere in any direction. Even with the reassurance that satellites, radar, radios, AND trained NOAA Corps officers steering in the bridge are all keeping track of us, I still swallow a moment of panic. What kind of person decides to sail out in search of new continents when it only takes a couple hours to lose track of where you came from? And yet, the Polynesians set out thousands years ago in canoes from mainland Asia, the Aborigine ancestors managed to find Australia, and of course, Europeans sailed across the Atlantic to the Americas, whether they knew it or not. It was all possible through careful observations of the winds, waves, ocean currents, stars and other indications of direction, but I still have to think that that’s a pretty bold move when you don’t know if land lies ahead.
At least we’re not alone out here. These are some other animals that we’ll leave for the mammal survey and birders to count.
Did You Know?
The CTD also shows the layers of ocean water. Looking at the graph again for the red (salinity) and blue (temperature) lines, we can see where they cross at about 15 meters. This shows where colder, saltier water starts compared to the warm surface water that is diluted by fresh water and mixed by wind.