CTD MVP’s

Author: Leah Chomiak

Meet Jay & Andy – Jandy, as they are collectively known. As the most beautifully orchestrated scientific tag-team out there, these guys are responsible for the heartbeat and blood flow of our scientific endeavor out here on the Gulf: maintaining and running the CTD. The two have worked together for the past 6 years, clearly demonstrated in their friendship and mutual enthusiasm onboard. The two work at NOAA’s AOML laboratory in Miami, FL; Andy in the engineering department, and Jay in the physical oceanography department. The two love being out at sea, seeing the world from a different point of view, but most importantly “escaping Miami traffic”, as Jay puts it.

The two are CTD geniuses, knowing the ins and outs of each sensor, wire, and software program pertaining to data collection. The CTD, which stands for Conductivity, Temperature, and Depth, is the most highly regarded oceanographic instrument used to assess a water column, from the surface to the ocean floor. Lowered by a conductive wire off the starboard side of the ship, this mighty instrument serves the needs of 20 of the 24 scientists on board through means of water samples and profile data. Although the instrument is collectively termed a CTD, the actual CTD probe is merely a small part of the totality of the instrument. Within the steel cylindrical frame lie 24 Niskin bottles for sampling water at different depths, two ADCPs (Acoustic Doppler Current Profiler) for measuring the speed and direction of water currents, a transmissometer for detecting the chlorophyll maximum, and a series of sensors for measuring oxygen, temperature, and depth within the water. Prior to arriving on station, our CTD techs ensure all sensors are clean, functioning, and talking to the main computer. Sensors must be kept moist in between stations when the instrument is onboard the ship, this is done by connecting tubing filled with water to the probes. Before the CTD is deployed the techs remove the tubes and turn the sensors on. On deck, there is one CTD tech and one Survey tech suited up to deploy and successfully recover the instrument. The techs are outfitted with hard hats, steel-toed boots, a life jacket, and a tether to the ship when handling the instrument, to ensure safety as a 3000lb instrument dangles on a wire above their heads. Sitting in the main lab of the ship, the Chief and Co-Chief scientists stand by a series of computer monitors that show the output of the instrument sensors, and as the CTD is lowered through the water column, profiles of temperature, salinity, oxygen, and density appear, giving the scientists a first-hand look at the structure of the water column. The scientists use radios to communicate to the deck techs and wire operator, directing them when to lower and raise the CTD in the water. The scientists at the computer look for interesting features in the profiles shown to them on the screen. Are there any unusual temperature spikes or oxygen minimums?  Based on these features and common features of a water column (thermocline, mixed layer, oxygen minimum zone, chlorophyll maximum) the scientists tell the wire operator where to stop the CTD, and then a signal is sent through the wire to close a Niskin bottle at that depth. As the CTD works its way back up the surface, Niskin bottles are triggered to close at other specified depths. The techs then recover the CTD and bring it back on board safely, the sensors are cleaned and tubes replaced, and a plethora of data is now ready for scientists to use in their analysis. As mentioned in previous blogs, once the CTD is back on board, a sampling frenzy ensues.

Pic 3 (2)
Tag team of the CTD Tech (Andy) and Survey Tech (Josh) safely retrieving the CTD

Jay and Andy make sure the sensors are calibrated by comparing the sensor values to that manually determined through salinity and oxygen analysis, the job I do here on board. Jay and Andy are certainly the silent heroes of scientific data collection here on the Brown, keep up the good work boys!

Advertisements

Breathing in Science: Oxygen Measurements At Sea

Author: Emma Pontes

Image 1_low
Scientist Emma Pontes performing Winkler Titration on a water sample collected from the first station of the cruise. Photo taken by Leah Chomiak.

Take a deep breath. The air you just inhaled contains about 20% oxygen, 78% nitrogen, and 2% of a few other minor gases. Some might assume that oxygen is only available to terrestrial air-breathers, however, this assumption couldn’t be further from the truth.

Oxygen (O2) generally exists in a gaseous state, but also exists in the world’s oceans as a dissolved gas. Fish and other ocean biology utilize the available dissolved oxygen just like humans do; taking up O2 and discharging carbon dioxide (CO2). Just like on land, the ocean is home to millions of photosynthetic organisms such as plankton, algae, and other underwater plants that take up CO2 and release O2 during a process called photosynthesis. Therefore, there is a constant ebb and flow of CO2 and O2 being ‘inhaled’ and released into ocean waters.

So what does this mean for ocean chemistry, and why do we care? Dissolved oxygen in the ocean is a sensitive indicator of climate-related changes. The dissolved oxygen concentration can be used to determine how much anthropogenic CO2 (carbon dioxide released by humans resulting from the burning of fossil fuels) is being taken up by the ocean. Just like oxygen, CO2 can dissolve in ocean waters, and most of human-created CO2 has been sequestered by our oceans. The uptake of anthropogenic CO2 by the world’s oceans is a leading cause of ocean acidification. Therefore, it is of high importance to determine the O2 concentration of various locations around the world’s oceans, not only to learn more about the how ocean biology is functioning, but also to examine the effects of ocean acidification.

Enter GOMECC-3, Ocean Acidification Research Cruise. In the past, research vessels have travelled our current route collecting the same data we are gathering now at the same locations. We can get an idea of how ocean chemistry is changing over time by comparing the data we get on this cruise, to the historic data sets collected on the same path we are on now.

Work days on the ship consist of lowering the CTD rosette (stands for conductivity, temperature, and depth) into the ocean at a predetermined location called a Station. The CTD is a large cylindrical ring of bottles, called Niskins, that are triggered to close and collect water samples at predetermined depths. The CTD is a useful tool for scientists onboard to get insight as to how ocean chemistry changes with depth.

Image 2_low
CTD being lowered into the water at the first station of the cruise. Photo taken by Leah Chomiak.

My job is to collect water samples from the Niskins and analyze each sample for its dissolved oxygen concentration using a technique called Winkler Titration. This procedure requires the addition of chemicals to the water sample that act as a fixative; the chemicals bind to the oxygen in the water and create a solid precipitate that eventually sinks to the bottom of the water sample. You can think of it as ‘pickling’ the oxygen to preserve it, so that the sample can be analyzed anywhere from 1hr to 4 weeks after being collected. To learn more about the titration procedure, check out the peer-reviewed paper entitled ‘Determination of Dissolved Oxygen in Seawater by Winkler Titration Using the Amperometric Technique’ written by Dr. Chris Langdon in 2010, which basically serves as my lab manual on the ship. I am looking forward to collecting some meaningful data that will contribute to OA research as we continue our trip around the Gulf of Mexico!

Image 3 low
Water sample collected by Scientist Emma Pontes to be analyzed for dissolved oxygen. The white milky-looking substance at the bottom of the sample is the bonded oxygen precipitate. Photo taken by Emma Pontes.

References:

Langdon, Chris. “Determination of dissolved oxygen in seawater by Winkler titration using the amperometric technique.” The GOSHIP Repeat Hydrography Manual: a Collection of Expert Reports and Guidelines, edited by: Hood, EM, Sabine, CL, and Sloyen, BM (2010).