Dissolved Inorganic Carbon

Author: Joletta Silva

Hello, my name is Joletta Silva, and I am a master’s student at the University of Miami RSMAS studying Marine Conservation. On the GOMECC-3 cruise I have been working alongside Patrick Mears completing dissolved inorganic carbon (DIC) analyses.

DIC is comprised of CO2, and all the nonliving carbonate species (primarily carbonate and bicarbonate) that are dissolved in the seawater. Generally areas which have high concentrations of carbon dioxide will have correspondingly high levels of DIC. When our data is coupled with data from other carbon parameters (alkalinity, pH, etc) it can be used to determine the rates of ocean acidification in the Gulf of Mexico.

The DICE lab on board Ron Brown. Image credit: Joletta Silva

The dissolved inorganic carbon lab is separate from the main lab on the ship and is built into a modified shipping container which is usually stored at the Atlantic Oceanographic and Meteorological Laboratory on Virginia Key, Florida. This makes transport and setup relatively simple and also allowed for me to become familiar with the machine setup before I got to the RV Ronald Brown.

Life on the ship:

I am working the night shift (11:30 pm to 11:30 am), and generally sleep or  nap during the day, and wake up at around 11 to start my shift. When we are on transect lines, the CTD (whom we have affectionately named Barbara) will descend at each station to various depths, and will return to the surface filled with seawater for sampling. We receive a daily schedule so that we know exactly when to be outside prepared to extract water. I generally take one full bottle from each of Barbara’s niskin containers (up to 24 total, each one containing seawater from a different depth). As soon as I fill the bottle and ensure that there are no bubbles in the sample, I poison it with a mercuric chloride solution to kill any living organisms and ensure that they do not breath, thus changing the CO2 concentration in the sample before it is run through the machine. After getting all my samples from Barbara, I return to the lab and begin to analyze them.

CTD going down at a station. Image credit: Joletta Silva

This can be a long process, as each one of our samples takes about 15 minutes to run. The machines also take about 1.5 hours to calibrate and set up, so a lot of time is spent doing this. Sample analysis is completed using a coulometer and a Dissolved Inorganic Carbon Extractor (DICE).  The coulometer is used to help determine the amount of carbon in the cell. The carbon in the sample is converted to carbon dioxide gas, which then reacts with a proprietary reagent causing the formation of OH- and H+ ions which are detected by the machine which uses photogrammetry, or light streams, to detect and quantify the ions. Basically, the DIC in the sample is converted to carbon dioxide, which is then measured through a titration that gives us a total carbon count.

During a normal shift (when we are not in transit between station lines) I will sample between 2-4 CTDs at varying depths, and have to calibrate the machine twice. There are several other scientists who work night shifts measuring other parameters such as dissolved oxygen and nutrients, and we have become fast friends (something about sampling at 3 am while listening to some great music creates an instant bond). We have been fortunate to have some incredible experiences including outrunning tropical storm Franklin in the previous week. In addition to this, we just witnessed a meteor shower on August 12th that lasted the majority of the night!

We have a mere few days left of our 35 day cruise, and it has gone by far too quickly. It has been interesting to view the profiles of DIC along the varying transect lines and observe trends and changes in different areas and depths. This last week is going to be one of the busiest, since the transect lines and CTD stations are so close together. I am excited to continue to learn about inorganic carbon profiles in the Gulf, and see how the remainder of our results turn out. Here’s to the last week at sea, and the adventures that it will bring!


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.

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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!

Outreach at Sea: Shrinking Styrofoam

Author: Gabrielle Corradino

Being a part of a field science team is what my younger self dreamed about. The idea of exploration, pioneering research and ocean travel took hold of my mind at a very early age, and has now become my reality. Through years of internships, jobs and now graduate school, I am at the onset of defining my dream as a marine ecologist. I am currently in my 3rd year as a Ph.D. student at the Department of Marine, Earth and Atmospheric Sciences at North Carolina State University working with Dr. Astrid Schnetzer. Alongside my love of marine science, I have found another passion in the realm of teaching and education. I am a product of the public-school system in Connecticut and truly feel it gave me the educational opportunities and stimuli to grow into the researcher I am today. As I start my career as a marine scientist, I believe a portion of my job is to teach and inspire the next batch of creative thinkers and scientific minds.

I have carried this passion for Science, Technology, Engineering and Math (STEM) education, developing innovative curriculum and scaffolded learning into all of my projects as a graduate student, including my current research aboard the R/V Brown. The GOMECC-3 trip has allowed for an exciting opportunity for art, music, and science, to meld into a cross-disciplinary project, expanding my vision into a Science, Technology, Engineering, Art and Math (STEAM) project.

The “Decorate a Cup” outreach project was sent to three collaborative schools: Clinton Avenue School, New Haven, CT, Corpus Christi School, Wethersfield, CT and Laurel Park School, Cary, North Carolina. The project description is as follows:

Decorate a Cup

Background: The students drew on a Styrofoam cup with permanent marker (Fig. 1), which was sent down on a research instrument that was lowered several hundreds of meters to the deep-sea (Fig. 2). On the travel down, the cups were compressed to ~25% of their original size due to the pressure (Fig. 3). At the end of the cruise the cups will journey back to the teachers and students with a STEAM lesson plan to learn about ocean research and the GOMECC-3 voyage. This will allow the students to progress toward a stronger understanding and make broader connections to the marine ecosystem.

Figure 1
Figure 1. These are a few of the full-sized Styrofoam cups decorated by the students. Each cup had a small piece of paper stuffed on the bottom to prevent the cups from stacking on-top of each other during the transit to the deep.
Figure 2. The first CTD cast with the cups attached. The cups are in mesh bags to allow for maximum water flow over each the cups.
Figure 3a
Figure 3a. The final product! From the pressure in the deep-sea, the air was removed and the cups were compressed into different shapes and sizes. The picture to the right gives a sense of scale of the starting size of the cups and the final compressed size.
Figure 3b
Figure 3b. The final product! From the pressure in the deep-sea, the air was removed and the cups were compressed into different shapes and sizes. The picture to the right gives a sense of scale of the starting size of the cups and the final compressed size.

The lesson includes:

  • A map of when, where and at what depth the cups were deployed
  • Discussion and synopsis of expected outcomes
  • A list of grade-appropriate vocabulary words with definitions, emphasis will be on categorizing Tier 1, 2, and 3 vocabulary to reflect scientific, art, and music disciplines
  • 1-page GOMECC-3 article
  • Scaffolded classroom questions
  • Before/After and deployment pictures

The project aims to engage the students in conversations on the different marine ecosystems (shoreline, photic zone, deep-sea, etc.) and organism adaptations to each habitat. With the guided questions, topics of geology, chemistry, physics and biology can be leveraged into the student discussion. The lesson will target the National Science Standards: Earth’s Systems (MS-ESS2) and Biological Evolution: Unity and Diversity (MS-LS4). Additionally, it will incorporate the art and music standards: MuCN 11.0.2a, MuCR1.1.2a, VA.CN.11.4.

Breathing in Science: Oxygen Measurements At Sea

Author: Emma Pontes

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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.

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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!

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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.


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).