Linkages between Ocean Acidification and Marine Organisms

Author: Jesus C. Compaire

We have all have heard about how ocean acidification has an important impact on marine ecosystems (if you don’t know what ocean acidification is, our colleague Jon Sharp tells you in his entry about pH onboard GOMECC-3). One of the most known effects is coral bleaching in tropical areas, but this phenomenon does not only affect the sessile organisms (who cannot run looking for better areas for their growth). At different scales, the rest of plants and animals in the ocean can also be affected by ocean acidification since this reduces the calcification in many organisms (Orr et al., 2005). Species affected include planktonic calcifiers (coccolithophores, foraminifera, pteropods), and also other animals like echinoderms, bryozoans, molluscs, crustaceans, fish, and a long etcetera.

coral infographic

But, what exactly does “reduce the calcification” mean, you might ask yourselves, and why is this a negative impact? To try to understand this phenomenon let’s see a few cases in different animals. For example it has been documented that elevated pressure of CO2 (i.e. high concentration of carbon dioxide) reduces the growth of molluscs and sea urchins, which means that compared to normal levels of CO2, the animals that grew in high CO2 conditions had smaller sizes and body weights (Shirayama & Thornton, 2005). In other experiments with crabs, the combination of increased temperature and lower pH reduced the energy for reproduction (Paganini et al., 2014). Now let’s talk about fish, and in particular about the ichthyoplankton (the eggs and larvae of fish found mainly in the upper 200 meters of the water column) of the marine coastal species. The survival of their larvae depends on them being able to find a suitable adult habitat at the end of an offshore dispersive stage that can last weeks or months. The way that they may return to adult habitats is with their ability to detect olfactory cues from these adult places. However, under experimental ocean acidification conditions it has been noted that this ability was disrupted. So if acidification continues unabated, the impairment of the sensory ability may reduce the population sustainability of many marine species, with potentially profound consequences for marine diversity (Munday et al., 2009) and impacts to wide sections of the population whose economies depend on these species.

It is for all these reasons that we are taking zooplankton samples throughout the Gulf of Mexico in this cruise (if you are not sure about what the zooplankton is, please check out this blog entry from July 29th where our colleague Lucio Loman explains this in detail). We aim to study the species composition and their abundances, and their relationships with the physical and chemical characteristics of the water column. The long-term study of the communities composition in the Gulf of Mexico will allow for the monitoring of changes and impacts due to increased sea surface temperature and ocean acidification, which in turn, will help managers to reduce this impact.


– Munday, P. L., Dixson, D. L., Donelson, J. M., Jones, G. P., Pratchett, M. S., Devitsina, G. V., & Døving, K. B. (2009). Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proceedings of the National Academy of Sciences, 106(6), 1848-1852.

– Orr, J. C., Fabry, V. J., Aumont, O., Bopp, L., Doney, S. C., Feely, R. A., Gnanadesikan, A., Gruber, N., Ishida, A., Joos, F., et al. (2005). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681-686.

– Paganini, A. W., Miller, N. A., & Stillman, J. H. (2014). Temperature and acidification variability reduce physiological performance in the intertidal zone porcelain crab Petrolisthes cinctipes. Journal of Experimental Biology, 217(22), 3974-3980.

– Shirayama, Y., & H. Thornton (2005) Effect of increased atmospheric CO2 on shallow water marine benthos. Journal of Geophysical Research, 110, C09S08, doi: 10.1029/2004JC002618.


What is pCO2, and why do we measure it?

An Interview with Denis Pierrot

Interview by: Emma Pontes

I’m pleased to introduce Physical Chemist and Co-Chief Scientist of GOMECC-3, Denis Pierrot. On a normal day, he can be found in the computer lab overseeing CTD operations, but today, he’s kind enough to escort me to the Hydro Lab where the pCO2 Underway System lives. pCO2 is slightly different than regular CO2 concentration; it is the partial pressure of CO2 in a liquid or gas. On the Ron Brown, we have a pCO2 Underway System which Denis proudly tells me is state of the art, and the result of collaboration between several esteemed scientists around the world.

Image 1. Image credit: Emma Pontes.

In Image 1, you can see the conglomerate of wires, equilibrators, and pumps that make up the system. A water line is connected to the system which pumps surface water from outside our ship in a constant flow into the system. The equilibrator (red circle) sprays the incoming water in a thin sheet which allows the air inside to become equilibrated with the water. This means that the pCO2 of the water will equal the pCO2 of the air inside the equilibrator. This equilibrated air is then sent to a gas analyzer (yellow circle) that measures the pCO2. In this manner, the pCO2 of the water is measured indirectly (by measuring equilibrated air pCO2) and graphed neatly on the laptop attached.

Additionally, the pCO2 Underway System has a gas line (green circle) that draws in air from the bow of the ship, ensuring the cleanest air possible with no contamination from ship emissions. This line is connected to the gas analyzer and the incoming air is measured for its pCO2 directly. The goal of this system is to measure the pCO2 of the water AND the atmosphere. The interaction and difference between ocean and air pCO2 is the basis of Denis’ work.

Image 2. Image credit: Emma Pontes.

Image 2 shows a graph of the output from the pCO2 Underway System. The blue and brown dots represent pCO2 of the water, while the purple and green crosses represent pCO2 of the atmosphere (purple line). The goal here is to determine where and when the ocean acts as a source and sink of CO2. The ocean is a source of CO2 when the water pCO2 is higher than that of the atmosphere (above the purple line). Conversely, the ocean is a sink of CO2 when atmospheric pCO2 is higher than that of the water (below the purple line). Since gases always move from high to low concentration in an endless quest for equilibrium, Denis and his colleagues can tell if the ocean is releasing (source) or absorbing (sink) CO2 and at what rate. The rate of this CO2 exchange between ocean and atmosphere is called flux. Denis hopes to create an up to date flux map of the Gulf of Mexico complete with spatial and temporal attributes. Flux is constantly changing both seasonally and temporally, and is dependent on wind, ocean current, temperature, and other atmospheric factors.

One quarter of anthropogenic CO2 is dissolved into the ocean. This has important and unfavorable implications for calcifying organisms such as certain plankton, corals, sea urchins, and any other creature that relies on carbonate to build its shell or skeleton. CO2 is an acidic gas that lowers the pH of water which it is dissolved in. A lower pH means more acidic water, which also means less available carbonate for calcifying critters to utilize in their shell building. A more acidic ocean is one with fewer ecologically important corals (and other carbonate-reliant species) and fewer commercially important seafood items like shellfish. Denis is very passionate about his work, which has ecological and commercial implications under ocean acidification conditions.

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Co-Chief Scientist Denis Pierrot, hard at work in the Hydro Lab. Image credit: Emma Pontes.

Ocean Acidification from a pH Perspective

Author: Jon Sharp

If you’re reading this blog, you’ve probably heard of and have some understanding of ocean acidification. Even the entirely uninitiated can deduce a bit of information from the term itself: “ocean acidification” must refer to a process by which the ocean becomes more acidic than it is already. That much is certainly true, but the details of the phenomenon are a bit more complex and—at least to ocean chemists—interesting.

Acidity is a measure of the amount of dissolved hydrogen ions (H+) in a solution (like seawater). And contrary to what the phrase “ocean acidification” may suggest, seawater is not acidic at all. Typical ocean water lies comfortably above neutral on the pH scale (within the basic range). Ahhh the pH scale; you remember it fondly from high school chemistry, right? In case not, let’s break it down.

The term “pH” can be divided into two parts. The “H” denotes what pH is actually a measure of: hydrogen ions. We chemists think about dissolved ions in terms of concentration, or the number of ions in one kilogram of seawater. The “p” in pH is simply a mathematical operation (the negative logarithm) that allows us to view hydrogen ion concentrations in numbers that are easy to digest and understand. Due to this numerical wizardry, low pH values denote high hydrogen ion concentrations, and vice versa.

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A visual representation of the pH scale. Figure courtesy of NOAA PMEL.

To learn even more about seawater pH and ocean acidification, click here.

So, “ocean acidification” implies that something is causing the quantity of hydrogen ions in seawater to increase. Conveniently, that something is easy to identify: the culprit is carbon dioxide (CO2). While CO2 is a naturally occurring gas, the burning of fossil fuels, along with other human activities, releases extra CO2 into the air. Excess CO2 that doesn’t stick around to warm our atmosphere dissolves into the ocean. Once there, CO2 undergoes a few interconnected chemical reactions with water (H2O). This process results in more dissolved hydrogen ions in seawater (lower pH). Another effect is fewer dissolved carbonate ions (CO32–), which is particularly bad news for corals and for many shellfish we like to eat.

While the mechanics driving ocean acidification are quite simple, Earth’s environment enjoys complicating things. That is why scientific expeditions like GOMECC-3 are important. Our group from the University of South Florida’s College of Marine Science is monitoring ocean acidification by examining large-scale environmental changes in pH and carbonate ion concentrations. We are also investigating localized patterns in the two parameters that may be influenced by factors other than CO2, such as ocean currents and biological activity. Multiple factors can work together to either accelerate or reduce the rate of ocean acidification in a region.

To perform measurements of pH, we use a form of analysis called spectrophotometry. We shine a beam of light through seawater that has been mixed with an indicator dye, called m-cresol purple, that forms chemical complexes with H+ ions. The dye has a basic form, which appears purple, and an acidic form, which appears yellow. Both forms absorb light at different wavelengths in the visible light spectrum. Our sensitive spectrophotometers detect how much light has been absorbed by each form of m-cresol purple, which corresponds to the pH of the sample. We perform measurements of CO32– in much the same way, only using a different indicator and examining absorbances in the ultraviolet light spectrum.

Briefcases filled with the 10-cm cuvettes we use for spectrophotometric pH and carbonate measurements. The cases make it easy for us to transport our samples to and from the CTD rosette. Photo credit: Jon Sharp.
Jon Sharp fills a glass cuvette from a Niskin bottle for pH measurement. The cuvettes are overflowed a number of times to ensure that our samples are uncontaminated. Photo credit: Courtney Tierney.

By measuring pH and carbonate ion concentrations with a high degree of accuracy, we are able to assess ocean acidification directly and rapidly. We can compare new measurements to those that have been made on past GOMECC cruises (2007 and 2012) to examine human-induced changes in ocean chemistry. Perhaps most importantly, we can use this information to identify locations that must be targeted and human activities that must be altered to best mitigate future ocean acidification.

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Seawater samples from greater than 3000 meters deep (left side) to the surface (right side) that have been mixed with m-cresol purple dye display an impressive spectrum of colors. Photo credit: Jon Sharp.

Ocean Acidification buoy validation measurements

An example of NOAA’s synergistic efforts to monitor coastal ocean acidification using a variety of platforms

Author: Leticia Barbero 

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OA buoy with the Ron Brown in the background. Image credit: Jay Hooper

We have just finished the third set of stations in our cruise, the Louisiana Line. This line is interesting for many reasons. The outflow of the Mississippi river into the Gulf changes the characteristics of the water we are sampling, sometimes dramatically. In the stations closest to the coast, which are more influenced by the riverine outflow, surface salinities are so low that they test the limits of the method we use for measuring pH with high precision and accuracy.  High nutrients from the outflow promote high primary production in the surface waters, which in turn ends up causing hypoxia (low oxygen concentrations) in the bottom waters. While regular oxygen values might be in the range of 120-250 umol/kg,  a sample from one of these bottom waters had an oxygen concentration of less than 20 umol/kg. Imagine having ten times less breathing oxygen than you are used to!

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One of many oil rigs we sailed close to during the sampling of the Louisiana Line. Image credit: Leticia Barbero

Besides the very interesting data we get from these stations, the Louisiana Line also affords us the chance to sail close to the dozens of oil rigs peppered along our route, which makes for good pictures for our personal albums.

And unexpectedly, two days ago the opportunity arose for an unplanned collaboration. We were notified that a buoy partially funded by NOAA’s Ocean Acidification Program, which also sponsors our GOMECC-3 cruise, has just been moved to a location close to our route. This buoy has pH, pCO2 and oxygen sensors. Our measurements on board can be used to validate the data from the buoy, so we decided to bring the ship as close to the buoy’s position as we could and take samples on site over a period of three hours. The scientists maintaining the buoy back on land will be able to use our data to calibrate their sensor data.

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Chief Bosun Mike Lastinger drives the Ron Brown’s small boat from the ship to the buoy. Image credit: Jay Hooper

Additionally, the ship was willing to accommodate a very last-minute request to use the ship’s small boat to get a water sample from right next to the buoy, for best quality comparisons. I am very grateful for our science team’s willingness to add extra samples to their already loaded stack of backed-up samples after a succession of stations that were very close together,  for Jay Hooper’s hard work handling the buoy sampling logistics on short notice and I am especially appreciative of  the efforts of the ship’s officers and deck crew to get us to the buoy in time to sync our sample with the buoy’s hourly measurements. We really have amazing science and ship teams working together on this cruise to collect the data we need to monitor ocean acidification conditions in the Gulf of Mexico.


On the dock. Ready, set, sail!

Author: Leticia Barbero

Ahoy, land-based shipmates! Welcome aboard our GOMECC-3 cruise!

We are only a few hours away from departure. After months of planning, of submitting requests for clearances, getting our health checks, coordinating with multiple agencies and making sure we packed all the gear we might possibly need (plus spares), we finally made our way to the ship. Our equipment arrived in containers, via Fedex and UPS directly to the ship, in rented U-Haul trucks, and even within our personal luggage! Some of us drove directly from our labs (in cars packed to the brim with equipment), while others flew from all across the country.

Main lab with most of the equipment in place. Picture courtesy of Denis Pierrot.

Communication with the ship is essential to keep track of everyone’s arrivals and to make sure we don’t lose track of any packages that may get misplaced on the ship. We are happy to report that all the equipment we will be using arrived as expected and without any major damage.

The research ship we will be using, NOAA ship Ronald H. Brown, has 4 laboratory spaces available for scientific use, and as soon as the science party started to arrive on board, everyone got down to work installing the different systems we will need. You will soon start to learn a little bit more about everything we will be doing on board, but suffice it to say that we will be obtaining chemical, biological and physical data. A truly multidisciplinary project!

Both the science party and the ship’s crew are very excited about GOMECC-3 and we are all looking forward to 35 days spent together evaluating ocean acidification conditions in our coastal waters. The first contact has been good and everyone is in high spirits.

Ongoing discussions among scientists in the Hydrolab during setup. Picture courtesy of Denis Pierrot.

We have just about finished setting up our labs and are looking forward to enjoying our last night on land for a while.

Main lab of the Ronald H. Brown before set up. Picture courtesy of Patrick Mears.

By the time of our next blog entry, we should have worked out all the kinks in our sampling equipment, in addition to finding our sea legs. Here’s hoping for calm seas and fair winds!

We ship out on July 18th

Follow our progress here.

Author: Sierra Sarkis

On July 18, NOAA AOML and partner scientists will depart on the Gulf of Mexico Ecosystems and Carbon Cycle (GOMECC-3) research cruise in support of NOAA’s Ocean Acidification Monitoring Program. This isn’t the first time researchers will head to sea in this region, previous cruises have taken place along the east and Gulf of Mexico coasts of the US in both 2007 and 2012. Together, these cruises provide coastal ocean measurements of unprecedented quality that are used both to improve our understanding of where ocean acidification is happening and how ocean chemistry patterns are changing over time. This will be the most comprehensive ocean acidification cruise to date in this region, set to include sampling in the international waters of Mexico for the first time. The importance of international collaboration should be noted, as ocean acidification is a global issue with global impacts, that will require a cumulative global effort to manage.

Please utilize this blog as a way to follow our progress, to familiarize yourself with the science behind the observations we are making, and to help improve your awareness and understanding of ocean acidification.