Mission & Project Info | NOAA’s Aquarius Undersea Laboratory
Mission Blog

We installed most of the heavy instrumentation required for our Ocean Acidification project at ARB during July 7-10 with professional diver support from the NURC-Key Largo staff. The scientists all got in about ten dives using Nitrox, an oxygen enriched gas mixture that enhances diver safety margins. We used both the R/V George Bond and the Sabena for this set-up work and got it done on Friday July 10^th. Yesterday, Saturday, we completed power and communications connections between the Life Support Buoy (LSB) for Aquarius and the Bond. Now we can watch the data from our instruments in near real time 24/7!

We have now set up several experiments to test our ideas about how local respiration versus global ocean acidification are affecting the acidity of bottom waters right next to coral surfaces. We call those waters the Benthic Boundary Layer, the BBL, since the oceanographic term for seafloor organisms is benthos. We hypothesize that local respiration by the benthos, especially sponges, will enhance acidity well above that resulting from injection of fossil fuel CO₂ into the world ocean.  The experiments now running involve monitoring seawater pH, carbon dioxide and oxygen concentrations in the BBL and at 5 meters above bottom. We expect a comparison of the data sets to reveal how important local benthic processes are versus global scale addition of CO₂.

Sponges dominate benthic biomass out on Conch Reef and we suspect that their respiration at night will be particularly important. Therefore we are directly measuring their impacts on reef water chemistry using the sophisticated instrumentation seen in the photos posted from our mission. On Saturday we ran our first sponge enclosure experiment during which we continuously measured sponge CO₂ production during respiration and the subsequent drops in pH.  We also monitored dissolved nitrate, a nutrient element usually present at very low concentrations in healthy reefs and simultaneously looked for N₂ gas production via a microbially-mediated process known as denitrification. Denitrification may help reefs get rid of excess nitrogen in its ammonium and nitrate forms- we are the first group in the world to measure this process underwater using membrane inlet mass spectrometry (MIMS). Our MIMS instrument that is named TETHYS can be seen in several of our posted photos.

A surprise addition to our mission is hydrocarbon monitoring out on Conch Reef. ARB is located right along the Florida Straits. Any oil and gas from the Deep Horizon disaster that makes it to the Keys will probably flow right past Aquarius and so we’ve gotten partial support from several private sector companies to mount a water column monitoring effort right out there on the reef. The support comes in the form of contributions to a data logging system from Aanderaa Data Instruments (AADI) that supports our existing light hydrocarbon sensors plus TETHYS from Monitor Instruments Company, the source of our MIMS instrument. You can see both of these instruments, HANDI and TETHYS, in the photos posted for this mission on the ARB webpage.

Take a look at the photos of our equipment out on the seafloor right now beneath the LSB and Aquarius. This is the first time that these sorts of ocean acidification experiments have been conducted out on a natural coral reef rather than with coral and sponge samples brought back to a laboratory.

I think that everyone’s heard about the extra carbon dioxide in the earth’s atmosphere that is coming from fossil fuel burning and other large sources such as land-use change and cement manufacturing. Not everyone has heard that this extra atmospheric CO₂ is increasing the acidity of the oceans and, as a result, the ability of corals and other calcifying organisms to prosper or just survive. The extra CO₂ upsets the natural balance by increasing the amount dissolving into the oceans. Once dissolved into the ocean it reacts with water to make additional carbonic acid (CO₂ plus H₂O = H₂CO₃). It’s like eating too much rich food that gives you an acid stomach. We have upset the equilibrium that occurs naturally, the sea has an acid stomach and coral reefs are among the antacids, literally the Tums of the sea.

So what’s the big deal about adding some more CO₂? In a nutshell, calcifying organisms need both calcium and carbonate to make what we commonly call calcium carbonate or limestone. Calcifiers extract these dissolved chemicals from seawater as they make reefs or shells. Coral animals are calcifiers who make their reefs of aragonite, a relatively soluble calcium carbonate mineral that dissolves more readily than other carbonate minerals such as calcite. When more CO₂ is added, and ocean acidity increases (or as scientists say, the pH is lowered), the concentration of dissolved carbonate declines, making it tougher for colonies of tiny coral animals to make their aragonite mineral homes that we call coral reefs, even if they have plenty of calcium in the surrounding seawater.

The scientific community and a growing number of concerned citizens have now recognized how serious the impacts of increasing ocean acidity are- the threats to coral reef ecosystems are imminent within our lifetimes. Our research team, including scientists, engineers and students from the University of North Carolina at Chapel Hill, the University of Hawaii and the University of South Florida, is one of several working on the problem with support from both government research agencies and private sector groups. Together these people have become alarmed as coral reef ecosystems have gone into a precipitous decline around the world: in most tropical environments coral cover has dropped from over 50% to less than 20% within just a few decades.

A problem that we all face in trying to help solve this problem is that there are now many threats to coral reefs including excess nutrient pollution, overfishing, coral diseases, sedimentation, global warming, and now, ocean acidification. Direct, around-the-clock access to coral reefs through working at the Aquarius Reef Base (ARB) facilities out on Conch Reef and the development of sophisticated new underwater instrumentation are now allowing us to conduct in situ experiments that we hope will help to determine what role global ocean acidification is playing along the Florida reef tract.  Our overall experimental goal is to be able to distinguish between the inputs of CO₂ from the atmosphere and local inputs from respiration by seafloor organisms such as sponges. Sponges are taking over reef surfaces that used to host coral colonies; they produce CO₂ just like us when they respire. Their local acidification impact needs to be sorted out from that due to global fossil fuel CO₂ input so that reef managers as well as scientists can understand what’s happening over time and develop new strategies to help deal with the change. To accomplish our goal we have developed and deployed a suite of state-of-the-art instruments, including an underwater mass spectrometer and pH metering system that can sensitively and continuously monitor changes in CO₂ and pH right on the seafloor. The purpose of these instruments is to make continuous observations to determine day-night differences in acidity and dissolved gases out in the reef ecosystem itself for extended periods of months or longer. We are also measuring water transport processes in the water right next to the seafloor (we call it the benthic boundary layer or BBL) plus concentrations of nutrient elements such as nitrogen and dissolved organic matter so that we can learn about how natural variations in these parameters come into play.

We have already detected significantly increased acidity in the BBL where coral colonies live. How much of this increased acidity is from global inputs of fossil fuel CO2 versus local respiration by sponges and other marine life taking over where corals used to dominate remains to be determined.

Ocean acidification has already decreased dissolved carbonate by about 10% in recent decades and if we raise atmospheric CO₂ concentration to the levels predicted by the year 2100, a further decrease down to about 50% will occur. The consequences for aragonite producing corals are potentially dire and we must all try to do what we can to alter this grim scenario.