Posts Tagged ‘photo degradation’

UGA Skidaway Institute scientists study role of sunlight on marine carbon dioxide production

July 21, 2016

Scientists at the University of Georgia Skidaway Institute of Oceanography have received a $527,000 grant from the National Science Foundation Chemical Oceanography Program to answer one of the long-standing questions about carbon in the ocean—the rate sunlight produces carbon dioxide from organic carbon molecules in the sea.

Jay Brandes, Leanne Powers and Aron Stubbins will use a new technique they developed to measure this process, which is known as photo-degradation.

Researchers Aron Stubbins (l) and Jay Brandes

Researchers Aron Stubbins (l) and Jay Brandes

The ocean is full of millions of different types of organic compounds. Some are consumed by bacteria, but many are not easily consumed and remain in the ocean for hundreds or thousands of years. However, near the surface, sunlight causes the breakdown of organic compounds and converts them into carbon dioxide through photo-degradation. Until recently, this process has been nearly impossible to measure directly in most of the ocean because the additional carbon dioxide produced per day is tiny compared to the existing high concentration of CO2 present in the sea.

Researcher Leanne Powers

Researcher Leanne Powers

Brandes described the problem as looking for a needle in a haystack.

“You might think this is not important because it is hard to measure, but that’s not true,” he said. “We’re talking about a process that takes place across the whole ocean. When you integrate that over such a vast area, it becomes a potentially very important process.”

The project became possible when the team developed a new technique to measure the change in CO2 concentration in a seawater sample. The concept was the brainchild of Powers, a Skidaway Institute post-doctoral research associate. The technique uses carbon 13, a rare, stable isotope of carbon that contains an extra neutron in its nucleus. Researchers will add a carbon 13 compound to a sample of seawater and then bombard the sample with light. The scientists will then use an instrument known as an isotope ratio mass spectrometer to measure the changes in CO2 concentration.

According to Brandes, this project will be breaking new ground in the field of chemical oceanography.

“We don’t know what the photo-degradation rates are in most of the ocean,” he said. “We are going to establish the first numbers for that.”

The team plans to take samples off the Georgia coast, as well as from Bermuda and Hawaii.

While they will continue to refine the carbon 13 technique, Brandes said it is now time to put that tool to work.

“It is now a matter of establishing what the numbers are in these different locations and trying to develop a global budget,” he said. “Just how much dissolved organic carbon is removed and converted to CO2 every year?”

The project is funded for three years. The team will also create an aquarium exhibit at the UGA Aquarium on the Skidaway Island campus to help student groups and the public understand river and ocean color.


Barrow — January 17

January 19, 2012

17 January 2012

We woke up a little late this morning after yesterday’s late night. Victoria and I met to go over plans for the day and to discuss the details of the experiment that we plan to start today. The experiment is a component of SSU graduate student Zac Tait’s thesis project. Zac couldn’t come this time because he is about to be a father. His daughter, who they will name Iris, is due on 4 February. Zac left me and Victoria with extensive notes and prepared all the supplies but we’ll run it.

The goal of this experiment, as in previous ones, is to test the hypothesis that Arctic Ocean bacteria can utilize the carbon locked up in the humic material that makes up the permafrost, but doing so will require them to acquire more nitrogen. The most abundant source of nitrogen in the water is found in the mineral form of nitrate (NO3). One of the major questions of our project is whether the release of the carbon stored in the permafrost will set-up increased competition for NO3 between the photosynthesizing autotrophs (phytoplankton) and the CO2 respiring heterotrophs (bacteria). The idea is that the more organic carbon that gets released into the ocean the more bacteria activity will occur.  However, that increase in activity will be at the expense of nitrate resources that the phytoplankton need in the spring (when the lights come back on) to grow.  If there is less nitrate available there will be less phytoplankton and therefore less fish, seals, whales etc that depend on a food web whose base is the phyotoplankton. So it’s somewhat of a counterintuitive idea; add more nutrients and get less out.

In previous experiments we found generally that this hypothesis is true, but that the carbon-rich humic material we collected directly from the tundra is used very slowly which makes the question hard to address given the practical constraints of our time here. Because our time is short and the temperatures are cold which slows everything down, we decided on a new twist for these experiments. This time, we are using humic material that has already been broken down some by exposure to sunlight. This process is called photo degradation. Photo degrading complex carbon molecules occurs naturally (It’s reasonable to expect that humics derived from melting permafrost will be exposed to sunlight on their trip to the ocean.) and it increases its availability to bacteria as a nutrient source. So, prior to the trip Zac exposed humics in a solar simulator for 0, 5 and 15 days resulting in increasingly degraded humic materials.  Amazingly, after 15 days of simulated exposure to sunlight the brown humic material was almost completely colorless. The carbon is still there but since it has been broken into smaller and less condensed molecules it doesn’t absorb as much light, thus it appears lighter in color.

Photo degraded humics used in our bioassay experiment

Our experimental design is relatively simple. We use 4 liter (1 gal) milk jugs (actually they are a special nontoxic plastic but they look like milk jugs) to incubate bacteria with the humics and allow them to grow.  Over the course of the week we’ll be here we take samples to watch the bacteria grow track the dynamics of the carbon and nitrogen. Our hypothesis will be supported if we see the bacteria grow and the carbon disappear in coordination with the disappearance of the NO3.

After 9 hours of filtering and rinsing we finally got the experiment set-up and running. We’ll sample it daily (or every other day) for the time we’re up here.

Zac’s experiment running


But the real excitement happened on the ice today. Because we are so concerned about the stability of the ice the UMIAQ crew went out to check our ice camp which we had left standing. When they got out there they realized that the ice was moving a lot and that large cracks were beginning to appear. The crew was scared enough that they just came back leaving the tent behind. But Brower thought they could get it and made a heroic trip back out with Tony and Glenn. They ripped the tents out of the ice leaving the stakes behind, quickly lashed it on two sleds, and hightailed it back jumping cracks with open water. We heard some of it on the radio. The whole situation has us pretty nervous and thinking very carefully about safety.

[Picture –

Brower and Glenn standing by the rescued tents.

Either way tomorrow we won’t go out.  We’ll re-group and re-evaluate.