New Year, New Papers!

Hi All,

Happy (belated) New Year!

I’ve been meaning to write this post for several weeks, but haven’t had the time to sit down and write it out. One of my goals this year is to blog more. I want to share research updates, thoughts on ocean solutions, and experiences of a scientist’s life with you all. Let’s see if I can stick to it.

I want to share two recent papers that just came out.

First, I just finished leading a team that explored whether stable isotopes can tell us more about coral reef community metabolism. As a reminder, stable isotopes are variations in molecules with slightly different weights (Wikipedia explanation here). Because different isotopes of the same atom (e.g. carbon or oxygen) weigh slightly different amounts, organisms will selectively use different amounts of the atom, often preferring to use more of the lighter isotope. This selective process is called “isotopic fractionation” and it has been used to study almost every major geochemical cycle on the planet. Here’s an analogy to help drive this point home.

Imagine that you had a big pile of bricks, most weighed 12 lbs, but some weighed 13 lbs. You wanted to build your house out of these bricks. You start selecting bricks and laying them down to build your house. Each day is long and hard in the sun. You are tired at the end of each day. Because it requires energy to build your house, you end up selecting more 12 lbs bricks than you do 13 lbs bricks. In the end, your house has more 12 lbs bricks relative to the 13 lbs bricks than did your initial pile of bricks. You have “fractionated” the bricks. The same process occurs when marine organisms are selecting the carbon and oxygen atoms to make food or build their skeletons. They fractionate carbon and oxygen isotopes.

In this paper we explored fractionation on a section of coral reef on One Tree Island, in the southern Great Barrier Reef. We asked the question: “Do different parts of a coral reef community fractionate carbon isotopes differently? And if so, can we use that to learn more about what’s living on the reef?”. We learned that, yes, different sections of the reef fractionate isotopes differently. This is really exciting and helps us understand how we can use isotopes to learn more about coral reefs in other locations. I have wanted to study these questions for several years, so it has been really nice to see this all come together.

Just like any good science, this study answered some of our questions and opened up new questions for us to explore. For instance, how much can isotopes tell us about coral reefs in deeper water? What about over longer distances? Or complex flows? We don’t know the answers to these questions right now, but they help set the stage for future research.

Second, I am proud to share a co-authored paper from my earliest time as a scientist, when I was working as a research assistant for the Oceanic Flux Program in Woods Hole, Massachusetts. This paper has been 10+ years in the making! In this paper, we provide a huge data set of the chemical composition of marine particles (solid material falling from the top of the ocean to the bottom of the ocean). We show how the chemical composition varies each year and discuss what controls the chemical composition of the marine particles.

This research took 100s of hours of work in a “clean” lab. This is a lab where you have to wear a Tyvek jumpsuit and a hair net to even enter the lab! Everything is done in the lab to prevent chemical contamination fo the samples. It was a great way for me to learn about the tremendous importance, and challenges, of doing laboratory work. I’m really happy to see that all of that time in the clean room 10 years ago has paid off!

Please note: this article is currently behind a “paywall”. If you are interested in reading it, but do not have access to the journal, please email me for a free author’s copy.

Can marine plants save us from ocean acidification-what do models say?

This blog sums up a peer-reviewed paper, Expected limits on the ocean acidification buffering potential of a temperate seagrass meadow.

Download the full paper here

Climate change is a big deal in California, and scientists keep searching for solutions. Common imprints of climate change on the daily life of Californians include increased droughts, more frequent and severe wildfires, stronger heatwaves, and less snowpack. Fossil fuel emissions change our climate, and these greenhouse gases present yet another sinister threat: they increase ocean acidity along our treasured California coast. Our more acidic ocean poses big problems for key marine organisms, so it’s important to understand the role of marine plants. Specifically, can marine plants save us from ocean acidification?

Yummy oysters, mussels, abalone, sea urchins and starfish all build their skeletons out of calcium carbonate, the same mineral as limestone. The active ingredient in antacid tablets, calcium carbonate dissolves under more acidic conditions. So, the more acidic the California coast becomes, the harder it is for key players to grow their skeletons. This situation could bring big changes to coastal Californian ecosystems. Just like human communities, ocean ecosystems work best when all members maintain health. When factors limit the ability of key members to grow to full potential, the community changes. Some win, but more lose.

The chemistry of ocean acidification is actually pretty simple. Carbon dioxide, the primary greenhouse gas and contributor to climate change, dominates fossil fuel emissions. As the atmosphere fills with carbon dioxide, the oceans absorb about 30 percent of the emitted gas. In this way, the oceans help fight climate change. They take up carbon dioxide that would otherwise end up in the atmosphere and contribute to further warming. But there’s no such thing as a free lunch. When the oceans absorb carbon dioxide, seawater becomes more acidic. This increase in acidity happens when carbon dioxide reacts with water and forms carbonic acid. This same reaction renders our sparkling water and Coca-Cola acidic.

Can anything be done to limit the effects of ocean acidification along California’s coast?

Well, yes.

We scientists, and marine resource managers, can increase monitoring networks to understand how acidic conditions vary along the California coast. We can take steps to make sure that naturally acidic spots don’t worsen from nutrient pollution and wastewater runoff. We can also evaluate whether nature offers a ready-made solution, seagrass.

Seagrass lines the California coastline. And, like terrestrial grass, seagrass makes its own food. In a process called photosynthesis, these plants combine carbon dioxide and water—in the presence of sunlight—to make sugar. This process removes acid-increasing carbon dioxide from ocean water.

In the same way that humans exhale carbon dioxide produced from metabolizing our food, seagrass produces carbon dioxide when it metabolizes its food. This process, called respiration, returns acid-increasing carbon dioxide to ocean water.

So, if photosynthesis outweighs respiration for an entire seagrass meadow, then seagrasses make the water less acidic—that is, more alkaline. Recently, scientists have wondered whether seagrasses may provide a natural refuge of alkaline waters, where marine organisms may grow healthy calcium carbonate skeletons. Could seagrass protection and restoration become a powerful tool to combat ocean acidification?

For the last two years, I led a group of scientists to study this question in depth. We worked together to develop a computer model of how seagrass changes, and is changed by, the seawater chemistry above it. We used mathematical equations to specify the relationships between seawater chemistry and seagrass growth. In the course of dozens of conference calls and hundreds of emails, we refined this model. Once we had built a working model, we unleashed it to help answer our questions.

Scientists and the public ask me about the value of computer models. We all agree that computer models are not the same as the real world. Rather, they provide simplified representations of the real world. But when built correctly, computer models function as non-invasive tools that help us understand nature’s complex behaviors and interactions. For instance, we used our model to help us understand how the amount of seagrass in a meadow may affect the meadow’s ability to counteract, or buffer against, ocean acidification. In the real world, we do not have an easy way to control the amount of seagrass to study its buffering effect. If we wanted to control the amount of seagrass, we would need to rip out healthy seagrass meadows. This is not something I recommend!

In addition to providing a non-invasive tool for knowledge, computer models cut research time. In our study, we wanted to understand how buffering changes in summer, compared to winter. Setting up the model with the appropriate conditions for summer and winter took five minutes. It took another minute to simulate a month of data on a computer. In the real world, we’d have to wait six months between summer and winter. And we would need to wait anxiously for winter weather that was calm enough to allow us to deploy the equipment needed to measure every factor we had waited all that time to observe. In some winters, these “weather windows” never happen.

So, what did our model say about seagrass?

Well, seagrass meadows might provide some buffering, but they are not a silver bullet to stop ocean acidification along all of coastal California. However, our model results suggest that seagrass meadows might provide localized effects within the meadow. These effects may be equivalent to turning back the clock a few decades on a 150-year-old problem that keeps worsening faster and faster. Hundreds of model simulations revealed the basic reason behind this limited effect: the more seagrass grows, the more food the seagrass has to metabolize to support its current biomass. In this way, seagrass resembles people. As we grow to adulthood, we eat more to support the energy needs of our larger bodies. Eventually, as seagrass reaches its greatest density, photosynthesis and respiration balance each other out. And that balance minimizes the buffering of ocean acidification.

As I mentioned earlier, models imperfectly represent the real world. At the same time, in many countries, scientists perform complementary lab experiments and take field measurements to determine whether seagrass can effectively buffer ocean acidification. Together, these multiple studies and overlapping approaches may provide a more complete answer to the question than our model has by itself. Meanwhile, I’ll keep at work to figure out what else we can do to fight ocean acidification and protect California’s productive coasts.

 

Thanks to Leslie Willoughby for her helpful feedback on this blog post